Sources

Uneven heating of the earth contributes to the strength and triggering of individual thermals.

Factors:
  • The angle of incidence of the sun's rays.
  • The moisture content of the ground.  More heat needed to evaporate the moisture before the air can be heated.
  • The type of soil.  Those that drain faster may produce thermals more quickly.  Others may be better heat conductors due to there composition.]
  • The nature of the vegetation. - transpiration of crops; - reflection of light etc.
  • Some terrain produces thermals early in the day while other terrain is a better source of late thermal.
  • Re-cycling of thermals.  A particular terrain or even conditions in general may appear to dissipate or strengthen in a cyclic fashion in the course of a day.