In a place like Verkhoyansk not only the changes from season to season but from day to night are often extreme. Out of doors on a March night one wants all the fur coats he can get, and even then one's nose may freeze during a short walk. The next noon, however, the warm sun and still air make it possible to chop wood with bare hands. By day in August light clothing is sufficient, but at night frosts may occur.
Verkhoyansk and the Lofoten Islands represent the extremes of continental and oceanic climates, but many other regions show some what similar conditions. In the typical continental climate the winter is long_and cold, and the summer long and hot, with brief v transition periods in fail and spring. The typical oceanic climate has transition a mild winter and a cool summer, with no sharply marked nsition seasons.
(2) How Continents and Oceans Affect Pressure.—Since the con tinents and oceans alter the distribution of temperature, they must also alter the atmospheric pressure. As the continents grow warm in summer the air expands. Therefore at high levels it flows away from the lands and accumulates over the cooler air of the oceans. This gives low_pressure in summer over the lands and high over the oceans. In winter the opposite occurs. The lands become cold much faster than the oceans. Therefore the air over the lands con - tracts, while 'that over the water remains expanded. Accordingly some of the upper air moves from the oceans to the lands. The result is low pressure in winter over the oceans and high pressure over the lands.
L/ The growth of the continental areas of high or low pressure does not entirely wipe out the pressure belts that have been described for a simplified earth, but it greatly r2)atI4c.s them. Look at Figs. 73 and 74, which show the distribution of atmospheric pressure in January and July. The dotted lines indicate high pressure and the solid lines low, with intermediate regions between them. In the January map notice how the northern sub-tropical belt of high pressure expands over the cold continents, while the southern belt is broken by the con tinents which are warm in the southern summer. In the July map notice how the northern high-pressure belt is broken by the low pressure areas over the warm continents, while in the cool southern hemisphere the belt is continuous.
(3) How Winds Blow in Respect to Continents.—The importance of the changing areas of high and low pressure over continents and oceans lies in their effect on the winds. Sine winds blow from areas of high pressure toward those of low, they tend to blow outward from the continents in winter and inward in summer. In Figs. 73 and 74 the arrows show how the winds blow during January and July. Of course the direction may change from day to day, but the average direction is what is here shown. Compare the two maps. In Jan uary the majority of the wind arrows point away from the high pressure areas of the interior of the northern continents. In July the arrows point inward toward the areas of low pressure in the northern continents. Thus in winter the cold du air of the con tinental interior blows outward while in summer the moist and rela tively cool air of the oceans blows inward. These outflowing winter winds and inflowing summer windsare strongest in Asia because of its great size and its location in a latitude where the contrast between summer and is extreme. They are weak in Africa in spite of the size, for that continent lies largely within the tropics.
Winds Cause Ocean Currents.—The movement of the winds causes a corresponding movement of the ocean waters. The cur rents thus formed carry ships out of their courses when the sky is cloudy and the true position cannot be determined. During and after the Great War they spread explosive mines far and wide to the great danger of shipping. Since the trades are the steadiest winds, they cause the strongest movements. On either side of the equator the trade winds blow the surface water westward, causing what are known as the Equatorial currents. If there were no continents these would combine so that one broad continuous current would pass completely around the world. The continents, however, deflect the currents either northward or southward. In Fig. 75 notice that Cape Saint Roque in South America divides the southern half of the Atlantic Equatorial current into two parts. One goes south ward as the Brazil current, while the other joins the northern equatorial current and swings around northward into the Gulf of Mexico.