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Divergence over a uniform surface is caused by..
  • A
    frictional force together with straight isobars.
  • B
    frictional force only.
  • C
    frictional force together with anti-cyclonic curvature of the isobars.
  • D
    frictional force together with cyclonic curvature of the isobars.

Refer to figures.

Divergence at the surface and convergence in the upper air => describes a HIGH PRESSURE/ANTICYCLONIC CURVATURE OF THE ISOBARS.

Winds below 2000ft (Friction Layer) are affected by friction – frictional forces can act to change wind’s direction and slow it down. Coriolis force will be decreased, the PGF is now more dominant. This causes a change in wind direction – wind blows somewhat across the isobars towards the low pressure centre and away from the high pressure centre. As we move higher, surface friction has less effect on the wind until the wind is indeed Geostrophic - and blows parallel to isobars.

=> Frictional forces cause the wind to convergence at the surface around a LOW and diverge around HIGH.

Rotation of air (winds) around a HIGH is:

  • Northern Hemisphere = outward from centre and clockwise,
  • Southern Hemisphere = outward from centre and anti-clockwise.
Rotation of air (winds) around a LOW is:
  • Northern Hemisphere = inward and anti-clockwise,
  • Southern Hemisphere = inward and clockwise.

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