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Meteorology Comment from Sunday 1/28/01
see also, [Tom's Flight Log
Narative from Sunday]
The meteorology on Sunday varied with
Early on, I think the climb rates were better above 35.
The air was nice early, I launched before 10 and climbed easily in nice thermals that had light drift from the SE. As the sun rose higher the solar heating became more direct and intense resulting in more dynamic temperature differentials and stronger thermals. I suspect the air mellowed quite nicely later in the day.
The lapse rate derived from the average surface high temperature to 6 grand was only average, but the air mass was cold. The average forecasted surface high temperatures were quite a bit lower than the transient local spikes. We were getting pronounced differential heating. There were sharp differences in temperature depending how much solar energy was being collected. The thermals were small partially because the exposed heat collectors would heat the air quickly but locally. With the sharp heating thermals would break away before they had a chance to grow very large.
The thermals had strong cores and turbulent edges. Because the thermals had a large temperature differential between them and the surrounding air they were quite buoyant and rose quickly. Their high vertical velocity resulted in vortex action on the edges due to the drag. In Solid Geometry, surface area varies with the square root of the volume, so if the volume is reduced by a factor of 9, the surface area is only reduce by a factor of 3. Small thermals have a lot of surface area in relation to their volume. There is drag on the surface of a moving object and drag varies with the square of the velocity. All that drag resulted in vortex action and mixing (turb). Visualize the mushroom head of the fireball from an exploding bomb.
In the areas that were partially shaded, the heating was more moderate and distributed. The slower heating allowed more even heating over a larger area which permitted a bigger bubble to build before breaking loose. The friendlier thermals were in areas that were recently shaded in. Areas that were previously shaded and now receiving new sun were cold. The cold areas receiving direct sun experienced sharp and rapid differential heating resulting in more punch.
The wind varied quite a bit with some local strong draw filling the voids left by the high velocity thermals. With peak thermal velocities approaching 15 mph you can expect significant horizontal draw. When trying to go upwind you can use the wind shadows. I'd rather be behind a thermal being drawn toward it, not out in front of it being pulled back. You need to be cautious in the wind shadows because they can have some sharp sheers that get worse with increasing velocity.
Obviously, the east couldn't have been too bad if you can do a 20+ mile upwind leg in a bag. The velocity and direction varied. We had drift from the north on some glides, but mostly drawing in down lower. The clouds out back showed lean form the NW but there were places that it was drawing strong out of the SE.
Commonly, the west will push through from the west, but it was my perception that on Sunday the lower level SE was stronger on the west end of the range. I think on a larger scale the wind might have been accelerating around the corner from the SE on the west end. There was less east wind the further east I went, neutral across Casitas Pass, and SW in Ojai and beyond. The wind out in the Santa Clara Valley was light up valley from the SW with a stronger draw pulling up the Sespe.
What goes up must come down. A good day to stay out of the sink which could be found in the canyons. The sink leaving thermals was particularly bad and you needed a little more altitude to make the glides. Plan ahead and pick your primary and secondary triggers. Have a plan "B" to fall off on a line that will take you over potential savers and not down the middle of a canyon. Don't fly 80% of the way to your trigger and turn around because the sink is bad on the way. Speed up in the sink but slow down defensively when the air gets twitchy.
I didn't take a collapse all day. Not even a tip fold. Nada. 5 hours. I'm much more apprehensive about lee side wind turbulence because it's more chaotic. Thermal turbulence has a predictable rhythm. You may not like the strong spikes but at least your intuition can sense them before you hit'em.
Evaluate the temperature dynamics. When there's a large spread it's goanna be a ride. You can only learn so much sitting on launch, to hone your intuition you got'ta jump in and hold on. Be cautious about what your jumping into. We all need to pass occasionally, and the rookies need to pass more often.
Sundowner
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