What are the processes that are capable of dissipating the existing fogs?

There are certain processes in nature which are capable of dissipating the existing fogs. Petterssen has classified them into three categories: (a) condensation and sublimation, (b) vertical mixing, and (c) heating.

Whenever foggy air passes across a snow-covered surface, the fog tends to disappear. In the arctic region in summer, when fog is carried over ice-covered areas, it dissipates. As the air temperature rises over 0°C, the fogs begin to diffuse when the air temperature reaches exactly 0°C, the process of diffusion almost comes at a standstill.

Again, when the temperature comes down below 0"C, the process of fog dissipation is accelerated. Highest diffusion takes place when air temperature ranges between -10° to -15°C.

In a descending air current, the temperature increases adiabatically. This condition also promotes fog dissipation. Solar radiation directly absorbed by the fog particles or the earth's surface is also a contributory factor in fog diffusion.

Atmospheric turbulence causes vertical mixing in the air which also results in the disappearance of fog. The intensity of atmospheric turbulence depends on the stability and the velocity of wind. When the wind velocity crosses a certain limit, the fog is completely destroyed.

This is so because vertical mixing carries heat downward which raises the temperature of the layer of air lying close to the earth's surface. Because of warming of the lowermost layer of air, the fog particles readily evaporate.