cumulus rider, great story! been there!
Thing, your verification of the fact that temperature declines with height must have been quite a chilling experience!
Let me share with all you good people; if you begin your flight when the weather is hot hot hot on the ground, how to prepare for the possibility of spending your five hour endurance flight at 8,000'?
I learned to dress cool, light shirt, long sleeve, long lightweight trousers, and hanging down within reach behind me, a baby blanket! and if it got horrible cold, simples, just pull the blanket down over your body, parachute and all.
Sandals are never a good idea, by the way. If the glider is primitive and draughty, wear proper trainers and thick socks. If the rest of you is cool, your feet will stay comfortable, and if you climb to cooler heights, still comfortable
under your little blanket.