Surface Wind Calculations MET

A common question: it will either give you the surface wind and ask you to find the upper wind or vice versa.

The first question to ask yourself is "am I in the northern hemisphere"? If you are, then the wind backs and slacks on the way down - that is, reduces in speed and changes in an anticlockwise direction - as you go from the upper wind to the surface. Going upwards in the northern hemisphere, the opposite happens - the wind veers and increases. If you are in the southern hemisphere, then the wind still decreases in strength on the way down but the directional changes are reversed - veering on the way down and backing on the way up.

The second question is "am I over the land or sea?" Over the land the directional change is 30 degrees and the change in wind factor is by 2 (doubled on way up, halved on way down). Over the sea the directional change is 10 degrees and the strength change is by two thirds - so multiply by two thirds going down, divide by two thirds going up. An obvious mistake is to pick the wrong corrections.

The third question to ask yourself is "which way am I going - up or down?" This tells you which way to apply the corrections. This is another of the obvious mistakes and it is certain the examiner will have picked wrong answers based on this mistake.

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If the wind above the friction later is reported as 93°/65.2 kts, what is the approximate surface wind over the land in the southern hemisphere?
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