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A few days ago, the temperature reached 98F/37C in Saint Paul, with high humidity. Any trip outside was a swim through the air, desperately making as few waves as possible. But during all of this, I was always heartened to know that very cold air was only about 10 miles away.

Not across town, that is, but up. The temperature is as low as -50C directly over our heads in a mysterious place called the “tropopause” before you hit the stratosphere. It gets that was because of some unique features of living on a wet planet.

The sun gives us the energy that created every living thing on this planet. When that sunlight strikes our little globe, the energy is absorbed in two places – when it first hits the thin, ethereal wisps of atmosphere on the edge, and then again when the air becomes thick or it hits the ground. The lower part of this cushion of air, called the “troposphere”, is where we live, and because the energy is absorbed at or near the ground it behaves like it sits on an enormous stove – it gets cooler as you get away from it.

When we have these hot days, it is nothing more than a temporary effect in the middle of a large continent. Hot air is less dense, and so it gradually gets out of its own way. The water in it becomes unstable, and sometime just after noon some of it starts to condense. That makes more vacuum, and pretty soon some high clouds way up have a pressure more like the very cool air around the tropopause. That cold makes more water condense. It becomes a dark thunderstorm, full of liquid water instead of wet air.

The heat that water needs to be in the air instead of a drop is released into the stratosphere, that water falls, and more water rises to be condensed. That’s how our atmosphere burps out the excess heat that accumulates near the surface. But it has to build to the point where it is ready to make these thunderstorms happen.

And so it goes, as water is moved around from one place on the planet to another. It’s all about how our little planet releases the excess energy back up the high atmosphere and into space. Relief comes when there’s enough energy and water to pull that stratospheric chill down to us.

This may not offer much in the way of hope on a day thick with summer sun. But I find it helps to be reminded that we are just very small animals on a large planet, and that everything is taken care of in its own time. Summer does not last forever, and one day it will be winter. In the time frame that our planet operates, these events are so fast they basically do not even happen. Our desperate search for relief is just an illusion as far as this ball under a heat lamp is concerned.

One thought on “Tropopause

  1. Pingback: The Gulf of Life « Barataria – the work of Erik Hare

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