Friday, January 14, 2011
The troposphere is where weather occurs and it is the only layer in the atmosphere where this happens. The stratosphere has wind, but no weather. This is because unlike the water cycle that takes place in the troposphere, the wind in the lower stratosphere travels in a parallel motion, and this phenomena is known as the "lee wave". There is also no water vapor in the other levels, an essential element in ensuring weather occurs.
The troposphere decreases in temperature as it goes higher up towards the stratosphere, where it increases in temperature again till it reaches the mesosphere. From the mesosphere, the temperature starts to drop yet again till it reaches the last layer, the thermosphere, where it increases for the last time. These changes in temperature are separated by boundaries. The first boundary between the troposphere and stratosphere is called the tropopause, the second boundary between the stratosphere and the mesosphere is called the stratopause and the last boundary between the mesosphere and thermosphere is called the mesopause. The reason for the terms given is because at the different atmospheric boundaries; the 'pauses', air starts to either decrease or increase in temperature as we go up the layers of atmosphere, hence the name.
Something interesting about the atmosphere is that despite the high temperatures at the thermosphere, if we humans were to go up to the thermosphere for example, we would not feel the heat and instead, feel cold. This is because even though the particles are of temperatures like 2500 degree celcius, they are positioned very far apart and even if one of the molecules hit us, it will simply only kill/vaporize a few cells on our body and this damage is so insignificant that we wouldn't even notice it. Therefore, because majority of our body is not in contact with any of the high temperature molecules at any one time, we feel cold instead. In simpler terms, there is no medium in the thermosphere to transfer the heat to our body. At least, not enough at any one point to let us feel the burning heat of the thermosphere. The same explanation can also be used to explain why pressure decreases as we go up the different layers, despite the increasing temperature.
Also, did you know that because the temperature at the tropopause and the lower stratosphere is nearly constant with increasing altitude, there is very little convective turbulence? This provides a good pathway for aeroplanes to fly at as this will optimize fuel burn. That is why aeroplanes have to go way up high into the sky after takeoff and not just a little high up where we are high enough to not crash and yet can still see the ground.
I hope this summarizes the lesson on 13/11 and you learnt something new as well as refreshed your memory. :)