Chapter 10 - Wind Flashcards
How is surface wind measured
By an Anemometer 10m above the ground
What is calm winds
1 knot or less
What is a Lull
A sudden drop in wind
What is a Gust
Sudden increase in wind 10 knots
gale =
43-47 knots
storm =
48 - 63 knots
Hurricane =
64 +
which north are runways aligned with
Magnetic
Squall =
An increase of wind that last more than a minute
Met reports use which north
True
ATC (ATIS) reports use which north
Magnetic
Wind moving clockwise is called
Veering
Wind moving anti clockwise is called
Backing
If isobars are close together which wind does it indicate?
Strong
Wind speed is directly proportional to? It also cause air to move from high to low pressure
Pressure Force Gradient
Where in the world is the Coriolis effect least?
Equator
Which way does the Coriolis effect deflect in the Northern hemisphere
Right
Which way does the Coriolis effect deflect in the Southern hemisphere
Left
Increase in Latitude (towards the poles) does what to the Coriolis effect?
increases
Geostrophic Wind is
When air is moving from H to L and is effected by the Coriolis effect.
The PGF and Coriolis combined when they are equal and opposite to change the wind direction to line up with the straight ISO bars
Gradient Wind is
PGF, CF and centrifugal force combine to create curved ISO bars.
Because the centrifugal force is opposing the CF it causes the wind to follow the ISO bars around a depression or high.
Surface Wind is and happens where?
In the friction layer (less 1000m) and causes the CF effect to reduce because of the stronger frictional forces near the surface.
Surface friction is increase by
Thermal activity making turbulent air. Increases with Diurnal Variation / during the daytime
Over the sea the Deflection and % of surface speed is
10 degrees
70%
Over land by day the Deflection and % of surface speed is
30 degrees
50%
Over land by night the Deflection and % of surface speed is
45 degrees
25%
In the northern hemisphere when climbing the wind will?
Increase and Veer
In the northern hemisphere when descending the wind will?
Decrease and back
On a Low Px what will the wind always do
Cut in
What is a Sea Breeze
Happens on a sunny day with no clouds
the land heats the air and creates a low pressure
the air rises and creates a high and diverse away back to the sea and then sinks again
low px causes a breeze from the sea to the land
Where does the sea breeze happen and what wind speed
During the day
10-15 NM in land
speed 10 knots
How does a land breeze happen and what are the typical figures
reverse of sea breeze
5 NM
5 Knots
Anabatic Winds happen how
Sun heats the surface of a mountain
that heated air then rises up the mountain
creates a low px at the bottom
A valley wind is created how and give a typical one
From the Anabatic winds leaving Low Px in the valley
By mid afternoon it causes more air to converge to replace the missing air creating winds
Mistral 70 knots
Katabatic winds is created how
At night the cold mountain side cools the air
Cold air sinking down the mountain
Creates a high pressure
Mountain winds at night is created how and give a typical one
High pressure is created because of the Katabatic
Diverges the air away
Bora - in winter up to 100 knots
Mistral is a valley wind that flows out of
Rhone Valley into Med (can reach 70 knots)
Foehn Wind is found where
In the Alps
Get cloud cap on top of the mountain
on the Lee side will get warm dry air
What is Foehn wind called in the Rockies
Chinook
x3 African winds called Sirocco, Ghibli and Khamsin come from which direction and bring what condition
Southerly
Dry, Dusty, Wind and air
Creating a low pressure over the Med
Strong winds and uneven surfaces =
Mechanical/ frictional turbulence
Mountain waves/ standing waves/ Lee waves require x3 things
Mountain
15 - 20 knots wind at the top
stable air on the Lee side with unstable air above or below
How far downwind can the mountain waves occur
50-100NM
Give the downwind distances for
Pennines
Rockies
Andes
250
300
500
Which clouds do you get with mountain waves
Cap cloud
Roll / rotor
lenticular
Cold Katabatic wind over the Adriatic?
Bora
x4 examples of Topographic windshear
Buildings
Trees
funnelling
mountains
Horse latitudes are where
Sub tropical highs
NE/SE trade winds are from where and heading to
subtropical highs and heading to the lows
Doldrums (forms at the ITCZ) what are the winds like
Calm because the two winds don’t converge right at the surface
Westerlies appear where
Midlatitude lows
Polar easterlies come from
The polar highs
Harmattan is NE trade wind what condition are usual for it
dry
dusty
visibility effected 10-15,000 feet
Pampero is what
A burst of cold air that crosses the pampas with strong winds oct-jan
