Atmospheric convection
Atmospheric convection, like other convection, is caused by temperature differences. This may be because the atmosphere is unstable. When parts of the Earth's surface become warmer this can also cause convection. The first type (unstable state of atmosphere) can be called spontaneous. The second type (convection caused by unequal soaking) can be called contact convection. Spontaneous convection starts at any level. Contact convection starts near the terrain.