Winds

Question 1

What measures wind?

Answer 1

Anemometer
33ft (10m) AGL

Wind Vane

Question 2

Wind Strengths

Answer 2

Calm = 1kt or less
Gale Force Winds = 34kt to 47kt
Storm force winds = 48kt to 63kt
Hurricane force winds = 64kt

Question 3

Definition of a gust

Answer 3

A variation of 10kt or more above average wind speed lasting a minute

Question 4

Definition of gustiness

Answer 4

Difference between min/max gust speeds

Question 5

Definition of a lull

Answer 5

Sudden drop in wind speed

Question 6

What is a variable wind

Answer 6

A variation of 60 degree or more in wind direction

Question 7

Wind Reporting

Answer 7

METARS/TAFS = Degrees true (reported avg 10 mins)

ATC = Degrees Magnetic (report average 2mins)

Question 8

PGF

Answer 8

Pressure Gradient Force - High to low

Question 9

Coriolis (Geostrophic Force)

Answer 9

Rotation of earth deflects the winds to the right in NH
Rotation of earth deflects the winds to the left in SH

Question 10

Coriolis is influenced by

Answer 10

Latitude - Higher latitudes more deflection in wind
Density - greater density more deflection
Wind speed - higher wind speed more deflection

Question 11

Geostrophic Winds

Answer 11

PGF + CORIOLIS

Balance in speed/direction
Parallel to straight isobars

Question 12

Gradient Wind

Answer 12

PGF + Coriolis + Centrifugal forces
Blows along curved isobars

Question 13

Gradient Wind around low pressure

Answer 13

Centrifugal force opposed the PGF therefore reducing wind speed.
Reduces Coriolis force and then leading to flowing parallel to isobars

Gradient in a depression is lower than the Geostrophic winds (overread)

Question 14

Gradient Wind around high pressure

Answer 14

Centrifugal force acts in same direction as PGF force wind speeds increase.

Gradient wind is greater than the Geostrophic winds (underread)

Question 15

Friction Layer

Answer 15

SFC to 2000/3000ft
Affected by terrain/wind speed/stability
Night time layer reduces from around 1500ft

Question 16

Surface Wind Model

Answer 16

Winds back in NH due to reduced Coriolis

Winds Veer in SH due to decreased Coriolis effect

Question 17

NH back and slack meaning

Answer 17

Heading reduces/speed reduces as you descend into surface friction layer

Heading veers and increases as you flight out of surface friction layer

Question 18

Surface Friction comparison between sea and land

Answer 18

Over land 50% decrease in wind speed in surface layer
Over sea 30% decrease in wind speed in surface layer

Over land direction changes by 30 degrees
Over sea direction changes by 10/15 degrees

Question 19

Diurnal Variation on surface winds

Answer 19

In afternoon strongest winds therefore more Coriolis force less deviation from Coriolis as surface winds stronger

At dawn winds are the weakest and therefore surface winds will deviate more in the surface friction layer more

Question 20

Wind Shear is measured in

Answer 20

Horizontal wind shear - knots per 1000ft
Vertical wind shear - knots per 100ft

Question 21

Low around a low and high around a high meaning

Answer 21

Gradient wind is less than the Geostrophic wind in a low pressure system

Gradient wind is higher than the Geostrophic wind in a high pressure system

Question 22

Gradient winds flows around

Answer 22

Curved Isobars

Question 23

Geostrophic winds flow parallel to

Answer 23

Straight isobars

Question 24

“NH back and slack” meaning

Answer 24

In the northern hemisphere descending down into friction layer the wind direction will back and speeds will reduce

Question 25

Dangers of flying close to the ITCZ

Answer 25

Showers
Strong winds
Thunderstorms at noon