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Meteorology > 50 02 Local Winds > Flashcards

50 02 Local Winds Flashcards

1
Q

What device measures the wind strength and what measures the direction?

How high are these placed above the ground?

A
  • Anetometer measures the wind strength
  • Wind Vane measures the wind direction
  • These are placed 10m off the ground to avoid interference from the ground
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2
Q

Conversions from kts to:

  • Km/h
  • m/s
  • mph
A
  • 1 kt = 1.85 Km/h
  • 1 kt = 0.5 m/s
  • 1 kt = 1.15 mph
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3
Q

Wind Speeds: Gust

A
  • Sudden increase in wind speed of 10kts above the average

- lasts for less than 1 min

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4
Q

Wind Speeds: Squall

A
  • A gust lasting more than 1 min
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5
Q

Wind Speeds: Lull

A
  • A sudden drop in wind speeds
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6
Q

Wind Speeds: Calm

A
  • Wind speeds of 1 kt or less
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7
Q

Wind Speeds: Gale

A
  • Wind speeds of 34kts to 47kts
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8
Q

Wind Speeds: Storm

A
  • Wind speeds of 48kts to 63kts
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9
Q

Wind Speeds: Hurricane

A
  • Wind speeds of 64kts+
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10
Q

What is it called when wind changes direction in:

  • Clockwise direction
  • Anti-clockwise direction
A
  • Clockwise: Veering

- Anti-clockwise: Backing

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11
Q

The Corilois effect bends the wind in what direction in:

  • Northern Hemisphere
  • Southern Hemisphere
A
  • Northern: Right

- Southern: Left

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12
Q

Buys Ballot Law

A

Someone standing with their back to the wind, in the northern hemisphere, will have low pressure to their left.

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13
Q

What is Geostrophic wind and what are the forces involved?

When is it fastest?

A
  • Geostrophic wind is wind moving along a straight line (i.e. straight isobars)
  • It is when the Pressure Gradient force (PGF) and the Coriolis Force (or Geostrophic Force) are equal and opposite
  • It is fastest when the CF is smallest (at the equator) as the CF slows Geostrophic wind down
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14
Q

What is Gradient wind and what are the forces involved?

A
  • Gradient wind is curved wind which follows the curved isobars
  • There are three forces involved in Gradient wind:
    ~ Pressure Gradient Force
    ~ Coriolis Force
    ~ Centripetal Force
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15
Q

Which pressure system (high or low), given the same spacing of isobars, would have the fastest winds?

A

A high pressure system will have faster winds since the the Centrifugal and Pressure Gradient Forces are working in the same direction.

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16
Q

At what height do the Geostrophic and Gradient winds sit at?

A

2000 to 3000 ft

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17
Q

What happens to winds below 2000 - 3000 ft with regards to the Coriolis effect and Pressure Gradient Force?

A
  • As the wind is closer to the surface its spd drops (due to friction)
  • This means that the Coriolis effect is smaller and PGF predominates
  • In the Northern Hemisphere the wind Backs and Slacks
  • Turns to the Left
18
Q

For the following what are the degree of deflection, and speed reductions?

  • Sea
  • Land Day
  • Land Night
A
  • Sea: 10 degrees, 70% of original speed
  • Land Day: 30 degrees, 50% of original speed
  • Land Night: 45 degrees, 25% of original speed
19
Q

Describe Anabatic Winds:

  • What they are
  • Speed
  • What they cause
A
  • Anabatic winds are caused when the sides of a valley or mountain are heated. This causes the air to rise up the side of the valley/mountain.
  • About 5kts
  • The resultant low pressure creates Vally Winds
20
Q

Describe Katabatic Winds

  • What they are
  • Speed
  • What they cause
A
  • Katabatic winds are caused by cooling air sinking down the sides of a valley or mountain.
  • Faster at 8 to 10kts
  • The resultant High pressure creates Mountain winds (sometimes referred to as Valley winds)
21
Q

What is the Head Land effect?

A

The head land effect is caused by an out crop of land which causes the streamlines across the sea to converge.

This increases the speed of the wind around the outcrop (or headland)

22
Q

Describe what causes a Sea breeze and when it occurs?

A
  • Sea breezes occur during the day
  • When the sun warms the land it warms much faster than the sea. The air in contact with the surface warms (through Conduction). This air rises and diverges out. The portion which moves out to sea cools and sinks. The relatively high pressure out to sea and low pressure on land causes the air to move back towards land.
  • The sea breeze brings moister with it and so clouds often form over land with precipitation.
  • As the day goes on the sea breeze becomes stronger and goes further inland.
  • About 10 kts.
  • 5 to 10nm inland
23
Q

Describe a Land Breeze and when it occurs?

A
  • Land Breezes occur only at night.
  • When the land cools much faster than the sea. They are the opposite of sea breezes
  • Generally weaker then Sea Breezes
24
Q

Describe the following regarding Mountain waves (aka Standing or Lee waves)

  • Conditions needed
  • Effects caused
  • Types of cloud produced
A

Conditions:

  • Winds increasing with speed with increasing altitude
  • Minimum speeds of 15-20 kts
  • Wind direction must within 30 degrees of the perpendicular
  • A layer of stable air between unstable layers on the lee side

Effects:

  • Creates ‘waves’ as the air rises and falls between the stable and unstable layers
  • Waves can reach lengths of 5 to 10 nm and heights of 1500 ft
  • Waves can reach 50 to 100 nm downwind from source
  • Under waves an area of turbulence is generated in the ‘Roll Zone’
  • Waves can go as high as the tropopause

Cloud produced:

  • Lenticular cloud in the waves
  • Roll cloud in the ‘Roll Zone’
  • Cap cloud on the top of the mountain
25
Q

Name the different local winds

A
  • Fohn
  • Bora
  • Chinook
  • Mistral
  • Etesian
  • Siroco
  • Ghibli
  • Khamsin
  • Levant
  • Harmattan
  • Haboob
  • Pamperos / Southwesterlies / Southern Busters
26
Q

Describe the Fohn Effect

A
  • Stable air approaches a mountain and is forced to rise
  • Air cools and becomes saturated so creates clouds
  • Cloud base is much lower on the windward side compared to lee side
  • Precipitation on the windward side
  • Warm anabatic wind down the lee side
  • Temperature is warmer on the lee side
27
Q

Describe the Fohn wind

A
  • South/Southeasterly up from Italy
  • Can occur all year round
  • Warm wind
28
Q

Describe the Chinook wind

A
  • Warm Fohn wind over the Canadian Rockies
  • Mainly in Spring
  • Cause rapid melting of ice and snow
29
Q

Describe the Bora wind

A
  • Cold catabatic wind
  • Northeasterly wind across Croachia towards Italy
  • Winter
  • 70 to 100kts
  • Caused by the Siberian High and the Mediterranean Low
30
Q

Describe the Mistral wind

A
  • Cold Northerly wind
  • Travels along the Rhone Vally
  • All year round
  • 40 to 70kts
31
Q

Describe the Siroco, Gilbli and Khamsin winds

A
  • Cool, dry Southerly winds
  • Travel from Africa up to Europe
  • Bring dust with them
  • Sub-tropical high pressure belt to the Mediterranean low
  • Winter to Spring
32
Q

Describe the Etesian wind

A
  • Warm, summer, northeasterly wind

- Travels across the Ageian Sea

33
Q

Describe the Levant wind

A
  • Easterly wind through the Gibraltar straight
  • All year (but mainly in summer)
  • Warm, humid wind
34
Q

Describe the Harmattan wind

A
  • Dry, cool, Northeasterly wind
  • Winter across North East Africa
  • Can generate large sand storms
35
Q

Describe the Haboob wind

A
  • Non-directional (rotational) wind over Sudan
  • Anti-clockwise direction
  • Summer
  • Generate large sand storms
36
Q

Describe the Pamperos / SouthWesterlies / Southern Busters

A
  • Southwesterly, Arctic winds
  • South America, Australia, South Africa
  • Summer (their Winter)
37
Q

At what latitudes would you expect to find Geostrophic winds?

A

Higher than about 15 degrees North and South

38
Q

In the Northern Hemisphere, during periods of prolonged clear skies associated with anti-cyclonic conditions, the wind speed is highest at?

A
  • Early afternoon / warmest part of the day

- Due to more turbulence/mixing of air which gives more energy to the surface wind, increasing the speed

39
Q

What direction do the ‘Rotors’ formed by mountain waves spin with regards to the prevailing winds?

A

Rotors spin such that the upper side of the rotor spins in the same direction as the prevailing wind and the lower side rotates in the opposite direction

40
Q

Between what two areas is a Polar Jet stream usually strongest?

A

Between a Trough and a Ridge

41
Q

What does a ‘Slack Pressure Gradient’ mean?

A

There is no other surface wind flow

42
Q

What happens to wind speeds as latitude increases?

A

Wind speed decreases

Meteorology (21 decks)

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