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!
Congratulations this week goes to one of our crew members, Justin Gillen, for earning his commercial add-on rating!
We’re still scheduling through e-mail, so please check availability on Schedule Pointe first (for Fri/Sat/Sun) and then e-mail us your reservation request. If you don’t have a Schedule Pointe account, please e-mail us date options for your reservation. Please include your cell number. Do not schedule reservations yourself, until further notice.
When we confirm with you, you’ll receive our mitigation procedures. We look forward to seeing you at the field!Late June means the longest days and highest sun, and this coming weekend should bring soaring conditions commensurate with the calendar. Expect tall blue boomers each day this weekend, and once the wind picks up PM, look for shear line activity coming from the west or south, depending on all the usual variables.
Don’t forget to checkout the Podcast “Soaring-the-Sky”. Chuck interviews glider pilots from all over the world, including many from our field, who tell stories of flying, provide their take on safety and more.
Stay safe and healthy and wishing you good spirits,
The Soaring Academy Crew
Discussing dust devils last week, we tried to stuff ten pounds of BS into a five pound bag, and sure enough some spilled over. Fortunately we had another bag handy, just the right size for what didn’t fit last time. Ready for the rest?
As always, the more you learn the more you know you don’t know. Technical descriptions of a ‘proper’ dust devil require certain specifics not always present in everyday garden variety whirlygusts. You may be surprised to learn that heat, per se, is not a critical element. As with convection more generally, what matters is temperature contrast, between a relatively warmer surface and cooler air above (scorching playa, alpine snowfield, even open water). Two other ‘ideal’ conditions are a uniformly flat surface and, odd as it sounds, light- to no ambient wind… The most magnificent examples we see in pictures represent these optimal ingredients, approaching helical symmetry because the physics in each quadrant are essentially identical. Such specimens are comparatively rare in most landscapes, though, and far from the only possible recipe.
Dust devils in mountains are even more rare, yet I remember sighting down the core of one as it tortured a high rocky peak, while climbing in the very best lift of an eight hour flight! And then there’s the influence of vegetation… in seemingly any landscape or season, warm air trapped between trees may spawn a day’s last lift, and frigid air above snowy hills can produce effects as spectacular as any.
Surface wind will pull a devil along like a cranky child through a supermarket, bumping into pretty much everything because it moves faster on one side than the other, endowing each quadrant with different character. Relative to the ground, one side will be moving at the speed of rotation plus the wind, while on the other side those two vectors cancel each other and horizontal movement is momentarily stopped. That’s the spot where you’ll see all kinds of stuff shooting straight up off the ground! The result is a discrete vertical wall on one side, and on the other a mess of sand and debris cast out before ever rising far.
Nearly all devils exhibit varying degrees of split personality, their sources ranging from 90% heat to 90% wind, encompassing a majority of 55/45 like any population. Sonoran monsters that stand straight like redwoods and hardly seem to move are mostly about heat, while the thousands of little catfights scuttling through hills are mostly about wind. Neither extreme offers much of practical use to soaring pilots; as with most things, in between is where they keep the good stuff. So much to learn!
One helpful trick is distinguishing weak devils who raise more dust than they know what to do with, from boomers showing almost none at all. Spindly tall and pencil thin may not look impressive, but could be your ticket to ride. A pile of murk wider than it is high is an invitation to land in a pile of murk wider than it is high… Devil don’t care.
And yes there really is a conceptual difference between dust devils and tornadoes, beyond their size and ferocity. Tornadoes are always suspended from big dangerous clouds, while devils come up from below and favor more benign weather. Still, exceptions abound for nearly everything. Could the example linked below be a rare hybrid of both? Twenty seconds in, you see only the devil on the ground and beginnings of an umbilical beneath a cloud far away in the upper left. No obvious connection — yet at that moment the clear air between them is accelerating in a huge diagonal spiral. Just before the video’s end (at exactly 2:30), the rope-like axis is bent over to nearly horizontal by wind aloft, and visibly connects both ends. Try to envision the air’s movement around that oblique axis! Assuming counterclockwise rotation, the near side would rise faster and faster as you approach the core, and on the far side catastrophic sink.
Until we meet again, here’s one to inspire ghastly nightmares, if you’re into that sorta thing. Imagine being a lunatic in a glider flying a miles-wide circle around some standard issue (vertical) tornado. The closer you cut in, the faster you’ll have to go to stay beneath a low, leaden ceiling. If you weren’t nuts you’d head straight away at absolutely top speed from what amounts to an atmospheric black hole, but being crazy, you can’t resist…
How should we suppose this adventure might end?