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MyMET > Local Winds > Flashcards

Local Winds Flashcards

1
Q

What measures surface wind?

A

Anemometer, 10m above the ground

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2
Q

Conversion for knots to m/s

A

1kt = 0.514m/s

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3
Q

What speed is calm wind?

A

1kt or less

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4
Q

What speed is gale force wind?

A

34-47kt

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5
Q

What speed is storm force wind?

A

48-63kt

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6
Q

What speed is hurricane force wind?

A

64kt+

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7
Q

What is a gust?

A

A sudden increase in wind speed of 10kt or more above the average wind speed , lasting less than 1 minute

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8
Q

What is a squall?

A

Gust lasting more than 1 minute

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9
Q

What is a lull?

A

Sudden drop in wind speed

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10
Q

How do we report wind direction?

A

The direction the wind is coming from

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11
Q

What is for the name wind direction moving in a clockwise direction?

A

Veering

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12
Q

What is the name for wind direction moving in an anti-clockwise direction?

A

Backing

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13
Q

What is an isotach line?

A

A line showing areas of equal wind strength

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14
Q

What are the4 forces contributing to wind direction and strength?

A
  1. Pressure gradient force PG
  2. Coriolis effect CF
  3. Centrifugal force
  4. Friction force
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15
Q

What is the pressure gradient force?

A

The winds desire to flow from high to low pressure

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16
Q

What direction does wind flow in relation to the pressure gradient force?

A

Perpendicular

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17
Q

What is the Coriolis effect?

A

Due to different rotational speeds at different latitudes, when a parcel of air changes latitude it retains its original rotational speed

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18
Q

What is the Coriolis force proportional to?

A
  • Wind speed (faster wind, more deflection)
  • Latitude (higher latitude, more deflection)
  • Density (greater density, more deflection)
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19
Q

What is geostrophic wind?

A

When PG and CF are equal and opposite and the wind blows parallel to the isobars

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20
Q

What is the equation for geostrophic wind speed?

A

V = PG/(2 x w x rho x sinLat)
V proportional to PG
V inversely proportional to density and latitude

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21
Q

What is gradient wind?

A

When air flows in a circular path and is influenced by centrifugal force, when CfG supports PG wind speed will be increasing, this occurs in a high pressure system, the opposite is true in a low pressure area

22
Q

What direction does wind flow around a high pressure system in the Southern Hemisphere?

A

Anti-clockwise

23
Q

What direction does wind flow around a low pressure system in the Southern Hemisphere?

A

Clockwise

24
Q

What is buys ballot law?

A

In the northern hemisphere if you stand with your back to the wind the low pressure will be on your left, on your right in the Southern Hemisphere

25
Q

What is the vertical extent of the friction layer?

A

2-3000ft

26
Q

How does wind vary with surface friction?

A

Friction reduces wind speed, as wind speed reduces, Coriolis force reduces

27
Q

How does the friction layer impact wind direction compared to isobars?

A

Due to the diminished impact of the Coriolis force, surface wind will somewhat flow across isobars towards an area of low pressure

28
Q

What is the diurnal variation surface wind?

A
  • During the daytime thermal turbulence mixes slow moving surface air with the faster stream above
  • No thermal activity at night so therefore no mixi, slower winds
29
Q

What is the deflection of surface wind from the 3000ft wind during the day over the sea?

A

10 degrees

30
Q

What is the deflection of surface wind from the 3000ft wind during the day over the land in the day?

A

30 degrees

31
Q

What is the deflection of surface wind from the 1000ft wind during the night over the sea?

A

10 degrees

32
Q

What is the deflection of surface wind from the 1000ft wind during the night over the land at night?

A

45 degrees

33
Q

What is the surface wind speed as a % of the 3000ft wind by day over the sea?

A

70% (2/3)

34
Q

What is the surface wind speed as a % of the 3000ft wind by day over the land during the day?

A

50% (1/2)

35
Q

What is the surface wind speed as a % of the 1000ft wind by night over the sea?

A

70% (2/3)

36
Q

What is the surface wind speed as a % of the 1000ft wind by night over the land at night?

A

25% (1/4)

37
Q

In the northern hemisphere, as you climb or descend how does the wind change direction?

A
  • Veer as you climb
  • Back as you descend
    Opposite true for Southern Hemisphere
38
Q

What direction does the Coriolis force act in the northern hemisphere?

A

Right

Left in the Southern Hemisphere

39
Q

What time does a sea breeze act?

A

Begins 10am, peaks 2-4pm

40
Q

What is the strength of a sea breeze?

A

10-15kt

41
Q

What is the horizontal and vertical extent of a sea breeze?

A

25-40km inland, 2-3000ft high

42
Q

What clouds are associated with a sea breeze?

A

Cumulus development over the land

43
Q

How does a sea breeze effect the temperature?

A

Air over the land is replaced by cold sea air

44
Q

When does a sea breeze usually occur?

A

During anticyclone due to weak PG

45
Q

What are anabatic and valley winds?

A

Anabatic - winds flowing up a mountainside
Valley - winds flowing up a valley
Caused by daytime surface heating

46
Q

What are katabatic and mountain winds?

A

Katabatic - winds flowing down the mountainside
Mountain - winds flowing down the valley
Caused by night time surface cooling

47
Q

What is the Bora?

A

A katabatic wind on the Adriatic coast where winds can exceed 100kt

48
Q

What is the mistral?

A

Cold and dry northerly wind which forms between Atlantic anticyclone and low over gulf of Genoa, wind is accelerated passing between the alps and the Massif Central, can reach 70kt

49
Q

What are Fohn winds?

A
  • Winds flowing perpendicular to a substantial mountain range
  • Must have high moisture content
  • The leeward side of the mountain will be warmer
50
Q

What are mountain waves?

A
  • Wind is disturbed by significant mountains
  • Forms a wave like pattern on the lee side
  • Can reach FL600 and can be found 100-300nm on the lee side
  • Distinguished by lenticular and roll clouds
  • Extremely dangerous, especially rotor zones near the surface
51
Q

What are the characteristics of rotor zones?

A

Severe turbulence, rotor/roll clouds will show as raged and rapidly rotating streaks

52
Q

How should you fly if you encounter mountain waves?

A
  • Overfly at 90 degrees
  • Fly as high as possible to reduce risk
  • Avoid flying on the leeward side and in rotor zones

MyMET (22 decks)

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