Cooler Temps at Higher Elevations?

Why is colder as you go up in elevation?  Why do plant communities change at different elevations?

Everyone has noticed the change in plants as they drive higher up in elevation or lower. A five-year-old could tell you that it snows high up where it is COLD and it is HOT lower down in the deserts.

However did you know that you can easily figure out the temperature at the top of the mountain or down in the desert with some simple math?  This post shows adiabatic rates of cooling and warming and shows how areas in a rain shadow are often so hot.

DRUMROLL PLEASE FOR……..The secret formula.

Where it is raining:  for every 1000 feet drop in elevation, add 3° F.  Subtract 3° for every 1000 ft gained.

Where it is dry:  for every 1000 feet drop in elevation, add 5.5° F.  Subtract 5.5° for every 1000 ft gained.

Here’s the scenario:

It’s 110 freaking degrees in Pheonix @ 1,000 ft.  (I know it’s ridiculous how many people live in such hell, but that’s another story).  If there is no rain in the region how hot will it be at the top of Mt Humpreys @ 13,000 ft?  How about at 1,000 ft elevation on the other side of the mountains.

adabatic_dry adabatic_wet

Okay cool pictures but now explain HOW this happens?  WHY is does the temperature cool down slower when it is raining?

Dry Adiabatic Rates of Cooling:  (When there is no moisture in the air):

Hot air from the low desert rises up and expands.  As the air expands it loses energy and therefore loses heat.  Heat is lost at a constant temperature of 5.50* F/1000 ft of elevation.

dry_air

Moist Adiabatic Rates of Cooling. 

However, when moisture is in the air, the air rises but finds other particles that have already reached their dew point. Dewpoint is the rate at water vapor cools enough to become liquid water. Now, the water in the air absorbs and contains the heat.  This heat stored in the atmosphere is called latent heat.  More details can be found here:

wet_rates

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