What Kind of Fog Results From Adiabatic Cooling?

The Adiabatic Process

• When a parcel of air rises, it experiences a drop in atmospheric pressure. This drop in pressure causes the air parcel to expand. The Laws of Thermodynamics require an inverse relationship between the volume of this air parcel and its temperature. As its volume expands, its temperature must drop and vice-versa.

  During this expansion or compression, the total amount of energy contained in the parcel of air must remain constant. Its energy can be used to power expansion or maintain its temperature, but not both. As the pressure drops, energy is converted to mechanical energy to power expansion and, as pressure rises, energy is converted to thermal energy, causing warming.

  This process is called adiabatic heating and cooling. Adiabatic refers to the change in temperature of an air parcel without the gain or loss of external heat. This adiabatic process is a major component of meteorology and is the primary cause of cloud formation.

The Diabatic Process

• Diabatic heating is the opposite of adiabatic. This process involves a change in the temperature of an air parcel that is not related to its vertical displacement. Diabatic heating involves a heat gain from an external source. The primary source of this heat is our sun. Diabatic cooling involves the loss of heat, usually through radiation.

Adiabatic Cloud (Fog) Formation

• As moist air rises on the windward side of a mountain, its temperature drops, moisture condenses and clouds of fog form. The dry air then descends on the leeward side of the mountain and warms. This produces a "rain shadow" on the leeward side of mountain ranges, forming arid regions.

Types Of Fog

• Radiation fog is caused by a reduction in surface temperature. As surface heat is radiated into space, the surface will cool and fog will form. This type of fog is diabatic because it involves a heat loss.

  Advection fog is caused by the horizontal movement of warm, moist air over a cold surface. As the air cools, the moisture condenses and fog is formed. This type of fog is also referred to as "sea fog" because it primarily occurs over water and drifts inland. This is another type of diabatic fog.

  Evaporation fog is formed when water vapor is added to cooler air through evaporation. As this moisture mixes with the cooler air, condensation occurs and fog is formed. This is a diabatic type of fog because it requires external heat to power the evaporation.

  Upslope fog occurs in all the mountain ranges in North America. Upslope fog frequently occurs during winter, when cold air drifts westward and collides with the windward slopes of the Rocky Mountains. This type of fog usually forms on lower slopes, covers a wide area and is adiabatic, being caused by the vertical displacement of the cold, moist air.