Wind Flashcards
What measures surface wind
Anemometer
, 10m or 30ft agl
Gust
Sudden change in wind speed by 10kts in less than a min
Calm
1kt or less
Gale force
34-47kts
Storm force
48 - 63kts
Hurricane force
Greater than or equal to 64
Squall
Gust lasting more than 1 min
Lull
Sudden drop in wind speed
What happens to the surface wind in the northern hemisphere
Backed and slacks
Sea breeze wind speed
10 - 5kts
Anabatic
Winds going up the mountain, low pressure which is caused by convection, air comes in and goes up the mountain
Katabatic wind
Typical at night, surface cools, get denser, falls down the mountain
Geostrophic wind
The CF and PGF are equal and opposite and the wind gets deflected 90 degrees so wind travels parallel to the isobars
Ballots law
Back to the wind, low pressure will be on your left
Gradient wind
Wind coming out a high/low pressure
Coming out a high due to centrifugal for acting in the same direction, the the wind is faster
Wind around a low is slower due to the centrifugal force and the corolis acting the opposite direction
Deflection of the wind over the sea and % of the 3000ft wind
10 degrees, 70%
Deflection of the wind over the land by day and % of the 3000ft wind
30 degrees, 50%
Deflection of the wind over the land by night and % of the 3000ft wind
45 degrees, 25 %
Diurnal variation
Durning the day, thermal activity on the surface causes fast high level air to get mixed with slow surface air to get a faster overall wind speed
Durning the night, less thermal air, no rising air, less mixing
Sea breeze formation
Surface heating on the land causes a low pressure to form and thus causing a PGF, goes in opposite direction in the night
Wind gets deflected due to the CF
About 5 - 10kts, faster the speed, bigger the deflection
Land breeze
Opposite to sea breeze
Katabatic wind
Typical at night, surface cools, gets denser and falls down the mountain
Example of the katabatic effect
The Bora, effects the adratic sea
Example of valley winds
High pressure in the north Western Europe to low pressure in the south
PGF goes through the alps causing a Venturi
Strong relatively cold and dry wind
Foehn wind
Stable, saturated air gets pushed up a mountain, cools, forms cap cloud, rains, dries, comes down the mountain as the DALR and is warmer
Examples of foehn wind
Alps
Chinook in the rockies
What happens in the med in winter
The low pressure over the med sea, drags the dry air from n Africa up
This mixes with the cold air from the European land mass and can cause intense storms
Strong winds in the Southern Hemisphere
Roaring 40s
Furious 50s
Screaming 60s
Doldrums
Calm surface conditions due to surface convergence at the ITCZ
Harmattan
NE trade winds over w Africa
Dry sands can impact visibility
Strongest in jan due to the ITCZ moving downwards
Reduces viz up to 3000ft
Can extend to 10-15,000ft
Pampero
S America
Cold polar air moves the flat land, increasing wind speed
Strongest winds occur early summer
