8.20 Inversions

8.20.2 Explain the factors involved in the development of a:

(a) radiation inversion;

This is a surface inversion caused by the earth cooling at night.

They occur on calm, clear winter nights and are at maximum development around dawn.

The drier the air the more readily the terrestrial radiation can escape, thus enhancing the likelihood of a radiation inversion.

Fog, dew and frost can form if the air has sufficient moisture content.

(b) turbulence inversion;

Turbulence inversions develop as a result of a surface radiation inversion and a shallow ELR near the surface.

There are two main requirements for the formation of a turbulence inversion:

• the presence of a shallow ELR involving the layers of air near the surface; and
• The presence of a wind that is not too light and not too strong

When surface heating begins after sunrise there is an increase in mixing due to thermal currents and increased wind strength. This causes turbulence which moves the air particles up and down randomly.

Some parcels of cold air which have been dormant on the surface, they will be picked up and thrown aloft, during that process the parcels will cool adiabatically.