Directional Shear

Directional Shear
Directional shear refers to a change in the direction of the wind with height. Notice in this image there is both speed and directional shear as both the angle and the length of the wind vectors are changing with height.

Directional shear
The component of wind shear which is due to a change in wind direction with height, e.g., southeasterly winds at the surface and southwesterly winds aloft.

DIRECTIONAL SHEAR The shear created by a rapid change in wind direction with height.

Transverse bands observed at low levels (called transverse rolls or T rolls) often indicate the presence of a temperature inversion (or cap) as well as directional shear in the low- to mid-level winds.

Directional shear is a frequent change in direction within a short distance, which can also occur vertically or horizontally. This can also occur vertically or horizontally.

Backing of the surface wind can increase the potential for tornado development by increasing the directional shear at low levels.BackscatterThe portion of power scattered back in the incident direction.

SHARSSubtle Heavy Rainfall SignatureShearVariation in wind speed (speed shear) and/or direction (directional shear) over a short distance within the atmosphere. Shear usually refers to vertical wind shear, i.e.

The index combines the effects of low-level moisture (850 mb dew point), convective instability (Total Totals (TT) Index), jet maxima (850 mb and 500 mb wind speed), and warm air advection (veering directional shear between 850 mb and 500 mb).

Helicity has units of energy and can therefore be interpreted as a measure of wind shear energy that includes the directional shear.

Shear - Variation in wind speed (speed shear) and/or direction (directional shear) over a short distance. Shear usually refers to vertical wind shear, i.e.

The latter example is a form of directional shear which is important for tornado formation. Compare with backing winds.
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SHEAR VECTOR - Measurement of the absolute vertical wind shear, incorporating both speed and directional shear, as a vector quantity (usually in knots with direction).

The difference between wind velocity measured at two specific locations divided by the distance between those two positions; wind shear consists of a combination of speed shear and directional shear.
wind vane ...

with time at a given location (e.g., from southerly to westerly), or which change direction in a clockwise sense with height (e.g., southeasterly at the surface turning to southwesterly aloft). The latter example is a form of directional shear which ...

a backing wind usually refers to the turning of a south or southwest surface wind with time to a more east or southeasterly direction. Backing of the surface wind can increase the potential for tornado development by increasing the directional shear ...

See also: Shear, Thunderstorm, Storm, Thunder, Radar