Wind at different scales

Wind is the movement of air, caused by the uneven heating of the Earth by the sun and the Earth’s own rotation. Winds range from light breezes to natural hazards such as hurricanes and tornadoes.

Generally on the basis of scale wind is classified into 5 types –

Molecular and eddy viscosity :-

When a fluid such as air-slows down because of the random motion of gas molecules, this is referred to as molecular viscosity. When a laminar flow gives way to irregular turbulent motion, the internal friction produced by turbulent whirling eddies is called eddy viscosity.

Microscale winds :-

Within smoke, small chaotic motions eddies causes it to tumble and turn. These eddies constitute the smallest scale of motion microscale. Here eddies with diameters of a few meters or less disperse smoke transport quantities vertically b/w the surface and atmosphere. They are usually short lived, lasting from seconds to a few minutes at best.

Mesoscale winds :-

In the previous case smoke rises, it drifts even higher and is carried many kilometers downwind towards the Centre of town. This circulating city air is one example of the mesoscale or middle wind. Typical mesoscale wind range from a few kilometers to a few hundred kilometers in size. Generally they last minutes to hours or as long as a day.

Synoptic scale winds :-

In the synoptic or weather map scale winds only the circulation around the high and low pressure over the region are visible. Circulation of this magnitudes dominate regions of hundreds to even thousands of squire kilometers. Although life span of these features varies, they typically last for days and sometimes weeks. They transport heat and moisture horizontally from warm humid tropical regions to cold, dry polar areas examples are Cyclones, Fronts etc.

Planetary/ Global/ Macroscale winds :-

The largest wind pattern are seen at the Planetary or Global scale. Here we have wind patterns ranging over the entire Earth. Synoptic and global scales can be combined and referred to as the Macroscale.