The Nature of Wind

Wind is the movement of air from atmospheric domes of high pressure, beneath which air is sinking, to zones of low pressure, where air is rising. The temperature of the air, relative to our location, depends upon two factors: the site of the high pressure and the presence or absence of intervening topography. In the U.S., high pressure to our south and low pressure to our north (the current scenario) generally produces a warm, southerly wind; however, should this wind cross a mountain range, it will cool as it rises and warm as it descends. The wind speed is also affected by two factors: the magnitude of the pressure difference between the high and the low and any funneling effects that the regional topography might produce (e.g. canyons, passes, downtown streets). In the case of hurricanes, the pressure within the storm is very low and the winds, which swirl counterclockwise around zones of low pressure in the Northern Hemisphere, are very intense.

Seasonal monsoons, generally thought of as rain events, actually refer to the wind pattern that brings this precipitation; low pressure over a heated land mass, produced by a rising column of hot air, pulls in moist air from high pressure over the adjacent sea. The Santa Anas of Southern California are the opposite of these rainy monsoons; they are the result of high pressure over the Great Basin and low pressure over the Pacific Ocean, which combine to produce hot, dry, downsloping winds that gain speed when funneled through the canyons of the Coastal Range.

During the winter months, conditions in Denver and Grand Junction, Colorado, are often just the opposite. If the wind is from the east, it rises, cools, and drops snow on Denver before plummeting down the west slope of the Rockies to give Grand Junction warm, dry, sunny weather; of course, a west wind across Colorado would reverse these scenarios. Pacific trade winds, produced by high pressure over the eastern Pacific and low pressure over the western Pacific, intensify in La Nina years, increasing heat and humidity off the coasts of Southeast Asia and northeast Australia and triggering heavy rains and cyclones; in El Nino years, this pattern is reversed and drought plagues the region.