3. Wind charts. These are drawn in various forms, to show the prevailing wind directions, the frequency of winds from different directions, the average force of the winds, etc. Charts of the winds at different levels above the earth’s surface will eventually be drawn for the use of aeronauts, but such charts are still in a tentative stage.
A MODERN ISOTHERMAL CHART OF THE GLOBE. (Hann, 1901)
The isotherms show the mean annual temperature in centigrade degrees.
As in the case of tabulated climatic data, the number of charts that might be drawn to bring out different features of climate is practically unlimited. Sunshine, cloudiness, humidity, barometric pressure, and the frequency of various special phenomena, such as thunderstorms, hail, tornadoes, droughts, etc., are all charted in some of the more extensive works on climate. Large atlases have been published to portray the climates of certain countries. The study of the actual distribution of climates over the earth, as distinguished from that of climate in general, is sometimes called climatography.
Climates are variously classified, usually on the basis of one or more of the climatic elements, but sometimes with reference to their effects. The most familiar classifications refer to temperature. We speak of tropical, temperate, and polar climates; but in using these terms it should not be forgotten that other things besides latitude control the distribution of temperature. Location with respect to the ocean or other large bodies of water is almost equally important. A land surface grows warm by day and in summer, and grows cold by night and in winter, much more rapidly than a water surface, and the adjacent air varies in temperature accordingly. Hence we have a classification of climates as marine and continental. The former, under the influence of oceanic winds, have a moderate range of temperature, while the latter are subject to extremes of heat and cold. With increase of altitude temperature is diminished, but rainfall is generally increased. The distribution of rainfall is also determined to a great extent by the paths of cyclonic storms. Such are a few of the many things that control the complex distribution of climates.
People who never travel far from their own homes usually cherish quite erroneous ideas regarding the climates of distant lands. It is hard for most Americans to realize, for example, that the Isthmus of Panama, in the heart of the tropics, never experiences temperatures nearly so high as those which occur every summer in the United States. A citizen of South Dakota, where the mercury, in the shade, frequently rises above 100° Fahr., and has been known to reach 115°, will be inclined to revise his definition of the term “tropical” when he learns that at Colon, the Atlantic terminus of the Canal, a temperature as high as 90° is decidedly exceptional, and that the maximum reading during a period of six years was only 92°. In thirteen years Canal Zone vital statistics showed only two deaths from sunstroke and twenty-one non-fatal cases of heat prostration among a population of 120,000. It will also surprise most Americans to learn that the highest natural air temperatures that have been recorded anywhere on earth were not observed near the equator, but in a California desert. At a place on the edge of Death Valley, rejoicing in the ironical name of Greenland Ranch, a temperature of 134° Fahr. was registered in July, 1913. The thermometer which furnished this remarkable reading was a tested instrument, installed in a standard screen over an alfalfa sod, and not exposed to the reflected heat of the desert. At the same place the temperature reached 100° or more on 548 days in four years. Outside of the United States the highest temperature ever recorded at a meteorological station was 127° Fahr. at Wargla (Ouargla), Algeria.
The lowest temperatures encountered by polar explorers are considerably higher than those experienced each winter by the inhabitants of northern Siberia. The “record,” so far as instrumental observations go, is held by the town of Verkhoyansk, at which the temperature fell to 90° below zero (Fahrenheit) in February, 1892. Strange to say, this “winter cold pole” of the earth has warm summers. At Verkhoyansk the temperature sometimes rises to 80° above zero, or higher. At Yakutsk, Siberia, the thermometer has been known to fall to 84° below zero in winter and to rise 102° above zero in summer; a range of temperature exceeding the interval between the freezing point and the boiling point of water!
Another climatic paradox is that experienced by mountaineers who, in scaling peaks mantled in eternal snow, often suffer with the heat, on account of the intensity of solar radiation in the pure, dry air of high altitudes. At the health resort of Davos, in the high Alps (altitude 5,250 feet), invalids sit out-of-doors without wraps in midwinter, and, indeed, are sometimes driven into the shade to escape the too ardent rays of the sun. At the same time the temperature of the air itself may be far below freezing, and the ground covered with snow.
Certain parts of the world are often loosely described as “rainless,” but, as we have stated elsewhere, there is actually no spot on earth at which rain (or snow, in the polar regions) has never been known to fall. In the driest part of the Sahara—the Libyan Desert, between Dakhel and Kufra—the explorer Rohlfs experienced a drenching rainstorm of three days’ duration in 1874. Neither is the Sahara, in spite of its proverbial heat, exempt from touches of real winter. Snow is a common occurrence in many parts of this desert, even at moderate altitudes. On the higher Saharan peaks snow lies on the ground all winter, and is sometimes found, in sheltered spots, in summer. Occasional falls of snow occur in all parts of Algeria, and several falls have been recorded in Lower Egypt.
When all is said and done, the whole fabric of what now constitutes the science of climatology leaves much to be desired. Climate is of practical interest, first of all, on account of its effects on human life and health, and secondly because of its influence upon the crops that are the mainstay of man’s material prosperity. Under both these heads climatic data, as now commonly presented, ignore certain atmospheric activities of the utmost importance. For biological purposes no description of a climate can be regarded as even approximately complete that does not furnish, for the region under discussion, a detailed account of the different kinds of radiation received from the sun, their intensities and fluctuations; and there are few places in the world at which even a beginning has been made in the collection of such data. Again, the phenomena of atmospheric electricity, including radioactivity, are probably of real climatic significance, but we are still in the stage of speculation with regard to this subject. Possibly there are still other elements of climate, now wholly neglected, that will figure prominently in the climatology of the future.