Why is there so much activity in the upper atmosphere, even though it is usually colder?

Question

My son thought the atmosphere (that is, above our heads as humans) is hotter than what we experience, and I told him that it is typically cooler. (I suppose there can occasionally be an "inversion".) It appears that the troposphere includes both where most of the storms are and also where we reside, so for purposes of this question I want to distinguish between where storms occur and the earth's surface where we humans dwell and walk around.

Why is there so much activity in the troposphere, even though it is usually colder than what we experience on the earth's surface as humans?

Why is there so much electrical activity in the troposphere compared to here on the earth's surface (or very near to it)?

And why (at least near the earth's surface) is lightning usually accompanied by rain?

As I understand it: electrical charged activity "causes" lightning, which in turn causes thunder. Can someone provide any more details on that chain of causation?

Answer 1

What causes the motion of air is, ultimately, differences in pressure and density. Dense air wants to sink down, light air wants to raise, and air wants to flow from areas of high pressure to areas of low pressure. What does not factor into this is the temperature of the air -- rather, whether air is dense or light depends on whether the temperature is lower or higher than in surrounding areas, or whether it contains more or less moisture. That is, it is temperature and moisture differences that lead to motion of air, not temperature or moisture.

You can now ask what causes temperature or moisture differences to form. This is where proximity to the Earth surface (i.e., to humans) comes into play. Land and sea surfaces differ in their ability to absorb sunlight (leading to different land temperatures) and their ability to evaporate water (leading to different moisture contents). This is what ultimately creates the weather activity you see. In contrast, twenty or thirty kilometers up, there is no reason for a blob of air to have a different temperature from its neighbor: They both receive the same amount of sunlight, and they are not in contact with land or sea surfaces that could lead to different temperatures. As a consequence, the "weather" at these altitudes is much less exciting.