Low Level Wind

Question 1

What is wind

Answer 1

The sustained horizontal movement of air created by a temperature gradient

Question 2

Is wind a vector or scalar quantity

Answer 2

Vector as it has direction and magnitude

Question 3

What is 1knot equivalent tok

Answer 3

1.852 km per hour
½ m per second

Question 4

What shows 5kt, 10kt and 50kt on a weather chart

Answer 4

5kt = line with a half feather
10kt = line with 1 full feather
20kt = solid triangle on end of li e

Question 5

What is a gust

Answer 5

Where there is a short increase in prevailing wind speed for a few seconds

Question 6

What is a lull

Answer 6

Where there is a short decrease in wind speed for a few seconds

Question 7

What is a squall

Answer 7

Where surface wind increases by 16kt or more to become 22kt or more
For more than 1 minute

Question 8

What is veering

Answer 8

The wind direction changes clockwise

Question 9

What is backing

Answer 9

The wind changes its direction anticlockwise

Question 10

When do you get weak or strong wind

Answer 10

Weak wind is a slack pressure gradient
Strong wind is a steep pressure gradient

Question 11

Why can’t air just flow from a high to low pressure

Answer 11

The coriolis effect

Question 12

What is the pressure gradient force

Answer 12

The force which is caused by pressure to move air from high to low pressure

Question 13

What is the coriolis also called

Answer 13

The geostrophic force

Question 14

What effect does latitude have on the coriolis

Answer 14

It increases with latitude
0 at equator
Max at poles

Question 15

What is buy ballots law

Answer 15

If you stand with your back to the wind in the NH then the low pressure will be to your left

Question 16

For a wind to be geostrophic it has to

Answer 16

Be above the friction layer
Be at a latitude greater than 15°
Occur in an unchanging pressure situation
Blow along straight and parallel isobars

Question 17

Why do variations occur in winds below 2000ft

Answer 17

Unequal heating of the Earths surface
Local topography
Varying effects of surface friction

Question 18

How does surface friction effect wind over Land

Answer 18

IN NH (opposite for SH)
It will back wind by 30° and decrease its speed by 50% when descending from 200ft
And the reverse when going up to 2000ft

Question 19

How does surface friction effect wind over Water

Answer 19

IN NH ( opposite for SH)
It will back by 10° and decrease speed by 70% when descending from 2000ft
And opposite when going up to 2000ft

Question 20

How does diurnal variation effect wind

Answer 20

Day - night then wind Backs and Decreases
At 1500ft Increases and Veers

Night - Day then wind Veers an Increases
At 1500ft Decreases then Backs

Question 21

What effect does cloud cover have on wind

Answer 21

Wind speed will reduce as less heating has occurred during the day so friction layer height decreases

Question 22

What is wind blowing along isobars called

Answer 22

The gradient wind

Question 23

Around a LOW how to the forces balance out for wind

Answer 23

PGF = Centrifugal Force + Coriolis

Gradient speed will be less than geostrophic wind

Question 24

Around a HIGH how do forces balance out for wind

Answer 24

Coriolis = PGF + CF
Gradient wind speed will be more than geostrophic wind speed

Question 25

What does wind do around a low

Answer 25

Converge (move anticlockwise in NH and clockwise in SH) Convergence is associated with cyclonic flow

Question 26

What does wind do around a high

Answer 26

Diverge ( move clockwise in NH and anticlockwise in SH) Divergence is associated with an anti-cylconic flow

Question 27

How does convergence and divergence differ in the NH and SH

Answer 27

It's the same phenomena so convergence around a LOW and Divergence around a HIGH Just the direction of wind changes in terms of clockwise or anticlockwise

Question 28

What does it meanby HIGH HIGH = LOW LOW

Answer 28

A HIGH pressure at a HIGH latitude can equal a LOW pressure at a LOW latitude * assuming the same isobar spacing

Question 29

On a weather chart what do the isobar represent

Answer 29

QFF readings of pressure