I am familiar with the properties of the troposphere, tropopause, stratosphere, etc--at least insofar as standard meteorology for pilots will take you. I wonder if anyone can tell me more about the mechanism for the tropopause: Why is it where it is? Why isn't it higher/lower? Why are there different tropopauses for the lower and higher latitudes?

WW

 

In the troposphere, significant and variable amounts of water vapor affect temperature change with altitude. Above the tropopause, there is little (or no) water vapor, so the stratosphere behaves differently (and is more stable). Essentially all weather originates in the troposphere due to the presence of water vapor...I think the only Wx that ever gets up there would be giant CB's which originate in the troposphere but have enough upward momentum to carry them above it.

I imagine the tropopause is lower at higher latitudes due to colder temperatures and less sun...less water vapor is driven into the troposphere when it is colder.

 

Rickair is right on with his reasoning for the varying height of the tropopause. Since there is less direct sunlight, and less heat in general near the poles, the entire atmosphere is more compact there, since air contracts when cooled. In the winter, the tropopause is also located at a lower altitude for a given latitude for the same reason. The changing height of the tropopause affects the way the jetstream changes from summer to winter and back.

 

OK, the water vapor makes sense, but it begs the question: why does the water vapor stop at the tropopause?

The problem that I had with the explanations of the tropopause were that they used circular reasoning--the tropopause is where the temp stops decreasing. The temp is relatively constant in the stratosphere because it is above the tropopause. I want a cause.

I like the water vapor explanation, but why does the H2O stop where it does? Is there "convective pressure" that reaches equilibrium with gravity at the tropopause? Something else?

Also, your water vapor explanation raises another question? I've always thought water vapor was regarded as a green house gas--a heat trap. What mechanism converts water vapor from a heat trap to one that allows temps to decrease with altitude.

Thanks for the helpful and interesting replies.

WW