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Wind speed in case of gradient wind is..
  • A
    always higher than geostrophic wind speed.
  • B
    depending on curvature of the isobars.
  • C
    affected by surface roughness.
  • D
    only depending on the horizontal pressure gradient.

Refer to figure.

=> The computation of the gradient wind involves a knowledge of curvature in the pressure field on a constant level surface. This information may be derived from the curvature of the isobars. Whether it occurs around a low-pressure centre or a High Pressure:

GRADIENT WIND IN A LOW

  • The Centrifugal force opposes the PGF => Reducing the wind speed.
Therefore, for the same isobar spacing, gradient wind speed in a LOW is less than the equivalent geostrophic wind.

PGF = CF + Centrifugal Force

GRADIENT WIND IN A HIGH

  • The Centrifugal Force acts in the same direction as the PGF => Increasing wind speed.
Therefore, for the same isobar spacing, gradient wind speed in a HIGH is greater than the equivalent geostrophic wind.

CF = PGF + Centrifugal Force

HENCE, the relationship being: VST < VHigh and VST > VLow.

Note that we are comparing the gradient wind in a LOW/HIGH to the equivalent Geostrophic wind and not the gradient wind around a HIGH to the gradient wind around a LOW.

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