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MET Key Facts > Low Level Winds > Flashcards

Low Level Winds Flashcards

1
Q

Anti-clockwise Movement of winds is referred to as

A

Backing

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2
Q

Clockwise Movement of winds is referred to as

A

Veering

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3
Q

Geostrophic winds refers to

A

PGF + Coriolis
Balanced in speed and direction
Parallel to straight isobars

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4
Q

What increases the Coriolis effect force (Geostrophic force)

A

Increase in density
Faster winds
Higher latitudes

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5
Q

Buys Ballot law

A

With back to wind in NH low pressure on your left
With back to wind in SH low pressure on your right

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6
Q

Gradient Wind

A

PGF + Coriolis + Centrifugal force

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7
Q

Gradient vs Geostrophic wind in a low pressure system

A

Geostrophic is stronger due to the opposing force on centrifugal which makes the gradient wind slower.

Gradient wind slower
Geostrophic wind faster

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8
Q

Gradient Vs Geostrophic winds in high pressure

A

Gradient winds are greater than Geostrophic in high as centrifugal force act in same direction.

Gradient is faster
Geostrophic is slower

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9
Q

Friction layer is

A

From SFC to 2000-3000ft
Affected by terrain etc which impacts wind and stability
At night can reduce slightly by 1000ft

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10
Q

Variation in surface winds

A

Geostrophic winds above friction layer are faster
Wind speed reduces in friction layer
Coriolis reduces because wind speed is reduced in friction layer

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11
Q

What happens in friction layer in NH with winds

A

Winds will back and reduce

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12
Q

What will happen to winds in SH in friction layer

A

They will veer and reduce

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13
Q

Figures for wind/direction change over land in friction layer

A

50% decrease in speed
25/30 degrees change in direction

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14
Q

Figures for wind speed change over the ocean within friction layer

A

25/30% reduction in wind speed
Directional changes around 10/15 degrees

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15
Q

Sea Breeze

A

Air over land warms and rises
Converging air creates onshore breeze
Can lead to convective cloud formation

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16
Q

Land Breeze

A

Wind from land to sea over night
Weaker PGF than daytime effect

17
Q

Calm wind strength

A

Below 1kt

18
Q

Gale force wind strength

A

34kt to 47kt

19
Q

Storm force wind

A

48kt - 63kt

20
Q

Hurricane force wind

A

64kt+

21
Q

How do we measure winds

A

Anemometer (33ft AGL)

22
Q

Mountain Valley Winds on altimeter

A

Air flows down mountain and along valley
Causes altimeter to over read due to decrease in static pressure

23
Q

The Mistral Wind is (south of France)

A

A valley wind
Winds up to 70kt/strong in winter
Cold/dry northerly wind
Blows along Rhône valley
Alps create a Venturi effect

24
Q

The Boar wind is a

A

Katabatic wind
Cold/dry north easterly wind affecting the Adriatic Sea
Strongest in winter
Winds can exceed 100kt

25
Q

Foehn Winds

A

Stable air that rises up surface of mountain
Cools below dew point and cools at SALR
Rain and cloud on upward side and dry air on lee side
Lower dewpoint on lee due to reduced vapour and warmer

Referred to as a chinook in Rocky Mountains

26
Q

NE trade Winds

A

Subtropical high to ITCZ
Blow Easterly

27
Q

S.E Trade Winds

A

Subtropical high to ITCZ
Easterly wind

28
Q

Westerly’s - “roaring 40s”

A

Faster in south than north
Higher speeds in winter season
West to east

29
Q

Horse latitudes

A

Around 30N/S light winds

30
Q

Doldrums

A

Light winds at ITCZ

31
Q

Harmattan - W Africa Wind

A

NE trade wind over Africa
Dry sand which impacts visibility
Reduced visibility to 1000m
10-15k ft

32
Q

S America - The Pampers

A

Burst of cold air from south
Blows across pampas of SA
Squall lines on passage of a cold front

33
Q

Local wind systems such as katabatic winds/sea breeze/valley wind have what in common

A

Flat uniform pressure distribution

34
Q

Mountain Waves develop when

A

Wind direction is perpendicular 30 degrees
Wind speed strong at least 20kt and increases with altitude
Marked layer of stability/strong inversion around altitude summit

MET Key Facts (25 decks)

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