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    The Meteorology of the Arctic Region

    Encyclopedia Arctica 7: Meteorology and Oceanography




    Unpaginated      |      Vol_VII-0005                                                                                                                  

    THE METEOROLOGY OF THE ARCTIC REGION

           

    By

    Sverre Petterssen, W. C. Jacobs,

    and B. C. Haynes



    Unpaginated      |      Vol_VII-0006                                                                                                                  
    EA: Meteorology

    [Sverre Petterssen, W.C. Jacobs and B.C. Haynes]


           

    THE METEOROLOGY OF THE ARCTIC REGION

    Page
    Introduction 1
    Composition and Structure 4
    Inversions and Lapse Rates 19
    Acoustic Phenomena 25
    Optical Phenomena 37
    Air Masses and Fronts 46
    Cyclones and Anticyclones 52
    Atmospheric Pressure 56
    Surface Wind 66
    Upper-Air Winds 98
    Air Temperature 107
    Precipitation, Snowfall, Thunderstorms 164
    Humidity 211
    Cloudiness and Ceilings 228
    Fog and Visibility 264
    Sunshine, Illumination 287
    Information on Diagram 302
    Reference to Literature 304
    Legend to Diagrams 308

            Note : The diagrams referred to in this paper are of a dimension too

    large to be included in the present binding. These diagrams

    may be consulted in the Stefansson Collection where they are

    filed. (December, 1954)



    001      |      Vol_VII-0007                                                                                                                  

           

    INTRODUCTION

            From the broadest point of view the climatic regions of the

    world may be divided into five principal types, vis.,

            A. Tropical Rainy Climates , which comprise the tropical rain

    forests, the tropical monsoon systems, and the adjoining savannas.

            B. Dry Climates , which comprise the deserts and steppes in

    subtropical and adjacent latitudes.

            C. Warm Temperate Climates , which comprise the part of the

    midlatitude rainy belt that is not normally covered by snow in

    winter.

            D. Snow-Forest Climates , which comprise the mid and high

    latitude belt with extensive forests and snow cover during the

    winter.

            E. Polar Climates , which comprise the tundra regions and the

    fields of perpetual snow and ice.

            Fig. 1 The distribution of these types of climatic regions in the nor–

    thern hemisphere is shown in Fig. 1. Each of these regions may be

    divided into sub-regions, depending upon the amount rainfall,

    002      |      Vol_VII-0008                                                                                                                  
    seasonal variations, and other limiting factors that affect the

    natural vegetation. In this respect the Polar Climate may be said

    to be the simplest of all principal climatic types, inasmuch as it

    suffices to divide it into two subtypes, namely the Tundra Climate

    and the Frost Climate .

            The Frost Climate occupies the regions of perpetual snow and

    ice, while the Tundra Climate is characterized by bare ground during

    the warm season. The vegetation typical of the tundra consists

    largely of mosses, lichens and grasses with dwarf trees in sheltered

    places. Along its equatorward border the tundra merges with the

    vegetation of the snow-forest climatic zone of the northern hemi–

    sphere, and the border between these two climatic zones has been

    found to coincide very nearly with the line along which the mean

    July temperature is 50°F (10°C). Using this isotherm as a criterion,

    it is convenient to extend the border between the Polar Climate and

    the adjoining regions across the oceans, as shown in Fig. 1.

            From a meteorological point of view it is convenient to define

    003      |      Vol_VII-0009                                                                                                                  
    the Arctic Region as the region around the North Pole occupied by

    Polar Climates (Fig. 1.), excluding the isolated islands of such

    climates that occur in certain mountainous regions in lower lati–

    tudes. It should be noted, however, the weather conditions typical

    of the arctic are normally encountered also in the regions occupied

    by the snow-forest climate (i.e., regions D in Fig. 1).

            Fig. 2 The normal distribution of the air temperature as a function

    of latitude and as a mean for all meridians is shown in Fig. 2.

    Using the 10°C July isotherm as the line of demarkation between the

    arctic region and the adjacent climatic zones, it will be seen that

    the mean position of this isotherm is about 66°N. The area of the

    arctic region, as defined above, is therefore about one-twelvth of

    the area of the northern hemisphere. Using the correspondence iso–

    therm of the warmest month in the southern hemisphere as the border

    of the antarctic region, it will be seen from Fig. 2 that this

    isotherm is found about 48°S, indicating that the area of the

    antarctic region is about three times as large as that of the

    [ ?] arctic region.



    004      |      Vol_VII-0010                                                                                                                  

           

    COMPOSITION AND STRUCTURE

            Composition of Dry Air . - The air consists of mixture of a number

    of gases. Most of these are present in a perfectly mixed state,

    with the result that their relative amounts are constant all over

    the world, at least up to 25-30 km. (80,000 - 100,000 ft.). The

    most important of the constituents are given in Table I, which is

    summarized from a recent publication of the International Meteoro–

    logical Organization [ 21 ] . The amounts are expressed in terms

    of mol. fractions, which for all practical purposes may be taken

    to indicate the volume percentage occupied by each gas.

    TABLE I. - Principal Constituents of Dry Air .
    Nitrogen 78.09 per cent
    Oxygen 20.95 per cent
    Argon 0.93 per cent
    Carbon Dioxide 0.03 per cent

            In addition to these principal constituents, there are traces

    of Neon, Helium, Krypton, Hydrogen, Xenon, Ozone and Radon, but

    005      |      Vol_VII-0011                                                                                                                  
    their amounts are so small that they are of no practical importance.

            The amount of carbon dioxide is not quite constant. The vege–

    table world continuously consumes carbon dioxide which, again, is

    produced by the animal world, through burning of fuels, volcanic

    action, and various processes of decay in the soil. Although these

    processes are not always balanced, the oceans, by dissolving the

    excess of carbon dioxide, so effectively regulate it that no great

    variations arise. In view of the absence of local sources, the

    amount of carbon dioxide in the arctic is likely to be rather less

    than the normal for the atmosphere as a whole.

            Ozone, which is present in minute amounts in the atmosphere,

    shows a considerable variation with season, latitude and height;

    it also varies with the weather situation.

            Extensive investigations by Dobson [ 11 ] , Tönsberg [ ], and

    Langlo Olson [ 46 ] , Craig [ 10 ] and others have revealed the fol–

    lowing broad features of the distribution and variation of the

    amount of ozone.

            (a) The amount of ozone per unit volume increases with

    006      |      Vol_VII-0012                                                                                                                  
    elevation, reaches a maximum value somewhere between 20 and 30 km.

    (65 - 100,000 ft.) and then decreases.

            Fig. 3 (b) The total amount of ozone (in a vertical air column) has

    a pronounced annual variation with a maximum in spring and a minumum

    in late autumn (Fig. 3).

            (c) The total amount of ozone in middle latitudes varies

    aperiodically with the general weather situation, the amount being

    larger when the air current is from a northerly direction than when

    it is from a southerly direction.

            From the foregoing discussion it follows that the composition of

    the dry atmosphere in the arctic region is essentially the same as

    elsewhere, except that the arctic region is particularly rich in

    ozone, and probably slightly deficient in carbon dioxide content.

    007      |      Vol_VII-0013                                                                                                                  
    Water Vapor . - The air also contains a variable amount of water

    vapor. In many respects the water vapor is the most important

    constituent of the atmosphere. The maximum amount of water vapor

    that the air can absorb depends entirely upon the temperature; the

    higher the temperature of the air the more water vapor can it hold,

    the air being saturated with moisture when the maximum is reached.

            The amount of water present in the air is conveniently

    expressed by the pressure that it exerts. This pressure is usually

    expressed in millibars, 1 mb. corresponding to 0.75 mm. or 0.029

    inches of mercury under standard conditions.

            The maximum amount of water vapor, or the saturation vapor

    pressure , various temperatures is given in Table II. Comparing

    these figures with the curves in Fig. 2, it will be seen that the

    maximum vapor pressure corresponding to the mean temperatures in

    the vicinity of the North Pole would be about 0.1 mb. in January,

    6.0 mb. in July, and 2.8 mb. as a mean for the year. The amount of

    water vapor in the arctic may, therefore, vary by several thousand

    percent during the year.

    008      |      Vol_VII-0014                                                                                                                  

    TABLE II. Saturation Vapor Pressure (E, in millibars) at various

    temperatures . E w refers to a water surface , and E i to ice surface .
    T(°C) T(°F) E w T(°C) T(°F) E w E i
    30 86.0 42.4 −5 23 4.21 4.02
    28 82.4 37.8 −10 14 2.86 2.60
    26 78.8 33.6 −15 5 1.91 1.65
    24 75.2 29.8 −20 −4 1.25 1.03
    20 68 23.4 −30 −22 0.51 0.38
    15 59 17.0 −40 −40 0.19 0.13
    10 50 12.3 −50 −68 0.06 0.04
    5 41 8.7 −60 −86 0.01
    0 32 6.1 −70 −104 0.003



    009      |      Vol_VII-0015                                                                                                                  

            Comparing the arctic region with the equatorial belt, it will

    be seen from Fig. 2 Table II that the saturation vapor pressure

    in the vicinity of the North Pole is about one-sixth in July, and

    about one-four hundredth in January, of the saturation vapor pressure

    near equator. Since the air normally is not quite saturated,

    the contrasts of the actual amounts of water vapor will be somewhat

    less. Nevertheless, the moisture content is expressed in ab–

    solute amounts, the arctic region stands out as being excessively

    dry during the cold season. This absolute dryness, together with

    the low temperature, constitutes an environmental factor of great

    importance.

            Although the arctic air is dry, on an absolute scale, it is

    not so in terms of relative humidity. Let e denote the actual

    vapor pressure and E the saturation vapor pressure corresponding

    to the air temperature. The relative humidity is then defined as

    100 e/E, i.e., the actual vapor pressure expressed as a percentage

    of the maximum value at the temperature in question. The distribu–

    tion of the relative humidity, as a function of latitude and a

    010      |      Vol_VII-0016                                                                                                                  
    Fig. 4 mean for all meridians, is shown in Fig. 4. It will be seen that

    the relative humidity in the arctic is normally about 10 per cent

    higher than in middle latitudes, and about 5 per cent lower than

    in the equatorial belt.

            Impurities. - Apart from the above-mentioned gaseous constituents,

    the atmosphere contains a variety of impurities, such as dusts, soots

    and salts.

            The main source of dust is the dry climatic regions (Fig. 1).

    The coarser material is never carried far from its source, but minute

    dust particles are readily kept soaring by the turbulent motion and

    carried long distances from their place of origin by the general

    air currents. Before dusty air from the arid regions arrives in

    the arctic, it will normally have been cooled so much that conden–

    sation has occurred; the precipitation of water from the clouds

    washes out the dust to a very large extent, with the result that

    the air in the arctic region is particularly free of dust. This

    is especially true in winter when the rate of cooling of the north–

    ward moving air masses is largest.



    011      |      Vol_VII-0017                                                                                                                  

            The industrial regions and forest fires constitute the main

    source of soot*, but since these sources are far removed from the

    arctic, the impurities will normally have been removed, either

    through precipitation or sedimentation, before the air arrives in

    the arctic.

    * In addition, soot may be supplied by volcanic eruptions.

            Observations show that the air normally contains considerable

    amount of salts. Through the action of the winds, spray is whirled

    up from the oceans, and when the spray droplets evaporate the salt

    remains in the air. These minute salt particles constitute highly

    effective nuclei of condensation, and are, therefore, washed out

    of the air through the precipitation processes.

            The arctic air masses are, therefore, characterized by ex–

    tremely low values of turbidity, and this influences the visual

    range very greatly. In the arctic, the sky, when clear, is

    characterized by the brilliance of stars during periods of darkness,

    012      |      Vol_VII-0018                                                                                                                  
    and by intense blueness during periods of light or dusk. Distant

    objects (e.g., mountain ranges) stand out with great clarity in

    shape and detail.

            The purity of the arctic air is noticeable even in low and

    middle latitudes when these regions are invaded by arctic air masses.

    As has been shown by Bergeron [ 3 ] , the opalescent turbidity can

    be used as a means of indentifying traveling air masses, and this

    technique has been of importance in the development of the methods

    of weather analysis and forecasting.

            Troposphere and Stratosphere . - Although the state of the atmosphere

    is subject to incessant variations, the mean (or normal) state indi–

    cates a division of the atmosphere into fairly well-defined layers.

    This stratification of the atmosphere is not immediately apparent

    in the distribution along the vertical of atmospheric pressure and

    density, but it stands out clearly in the distribution of tempera–

    ture.

            Fig. 5 Some typical examples of the distribution along the vertical

    of the air temperature are shown in Fig. 5, which is reproduced

    013      |      Vol_VII-0019                                                                                                                  
    from a recent publication of the Canadian Meteorological Service [ 27 ] .

    Disregarding for the moment the conditions near the earth’s surface,

    it will be seen that the temperature decreases with elevation at a

    fairly regular rate of about 60°C per km. (10°F per 3,000 ft.) up to

    about 8 km. (26,000 ft.) in winter and to about 10 km. (33,000 ft.)

    in summer. At higher levels the temperature is either constant or

    increases slightly with elevation.

            The lower part of the atmosphere, in which the temperature de–

    creases with elevation, is called the troposphere , and the upper

    part, in which the temperature is constant or increases with eleva–

    tion, is called the stratosphere . The transition from the tropo–

    sphere to the stratosphere, which usually is quite distinct, is

    called the tropopause .

            The examples shown in Fig. 5 represent the conditions on the

    fringe of the arctic. In the central part of the arctic region

    still lower temperatures would be observed, particularly in the

    lower half of the troposphere.



    014      |      Vol_VII-0020                                                                                                                  

            Fig. 6 Fig. 7 The mean thermal structure of the atmosphere up to 20 km.

    (62,000 ft.) above sea level is shown in Figs. 6 and 7 for winter

    and summer respectively. These diagrams represent the mean con–

    ditions for 18 meridional sections at intervals of 20 degrees

    starting from Greenwich meridian. The observational material used

    for the construction is that contained in “The Normal Weather Maps”

    [ 47 ] . The northernmost parts of the diagrams are largely based

    upon extrapolations and tests for consistency. Although this may

    have led to errors in detail, there can be little doubt that the

    diagrams represent the essential features of the thermal structure.

            Considering first the conditions in January, it will be seen

    that the mean positions of tropopause, which is found at about

    8 km. (26, 000 ft.) in the polar region, rises slowly southward to

    about 50°N, and then rises at a rapid rate to about 25°N, where it

    becomes horizontal at about 17 km. (56,000 ft.).

            It will be seen from Fig. 6 that there are five regions in the

    atmosphere (below 20 km.) which are characterized by extreme tempera–

    tures. The coldest region is found at about 17 km. (56,000 ft.)

    015      |      Vol_VII-0021                                                                                                                  
    above sea level in the equatorial belt, where the mean temperature

    is about −75°C (−105°F). The next coldest region is found in the

    vicinity of the arctic tropopause, where the mean temperature is

    about −63°C (−81°F). The third coldest region is found at the sur–

    face over the arctic fields of snow and ice, where the mean tempera–

    ture varies between −25 and −41°C (−13 and −42°F). This lower cap

    of cold air is separated from the upper cold region by a layer of

    relatively warmer and fairly uniform air with temperatures in the

    vicinity of −26°C (−13°F) at about 2 km. (6500 ft.) above the ice.

            In contrast to these cold regions we find two warm regions,

    one at low levels near the equator, and a second in the troposphere

    in subpolar latitudes.

            In summer (Fig. 7) the conditions are largely the same as in

    winter, except that the cold regions in the arctic are less distinct.

    In all seasons, the temperature in the troposphere decreases north–

    ward, whereas in the stratosphere the temperature decreases, on the

    whole, from the arctic toward the equator.



    016      |      Vol_VII-0022                                                                                                                  

            Fig. 8 The annual variation of temperature, as a mean for all meridians,

    is shown in Fig. 8. It will be seen the maximum variation occurs

    at low levels in the arctic. This variation decreases rapidly with

    elevation and reaches a minimum of about 20°C (36°F) at about 3 km.

    (10,000 ft.) above which level there is a slight increase up to

    about 5-6 km. (16,000-20,000 ft.) and then a rapid decrease up to

    10 km. (33,000 ft.) which is the mean summer position of the tropo–

    pause. In the stratosphere the annual variation is relatively small.

    Considering the conditions level for level, the annual variation of

    temperature of the free atmosphere decreases from the pole to the

    equator. The same is true of the conditions at the earth’s surface

    if one considers the mean for all meridions It should be noted,

    however, that the annual variation near the earth’s surface is

    larger in Northern Russia, Siberia, and Canada than it is at the

    pole (see p. ).

            At heights greater than those shown in Figs. 6-8, ordinary

    observations are so sparse that the meridional structure and annual

    017      |      Vol_VII-0023                                                                                                                  
    variation cannot be evaluated with much confidence. From observa–

    tions of meteors and sound waves and from a few direct observations

    by rockets and sounding balloons it is possible to piece togather

    a picture of the broad features of the uppermost atmosphere, and

    these may be summarized as follows. The stratosphere is almost

    isothermal up to about 35 km. (21 miles); above this level the

    temperature increases rapidly and reaches a maximum of about 75°C

    (167°F) at a height of about 60 km. (37 miles) whereafter it de–

    creases to about −25°C (−13°F) at about 80 km. (50 miles). This

    warm layer is sometimes called the mesosphere.

            Above the mesosphere lies the ionosphere which extends up to

    great heights and merges gradually with empty space. The ionosphere

    is characterized by free electric charges. Some of the gaseous par–

    ticles are broken down into ions and free electrons by absorption of

    the ultraviolet radiation from the sun, which also causes a dissocia–

    tion of oxygen and nitrogen molecules into their atomic forms and

    causes very high temperature at extreme heights. The ionosphere

    018      |      Vol_VII-0024                                                                                                                  
    is the abode of the aurora borealis; it is divided into several

    layers that reflect radio waves in various wave lengths.

    019      |      Vol_VII-0025                                                                                                                  

           

    INVERSIONS AND LAPSE RATES

            Fig. 9 Although the temperature normally decreases with height in the

    troposphere as a whole, the lower part of the arctic region forms

    an exception (see Fig. 6). Here the temperature normally increases

    from the earth’s surface up to a distance which rarely exceeds 2 km.

    (6,000 ft.) and sometimes may be as low as 200 m. (600 ft.) or less.

    Some examples are shown in Fig. 9.

            The rate at which the temperature decreases with elevation is

    called the lapse rate . A layer through which the temperature in–

    creases with elevation is called an inversion , and such layers are

    characterized by counterlapse . The base of the inversion is the

    level where the counterlapse commences, and the top of the inversion

    is the level where the counterlapse changes into a lapse of tempera–

    ture.

            It is convenient to compare the observed lapse or counterlapse

    with the adiabatic lapse rate, which is the rate at which a unit of

    air would cool if it were thermally isolated and lifted against the

    gravitational force. The adiabatic lapse rate, which is a critical

    020      |      Vol_VII-0026                                                                                                                  
    value for many processes, is expressed by the formula

    Γa = g/Cp

    where g is the acceleration of gravity and Cp the specific heat

    of air at constant pressure. Substituting the numerical values for

    g and Cp, it is found that Γa =1°C per 100 m. = 5.5°F per 1000 ft. for nonsaturated

    air.

            Above the top of the inversion the lapse rate is normally about

    1/2 to 2/3 of the adiabatic rate. Occasionally, the adiabatic rate

    may be approached, but it is never exceeded by any appreciable

    amount.

            In the inversion layer, the counterlapse may be very large;

    numerical values as high as 5°C per 100 m. are quite common, and

    close to the snow surface values as high as 1°C per meter are not

    uncommon, particularly in calm and cloudless conditions in winter.

            In calm air or when the winds are light the base of the

    inversion is found at the earth’s surface. However, when the wind

    021      |      Vol_VII-0027                                                                                                                  
    Fig. 10 is sufficiently strong, friction along the earth’s surface causes

    the lower layer to be mixed, and a normal lapse rate is established

    in the lower layer while an inversion may be present at some distance

    above the surface. These elevated inversions are usually less

    intense than the ground inversions. Sverdrup [ 43 ] investigated

    the occurrence of inversions by the aid of kites carrying instruments.

    Since kites could be used only when the wind speed was sufficiently

    high, his results (Fig. 10) apply to elevated inversions. It will

    be seen that the inversion is lower in winter than in summer.

            Fig. 11 The intensity of the inversion increases with decreasing could

    cover, and the most intense inversions occur after spells of calm

    and clear weather. An example of the dependence of the inversion

    on wind speed and cloud cover is shown in Fig. 11, which is reproduced

    from a recent publication by the Canadian Meteorological Service

    [ 27 ] .

            The inversions are most strongly developed over land and ice.

    When the arctic air streams over open water of appreciably higher

    temperature (e.g., in winter), the inversion is destroyed through

    022      |      Vol_VII-0028                                                                                                                  
    heating of the surface layer. In such cases, an adiabatic, or

    even superadiabatic, lapse rate develops above the water surface.

    The same is true of arctic air that invades warm continents in

    summer.

            From the foregoing discussion it follows that the central

    arctic is characterized by a well - developed inversion layer, and

    that along the fringe of the arctic extreme variations occur, with

    changes from large counterlapses to the adiabatic or superadiabatic

    lapses.

            The processes leading to the formation and maintenance of the

    arctic winter inversions have been investigated by Petterssen [ 32 ]

    and Wexler [ 53 ] . These involve the general circulation of the

    atmosphere and the radiative and eddy flux of heat.

            The snow surface, being an efficient radiator, will lose heat

    toward space, and the air in contact with the snow will cool faster

    than the air aloft. The snow surface will, therefore, act as a cold

    source relative to the overlying layer of air. Since the atmospheric

    023      |      Vol_VII-0029                                                                                                                  
    pressure over the arctic is higher than over the adjacent oceans

    (heat sources), the distribution of heat and cold sources is such

    as to constitute a hindrance to the circulation, and a layer of

    stagnant air develops over the arctic snow and ice fields. Since

    the air is stagnant, it becomes subjected to continued cooling from

    below. As the surface layer becomes very much colder then the over–

    lying air, downward radiative flux of heat will tend to balance

    the cooling of the ground. The maximum difference in temperature

    between the top and the base of the inversion, which depends upon

    the contents of moisture and carbon dioxide of the air, has been

    determined by Wexler to be about 30 °C ( 54 °F), and this

    value agrees well with observation.

            In summer the conditions are largely similar to those in winter,

    except that the cold source is due mainly to the melting of snow,

    while the air at higher levels is heated by radiation.

            If the wind is sufficiently strong, the radiative cooling of

    the surface layer will be offset by the downward eddy flux of heat,

    024      |      Vol_VII-0030                                                                                                                  
    and the inversions become weaker, or may disappear temporarily and

    locally. If the sky is cloudy, the back - radiation from the clouds

    will have a similar effect.

            The arctic inversions are of great importance in many ways,

    notably in connection with propagation of sound and light.



    025      |      Vol_VII-0031                                                                                                                  

           

    ACOUSTIC PHENOMENA

            No one who has lived in the arctic can have failed to observe

    the frequent occurrence of supernormal audibility and the wide

    variation in the audible range. For example, Captain Perry [ 35 ] ,

    on his third voyage, noted a case where conversation was carried on

    over a distance of 1.2 miles, and Collinson [ 9 ] reported on a

    case where spoken words were heard at a distance of 2 miles. The

    most extraordinary case of abnormal sound effects in the arctic is,

    perhaps, the one described by Wegener [ 52 ] . On the Danish Green–

    land expedition, 1907-08, observers at Pustervig, on the northeast

    coast of Greenland, heard a tone of deep pitch (estimated at about

    30 c.p.s.) which lasted for several hours and appeared to emanate

    from a closed fjord called Dove Bay. This sound was heard on several

    occasions when the fjord was filled with cold stagnant air.

            These abnormal sound effects can readily be explained by

    reference to the structure of the arctic atmosphere and the properties

    of the snow and ice.

            The range at which sound can be heard depends upon the temperature

    026      |      Vol_VII-0032                                                                                                                  
    of the air, the speed and direction of the wind, and the rate at

    which sound energy is absorbed by the earth’s surface.

            1. Influence of Snow and Ice . - It is well known that soft

    snow falling through the air absorbs sound energy very effectively.

    The same is true of soft snow on the ground. On the other hand,

    a hard crusted snow surface absorbs but little energy, and a smooth

    ice surface is an almost ideal reflector of sound. The rate at

    which sound energy is absorbed depends upon the pitch. Kaye and

    Evans [ 22 ] measured the absorbtion coefficient of newly fallen

    snow in England and found the values reproduced in Table III. It

    TABLE III. Absorbtion Coefficient of Newly Fallen Snow .
    Snow depth

    inches
    Frequency (c.p.s.)
    125 250 500 1000 4000
    1 0.15 0.40 0.65 0.75 0.85
    4 0.45 0.75 0.90 0.95 0.95

            will be seen that for a pitch higher than 500 cycles per second, a

    snow cover 4 inches, or more, deep absorbs almost all sound energy.

    Although comparable figures for hard snow surfaces are not available,

    027      |      Vol_VII-0033                                                                                                                  
    it is evident that the absorbtion coefficient decreases rapidly

    with the hardness, and is almost negligible for a smooth ice sur–

    face. The audible range will, therefore, be short over a soft snow

    surface, relatively large over hard snow, and excessively large

    over ice fields.

            2. Influence of air temperature . - One of the major causes of

    the supernormal audible range in the arctic is due to the distribution

    of temperature, and in particular to the inversion layers described

    in the foregoing section. Let C denote the speed of propagation

    of the sound, and T the absolute temperature of the air. In still

    air, the velocity of sound is proportional to the square root of the

    absolute temperature. We may, therefore, write

    C = A√(T)

    where A is a constant for any given composition of the air. The

    minor variations in composition, discussed in a foregoing section,

    are too small to have any noticeable effect on the speed of propa–

    gation



    028      |      Vol_VII-0034                                                                                                                  

            Although the air temperature may very vertically as well as

    horizontally, the latter variation is usually negligible in com–

    parison with the former, and as shall here be concerned to discuss

    only the influence due to the variation along the vertical.

            We consider first the idealized case when the temperature is

    uniform in all directions (isothermal conditions). The speed of the

    sound would then be uniform, and the “sound front” would be a

    spherical shell expanding with a constant speed.

            Fig. 12 Instead of the “sound front” it is more convenient to consider

    the “sound beams” or “sound rays”. These are represented by lines

    originating in the sound source and being everywhere perpendicular

    to the sound front. The sound rays in an atmosphere of uniform

    temperature are shown in Fig. 12A, where the sound source is at

    the earth’s surface. The rays are straight lines through the source.

    Since the energy of a sound impulse is distributed uniformly on a

    spherical surface, it is evident that the sound intensity must be

    inversely proportional to the square of the distance from the

    source, or

    029      |      Vol_VII-0035                                                                                                                  
    I = I1/R2

    where I 1 is the intensity at unit distance from the source, and

    I is the intensity at the distance R from the source. In the fol–

    lowing, we shall refer to eq. (2) as the inverse square law.

            Let us now consider the case when the temperature decreases

    along the vertical, as it normally does in middle and low latitudes.

    The sound will travel faster in the horizontal than in the vertical

    direction. The sound front will no longer be spherical, and the

    sound rays will be curved upward as shown in Fig. 12B. The beams

    that leave the source horizontally will lose contact with the earth’s

    surface, and in the space below these beams, a sound shadow will be

    found. This shadow refers to the beams, or the direct sound. A

    certain amount of sound is, however, diffracted across the beams

    into the shadow, but the intensity of this sound is small and it

    decreases at rate which exceeds the inverse square law.

            The conditions represented in Fig. 12B being typical of middle

    and low latitudes, it is evident that most people’s experience

    030      |      Vol_VII-0036                                                                                                                  
    about sound from distant sources is based upon the rather faint

    sound which is diffracted into the beam shadow. Above the beam

    shadow, the beams are more concentrated in Fig. 12B than they are

    in Fig. 12A, with the result the intensity of the sound is corre–

    spondingly increased. It will, thus, be seen that when the tem–

    perature decreases along the vertical, the sound tends to escape

    upward, and but little energy is transmitted along the earth’s

    surface.

            As was shown in the foregoing section, inversion layers are

    almost always present in the arctic. We shall, therefore, consider

    this case in some detail. Since the temperature increases upward

    through the inversion layer, the sound will travel faster vertically

    than horizontally; the wave front will now be elongated upward, and

    the sound beams will be curved downward. Fig. 12C shows the rays

    from a sound source ( ) at the earth’s surface when tempera–

    ture distribution is as shown to the right of the beams. It can

    easily be shown that a beam that leaves the source at certain

    critical angle will become tangent to the top of the inversion

    031      |      Vol_VII-0037                                                                                                                  
    layer where it splits, one branch (b) being curved downward and

    the other branch (c) being curved upward. This critical angle

    depends entirely upon the temperature difference between the top

    and the base of the inversion, and is independent of the depth of

    the inversion layer. The space between the beams b and c in

    Fig. 12C is silent as far as direct sound is concerned.

            The beams that leave the source at angles less than the critical

    value, will be refracted toward the earth’s surface. A considerable

    portion of this sound is, again, reflected from the earth’s surface,

    and this together with sound that is diffracted across the beams

    will penetrate into the part of the shadow that is below the top

    of the inversion. On the other hand, beams that leave the source

    at angles greater than the critical value, will penetrate the in–

    version and escape into space.

            Referring again to Fig. 12C, it is of interest to note that

    the concentration of the beams is larger in the inversion layer and

    less above this layer than in the radial case shown in Fig. 12A.

    032      |      Vol_VII-0038                                                                                                                  
    From this it follows that the sound intensity below the top of the

    inversion decreases more slowly than indicated by the inverse square

    law; above the top of the inversion, the reverse is true.

            We shall next consider Fig. 12D which illustrates the con–

    ditions when the sound source is above the top of the inversion.

    The inversion layer will now act as a hindrance to the propagation

    of sound toward the earth’s surface. Except where the sound source

    is directly overhead, or nearly so, very little sound energy reaches

    the earth’s surface. Thus, an aircraft flying above the top of

    the inversion is not readily detected by acoustic means.

            From the foregoing discussion it follows that an inversion

    layer acts as a duct for sound emanating from sources below its top,

    and as a cushion against sound that emanates from sources above its

    top. Neither the duct nor the cushion is perfect, and their

    efficiency (in still air) depends upon the intensity of the inver–

    sion.

            The sound intensity may become greatly supernormal when the

    sound source is situated below an inversion in a fjord (or valley)

    033      |      Vol_VII-0039                                                                                                                  
    surrounded by steep walls. If the fjord is frozen and the mountain

    sides covered by hard snow, an almost ideal sound channel is estab–

    lished, sound being reflected from the ice, the mountain sides and

    the top of the inversion. If the fjord has a local contraction, a

    basin is formed which, when the dimensions are suitable, may form

    a resonant box. The case described by Wegener (loc. cit.) apparently

    belonged to this category of sound effects.

            Although the mean state of the lower arctic atmosphere is

    characterized by one inversion layer (see Fig. 6), multiple inver–

    sions occur quite frequently, particularly over and near arctic

    land masses (e.g. Greenland). The sound effects associated with

    multiple inversions are extremely complex, and several zones of

    shadow and zones of maximum intensity may occur, depending upon the

    position of the source. Fig.12E shows, as an example, the sound

    pattern of a source situated between two inversions. It will be

    seen that the sound tends to become trapped between the top of the

    lower and the base of the upper inversion, and that several shadow

    zones may result.



    034      |      Vol_VII-0040                                                                                                                  

            3. Influence of wind . - If V denotes the speed of the wind,

    the velocity of sound can be expressed by the formula

    C = A√(T) + V

    which is the same as the velocity in still air plus the velocity of the

    medium through which the sound travels. Now the former of these

    velocities is of the order of 300 m/sec. (700 mph) while the latter

    is of the order of 10 m/sec. (20 mph). The direct influence of the

    wind is, therefore, very small if the wind is uniform in all direc–

    tions.

            Owing to friction along the earth’s surface, the wind increases

    with elevation up to about 500-1000 m. (i.e., 1500-3000 ft.). Al–

    though the increase varies with the roughness of the ground, the

    wind speed over a snow surface will normally be twice as large at

    about 600 m. as is at 10 m. above the ground. Above this layer,

    which is called the friction layer, the wind may increase or de–

    crease with elevation depending upon the horizontal temperature

    gradient.

            The variation along the vertical of the wind has a marked

    035      |      Vol_VII-0041                                                                                                                  
    influence on the propagation of sound. To demonstrate the nature

    of this influence, we consider Fig. 12F, in which it is assumed

    that the temperature is uniform along the vertical, while the wind

    distribution is as indicated to the left. The beams that go down–

    wind will be curved toward the earth’s surface. A beam that leaves

    the source at a certain critical angle, will just touch the level

    where the wind becomes uniform, and at greater distance from the

    source, a sound shadow will be found below this level. The beams

    that go upwind will be curved away from the earth’s surface, above

    which another sound shadow is found. The greatest concentration of

    sound beams is found in the downwind direction in the layer where

    the wind increases, and it is here that the supernormal audibility

    is observed.

            In the arctic both the wind and the temperature will normally

    increase with elevation through the friction layer, with the result

    that both effects combine to give supernormal sound intensity down–

    wind. In the upwind direction, the temperature effect is counter–

    acted by the wind effect, and except when the wind is very light,

    036      |      Vol_VII-0042                                                                                                                  
    the wind effect predominates.

            4. Sound ranging . - From the foregoing discussion it follows

    that for any given source intensity the audible range depends upon

    the curvature of the sound beams in the vertical plane, and this

    curvature is determined by the distribution along the vertical of

    temperature and wind. Provided that soundings of temperature and

    wind are available, the path of the sound beams can be reconstructed

    and the position of the sound source identified. A convenient

    method of sound ranging has been developed by Bedient [ ] .

            For further information on propagation of sound in the atmosphere,

    reference is made to the works of Wa e lchen [ 50 ] , Rothwell [ 36 ] ,

    Whipple [ 55 ] , Gutenberg [ 15 ] , and Saby and Nyborg [ 37 ] .



    037      |      Vol_VII-0043                                                                                                                  

           

    OPTICAL PHENOMENA

            In addition to the aurora borealis, the abode of which is in

    the ionosphere (see pp ), the sojourner in the arctic

    will observe a number of optical phenomena of great beauty and in–

    tensity. Some of these, such as the rainbow, the corona and the

    halo, are not essentially different from those observed in middle

    latitudes and will not be described here. The optical phenomena

    which are most typical of the arctic and of some importance to the

    arctic traveler are the mirages which are due to abnormal bending

    of the light rays, and the ice blinks and the water sky which are

    due to reflection of light from ice and water surfaces by the lower

    face of a cloud layer.

            The mechanism of the formation of mirages is readily explained

    by reference to the fact that light travels slightly faster in thin

    air than it does in denser air. Thus, since the air density decreases

    with elevation (except in very rare cases), a slant beam of light

    will be curved downward, and this curvature depends upon the rate

    at which the density decreases across the beam. In the following

    038      |      Vol_VII-0044                                                                                                                  
    we shall be concerned to discuss the bending of light beams between

    points on the surface. Since these beams are quasi-horizontal it

    suffices to consider the lapse of density along the vertical.

            Using the equation of state and the hydrostatic relationship,

    it is readily shown that the rate of decrease of density (p )

    with height (z) is expressed by

    -(∂p/∂z) = (p/RT2)((g/R) – Γ)

    where p denotes pressure, T absolute temperature, Γ lapse rate

    of temperature, R the gas constant, and g the acceleration of

    gravity.

            Since g and R are physical constant and p varies but

    little in any given place, it will be seen that the lapse rate of

    density (and the refractive index) is determined almost exclusively

    by the temperature conditions.

            Travelers in the arctic have noticed a marked annual variation

    in the optical phenomena, and this can readily be explained by

    reference to equation (1). Let us assume for the moment that the

    039      |      Vol_VII-0045                                                                                                                  
    lapse rate of temperature is the same in winter as in summer.

    Under typical arctic conditions the absolute temperature would be

    about 275°A in summer and about 230°A in winter. It is then readily

    seen that the refractive index is normally about 40 per cent greater

    in winter than in summer. In addition to this effect of the annual

    variation of temperature there is a large annual variation in the

    lapse rate of temperature (see Fig. ), with the result that

    the refractive index may vary several hundred per cent during the

    annual cycle. In fact, the largest variations are due to the change

    in lapse rate of temperature.

            As was shown in a foregoing section (p. ) the temperature

    of the troposphere normally decreases with elevation such that

    = 0.6°C per 100 meters (or 3.3°F per 1000 ft.), and this

    together with the first term within the parentheses of eq. (1)

    accounts for the normal refraction of light in the atmosphere. In

    the arctic, however, the lapse rate may vary within very wide limits,

    thus giving rise to abnormal bendings of the light beams.



    040      |      Vol_VII-0046                                                                                                                  

            1. The superior mirage occurs in connection with temperature

    inversions (p. ). In the inversion layer the temperature in–

    creases with elevation, and the lapse rate of temperature (i.e., )

    is negative. It will then be seen from formula (1) that the den–

    sity decreases along the vertical at an abnormally fast rate, with

    a consequent abnormal downward refraction of the light beam. An ob–

    ject seen through the inversion layer will become distorted so that

    it appears elongated in the vertical direction. For example, a

    relatively flat strip of coast land may appear as an erect strip

    and give the false impression of being a steep cliff; irregulari–

    ties in the coast line will appear like columns, and the distor–

    tions produce a picture which resembles architectural pseudo–

    prostyle. In pronounced cases, the erect image is surmounted by

    an inverted image, and in rare cases the inverted image is, again,

    surmounted by second erect image.

            Fig. 13 An example of a superior mirage is shown in Fig. 13. The

    upper picture shows the natural shape of Gundahl’s Knold while the

    lower picture shows strong vertical distortion due to the presence

    041      |      Vol_VII-0047                                                                                                                  
    of an intense inversion.

            The superior mirage may occur without inverted image and dis–

    tortion, in which case objects which are actually below the obser–

    ver’s true horizon will appear above his apparent horizon. This

    phenomenon is called looming. This, together with the pronounced

    purity of the arctic air (p. ), probably accounts for many

    instances of erroneous estimates of distances and reports of dis–

    covered land masses and mountains in places where none exist. In

    1818 Captain John Ross saw snow-covered peaks in Lancaster Sound

    (74°N, 85°W), at an estimated distance of thirty miles, which appeared

    to bar his way into the Northwest Passage. Subsequent explorations

    have made it evident that the peaks seen by Ross were those of

    North Somerset Islands (73°N, 93°W) at a distance of about 200

    miles. Pearly and his companions clearly saw on two occasions in

    1906 an extensive mountainous snow-covered land northwest of Cape

    Colgate (82°N, 91°W) in Grant Land at an estimated distance of 130

    miles, and named it Crocker Land. In 1914 MacMilland and Green

    042      |      Vol_VII-0048                                                                                                                  
    sighted Crocker Land and sledged 130 miles in its direction, seeing

    the mountains once on the journey but never reaching them. The

    exact location of Crocker Land is still a mystery, and it appears

    certain that the sightings were caused by looming of unusual in–

    tensity.

            The distance over which an object may loom depends upon the

    height of the inversion and the difference in temperature between

    the top and the base of the inversion. In calm and cold weather

    the inversions are likely to be deep and intense; distances esti–

    mated in such conditions are likely to be much in error.

            It is of interest to note that looming is a local phenomenon;

    at some point closer to the loomed object than the observer, the

    object will not be visible. The effect may be likened to the

    “skipping” of radio waves which permits reception close to the

    transmitting station and at considerable distance from it, but not

    at intermediate distances. As a consequence of this, it is readily

    seen that for an aircraft that sees a loomed sun, there must be

    points both above and below the aircraft for which the sun will

    043      |      Vol_VII-0049                                                                                                                  
    Fig. 14 have set, and twilight will prevail both above and below an

    aircraft illuminated by the loomed sun. These conditions are shown

    diagrammatically in Fig. 14.

            2. The inferior mirage forms when the temperature decreases

    with elevation at an excessive rate. These mirage, which are

    common occurrences is southern deserts, may be observed locally in

    the arctic, particularly where cold air from the ice fields is

    heated by streaming over open water, or where bare land adjacent

    to ice, is heated in sunshine. The superheated layer is usually

    quite shallow (4 to 10 ft.), and within it the lapse rate of tem–

    perature is large and positive. It will be seen from formula (1)

    above that the density decreases with elevation at a subnormal rate;

    in extreme cases when

    [Math Formula]

    is greater than g/R, the lapse of

    density is reversed, and the light beams may be curved away from

    the earth’s surface. In such cases, the true horizon disappears,

    and an apparent horizon is formed below the true horizon leaving

    a gap between the apparent horizon and the inferior mirage of objects

    044      |      Vol_VII-0050                                                                                                                  
    Fig. 15 above the true horizon. An example of an inferior mirage is shown

    in Fig. 15.

            As with the superior mirage, the inferior mirage results in

    a change in the apparent distance of objects. In the case of in–

    ferior mirage, the effect is that of disappearance over the apparent

    horizon of previously seen objects which are known to be above the

    true horizon. This phenomenon is called sinking.

            Fig. 16 Fig. 17 3. The Fata Morgana is a combination of superior and inferior

    mirage occurring when a superheated layer is surmounted by a

    single or multiple inversion. Two examples of these extraordinary

    optical distortions are shown in Figs. 16 and 17. A most vivid

    account of such deformations has been rendered by Koch [ 23 ] in

    the description of his journey across Greenland on 12 April 1913.

            4. Optical haze , or shimmer, occurs in a layer of air next

    to the ground within which the lapse rate of temperature is ex–

    cessive. Within this layer small-scale convective currents develop

    with the warmer lumps of air ascending and the colder descending.

    045      |      Vol_VII-0051                                                                                                                  
    The differences in the refractive index of these lumps cause a

    blurring of objects seen through the layer. Optical haze occurs

    quite frequently in the arctic in the same meteorological condi–

    tions as the inferior mirage; it makes it difficult to identify

    details in the landscape and is annoying for telescopic observa–

    tions, particularly range finding by the aid of coincidence range–

    finder.

            5. Ice blink and water sky . - In the summer season (when the

    sun is above the horizon at a small angle of elevation) light is

    reflected and scattered between the ice surface and the base of

    low layers of clouds. The whitish glare that is often seen on low

    clouds is due to refection of light from distant ice fields. Some–

    times, these reflections are quite intense and are thus called ice

    blink. Conversely, if there are patches or lanes of open water in

    the ice, dark patches or lanes will be seen on the base of cloud

    layers. This is called water sky. Observations on water sky and

    ice blink are extremely useful for navigation on the ice, for they

    indicate, as if seen in a mirror, what lies beyond the horizon.



    046      |      Vol_VII-0052                                                                                                                  

           

    AIR MASSES AND FRONTS

            The concept of air masses, introduced by Bergeron [ 3 ] ,

    is much used in modern meteorology and denotes a vast body of air

    whose physical properties are more or less uniform in the horizontal

    direction. The air, being almost transparent relative to high–

    temperature radiation, absorbs only a small portion of the direct

    solar radiation, and the earth’s surface, which is an efficient

    absorber, takes up a large portion of this radiation, converts it

    into sensible heat and gives it back to the atmosphere, partly

    through low-temperature radiation but mostly through eddy motion,

    or mixing. Consequently, the physical properties of the earth’s

    surface constitute a predominant factor in the formation of the air

    masses.

            The air masses typical of the arctic region in winter are

    characterized by low temperature at all levels, extreme absolute

    dryness and excessively stable stratification. Some examples of

    typical winter conditions are shown in Table IV. It will be seen

    that the relative humidity at high levels is very low; this condition

    047      |      Vol_VII-0053                                                                                                                  

    TABLE IV. Typical Temperature (T) and Relative Humidity (R) of

    Arctic Air Masses in Winter
    Eureka Sound

    (8 ft. above MSL)

    Jan. 19, 1949.
    Fairbanks

    (440 ft. above MSL)

    Jan. 14, 1949
    International Falls

    (1112 ft above MSL)

    Jan. 28, 1949.
    Height T(°C) R (%) T(°C) R(%) T(°C) R(%)
    Station level −45.0 25 −32.8 42 −17.2 68
    2,000 ft. −25.4 50 −18.1 68 −17.2 67
    4,000 ft. −24.8 54 −17.5 75 −15.7 67
    6,000 ft. −23.4 35 −17.0 67 −14.0 32
    8,000 ft. −21.8 24 −20.6 53 −13.7 40
    10,000 ft. −24.9 - −22.6 28 −14.0 31
    15,000 ft. −35.1 - −31.4 - −19.3 32
    20,000 ft. −44.7 - −40.5 - 29.3 -



    048      |      Vol_VII-0054                                                                                                                  
    is due to the circumstance that the air, on account of radiative

    cooling aloft, takes part in a sinking, or settling motion. As

    a result of this prevailing sinking motion and relative dryness,

    high clouds are extremely rare over the central arctic in winter

    (see p. ).

            Fig. 18 The source region of arctic air masses in winter is shown in

    Fig. 18. On the North American and on the Eurasian sides it borders

    onto the source regions of polar continental air masses. These

    latter air masses are in many respects similar to the arctic regions,

    except that the air masses are more shallow and have less extreme

    properties.

            It will be seen from Fig. 18 that warm air from the North

    Atlantic (polar maritime air) normally invades the arctic in the

    region between Iceland and Norway as far east as Novaya Zemlya.

    Less frequently, warm air from the Pacific invades the arctic along

    the west coast of Alaska. On the other hand arctic air invades the

    midlatitude belt most frequently over the eastern parts of North

    America and Siberia. On the whole, more arctic air is shed

    049      |      Vol_VII-0055                                                                                                                  
    southwards than warm air northwards at low levels, the differences

    being made up by an excess of northward transport of warm air at

    greater heights in the troposphere.

            The southward flow of arctic air is by no means a steady one;

    it appears to occur in outbursts of considerable strength, at in–

    tervals of 3 to 10 days, the outburst being associated with intense

    traveling cyclones. These outbreaks of arctic air may sometimes

    reach as far south as 25°N, and are the main cause of cold spells

    in low latitudes. The preferred regions for these outbreaks of

    arctic air are the eastern part of North America and the western

    part of the North Atlantic, and the eastern part of Siberia and the

    adjoining part of the North Pacific.

            Fig. 19 In summer the arctic source region is less effective, owing

    to the sun’s being above the horizon, and the contrast between the

    arctic and neighboring air masses is less extreme. The source region

    of arctic air masses in summer is shown in Fig. 19 in relation to

    neighboring sources. Some examples of typical arctic air masses in

    050      |      Vol_VII-0056                                                                                                                  
    summer are given in Table V. On the whole, the relative humidity

    aloft is higher in summer than in winter, and, as a result, the

    amount of high clouds reaches a maximum in the warm season.

            Fig. 20 Fig. 21 Fig. 22 The transition from the arctic to the neighboring air masses

    is usually not continuous. The mean circulation of the atmosphere

    is such that there is a tendency for the air masses from neighboring

    source regions to be brought together along zones of convergence,

    Along these zones of convergence, which are called fronts , or

    frontal zones, more or less abrupt transition in wind, temperature,

    humidity, and weather will be found. The mean positions of these

    principal frontal zones are shown in Figs. 20 and 21 for winter

    and summer respectively. It will be seen that, on the average,

    the arctic front is not continuous around the pole; it is normally

    absent in the preferred regions of outbreaks of arctic air. A

    schematic meridional cross-section of the principal air mass sources

    and frontal zones is shown in Fig. 22.

    051      |      Vol_VII-0057                                                                                                                  

    TABLE V. Typical Temperature (T) and Relative Humidity (R) of

    Arctic Air Masses in Summer
    Eureka Sound

    (8 ft. above MSL)

    July 1, 1950.
    Fairbanks

    (440 ft. above MSL)

    July 20, 1946
    International Falls

    (1112 ft. above MSL)

    July 12, 1946.
    Height T(°C) R (%) T(°C) R(%) T(°C) R(%)
    Station level 7.2 61 14.0 88 17.0 70
    2,000 ft. 3.5 62 10.2 88 17.6 59
    4,000 ft. −0.3 64 5.3 92 12.5 59
    6,000 ft. −4.2 59 1.8 92 10.5 22
    8,000 ft. −7.9 63 −0.6 98 8.3 -
    10,000 ft. −11.0 66 −2.9 100 5.3 -
    15,000 ft. −18.3 86 −10.8 16 −2.0 20
    20,000 ft. −28.1 62 −20.5 58 −11.6 -



    052      |      Vol_VII-0058                                                                                                                  

           

    CYCLONES AND ANTICYCLONES

            The frontal zones discussed in the foregoing section are

    rarely stable. On account of the contrasts in energy stored along

    frontal zones, perturbations (known as cyclones, depressions, or

    lows) develop and travel along the frontal zones, generally from

    the east to the west with a component toward the north. In the

    areas between the cyclones, regions of high pressure, or anti–

    cyclones, develop and travel, generally eastward with component

    toward the south. Most of these traveling cyclones remain in the

    sup-polar belt and affect the fringe of the arctic region; some

    of them, however, move into and cross the arctic.

            Fig. 23 An example of such a chain of fronts, cyclones and anticyclones

    around the arctic is shown in Fig. 23. It will be seen that, on

    this occasion, the arctic front is well developed over North

    America and over northern Siberia. The polar front, too, is well

    developed, more or less in its normal position. A series of cy–

    clones is associated with the frontal systems, with anticyclones

    in between.



    053      |      Vol_VII-0059                                                                                                                  

            Fig. 24 As compared with middle and low latitudes, the arctic region

    is a relatively quiet area as far as traveling disturbances are

    concerned. The mean meridional distribution of frequencies of

    cyclogenesis (formation of cyclones), cyclones, anticyclogenesis

    (formation of anticyclones), and anticyclones is shown in Fig. 24

    as a mean for all longitudes.

            In summer most anticyclones form about 50°N and move southward

    such that their mean position if about 38°N. There is, however,

    a secondary maximum of anticyclogenesis at about 75°N and a rela–

    tively large maximum north of this latitude. It will further be

    seen that most cyclones form about in latitude 50°N and move such

    that their mean latitude is about 60°N. It has been shown by

    Petterssen [ 32 ] that this poleward tendency of cyclone move–

    ment is due to the thermal structure of the atmosphere and the

    rotation of the earth.

            In winter the frequency distribution is, in principle, the

    same as in summer. In all seasons the arctic region as a whole

    054      |      Vol_VII-0060                                                                                                                  
    is characterized by a low frequency of cyclones and a relatively

    high frequency of anticyclones.

            The low frequency of cyclones is not typical of the entire

    arctic region. As has been shown by Petterssen [ 32 ] , general

    dynamical principles require that cyclonic circulation (vorticity)

    must be produced in the cold sources above cold land and ice fields

    and exported along isentropic surfaces downward to sea level along

    the arctic coast. Hence all the bays of open water along the

    fringe of the arctic will be characterized by cyclonic activity.

    These areas of maximum cyclonic activity are also regions of

    generally bad weather.

            Fig. 25 Fig. 26 Figures 25 and 26 show the geographical distribution of

    cyclone centers in winter and summer, respectively. The following

    regions in arctic and subarctic latitudes are characterized by high

    frequency of cyclones: The Gulf of Alaska and the Aleutian Chain

    (winter and summer), the Baffin Bay and Davis Strait (winter and

    summer), the waters south and west of Iceland (winter and summer),

    the Norwegian Sea (winter and summer), the Barentz Sea (mostly winter).



    055      |      Vol_VII-0061                                                                                                                  

            Fig. 27 Fig. 28 The corresponding frequencies of anticyclones are shown in Figs.

    27 and 28. It will be seen that winter anticyclones are quite fre–

    quent over the central arctic, with a maximum over the north coast

    of Alaska. In summer (Fig. 28) anticyclones are rare on the out–

    skirts of the arctic, but quite frequent over the ice pack.



    056      |      Vol_VII-0062                                                                                                                  

           

    ATMOSPHERIC PRESSURE

            Until seventy years ago, all theoretical considerations concerning

    the general atmospheric circulation postulated a zonal system of westerly

    winds circulating about a low-pressure area centered at the North Pole.

    Subsequent expeditionary data on winds and pressures within the Arctic,

    however, failed to verify this simple concept. Furthermore, as early as

    1888, Helmholtz [ 18 ] had deduced from hydrostatic considerations that

    the prevailing low Arctic temperatures should produce a shallow surface

    anticyclone in polar regions. As a result of the mounting evidence from

    Arctic observations, together with the general acceptance of the Helmholtz

    theory, it became popular during the next four decades to consider the

    existence of a permanent polar anticyclone even though the details of the

    Arctic pressure distribution remained essentially undetermined.



    057      |      Vol_VII-0063                                                                                                                  

            However, from charts published in 1929 depicting the monthly

    averages of temperature, pressure, and cloudiness, Baur [ 1 ] was able to

    show that the centers of high atmospheric pressure tended to correspond

    closely to the regions of minimum hemispherical temperature. He traced

    the movement of the principal Arctic center of maximum pressure (and

    minimum temperature) from a winter position in Eastern Siberia to a

    position north of the Canadian Archipelago in spring, i.e., at a time

    when the sub-Arctic continental regions become relatively warm in comparison

    to the Arctic Ocean. He then made note of a continued easterly movement

    of the centers to a position northeast of Greenland and Spitzbergen in

    early summer. In early autumn Baur found a secondary maximum in pressure

    over the Polar Sea which he ascribed to the effects of rapid cooling in

    the Canadian Archipelago and adjoining ice pack, but on his series of

    charts this center is soon superceded by the Siberian high and a weaker

    counterpart over the Yukon Territory.



    058      |      Vol_VII-0064                                                                                                                  

            The next published series of charts showing the distribution of

    pressure over the Arctic was prepared by Sverdrup, Peterson and Loewe

    [ 42 ] and drew heavily upon the analyses of Baur, Birkeland and Føyn

    [ 1 ] . Dorsey [ 12 ] has more recently revised Sverdrup’s charts upon the

    basis of modern observational data. Dorsey also has considered the charts

    prepared by Dzerdzeyevski [ 13 ] in 1945 - a series which had made use of

    the pressure data obtained near the pole by the Russian North pole Expedition.

            The charts prepared by Dorsey are apparently the most up-to-date and

    figs 29-32 here are the ones presented here as Figures 29 to 32 . While the accuracy of

    the pressure field indicated for the Arctic Ocean, Greenland, and the

    Canadian Archipelago may be open to some question, it is, nevertheless,

    probable that the charts do contain the essential characteristics of the

    true pressure field at the surface. The prevailing wind directions usually

    agree with the isobars and the locations of the principal cyclone tracks

    and frontal systems are in accord with the resulting wind distribution.



    059      |      Vol_VII-0065                                                                                                                  

            In winter (January, Figure 29 ), the Arctic pressure field is

    dominated by the extensive anticyclonic system centered over the Asiatic

    Continent and extending as a ridge toward the Chukchi Peninsula and two

    very large low-pressure areas - one centered southwest of Iceland and

    extending northeastward over the Barents Sea and northwestward over Davis

    Strait, and a second centered over the Aleutians and occupying the entire

    Bering Sea and Gulf of Alaska. A secondary anticyclone with a central

    pressure in excess of 1020 mb is centered over the Mackenzie River Valley.

            In spring (April, Figure 30 ), high pressure exists over the greatest

    part of the Arctic Ocean and it is during this season that pressures reach

    their annual maxima over the Canadian Archipelago and northern Greenland.

    Meanwhile, the Siberian anticyclone has so weakened in intensity that it

    can no longer be discerned in the mean isobaric pattern. The Aleutian

    low weakens somewhat during this season but retains approximately the same

    position as in winter. The Icelandic low, on the other hand, is very much

    less intense and occupies its southernmost position of the year (south

    of Greenland).



    060      |      Vol_VII-0066                                                                                                                  

            During summer (July, Figure 31 ), the pressure gradients at

    their weakest over the Arctic. This is to be expected when one considers

    that summer is also the season of minimum thermal contrast between polar

    and temperate zones. It is during this season that the so-called

    circumpolar belt of low pressure is located at its highest latitude. The

    Polar Sea during this season is occupied by a true anticyclone as a result

    of the contrast between the low surface temperatures over the cold sea

    and the relatively higher temperatures which exist at the same time over

    surrounding coastal and inland regions. (see Figure 45 .)

            In autumn (October, Figure 32 ), there is a return to a pressure

    distribution which is more typical of winter conditions. The Icelandic

    and Aleutian lows increase in intensity as the deep cyclonic disturbances

    over the northern North Atlantic and North pacific become more frequent.

    Meanwhile, the Siberian high has begun to make its appearance, although

    a closed anticyclone still remains over the Arctic Ocean north of Greenland

    and the Canadian Archipelago as pointed out in a previous paragraph.



    061      |      Vol_VII-0067                                                                                                                  

            At this point it should, perhaps, be mentioned that the details

    of the pressure distribution over interior Greenland have little meaning

    as shown on the sea-level pressure charts. It is possible, on the basis

    of theoretical considerations and actual pressure data, to construct an

    idealized picture of the pressure field which would obtain over the region

    were Greenland not in existence. However, such a picture has no physical

    or meteorological significance. Greenland is not merely a positive

    topographic feature but it is, in itself, an important air-mass source

    because of the altitude and extent of the Ice Cap and because of the

    abnormally steep horizontal (and vertical) temperature gradients which

    are produced by the temperature contrasts between ice fields and coasts

    [ 42 ] . It is because of these facts that there is found to be so little

    connection between the pressure field as charted and the wind speeds and

    prevailing directions which are recorded for various points over Greenland

    or along its coastline.



    062      |      Vol_VII-0068                                                                                                                  

            Pressure Fluctuations . - The pressure variabilities observed from

    day to day at any Arctic location are directly related to the number

    and intensity of migratory cyclones and anticyclones which pass near

    enough to affect the area (see pages to ). The extreme ranges

    occur during winter in connection with intense cyclonic activity and at

    most Arctic meteorological stations both the absolute maximum pressures

    and the absolute minimum pressures have been recorded during one of the

    colder months. For example, the absolute maximum pressure for a Kara Sea

    location occurred at Ostrov Domashnii on February 17, 1933 (1058.5 mb),

    while the absolute minimum pressure for the same area occurred at Ostrov

    Belyi on November 19, 1933 (950.1 mb) [ 45 ] . The average daily variability

    of pressure shows a characteristic annual course with the maximum values

    in winter (8 to 10 mb) and the minimum values in summer. In some Arctic

    areas there appears to be an additional secondary maximum in April. The

    monthly pressure variations also show the same general trend as the daily

    variations, as is illustrated by the following typical Arctic data [ 43 ] :



    063      |      Vol_VII-0069                                                                                                                  

           

    Monthly Pressure Variation (in mbs)

    Yrs
    Location Rec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    Arctic Ocean

    Fram and Maud
    5 52.9 53.0 41.0 40.5 32.6 28.1 32.9 27.5 42.8 41.0 44.1 49.4
    Central Canadian

    Archipelago
    15 42.7 45.7 39.6 35.5 30.8 26.8 26.1 27.7 33.2 34.1 37.6 42.0

            Extreme pressure changes of as much as 50 mb in 24 hours have been recorded

    at some stations on the coasts of the Arctic Ocean in connection with the

    passage of an intense cyclone or anticyclone.

            The mean monthly pressure values in individual years and even the

    annual pressures for different years may deviate considerably from long–

    term averages [ 45 ] . For example, the mean annual pressure at Yugossky

    Shar was 1031.1 mb in 1933 and 994.3 mb in 1914. These differences are

    completely accounted for by differences in the frequencies of cyclonic

    activity between the individual months or years.



    064      |      Vol_VII-0070                                                                                                                  

            The preceding discussion applies only to true Arctic conditions

    In lower latitudes around the periphery of the Arctic, the non-periodic

    variations in pressure are of greater magnitude.

            Pressures in the Upper Atmosphere Pressures in the Upper Atmosphere . - When Helmholtz [ 19 ] deduced the

    existence of a polar anticyclone upon the basis of hydrostatic considera–

    tions, by the same reasoning he also concluded that low pressure must exit

    aloft over the Arctic to compensate for high pressure at the surface. Modern

    information concerning pressures aloft over the Arctic verify the basic

    concept of Helmholz but the relations between the surface pressure and the

    pressure aloft are not as simple as was at first believed. The Siberian

    high in winter appears to be a relatively shallow phenomenon and is probably

    superceded by relatively low pressures at a comparatively low altitude.

    Details concerning the vertical structure of the atmosphere at low levels

    over this region are lacking, however. The essentials of the vertical

    distribution of pressure elsewhere within the Arctic can probably best be

    described by examining the pressure field at the 700-mb level.



    065      |      Vol_VII-0071                                                                                                                  

            Namias [ 30 ] has recently prepared upper - level charts illustrating

    the height of the 700-mb surface over the Northern Hemisphere. His (slightly revised)

    January and July charts are given as Figures and , with the altitudes

    Figs. 33 and 34 here of the pressure surface represented by isolines plotted for 100-ft

    intervals. The January chart (Figure ) shows the pressure field to have

    a rather simple structure with two closed low-pressure centers - one over

    the southeast portion of the Canadian Archipelago and a second in the

    sub-Arctic over the Kamchatka Peninsula. The July chart (Figure 34 ),

    on the other hand, shows much weaker pressure gradients than the winter

    chart, and the pressures are higher as would be expected on the basis of

    the higher surface temperatures. Three closed low-pressure areas are

    shown within the Arctic during this season, the most important of which

    is centered very nearly over the Pole. This is also an expected condition

    when it is considered that the Arctic Ocean is essentially a “cold sources”

    during warmer months in the Northern Hemisphere.



    066      |      Vol_VII-0072                                                                                                                  

           

    SURFACE WIND

            It is extremely difficult to generalize upon the surface wind

    field in the Arctic because of several circumstances which are of

    peculiar importance at high latitudes. In the first place, the

    character of the wind regime at most coastal points and at many

    inland locations is largely determined by local factors which are

    not amenable to regional generalization. Secondly, the periodic

    changes and spa e t ial deformations in the general wind field are no

    less variable than are the highly irresolute Arctic pressure distri–

    butions which produce the winds in the first place. (See page .)

    The third, but not the least important, difficulty is occasioned by

    the fact that the scanty observational data available for analysis

    do not represent a homogeneous period of record at all points of

    observation. For this reason it is often difficult to ascertain

    whether the differences in the wind conditions between two weather

    stations represent true regional differences in the circulation or

    whether they merely indicate that the observations were recorded

    during different years — a difficulty which is particularly serious

    when wind observations obtained on shipboard within the Polar Sea are



    067      |      Vol_VII-0073                                                                                                                  

            The General Wind Circulation . - The Arctic circulation is, of course,

    dominated by the polar anticyclone which, during all seasons except

    winter, is centered somewhere over the Arctic Ocean. So far as can

    be determined from the scanty observational materials available, the

    prevailing wind directions over the Arctic Ocean and surrounding

    coasts appear to correspond to the mean pressure distribution. It is

    apparent that easterly winds prevail over the well-explored portions

    of the Arctic Ocean, over Iceland, the northern portions of Greenland,

    and Alaska, and that northeasterly winds prevail in interior Alaska

    and Greenland, all of which fits the prescribed mean pressure field.

    (See Figs. 29 to 32 .)

            Wind conditions over the interior and coastal portions of Arctic

    Eurasia, however, appear to be less well-defined. The Siberian anti–

    cyclone dominates the interior and coastal circulations during winter,

    but during other seasons the winds are regionally highly irregular.

    Along the Siberian coasts of the Arctic Ocean in summer there appears

    to exist a large onshore wind component resulting from summer heating

    over the interior.



    068      |      Vol_VII-0074                                                                                                                  

            In the more southerly portions of the Arctic, and particularly

    in the peripheral maritime regions of frequent cyclone activity, the

    surface winds are highly variable and do not exhibit a pronounced

    “prevailing” direction. At several stations, for example, the

    frequency data show that during the course of a year the winds tend

    to blow almost as often from one direction as from any other. In

    such regions the non-periodic features of the circulation far outweigh

    any periodic or permanent characteristics.

            The preceding generalization of the Arctic surface circulation

    appears to be about as complete a description as possible of the

    large-scale aspects of Arctic winds. The remaining periodic and

    regional differences in the surface circulation are the result of

    local factors which will be described in greater detail.



    069      |      Vol_VII-0075                                                                                                                  

            Surface Wind Speeds . - A large proportion of the description given

    by polar explorers have stressed the prevalence of high winds and have

    almost invariably given the impression that the Arctic is indeed a

    stormy and inhospitable place. One fairly recent publication on

    Arctic weather conditions, for example, presents a 3 1/2 page

    discussion of winds and storms and, of this discussion, at least 3

    pages describe extreme winds reported by various Arctic expeditions

    since 1836. It is true that in some restricted areas within the

    Arctic the almost continuous high winds are the most noticeable

    feature of the climate. It is also true that excessive winds have at

    one time or another been reported from nearly every Arctic observing

    station. These circumstances, however, do not suffice to ascribe an

    unusual severity to Arctic wind conditions.



    070      |      Vol_VII-0076                                                                                                                  

            According to Sverdrup / [ 42 ] / , relatively low wind velocities are

    characteristic of the Arctic Ocean and Canadian Archipelago. The annual

    mean wind speed as recorded over the Polar Sea was only 10 mph during

    the Fram Expedition from 1893 to 1896, and 9 mph during the Maud

    Expedition of 1922 to 1924. Summarizing the observed conditions,

    Sverdrup states, “It is remarkable that very high wind velocities are

    so rare.” The highest wind speed observed on Fram was 40 mph,

    and on the Maud Expedition, 34 mph; the latter, however, is an hourly

    mean value. The Russian North Pole Expedition of 1937 / [ 5 ] ] / found

    that high winds occasionally do occur near the North Pole since they

    reported from the Pole on June 8 and 9 to the effect that gusts had

    attained speeds of 60 feet per second (41 mph).

            The relative frequencies of high wind speeds at various Arctic

    points can be judged from the data on the average monthly number of

    days with winds of gale, force, which are presented in Table VI . Table VI here

    071      |      Vol_VII-0077                                                                                                                  

    Table VI. Mean number of days with “gales”*
    Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann Yrs Rec
    Oceanic:
    004 5 4 4 3 2 1 ** ** 2 3 5 4 33 ..
    006 5 4 3 3 2 4 1 2 4 3 4 4 39 7
    007 5 3 3 5 2 3 1 2 7 8 5 7 50 5-6
    Alaska, Coastal and Insular:
    100 2 1 ** 1 1 0 1 1 2 5 3 2 19 5
    101 8 9 8 1 1 .. 1 4 5 11 18 14 .. 0-2
    103 14 19 13 7 4 9 9 7 7 10 13 12 121 2
    104 4 2 3 3 1 ** ** 1 1 2 1 4 21 10
    106 1 2 4 4 7 6 4 6 3 6 4 2 50 6-7
    Alaska, Inland:
    155 0 2 2 0 0 0 0 0 1 0 1 1 7 1-3
    156 1 0 ** ** ** ** 0 0 0 0 0 0 1 10
    Canada, Coastal and Insular:
    222 4 2 2 4 3 1 2 1 2 6 4 7 38 2-3
    224 3 1 2 2 1 ** 1 1 1 1 4 3 17 2-3
    225 8 8 7 5 4 3 3 3 4 5 8 8 66 5-6
    228 3 4 5 4 3 1 1 3 5 8 5 7 50 3
    Greenland, Iceland, Coastal and Insular:
    301 1 1 1 ** 1 2 1 2 2 1 1 ** 12 5-6
    302 4 4 1 1 3 2 3 3 4 2 2 ** 28 2-3
    304 1 2 1 1 2 1 2 1 1 2 2 ** 15 10
    305 10 11 10 6 8 2 5 3 6 10 7 5 82 3-4
    306 2 2 1 1 ** 1 ** 1 1 3 1 1 14 5
    308 10 6 9 10 6 4 6 3 8 10 8 6 84 2

    * Wind Speed 32 mph. ** Less than 0.5 day.

    072      |      Vol_VII-0078                                                                                                                  
    Table VI. Mean number of days with “gales”* (cont.)
    Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann Yrs Rec
    Greenland, Iceland, Coastal and Insular (cont.):
    309 4 ** 2 ** ** ** ** 1 1 2 2 2 15 4-5
    310 4 5 6 3 2 ** 1 ** 5 5 5 8 43 2-3
    311 4 2 1 1 1 ** ** ** ** 1 2 1 11 2-3
    312 4 2 2 1 2 2 1 1 2 2 2 2 22 6-7
    313 21 22 24 17 9 5 5 5 8 15 15 20 167 3-4
    314 4 1 2 3 ** 5 2 2 3 2 2 2 29 4-5
    315 6 2 2 2 1 1 ** 1 ** 1 3 5 23 4-5
    316 10 15 15 9 10 4 3 3 13 5 12 21 121 2
    317 7 5 4 2 1 1 ** 1 3 2 4 5 36 10
    318 4 5 1 3 1 1 1 1 1 2 3 2 22 8
    319 9 7 6 6 1 2 1 1 3 3 6 10 54 2-3
    320 12 10 8 7 4 4 3 4 6 9 10 8 84 10
    321 19 17 19 15 12 11 4 8 8 10 12 19 153 4-5
    330 2 2 1 1 1 1 ** 1 1 1 2 2 14 16
    331 3 2 1 1 ** ** 0 ** ** 1 2 3 13 16
    332 3 2 1 2 1 1 ** 1 2 2 1 1 17 9
    334 3 2 2 1 ** ** 0 ** 1 2 2 2 15 14
    335 1 1 1 ** ** 0 0 ** ** ** 1 1 5 15
    337 ** 0 0 ** 0 0 0 0 0 0 ** ** 1 11
    339 2 1 1 ** ** ** 0 ** 1 1 1 ** 9 10
    340 0 0 1 0 0 0 0 0 1 0 0 0 2 1
    Greenland, Iceland, Inland:
    361 ** ** 0 ** 0 0 0 0 ** ** 0 ** 1 16

    * Wind Speed 32 mph. ** Less than 0.5 day.

    073      |      Vol_VII-0079                                                                                                                  
    Table VI. Mean number of days with “gales”* (cont.)
    Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann Yrs Rec
    Europe, Coastal and Insular:
    400 110 9 7 5 3 3 2 2 4 6 8 11 69 10
    401 11 8 7 9 3 3 2 2 6 6 11 11 79 1
    406 7 7 6 4 3 2 1 2 3 4 6 7 52 19
    408 5 5 4 3 2 1 1 2 2 3 5 5 38 31
    412 2 2 2 1 0 ** 0 ** 1 1 2 2 13 28
    414 2 2 2 1 ** ** ** 0 ** ** 1 2 1 9 26
    415 4 4 4 2 3 2 2 1 2 3 5 4 36 18
    417 6 3 3 6 2 2 0 1 3 4 5 4 37 ..
    420 3 3 2 1 ** ** ** ** 1 2 2 3 17 26
    421 ** 0 ** ** 0 0 0 ** ** 0 ** ** ** 8
    423 0 0 0 ** 0 0 0 0 0 0 0 0 ** 7
    425 2 1 2 1 2 2 1 1 2 2 1 1 19 18
    426 ** ** ** 0 0 0 0 0 ** 0 ** 0 1 17
    428 2 2 2 1 2 2 1 1 2 2 2 2 20 18
    429 1 1 1 1 1 1 1 ** 1 1 1 1 8 18
    Europe, Inland:
    450 ** ** ** 1 0 1 0 0 ** ** ** 1 3 7
    451 ** ** ** ** 1 ** 0 ** 1 1 1 ** 4 14
    455 0 0 0 0 0 0 ** 0 0 0 0 0 ** 8
    456 ** ** 0 ** ** ** ** 0 1 ** 0 0 1 7
    Asia, Coastal and Insular:
    500 14 8 11 11 7 11 10 10 8 9 13 14 126 7-8
    502 9 8 6 8 6 6 6 5 4 3 8 8 76 4-5

    * Wind Speed 32 mph. ** Less than 0.5 day.

    074      |      Vol_VII-0080                                                                                                                  
    Table VI. Mean number of days with “gales”* (cont.)
    Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann Yrs Rec
    Asia, Coastal and Insular (cont.):
    503 8 4 4 2 2 4 3 2 3 3 6 6 47 7-8
    506 6 5 5 5 5 3 1 2 3 6 7 5 53 24
    507 11 10 13 13 10 11 8 6 8 6 8 11 114 17
    508 4 3 5 4 3 2 1 2 4 5 5 4 41 6
    509 5 6 6 6 7 2 2 4 4 8 10 5 65 6-7
    510 11 19 8 7 5 3 1 3 5 6 9 8 75 19
    513 1 1 0 1 ** 2 3 2 2 2 1 2 18 4
    515 ** ** 2 1 1 2 2 2 1 2 1 1 15 5
    517 8 3 6 2 3 3 1 2 8 7 8 4 55 3
    518 10 9 8 8 7 5 3 2 5 7 10 9 82 26
    519 6 6 5 6 6 2 1 2 5 7 8 8 60 22
    521 4 4 5 4 5 2 1 3 4 5 4 4 46 13
    522 1 ** 1 1 1 1 ** 2 1 0 0 1 9 5
    523 10 6 8 5 5 4 2 4 5 7 4 8 68 3
    525 5 5 5 5 5 3 6 6 6 6 8 8 68 9
    526 3 2 3 2 1 1 1 1 1 2 2 2 21 14
    527 4 4 4 2 1 ** 2 1 2 2 4 3 29 12
    531 1 ** 2 ** 0 1 0 0 0 2 2 3 11 4
    Asia, Inland:
    550 4 4 2 2 1 0 1 ** 1 1 2 3 19 5
    551 6 6 2 2 2 0 2 4 0 1 5 6 35 1
    553 5 6 7 5 3 2 1 2 3 4 5 4 48 18
    554 7 10 8 11 10 7 6 7 6 7 12 9 100 4
    556 ** ** ** ** ** 2 2 1 1 ** ** 0 7 17

    * Wind Speed 32 mph. ** Less than 0.5 day.

    075      |      Vol_VII-0081                                                                                                                  
    Table VI. Mean number of days with “gales”* (cont.)
    Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann Yrs Rec
    Asia, Inland (cont.):
    558 0 0 ** 0 ** 1 1 1 ** 1 0 0 4 8
    560 ** 2 3 2 2 2 2 1 2 1 2 1 20 8
    561 1 1 1 1 1 ** ** ** ** ** ** ** 5 11
    562 ** 2 3 1 3 2 ** 1 2 1 3 1 18 10
    563 2 2 1 2 1 1 1 1 1 2 2 2 17 6
    566 ** ** 1 ** 1 1 1 ** 1 1 1 0 7 13
    568 ** ** 1 1 2 2 1 1 1 1 ** ** 10 18
    571 0 0 0 0 0 0 0 1 0 4 0 1 6 1
    572 1 1 1 ** ** 1 ** ** 1 ** 1 1 7 16
    573 2 2 2 3 3 2 2 1 3 2 2 2 25 9
    574 1 ** ** ** 1 ** 0 ** ** ** 1 ** 5 10
    575 1 ** 0 0 0 0 0 ** ** ** ** ** 2 18
    576 ** 1 1 2 1 2 1 1 ** ** 1 1 11 13

    * Wind Speed 32 mph. ** Less than 0.5 day.

    076      |      Vol_VII-0082                                                                                                                  

            Data from coastal stations along the Arctic Ocean indicate that

    average wind speeds at most points are higher than over the ocean

    areas, but even here the wind speeds are low except where strongly

    influenced by local factors. In general, the average wind speeds at

    coastal points are of the order of 10 to 15 mph except at more exposed

    locations where averages of 15 to 20 mph are fairly common. (See

    Table VII .) However, the coastal areas may also experience excessively Table VII here

    high winds at times. For example, on February 8, 1909, Note: Possibility that this may be an incorrect date See Reference title, J.P.J. a temporary

    weather station s at Winter Harbor, Melville Island, recorded a 1-hour

    average wind speed of 86 mph and a speed of over 100 mph for a

    20-minute period. The average speed for the 24-hour period was in

    excess of 60 mph / [ 6 ] / .

            Wind speeds over inland areas at low elevations within the Arctic

    are usually much lower than those over either the Polar Sea or its

    coasts. The mean annual wind speed at Verkhoyansk, for example, is

    only 3.2 mph and at Yakutsk, 3.9 mph.

    077      |      Vol_VII-0083                                                                                                                  

    Table VII. Average specified wind speed (mph)
    Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann Yrs Rec
    Oceanic:
    001 11 9 10 11 13 14 12 11 13 14 14 .. .. 1
    002 11 9 8 8 11 12 12 11 11 10 9 10 10 1
    004 21 21 18 17 13 14 12 14 16 18 19 18 17 ..
    006 14 14 11 11 13 13 11 12 16 14 14 12 13 5-6
    007 15 13 13 13 14 14 13 15 17 18 17 16 15 5-6
    008 11 .. .. .. .. .. 8 11 7 8 9 10 .. 0-1
    Alaska, Coastal and Insular:
    100 10 10 11 12 11 11 13 13 14 15 12 10 12 3-17
    101 15 18 18 11 11 12 13 15 15 17 22 19 16 1
    103 22 24 21 17 15 16 18 15 17 17 22 20 19 1
    104 9 9 9 9 7 7 8 8 9 9 9 9 8 18-30
    106 4 5 6 6 6 5 4 4 4 5 5 5 5 8
    Alaska, Inland:
    155 6 8 8 8 7 7 8 7 7 7 7 6 7 3
    156 3 4 5 6 7 6 6 6 5 5 4 4 5 8
    Canada, Coastal and Insular:
    206 12 11 10 13 14 12 9 13 12 15 15 14 13 6
    207 3 4 2 3 4 4 3 3 3 4 3 4 3 4
    209 5 4 3 3 5 3 2 2 1 3 3 3 3 6
    211 4 4 4 4 6 8 9 8 7 7 7 3 5 4
    216 8 8 7 7 7 7 8 9 10 10 10 8 8 8
    221 15 15 14 14 14 12 8 13 15 17 15 16 14 8
    222 3 3 2 3 3 2 3 4 4 4 3 2 3 1-2



    078      |      Vol_VII-0084                                                                                                                  
    Table VII. Average specified wind speed (mph) (cont.)
    Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann Yrs Rec
    Canada Coastal and Insular (cont.):
    223 11 11 11 13 12 12 10 11 12 13 15 13 12 15
    224 11 7 9 9 11 8 9 8 9 9 11 10 9 5-6
    227 18 18 17 17 14 13 13 13 15 18 19 18 16 15
    228 15 15 14 14 13 12 11 13 16 17 17 15 14 12
    Canada, Inland:
    251 3 3 3 3 4 4 5 3 3 3 3 3 3 3-7
    253 9 9 10 8 9 8 8 9 9 11 8 8 9 5
    254 5 4 7 7 10 10 10 8 6 7 5 4 7 6-21
    255 2 3 6 6 6 6 6 6 6 6 3 2 5 7
    Greenland, Iceland, Coastal and Insular:
    301 2 2 3 1 .. 6 3 2 4 6 2 2 .. 5
    302 7 10 10 9 6 6 6 7 10 10 9 8 8 2
    304 5 4 4 4 5 6 4 4 5 6 6 6 5 30
    307 10 8 6 5 5 6 7 6 8 9 11 9 7 ..
    308 5 5 5 4 3 3 3 3 3 4 4 4 4 12
    314 14 14 13 11 9 9 8 9 4 11 12 12 11 30
    317 6 6 5 3 3 3 3 3 3 4 5 5 4 30
    318 4 4 3 2 2 2 1 1 2 2 3 2 2 30
    320 13 12 12 11 8 10 8 7 9 10 11 11 10 23
    330 12 11 10 9 6 6 5 6 8 9 10 10 8 16
    331 14 14 13 12 11 11 9 9 10 12 12 13 12 4
    338 9 10 9 9 9 8 7 7 8 8 9 9 7 15
    340 6 6 4 4 4 4 3 3 4 4 5 5 5 19
    Greenland, Iceland, Inland:
    351 11 9 13 12 9 9 9 8 11 10 9 14 10 2



    079      |      Vol_VII-0085                                                                                                                  
    Table VII. Average specified wind speed (mph) (cont.)
    Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann Yrs Rec
    Europe, Coastal and Insular:
    400 16 15 12 12 11 10 8 9 13 15 15 17 13 10
    401 20 17 14 15 13 11 8 10 13 15 18 18 14 1
    407 10 10 9 7 5 6 5 4 5 7 8 9 7 10
    408 22 21 21 19 16 16 13 14 17 19 21 21 18 28
    412 17 16 16 13 11 11 10 10 13 13 14 16 13 28
    415 10 9 9 8 9 10 9 7 8 9 10 9 9 10
    417 18 17 15 15 16 16 14 14 15 15 16 17 16 ..
    421 8 8 8 8 9 9 7 8 8 7 7 7 8 8
    423 10 11 11 11 12 12 10 10 11 11 11 11 11 8
    424 10 9 9 8 8 8 8 8 9 10 10 10 9 26
    425 11 9 10 9 11 10 9 10 11 10 12 10 10 10
    426 10 10 10 9 9 9 9 9 10 10 10 11 10 10
    428 12 10 11 9 10