Wind Flashcards
Veering change
Means wind changes in clockwise direction
Backing means
If the direction change of the wind is anti clockwise
Wind directions are usually reported in
True north
1 kt = x
1kmh = y
1 mps = z
X =0.5144 m/s
Y = 1.15 mph
Z= 1.852
Geostriphic wind
Composed of 2 forces acting opposite and in balance - PGF and Coriolis force
Higher wind speed =
Greater deflection due to Coriolis
Lower wind speed =
Smaller deflection due to coriolis
Gradient wind
Centrifugal force and PGF
Buys ballots law
In the n hemisphere .. with back to wind low pressure we be on left
Geostrophic wind blows
Parallel to isobars
In the friction layer - speed is reduced
Coriolis proportional to speed so surface wind decreases then Coriolis decreases .
N.Hemi - backs
S.hemi - Veers
Friction level is up to
3000ft
N.Hemi
Land
Deflection
30 degrees backed
50% reduction of geostrophic wind speed
N.Hemi
Sea
Deflection
15 degrees back
70% of the geostrophic wind speed
When surface temps are max (2pm)
Surface winds increase
At night there’s no thermal currents
No mixing so surface wind speed remains low . (0600hrs)
Wind speed increases in the valleys due to
The Venturi affect
An example of the foehn wind
Is the chinook
The bora is
Cold katabatix wind over the Adriatic
Geostriphic wind increases
As latitude decreases
Stronger the wind speed surface in day means
Less deviation from Geostriphic wind
At night we get land breezes and in the day we get sea breeders
Linked with rising air - density decreasing and cold air being heated from the surface of the sea at night to create a land breeze
Foehn winds - windward side of the mountain
Saturated air cools adiabatically and can form clouds
Leeward side of mountain it warms and becomes unsaturated so conditions are dry and clear
