What mechanisms are responsible for causing the wind to blow in gusts?

4 Meteorology

Gust quest

What mechanisms are responsible for causing the wind to blow in gusts?

Chris Long

Sussex, UK

Near the surface of Earth, friction slows the wind. Turbulence is almost

always created by layers of air moving at different velocities and this

enhances or reduces the surface wind. The enhancements are the gusts.

Strong turbulence is also created by obstructions such as buildings, which is

why city centres are notoriously gusty.

If the surface is sufficiently warmer than the air above, then convection

will produce columns or walls of warm air called thermals. These will rise

from the surface, and draw in currents of air to the base of the rising

column. These currents can add to the mean wind to produce gusts that are

longer lived than the usual turbulent gust.

In addition, if the convection is strong enough, it may produce shower

clouds by condensation of moisture in the thermal as it rises and cools.

Subsequent evaporation can then result in columns of cold air rapidly

descending from these clouds to produce violent gusts at the surface. These

are sometimes called squalls.

Mike Brettle

Cardington, Bedfordshire, UK

Cloud line

Richard Booth

Lewes, East Sussex, UK

The clouds with the most clearly defined edges are the billowing white

cumulus clouds rising into a clear sky. These are formed by the

condensation of water vapour as air expands and cools. This does not occur

in a homogeneous layer but in a discrete parcel or column of warmer and

less dense air rising from below through colder air above.

Although the cloud is cooled by expansion as it ascends, it continues to

rise as long as its temperature is higher than that of the air surrounding it.

Only when the air forming the cloud reaches a level at which the

surrounding temperature is the same does it mix with that air and become

fuzzy. Until then there is a sharp boundary between the different air masses.

Barrie Watson

Shoreham-by-Sea, West Sussex, UK

Clouds may appear to be static objects. In fact they are dynamic and there is

usually a convection current of air rising up into a cloud. As this air rises, it

expands and cools. At a given altitude, condensation occurs, thus defining a

sharp lower boundary to the cloud. The sharpness of the upper surface

depends on how fast the air is rising and the extent to which turbulence

mixes this damp air with the surrounding, drier air. When the convection

current ceases, the cloud will tend to become diffuse and lose its welldefined

edge.

Glider pilots use the appearance of the clouds above them in order to

recognise where there are thermal currents that will enable their planes to

gain altitude.

David Shirtliff

Tamworth, Staffordshire, UK