CONVECTIVE LAYER This layer extends from about i km. above the ground to the top of the troposphere at about io km. As in all the layers constituting the tropos phere, the temperature continues to decrease with height to the top of the convective layer, though diurnal temperature variation is almost absent. Frictional turbulence does not reach here, but, as already indicated, particles from the Earth's surface can be carried into this layer by large scale convection currents when the ground is heated by sunshine.
The height above the ground attained by a mass of heated air before it loses buoyancy, depends on the temperature gradient and water-vapour content of the air at the time, as explained in the standard works on dynamical meteorology. Ascent may be halted if there is a temperature inversion layer in the upper atmosphere. Under conditions of thermal instability, `bubbles' of heated air may arise intermittently from areas where the ground or vegetation is being heated by the sun. These bubbles may rise to the convective layer, carrying spores and other particles as well as water vapour to the level at which cumulus clouds are formed, and at times reaching to the base of the stratosphere (Mason, 1957).