balloon

Photo by Cathy Mason

Sometimes people ask me to give a short talk about weather. That is a really big challenge because weather is a pretty big topic and a short talk is pretty short. But it got me thinking: what would be the shortest talk I could give, say one word, that would sum up the biggest part of the topic of weather? And I think the answer might be “convection.”

Convection is one of those words that is often used and less often understood. To really understand weather, (or a lot of other topics like plate tectonics in geology) a person needs to really understand the concept of convection. If you understand cycles, putting the old back to use in a new way before coming around full circle to where it was before and starting again, then you already understand convection. That’s what weather is all about, on both a global scale and in a space as small as your back yard.

Warm air rises. That’s a good starting place for understanding why convection is the basis of weather as we know it. But for air to be warm, there needs to be a source of that warmth, and in the case of weather, that source is the Sun, hands down. The sun heats the ground which heats the air above it, and anyone who’s seen a hot air balloon fly knows what happens next. Rising hot air might be over a dark plowed field, a mostly blacktopped city, or at the equator of the Earth where the sun is most directly overhead. So on both a large and small scale, even inside the envelope of a hot air balloon, air that is warmer than the surrounding air rises.

If hot air rose and nothing else happened, we’d be out of air to breathe here on the surface. Luckily, nature hates a vacuum. When hot air rises, the cooler air around it rushes in to fill the space and keeps us from being literally out of breath. Good thing for us, and good thing for the weather. That air rushing in creates the wind, and the rising air creates clouds as it rises and cools if it has enough moisture in it. The crystal clear skies despite hot temperatures this week are one example of when the rising hot air didn’t form clouds because it was so dry.

But then what happens when the cooler air rushes in to fill the upside down hole left by rising warm air? Well, that rising warm air can’t rise forever. At some point, it’s going to either cool off enough to fall or hit some kind of “atmospheric lid” and come back down again to fill the void that would have been left behind as the cooler air moved in to fill its place. Then we have a cycle, up and down, over and over again, in slightly different spots and on many different scales, little swirls going on inside of bigger ones, over and over again for millions of years. The big, well known worldwide cycles of convection have been seen and given names like Hadley Cell and Polar Cell. The smaller ones that pop up and create storms in Victor but not Tetonia are not as predictable and are what weather forecasting is all about trying to foresee. But it’s all convection, with all of the complications that geography and time of year and human activity add to the mix.

Maybe instead of asking how the weather is today, we should ask, “How’s the convection going in your neck of the woods?”

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