Definition

A region of low pressure at the surface. The pressure gradually rises as you move away from the centre.

Description

Air in the upper Troposphere can be caused to change direction and speed, sometimes leaving a gap or void behind it which is filled by air rising up from the surface. The outflow of air from an area is known as "Divergence", while the inflow of air to the area of low pressure is called "Convergence".

Air flows from high pressure to low pressure and, because of the rotation of the earth (coriolis effect), the strength and direction of the air flow depends on the pressure gradient, latitude, and hemisphere:

• In the Northern Hemisphere, winds circulate around a depression in a anticlockwise direction
• In the Southern Hemisphere, winds circulate around a depression in a clockwise direction

Formation of a Depression