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In the Northern hemisphere with an anti-cyclonic pressure system the geostrophic wind at 2 000 ft over the sea is 060° / 15 kts. At the same position the surface wind is most likely to be:
  • A
    070° / 20 kts
  • B
    060° / 10 kts
  • C
    060° / 20 kts
  • D
    050° / 10 kts

Refer to figure.

SURFACE WIND OVER LAND AND OVER SEA:

  • OVER LAND
In the Northern Hemisphere, the surface wind backs by 30º compared to the geostrophic wind and speed is reduced by 50%. (figure a.)
In the Southern Hemisphere, the surface wind veers by 30º from the 2000ft wind and speed is reduced by 50% compared to the geostrophic wind.
  • OVER SEA – friction is much less, and the surface winds are closer to geostrophic values.

In the Northern Hemisphere, the surface wind backs by 10º from the geostrophic wind and speed reduces to 70%.
In the Southern Hemisphere, the surface wind veers by 10º and speed reduces to 70% when compared to geostrophic winds.

=> In this case, the wind will back 10º compared to the 2000ft wind => 060º wind will back to 050º.
Speed will reduce 30% - 15 kt x 0.7 = 10.5 kt approx.
CLOSEST OPTION 050º/10KT.

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