October 13, 2010


Last night we started learning about wind.  I was surprised about how much there is to know about wind, and how great of an effect it has on the weather.  Today I'm going to review how the wind causes the monsoon's in India and the US Southwest.

Like everything in meteorology it all starts with air.  We'll start over the water.  We all know that water heats and cools slower than the land, so in the summer months, especially the early summer months, the air over the water of the Indian Ocean, or the Pacific Ocean is cool.  The cool water allows the air above it to stay cool. Cool air, means the pressure is high and there is not much lifting going on in the atmosphere.  The land on the other hand soaks up the sun's moisture quickly and heats up fast. The warm land radiates the heat back into the air and causes the adiabatic rising of air we talked about earlier.  Warm rising air creates low pressure in the atmosphere.  Remember that air that is under high pressure(over the ocean) is drawn to air under low pressure(over the land). The cool air is drawn in over the land, heated and then it rises(moist adiabatically), condenses into clouds and rains.  The warm air up high is now drawn back out to sea by the high pressure,  and cools as it lowers back toward the surface.  The whole process starts over again.  This process will continue until the temperature of the water warms and the pressure difference between the water and the land isn't so great.  Hence the reason that the monsoon seasons in India and the desert southwest last for months.   During the winter the exact opposite of this occurs and the land becomes very dry and barren, which explains the desert like conditions in India and the Southwest.    

Until tomorrow!


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