What is wind velocity and how is it expressed?
It is a vector quantity.
It is expressed in magnitude and direction
What height is wind velocity measured and over what average time?
10M and 10 minutes
Define a GUST
A SUDDEN increase in wind speed lasting a short time and dying away suddenly
Define a SQUALL
A sudden increase in wind speed of at 16KTS OR MORE lasting at least 1 MINUTE and reaching a TOP SPEED OF 22KTS
When wind direction changes CLOCKWISE it is said to BACK or VEER?
VEER
When wind direction changes ANTICLOCKWISE it is said to BACK or VEER?
BACK
Where is the Coriolis force greatest?
The poles
What direction does a low pressure system rotate in the Southern Hemisphere?
Clockwise
Summarise Buys Ballots law:
An observer standing his back to the wind in the Southern Hemisphere the LOW pressure region will be on the RIGHT and the HIGH pressure region will be on the LEFT
Summarise the EQUATORIAL TROUGH
- Air contact with earths surface over equator warms and rises = large scale convection
- The rising air creates an area of low pressure known as the EQUATORIAL TROUGH
- This region also known as the Inter Tropical Convergence Zone (ITCZ) or the Doldrums
Summarise the SUB TROPICAL RIDGE
- Convective air from equator moves towards poles at higher levels and COOLS
- The air descends and forms a belt of high pressure known as the SUB TROPICAL RIDGE
Summarise the SUB POLAR LOW
- Over the poles the dense air results in the region known as the polar high
- This air moves out and converges with air flowing out of the subtropical ridge
- When they converge they rise and form a belt of low pressure known as the SUB POLAR LOW
Summarise the NORTHWEST MONSOON
- During summer in the Southern Hemisphere the equatorial trough moves south to low across northern Australia.
- As a result Australia is influenced by a north westerly air steam due to the air flowing towards equatorial trough crosses equator and is deflected LEFT due to CORIOLIS FORCE
- Wet season in northern Aus
Summarise the SOUTH EAST TRADE WINDS
- Wind blowing from the subtropical ridge towards equator during winter months
- Cloud development limited in the south east trades to to large scale subsidence inversion
Summarise the ROARING 40’s
- 40 deg S latitude
- Air flowing FROM the SUB TROPICAL RIDGE towards the SUB POLAR LOW
- NORTH WESTERLY DIRECTION due to Coriolis deflection
Gradient Wind follows …… isobars when Coriolis force matches the gradient force
CURVED
GEOSTRAPHIC FLOW follows …….. isobars when the forces are matched
STRAIGHT
The surface wind around an area of low pressure in the Southern Hemisphere blows:
A. Clockwise and outwards
B. Anti clockwise and inwards
C. Clockwise and inwards
D. Anti clockwise and outwards
C. Clockwise and inwards
If the forecast wins is 030M/20KT, it will blow:
A. From 030M
B. To 030T
C. From 030T
D. To 030M
C. From 030T
When flying towards a low in the Southern Hemisphere, an aircraft would experience:
A. Left drift
B. Right drift
C. Head winds
D. Tail winds
A. Left drift
What is the depth of the FRICTION LAYER?
3000FT
How much is wind speed reduced over land in the friction layer?
2/3rd’s
How much is wind speed reduced over water in the friction layer?
1/3rd
How does wind flow above the friction layer?
Wind tends to flow parallel to isobars (gradient wind)
