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## diurnal winds

• Posts: 11

### srodneyrahul created the topic: diurnal winds

Just wondering if you can help me with a question I got wrong in the CPL Met exam. Went something like this:

A pressure system has been stationary over a flat inland surface for 12 hours from midnight to midday. Describe the variation expected in wind speed and direction:

a) Remain the same
b) Increase and veer
c) Increase and back
d) Decrease and veer
e) Decrease and back

Can't seem to find any reference to this in the text book.

• Posts: 4

### CptKramer replied the topic: diurnal winds

the answer should be C, bob replied to a post similar to this with this response. Hope it helps.

Since diurnal means throughout the day, the surface wind would have veered during the night as surface friction would have slowed it down giving the pressure gradient more time to act on it and push it out of the system. By early morning, the surface wind will be almost stationary and so will have veered by the greatest amount. As temperature increases after sunrise, convection mixes the surface wind with the faster wind above so the average speed of the surface wind increases. That means that is is 'less veered' during the day-especially by mid afternoon. Since in is 'most veered' a dawn and 'less veered' during the day, the surface wind in the afternoon would have backed with respect to the surface wind in the early morning and its speed would have increased with respect to the surface wind in the early morning.

• Posts: 260