Think back. What’s the most surprising thermal source you can remember? If you’ve had much experience it may take a while to decide. Each one has something unique to teach us. Most exemplify basic concepts we all should understand, and those become more obvious the lower you are. Others seem to defy the principles until you look closer, and often it’s combinations of effects that turn junk into treasure. So much data!
My most surprising source? I’ve stumbled into too many unexpected freebies to count. So like choosing from fish in the sea, here in no particular order are a few surprising kinds of thermal sources.
Least but not last, a concrete pad 30’ x 40’ (measured later on Google Earth) in a huge open field with no other features except flatness. As we climbed away we sniffed elsewhere over that field, but always came back to the pad. Pretty sure that student would have written me off if it hadn’t worked. Not many miles from there one very isolated shack offered similar benefit, though I suspect it was more a thermal trigger than a thermal source, a distinction with a real difference we’ll get back to.
Looking for a sure thing? Find a farmer. Wherever they’re cutting hay or corn in direct sunlight, you might find the best thermal around. Or if they’re spreading liquified manure under full sun, same deal… almost. That can get smelly if thermals aren’t going very high, but contrary to what you’re thinking, there’s generally no brown cumulus. Just for the heck of it though, imagine you have both kinds of field, which happens often in farm country, but they’re a mile apart and you have to choose. If you fail to climb where they’re harvesting, they just cleared a landing area for you, and no surface is softer than unraked hay. Fail to climb above the liquified manure though, and you’re on your own!
Here’s one I can’t claim as my own discovery, but it merits inclusion for novelty alone. A former student not known for prevarication claims the thermal rose from a freight train stopped on a siding. The train decided to move on while he was still climbing, and his thermal went with it — into the wind! Gotta love when that happens.
Now we all know lakes are sinkholes, right? Well… exposed water raises humidity down near the surface, making the air there more buoyant, and a pond of just the right size can sometimes spawn weak thermals! Also, on autumn days in New England, scum-covered swamps may work while clear ponds don’t. Is that because of cooties in the mud and water? I say it’s the frogs who eat the cooties. Either way, with pond-sourced thermals, don’t bet on a rocket ride to cloud base.
So… a half-mile square under intensive irrigation? No, seriously. Local experts hypothesize that air above the field becomes so cool and dense it creates an obstruction to surface wind, and therefore a large thermal trigger. Expect such lift to be softer than from an earthen hill, but fairly steady… until they throttle those giant sprinklers and turn everything to sink.
Okay, could you believe a flock of sheep high in the Rockies? True, they wear thick wool coats, but don’t forget they’re expelling warm moisture from both ends almost constantly! Not much different from a feed lot or industrial armpit really, except the aesthetics. I’ll take sheep farts over belching smoke stacks, how ‘bout choo?
Which brings us to my very first thermal, ever. It was April, gray and gusty, above a small town racetrack. Wind pushed fumes from raging stock cars against bleachers, where the rambunctious crowd added heat, and an elevated grandstand kicked the whole bubble loose. Those factors and little else allowed us to orbit not far overhead, at constant height, apparently as long as the race might last.
I remember thinking we had to be having more fun than those below us, until the stink finally drove us away. My first assisted landing came next, of course, an experience somewhat less inspiring. But I had trodden the much trespassed bottom of space, put out my hand and touched, if not the very face, perhaps the dusty toe of God. I smiled myself to sleep that night at the promise of better things to come, a promise I’ve had a ball fulfilling!