Word: circumpolar
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This crazy-quilt winter weather was the result of erratic changes in the usual pattern of westerly winds-especially the high-altitude jet stream-that whip across the U.S. Part of a broader global feature known as the circumpolar vortex, the winds in winter usually follow a sharply undulating path round the Northern Hemisphere, like the bottom of a whirling crinoline skirt. Sweeping northeast over the Pacific, the winds pick up warmth and moisture. Heading down again from the cold north, they cause heavy rain and snowstorms from the Rockies through the heartland to New England...
Scientists disagree sharply about the cause of the earth's cooling and whether it will continue. But a flood of observations by weather satellites and other new instruments show its major effect: a gradual expansion in recent years of the so-called circumpolar vortex-the great icy winds that whip around the top and bottom of the world. Those winds move generally from west to east, but the outer edge of the vortex twists and bends, like the bottom of a large, swirling skirt. In the U.S. Far West, for instance, the winds bring down cold, dry Arctic...
...most devastating influence of the circumpolar vortex has been felt in a broad tropical belt stretching round the globe. As the edge of the great wind system reaches closer to the planet's midriff, it has blocked moisture-laden equatorial winds. No longer have they been able to bring needed rain to such diverse areas as India, parts of Central America and West Africa's Sahel. Already suffering from years of overgrazing, the Sahel has dried up so badly that the Niger River can be forded by foot for the first time in centuries. In effect, the Sahara...
Scientists have found other indications of global cooling. For one thing there has been a noticeable expansion of the great belt of dry, high-altitude polar winds -the so-called circumpolar vortex-that sweep from west to east around the top and bottom of the world. Indeed it is the widening of this cap of cold air that is the immediate cause of Africa's drought. By blocking moisture-bearing equatorial winds and preventing them from bringing rainfall to the parched sub-Sahara region, as well as other drought-ridden areas stretching all the way from Central America...
Waves Around the World. If the earth were a smooth sphere, the circumpolar wind might flow in a neat circle following the parallels of latitude. But the earth is ridged with mountains and mottled with alternate patches of land and ocean. These blemishes scallop the great wind into snakelike, horizontal waves whose southern lobes sometimes reach the tropics. On the western sides of the waves the wind aloft blows toward the southeast, carrying with it masses of cold northern air. On the eastern sides the wind blows toward the northeast, carrying tropical air into the temperate zone. When two such...