No, this isn’t about ramifications of economic policy, or Brazilian butterflies either. You already know all that stuff. Our topic today is a peculiar house thermal here at Crystal, called ‘the ripples’. Every glider port needs a house thermal, where the emphasis is not so much great lift as ready convenience. Our most potent one is the riverbed, eighty acres of barren boulders a mile off the west end where thermals can be bodacious right on into evening. Unfortunately though, departures and landings in either direction make it the wrong airspace for digging around low. That’s alright, we have other options.
My sentimental favorite, strange to say, doesn’t actually work in most ordinary weathers, demanding always and only one single condition to activate its magic: a northeast breeze. This simple requirement, however, is all it takes. You don’t even need strong sunlight. We’ve seen thermals there, admittedly feeble, on chilly overcast winter days when there were none anywhere else. And for sweetener, the ripples are adjacent to our east IP, so if you fail to climb you can roll straight onto the forty-five entry leg for downwind to 07 (always the active runway whenever the ripples are in play).
Looking from above the airport, you’d think they’re a couple square miles of dunes, but that’s not sand down there. It’s a dendritic pattern of stony ridges ten to twenty feet high, last vestige of hill country before the desert goes completely flat everywhere to the north.
My theory on the ripples is as simple as the effect itself, if only it were so easy to describe. While wind from any northern quarter can generate fine soaring in our local mountains, it’s typically cool air with anemic convective potential in the desert. Under such conditions, baby thermals skidding across flat ground lack the energy to rise away until they bump up against something like our ripples and break free.
Fine, so why in only a northeast breeze?
One edge of the ripple formation amounts to a small but abrupt step, a uniform obstruction perpendicular to only northeasterly flow. Apparently that’s the key. And incipient thermals that don’t rise at first are then pushed across a coarse washboard of ripple after ripple, rubbing loose more soft bubbles.
Thus a distinction with a real difference, the ripples as more a thermal trigger than a source. Granted, in many instances the same terrain feature is both, which may be true here as well, sometimes. But only in a northeast breeze…
Source or trigger, your best path to the whole truth must include sampling these ripples yourself to see what you think.
Everything’s small-scale in this case; light wind, moderate temperatures, minimal topographic relief; so the effect is limited too (character building, we like to say). Expect reluctant one- to two-knot bubbles, seldom much higher than 2000 AGL, but enough to keep you aloft on the kind of day when there may be little else available. If you find one, there might be two more nearby. Hold your mouth right, and a climb with real legs might drift you eventually clear up over the airport — which itself is also one heck of a house thermal!