October 12, 2010

The Adiabatic Process Part 2

Yesterday we covered the dry adiabatic process.   It is very rare that the adiabatic process stays 100% dry like the scenario we talked about.  There is almost always some level of moisture in the air, and that changes the process fairly dramatically.   The process still starts in the same way though, sun heats the atmosphere, heats the earth, and the earth radiates heat back into the air. The air absorbs the heat and warms, but here's where things change.  Air that is moist or saturated with moisture will still rise, but it will cool(release latent heat) and expand less quickly than dry air.  There isn't a constant for the cooling rate of moist air, the closest thing we can come to is ~6 degrees Celsius per 1000m. Again, that rate is subject to change.  Also, there are some different things that happen to the air as it rises, cools and interacts with the air around it.  Moist air will rise and cool until the temperature of the rising air reaches the dew point(temperature where the air is 100% saturated) and then the vapor in the air will begin to condense and form clouds.  The stronger the current of warm air rising, the farther up the condensation will take place, hence you will start to see clouds that form in what looks like columns building upward.  Eventually that rising/cooling/condensing air will reach a level where it matches the temperature of the air around it and stop rising. It is also possible, just like in the dry adiabatic process that the warm air will cool too quickly and start to sink back toward the ground until it reaches that stable temperature.  There you have it, the moist or saturated adiabatic process is one of the ways to create clouds.  This process is particularly evident in the summertime as we get more of the sun's direct rays and our part of the earth gets heated more intensely.  There are still other scenario's where the adiabatic process can start as dry, but as the air lifts and cools it becomes moist(remember cool air holds less water vapor than warm air)and then the moist adiabatic rules start to take effect.   The whole process is quite complicated, but it's neat to know how it works.   Enjoy!

No comments:

Post a Comment