What’s a Skew-T, part 5

Posted: 6th March 2013 by Jason in Tutorial

moistThe wet (or sometimes called moist) adiabat is a dashed line on the Skew-T that starts at the bottom of the graph and, depending on the starting temperature, wiggles it’s way towards the north west or north east.  The wet adiabat is very similar to the dry adiabat, but the rate of temperature change is different. Where the dry adiabat was changing roughly 1 C for every 100 meters, the moist rate is closer to .5 C for every 100 meters.  Why the difference?  Part of the reason is because as air saturates and condenses, a little bit of heat is released called latent heat. That latent heat adds to the temperature of that box of air that we’ve been talking about and slows the overall cooling rate.

Our box of air starts it’s life on the ground and follows the dry adiabatic line towards the sky. Depending on the amount of moisture in our box of air (humidity) our air will eventually get cold enough that it can no longer hold onto the water in it and it will have to condense it out (dew point). Now our box of air is still climbing, but since it has condensed it has to follow the wet adiabat.

So far, we have defined what each axis of the Skew-T represents,  lets see how these things work together.