1st of 2011

For my first entry of 2011 I'm gonna do something a little different. Here are some awesome pictures I took while flying in the Tararua Ranges yesterday morning.

Sweet yeah?

So what's going on here?
Well the tops of the clouds you can see on the other side of the ridge are at about 4,000 feet. The clouded in side is to the east and the clear side is west. Whats happening is the moist air forming the clouds is blowing ever so slowly over the ridges and falling down the sides. Once that happens it disappears. Why?
Well it all has to do with cloud formation. Very briefly. Clouds are formed when the air becomes saturated with water vapor. This means that the air cannot hold any more water in it than it has already. The level at which the air saturates is dependent on the moisture content and is given as a temperature. This saturation temperature is known as the dew point. The warmer the air the more water it can hold. So if air is at the same temperature as it's dew point cools down, it will no longer be able to hold the water vapor it contains.
And thats when clouds form.    

So back to the question. Why do the clouds disappear when they flow over the ridge? The reason is two fold. 1st) the air containing the clouds is colder than the surrounding air. It's colder because the clouds reflect the suns energy and also because saturated air has a higher specific heat capacity than dry air (This means that it takes more energy to heat it up by the same amount). Because the clouds are colder they are more dense than the surrounding air and so they sink.
2nd) As they sink they warm up. This happens because the sinking air increases in pressure and when the pressure of a gas increases, it's temperature also increases. As they warm up, the temperature of the air pases it's due point and the clouds evaporate.

Neat yes?