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Mid-Level Atmospheric Shear
Background:
Using the gridded atmospheric
motion vector output u and v AMV components are averaged
over a mid troposphere layer (400, 500, and 600 hPa) and a lower layer
(700, 775, 850, and 925 hPa). The difference in these averaged components
is used to compute the speed shear between the lower and mid
layers. The contours show the vector magnitude shear (absolute value, kts).
The streamlines indicate the direction of the shear.
In the case when a tropical cyclone (TC) is present, the analyses
are modified in the storm region by a procedure which removes
the storm circulation within a prescribed radii. This allows a more
representative depiction of the environmental shear acting on
the storm.
Uses:
The presence/lack of atmospheric wind shear is vital to
hindering/supporting TC development.
A low shear environment is favorable for tropical cyclone development,
while a high shear environment will deter a immature TC region from
(further) developing or destroy an already mature TC.
Shear values below 20 kts (10 m/s) are considered low enough for
tropical cyclogenesis.
For more AMV information, please visit the
International Winds Working Group (IWWG)
page.
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