On Sunday, November 2, 2014 4:51:43 AM UTC-8, krasw wrote:

Could you elaborate? I ran the numbers quickly, there is usually temperature gradient of 0,5-2 degrees (centigrade) between thermal core and "free air" around it. If we think normal smallish thermal as couple of hundred meters in radius, we would get average temperature gradient of 0,25-1 degree/100meters between core and surrouding air. Glider with temp sensors at wingtips would probably reguire 0,01-0,05 deg resolution of sensors to give any information. It could be doable, though, relative differences are easier to measure than absolute. It could give you a sort of "left or right"

That is the basic idea. I know from experimentation that there are measurable temperature variations out there, it's just not obvious to me what they mean with respect to the vertical movement of the airmass.

I'm curious what your running the numbers looks like. I admit I don't have a good mental model for how thermals work from a thermodynamic and aerodynamic perspective. I thought it had something to do with the fact that warm air was less dense and therefore buoyant. How that buoyancy accelerates a volume of air until some form of resistance at the edges progressively resists the acceleration and a steady rate of upward velocity is reached is beyond my understanding at a level detailed enough to relate thermal strength to temperature differences.

As to the temperature gradient across the thermal - I'm not sure it's linear from the edge to the center. Imagine a volume of air rising at 500 FPM. Presumably you have some mixing at the edges but the rest of the heat transfer would mostly be conductive over a period of 10 minutes before the thermal reaches, say, 5000'. I'm not sure what all the coefficients are, but it isn't 100% obvious to me that you'd end up with a linear temperature gradient all the way to the center of the thermal since there is so much new warm air being introduced continuously from the bottom, there isn't much time for heat to transfer to the outside air and air isn't that great a heat conductor in the first place. Have there been studies done?

9B