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CPL/ATPL Meteorology > The Wind > Flashcards

The Wind Flashcards

1
Q

Describe the effect of the Coriolis force on moving air.

A
  • A mass moving in a rotating system experiences a force
  • This acts perpendicular to the direction of the motion/wind
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2
Q

State the horizontal component of the Coriolis force equation.

A

Horizontal Coriolis Force = 2x Earth’s angular velocity x sin(latitude)

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3
Q

State the change in the magnitude of Coriolis Force with latitude.

A
  • Higher latitudes = increased Coriolis Force
  • Equator = 0degrees latitude therefore zero horizontal Coriolis Force.
  • Strongest at the poles
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4
Q

State the relationship between the wind speed and the Coriolis Force.

A
  • Directly proportional to wind speed
  • Increase in wind speed = increase in Coriolis Force
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5
Q

State the direction of the Coriolis Force relative to the wind direction in the Southern Hemisphere.

A
  • Deflects LEFT in the SH
  • Deflects RIGHT in the NH
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6
Q

State the direction of the Coriolis Force relative to the wind direction in the Southern Hemisphere.

A
  • Deflects LEFT in the SH
  • Deflects RIGHT in the NH
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7
Q

Define the ‘geostrophic wind’ in the Southern Hemisphere.

A
  • Exact balance of Coriolis Force and Pressure Gradient
  • Straight parallel isobars
  • Absence of any friction
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8
Q

Describe the ‘geostrophic wind’ in the Southern Hemisphere with respect to anticylonically curved isobars.

A
  • Anticyclones move anti-clockwise in the SH.
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9
Q

Describe the ‘gradient wind’ in the Southern Hemisphere with respect to cyclonically curved isobars.

A
  • Cyclones move clockwise in the SH.
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10
Q

Describe the ‘frictional wind balance’.

A
  • Results from how rough the surface is
  • Slows down air which reduces Coriolis force
  • Causes pressure gradient to dominate
  • Veers wind
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11
Q

State typical wind deflections due to friction over the sea.

A
  • 10 - 20 degrees
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12
Q

State typical wind direction deflections due to friction over flat to undulation ground.

A
  • Flat = 30 degrees
  • Undulation = 40 - 60
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13
Q

State the typical wind direction deflections due to friction over mountainous regions.

A
  • 90 degrees
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14
Q

Explain how atmospheric stability affects the depth of the friction layer.

A
  • Stable = reduced vertical extent
  • Unstable = increased vertical extent
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15
Q

Explain how the wind strength affects the depth of the friction layer.

A
  • Stronger wind = deeper friction layer
  • Weaker wind = reduced friction layer
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16
Q

Explain how surface roughness affects the depth of the friction layer.

A
  • Rougher surface = Deeper friction layer
    -Smoother surface = Reduced friction layer
17
Q

Describe the basic concepts expressed in the horizontal component of the Coriolis Force formula.

A

Horizontal CF = 2 x Earth’s angular velocity (one rotation every 24hrs) x speed of wind x sin(latitude)

18
Q

Describe the development of the geostrophic wind balance in both hemispheres.

A
  • Balance of Coriolis force and pressure gradient force
  • When air starts moving Coriolis Force starts effecting it
  • Deflection increases until Coriolis Force balances Pressure Gradient Force
  • Isobars are straight, wind parallel to the isobars
19
Q

Describe the development of the gradient wind balance in both hemispheres.

A
  • Coriolis force and pressure gradient force are not equal
  • If CF is greater the wind will be anticyclonic/ridge
  • If PG is greater the wind will be cyclonic/trough
  • Stronger force will provide centripetal force
  • Isobars are curved
20
Q

Given equal spacing between isobars, explain why the wind speed is stronger around an anticyclone (high) than around a depression (low).

A
  • Coriolis force dominates the high
  • CF proportional to wind speed
  • Pressure gradient force dominates the low
  • There’s less CF which was proportional to wind speed
21
Q

Demonstrate the effects of friction on surface wind in both hemispheres.

A
  • Frictions layer surface to 2000 - 3000ft
  • Friction reduces wind speed
  • Reduced wind speed reduces Coriolis force
  • Pressure gradient force strongest, wind VEERS towards low in SH or BACKS towards low in NH
22
Q

Describe the typical diurnal variation of surface wind in the Southern Hemisphere.

A
  • Increases/backs during the day
  • Decreases/veers at night
23
Q

Describe the typical diurnal variation of surface wind in the Northern Hemisphere.

A
  • Increases/veers during the day
  • Decreases/backs at night
24
Q

State the change in wind velocity when climbing out of, or descending into, the friction layer.

A
  • SH climbing = ABI (ascend, back, increase)
  • SH descending = DVD (descend, veer, decrease)
  • NH climbing = AVI
  • NH descending = DBD

CPL/ATPL Meteorology (19 decks)

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