Hi Milt,
The ISA tropopause is at 11,000m, i.e., about 36,100ft.
Never too old to learn... I thought there was an international (ICAO or otherwise) Tropical SA, but obviously not!
Phenomenon well known... it was one of the things that allowed Concorde to get up to 60,000ft on the Barbados run, while on the New York run 57,000ft was generally the limit.
Another nasty in the tropics is the sharp temperature gradients you can run into, which tends to play havoc with a basic Mach Hold.
A bit out of topic here, since BA038 did certainly not pass through the tropics....