"Nor shall Thule be the extremity of the world."—Seneca.
When the United States purchased Alaska from the Czar of all the Russias in 1867 it was popularly supposed that Mr. Seward and Mr. Lincoln were returning the favor for the kindness of having Russian ships of war as frequent visitors in San Francisco while trouble was expected from England in that quarter during the darkest days of the Civil War. Whatever the reason, and it was not entirely Mr. Seward's desire to furnish the Czar with pocket money, Alaska was a bargain; how big a bargain is not realized even today. Literally speaking, the extent and geographical location of many prominent features of Alaska are a matter of conjecture. This is true of the interior as well as of the coasts. Every so often a local navigator puts new land on the charts by grounding his vessel thereon, in all likelihood removing half the bottom from his ship in the process. The Aleutian Islands are fertile fields for this type of exploration. The late Captain Nelson of the ship Eunice was adept at increasing the sum total of geographical knowledge by this method. While maintaining his irregular schedule between Unalaska and Attu in the service of the blue-fox trappers, it is said that his method of making a landfall in the fog was to run on a bearing until he brought up in a kelp bed. The sinuous streamers and waving fronds of these submarine gardens served as helpful aids to the navigation of these waters by this hardy character. If, by chance, he touched his vessel on one of the rocks or shoals unknown to the meager charts in his possession, his thunderous voice would boom out from the grimy depths of the engine-room of the little Eunice as he backed her away from the obstruction: "Put on der chart a cross, Mike. Ve have found unoder vun."
The United States Navy has conducted hydrographic and aerial surveys in this region which have revealed much of our Ultima Thule to the imprint of the lithographic stone and the copper plate.
From the point of vantage of pure meteorological theory, the sector of the Pacific Ocean and Bering Sea north of latitude 50° between Kamchatka and the Peninsula of Alaska is one of the most interesting regions in the world. This sector is the domain over which the persistent center of low barometric pressure popularly known as the Aleutian low holds sway during the winter months in the Northern Hemisphere. During the summer, at least from July to September, an equally persistent condition of fog and low visibility prevails. The physical causes of these phenomena are partially revealed by quoting in free translation from Art. 177, Physikaliscize Hydrodynamik, V. Bjerknes, J. Bjerknes, H. Solberg, and T. Bergeron:
All polar air north of the Pacific polar front comes through the gateway between the Asiatic monsoon high and the Aleutian low. The polar air still remaining in its place of origin—in the actual arctic regions—will be designated as "arctic polar air" or (shorter) "arctic air." Whenever the arctic polar air passes over the open sea, it gradually warms up and is appropriately designated by the name of "maritime polar air." Between the arctic polar air and the maritime polar air, there is, west of the Aleutian low, a constant transition.
The situation is different east of the Aleutian low. The southwest current of warmed maritime air strikes the Rocky Mountains, rises over them, and then remains in the high altitude, because the arctic polar air northeast of the mountain range cannot be dislodged from the lowest layers. Hence, between the arctic polar air on the one side and the maritime polar air on the other a front is formed which is supported by the Rocky Mountains. This front will be called the Pacific arctic front (FAPac), since it forms the southern boundary of the arctic air. The arctic front in question has a blind end toward the Aleutian low, and west of it, of course, this front does not exist at all.
The above quotation applies to the winter months in the North Pacific. The following quotation continues the reasoning for the summer:
Since the meridional temperature gradient in summer is smaller than in the winter, the summer front formations described hereinafter are feebler than those of the winter.
The col of the Western Pacific has disappeared, because instead of the Asiatic monsoon high a monsoon low has developed. Between the great Pacific subtropical high and the flat polar high there is, somewhere about 65° N., a low pressure trough with one or more frontogenetic cols. It is there that the Pacific polar front (FPPac) develops, which accordingly is located in the summer over land north of the Pacific Ocean. It ends blind both toward the Asiatic side and toward the American side.
The key to the weather of the North Pacific Ocean is to be found in the foregoing statements. Knowing the key to the situation makes it none the less severe but removes the element of surprise from the itinerary of the vessel which shapes a course into this region. It is remarkable that the meteorological situation can be so simple and still the manifestations of the weather experienced in these waters can be so baffling to the mariner who makes an acquaintance with them for the first time.
Mariners have been accompanied by ill-fortune in these islands since the days of the Russians. The sea otter hunters in the eighteenth and nineteenth centuries were constantly meeting wreck and disaster here by being cast upon the islands and constrained to suffer the privation of a subarctic climate attended by the misery of starvation and scurvy until death or rescue intervened. The United States Coast Guard cutter Tahoma gave her name to the submerged obstruction which destroyed her. A recent disaster was the loss of the merchant vessel Nevada on the south shore of the island of Amatignak. The grim record of the Aleutians has given rise to legends concerning their sinister character which it is high time to dispel or at least to "debunk."
The native Aleuts and the lonely fox trappers can give accounts of smoking and burning islands being torn asunder by terrific earthquakes, islands which wander about in the sea and place themselves athwart the courses of vessels; ledges of cruel rock which rise from the bottom of the sea only in time of storm but withdraw beneath the surface when the gales have abated. Tales are told of boiling tide rips and raging stretches of water, in the passes between the islands, where no vessel can live. The most awe-inspiring myths of all are those concerning the fury of the storms. The dreaded williwaw of Alaska can only be compared to the wrath of Jehovah, if credence is given to local description. It is interesting to consider, moreover, that the existence of all these things is a fact but that unbridled exaggeration, pardonable ignorance of physical processes, and undisciplined observation has introduced what the London Times would call "an element of terminological inexactitude" into the accounts.
The collection of information concerning these waters by intelligent and careful investigators will eventually relegate each myth to its proper co-ordinates of truth. The smoking and burning islands will be listed in the geographical publications as active or extinct volcanoes; and there are plenty of these as yet unlisted in the Aleutians. The migrating island of Bogoslof will be assigned to its circle of probable position. The hidden obstructions to navigation will be discovered by the sweep wire, and the sailing directions will be so written that the dangers can be avoided. Certain of the passes which contain the rips and overfalls need never be used in the ordinary course of navigation. An attempt to explain away the Boreal terrors of arctic polar air will be found in the subsequent paragraphs of this article.
The annual period in the weather cycle of the North Pacific Ocean divides itself roughly into the winter regime, November to March; the summer regime, June to September; and two intervals between, consisting of April—May and October, which supply the transition between regimes. The winter regime will be considered first.
It will be called to mind that the monsoon is caused by the seasonal difference of temperature between land and ocean. Owing to a suitable combination of the various factors, monsoon conditions reach their greatest development over eastern and southern Asia. The continent of Asia, in winter, contains the coldest surface temperatures of the globe. In the platter of absolute cold, the depths of the polar basin cannot approach the values recorded annually in north central Siberia. As a result Siberia is dominated by a great cold air mass which goes to make a feature of the general circulation of the atmosphere known as the Asiatic anticyclone. It is this pressure field which Bjerknes means when he speaks of the monsoon high. Anticyclonic circulation postulates winds blowing in a clockwise sense around a center of high barometric pressure and in the low levels, at least, away from it, if the center is in the Northern Hemisphere. This monsoon high is active throughout the winter in contributing a current of cold dry polar air which flows out of Siberia from the north and northwest. The current crosses the Sea of Okhotsk and Kamchatka or it comes more from the north across Bering Sea to invade the Asiatic side of the North Pacific Ocean. Bjerknes has pointed out that this polar arctic air is quickly transformed into polar maritime air by traveling over the relatively warm water of the open Pacific Ocean. This transition is accomplished rapidly in the bottom layers of the polar air mass. The transition works aloft progressively layer by layer, as its maritime history becomes prolonged into a period of several days. This transition is a thermodynamic process which involves the absorption of heat from the surface of the sea, the evaporation of enormous quantities of water vapor from the same source, and the change in the stability characteristics in the horizontal stratification of the air mass. The polar arctic air mass arrives over the ocean with a stable stratification which resists the vertical displacement of its integral layers. After the transition into a polar maritime air mass this stable stratification has been changed into a condition of labile stratification which is conditionally instable in its lower layers; a state which is favorable to vertical displacement of the bottom layers of the maritime air mass. Fresh maritime polar air is replete with the hydrometeors of instability among which can be enumerated showers, squalls, flurries of snow and sleet, and the characteristic towering dome-shaped cumulo-nimbus (Cu.Ni) clouds which are produced by active vertical air currents within an air mass.
Presupposing the quasi-stationary cyclonic depression of the Aleutian low mentioned by Bjerknes, and remembering that a cyclonic circulation in the Northern Hemisphere requires an air stream to move about the center of lowest barometer in a counterclockwise sense, it can be realized that arctic polar air is also drawn around the Aleutian low from continental polar America and contributed to the northerly currents, which are transformed into maritime polar air in the same fashion as the polar arctic air from Asia. This region of the North Pacific is in fact the gateway which Bjerknes describes, through which the polar air masses gain access to more southerly latitudes and there meet the tropical air masses which are in turn working themselves northward in order to/distribute the heat and humidity of the tropics more evenly over the surface of the globe.
The Pacific basin itself contains another bold feature of the general circulation of the atmosphere known to meteorology as the Pacific subtropical anticyclone. This prominent high-pressure area is usually centered during the winter months close to the coast of California with its major axis extending westward in latitude 30°N. Its general clockwise circulation gives rise to the moist northerly and northwesterly winds which supply moisture to California during the winter. It likewise causes the northeast trades, which are a feature of the climate of the Hawaiian Islands. On the poleward side of the Pacific subtropical anti-cyclone there arises a strong current of air moving northeastward from the mean position of the neutral point or col between the monsoon high of Asiatic origin and the Pacific subtropical high. This col is usually found a little south of latitude 30°N. and longitude 150°E. Between the southwest wind composing the tropical maritime air mass arising in the Pacific subtropical anticyclone and the northwest and westerly winds composing the polar maritime air masses which originated in the polar arctic currents from Asia and America there comes into being the zone of transition known as the Pacific polar front. This front extends from the neutral point or col northeastward to intersect the continent of North America in about the latitude of Puget Sound.
When air masses in close proximity possessing different components of velocity are separated by a transition zone through which there is rapid discontinuity of certain of the properties as well as velocity, the dynamic conditions are favorable to the formation of waves in the surface of discontinuity. Such is the case in the Pacific Ocean along the Pacific polar front. When the differences in temperature on the two sides of the front are most marked the front produces the most intense wave disturbances, but throughout the winter the discontinuity is usually quite active. In fact these conditions, so briefly sketched in words, contribute to the world's weather chart one of the two most active centers of action in the Northern Hemisphere, namely, the Aleutian quasi-permanent area of low barometric pressure or (shorter), the Aleutian low. The other intense center is the Iceland low of the North Atlantic.
The wave disturbances which form on the front develop into the extra-tropical cyclones or storms which characterize the weather in the middle and higher latitudes of the Pacific Ocean. These storms have associated with them falling barometer, acceleration of the wind to values of "strong" or "whole gale" on the Beaufort scale, overcast skies with nimbostratus (Ni.St) clouds, giving rain and sleet, followed by squalls, giving hail and driving sleet. The barometer usually begins to rise with the advent of the squally stage. The squalls eventually give way to showers, falling temperature, breaks in the clouds, and a general improvement of weather conditions, although the wind may remain at "gale" on the Beaufort scale. These storms travel northeastward and northward, and each in succession serves to deepen the Aleutian low or to cause pulsations, at least, in the value of its barometric pressure. Fluctuations in the value of the Aleutian low introduce variables in the pressure gradient which m turn regulate the flow of arctic air into the system. The more active the situations become, the more rapid become the movements of the Pacific arctic front mentioned by Bjerknes. When a new depression enters the Aleutian low there is a deepening at the point of entry and a general acceleration of the winds in the vicinity of the deepening. It sometimes happens that the migratory depressions become so frequent that the Aleutian low maintains an abnormally low barometer, of approximately 28 inches of mercury, for a relatively long period of time. Such a depressed barometer will cause a pressure gradient sufficiently strong to produce gales throughout the entire North Pacific Ocean, the Aleutian Islands, and the Bering Sea. Persistence of this circulation eventually drains the polar air Masses completely away from their source regions and causes the entire northern oceanic area to be covered by polar air. Then for a time weather conditions become quiescent, the barometer rises, the Aleutian low fills up and apparently migrates into the continent of North America. Gentle winds, cold and dry, will invade the Aleutian Islands and Bering Sea. The skies will clear, and the atmosphere will take on the transparency of crystal. The temperature assumes a value along the Aleutian chain, which is seldom lower than between zero and freezing, Fahrenheit. Visibility is limited only by the curvature of the earth. At these times during the winter, when the polar air mass actually takes charge of the area and displaces the Aleutian low, it is said that the best weather of the year occurs.
The inhabitants admit that their best weather occurs in winter. Statistics show that the mean temperature is well above zero for these months; in fact it is quite close to 32°F. for all existing observations. The harbors and anchorages are ice-free. The limit of the ice pack in Bering Sea seldom, if ever, reaches the Aleutian chain, although it comes to the southward of the Pribilofs. The elements of climatology teach that these Aleutian Islands must have what is known as a marine subarctic climate. This indicates that the temperature at all times must be equable; that is, must have a small seasonal range. The precipitation can be frequent but, considering the rather low temperature, must be moderate. On the Asiatic side, however, the climate will be that of a subarctic continental east coast. In this case, the Sea of Okhotsk, Kamchatka, and eastern Siberia are included in the Siberian climatic province. It is manifestly incorrect to assume that the climates of the two places are alike.
Coastal Alaska has two modern means of transportation in winter, namely, by sea and by air. The pilots of the local air transport companies look forward to winter as ushering in the return of favorable flying conditions. Coastal Alaska is described by these men as being a "seaplane country." Aside from the higher latitude of the Aleutian Islands which, of course, with the sun in southern declination, decreases the length of daylight, they should be more comfortable as a place to live during the winter months than the Puget Sound country of the United States. Temperature is probably more equable and the amount of precipitated moisture is certainly less.
Figure I accompanying the text is a sketch after Bjerknes of the mean pressure field and mean position of the principal fronts during January, which is typical for the winter period.
The transition period begins about March as a result of the northward movement of the sun in declination. More radiant energy becomes available to dispel the cold of the Siberian anticyclone and the source region of the polar arctic air mass along the northern margins of anticylone becomes progressively more intense as the heat equator of the globe moves into the more northern latitude. The Pacific polar front is pushed slowly northward as the volume of the tropical maritime air mass increases and the volume of the polar maritime air mass decreases. The polar arctic air mass becomes feeble in its circulation and its flow-out through the gateway, described by Bjerknes, gradually ceases. The Pacific arctic front along the ridge of the Rocky Mountains of Alaska fades out of existence, since it no longer has a polar arctic air mass to maintain it as such.
The transition period continues until the end of May, or until such time as the Pacific polar front moves northward across the Aleutian chain and takes up its position in about latitude 65°N. During the period of transition the snow line creeps up the mountain sides, the days rapidly become longer, and there is a mildness and a transparency in the air favorable to surveying and aviation. The period lasts while the area remains northward of the Pacific polar front within what remains of the Polar arctic air mass. The monsoon high in Asia is about ready to be replaced by its summer seasonal counterpart, the monsoon low. In June when the monsoon shifts over Asia the Pacific polar front becomes firmly established along the arctic circle and the summer regime sets in.
The Pacific subtropical anticyclone now attains its maximum strength and fills the whole basin of the Pacific Ocean from the trade wind belt to the arctic circle with a warm air mass of subtropical origin. As these warm humid winds move northeastward into higher latitudes the stable stratification of the air mass is further intensified by the cooling effect of the cold ocean surface. Soon the bottom layers of the warm mass which has reached the latitude of the Aleutian Islands become cooled to the saturation point or dew point of the water vapor held in suspension. A low-lying persistent fog—the advection type of fog common to Alaska as well as to the Grand Banks of Newfoundland—invades the Aleutian Islands. This fog envelops the island bases, it swirls and steams through the passes, it blankets the sea. Fresh to strong winds have little effect toward dispelling it through turbulent mixing because the moisture content of the air mass is too high and the atmospheric stratification is too stable. This fog lies in a shallow layer over the face of the region. It is thin enough to allow the sun to shine through but dense enough horizontally to allow the navigator to beach a ship. The mountain tops are out in the clear. The slopes of the islands receive light and heat sufficient to support an astoundingly prolific flora. It remains broad daylight for 24 hours at the end of June and into July. Birds sing, fish leap, whales play, and foxes bark. All nature is happy. The navigator of a ship or the pilot of an airplane might just as well go fishing because summer has come to the Aleutians and there will be no more visibility until the Pacific polar front moves south.
During September another period of transition begins which embraces October This transition from summer to winter conditions is doubtless more rapid that the transition in the spring. In effect it is period of mild weather during which the atmospheric processes become progressively more energetic. The eventual development of the monsoon high over Asia completes the cycle of weather for the year in the North Pacific Ocean.
Figure II accompanying the text is a sketch after Bjerknes of the mean pressure field and mean position of the principal fronts during July, which is typical for the summer period.
The story has now been told which briefly explains the basic processes of the weather in our Ultima Thule. These processes are similar to those which led the ancients to believe that Ultima Thule, the real Thule, delimited the extent of the world; was, in fact, the extreme of remoteness beyond which there was nothing but ice, storm, and destruction. Progress knowledge, and experience have accomplished the development of the Americas beyond the limits of Thule, even as Seneca predicted. The same qualities which prompted our remote ancestors to venture into unknown fields are still native to the character of the modern American. These qualities will urge American citizens to occupy these new islands of Thule, to develop them as grazing lands for hardy cattle and sheep. The waters which surround them will be exploited for their myriads of food fishes. The kelp beds will be harvested for their phosphates and iodine. Ships will ply east and west throughout their serpentine of channels and passes. All this will happen when economic pressure from behind be gins to force real men again into the field. Our islands of Thule are the last, absolutely the last, frontier.