Because the atmosphere is semi opaque to IR this corresponds to the temperature of approx 6000 metres high, essentially the top of the troposphere, given the measured lapse rate of about 6degC / 1000m..
Windows: «My windows are all Anderson and the window treatments (which are barely visible when closed) are Hunter Douglas Duette Classic 3/4» SemiOpaque, top down / bottom up, literise (cordless) and the color is Journal.»