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Climate System > Lec 6 - Winds, Moisture, Precipitation > Flashcards

Lec 6 - Winds, Moisture, Precipitation Flashcards

1
Q

What is wind?

A

the expression of atmospheric motion

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2
Q

In what dimensions does wind move?

A
  • x & y: latitude and longitude
  • z: vertical component
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3
Q

What causes parcels of air to move?

A

parcels of air move as a result of forces acting on it!

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4
Q

How can you tell from looking at isobars on a map whether a pressure gradient is strong or weak?

A
  • Weak: bars spaced out
  • strong: many bars close together
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5
Q

What is the Pressure Gradient Force?

A
  • the initial force that causes air to move
  • equal to inverse of density *(change in Pressure / change in distance)
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6
Q

What factors influence air movement?

A
  • Pressure gradients
  • Coriolis force
  • Geostrophic flow
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7
Q

What is the Coriolis Force?

A
  • objects in atmosphere = influenced by Earth’s rotation
  • deflective force that causes objects to ‘drift’ from their original path
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8
Q

What direction does the Coriolis force act in?

A
  • N hemisphere: right
  • S hemisphere: left
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9
Q

How does geostrophic flow work?

A
  • air moving along a pressure gradient is subject to Coriolis force
  • air eventually flows parallel to straight isobars
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10
Q

What is geostrophic flow?

A
  • the wind vector achieved when forces of pressure gradient and Coriolis force come in to balance
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11
Q

What are supergeostrophic/subgeostrophic winds?

A
  • supergeostrophic: high pressure centres where Coriolis Force dominates the pressure gradient force
  • subgeostrophic: low pressure centres: low pressure centres where pressure dominates over Coriolis force
  • BOTH kinds of conditions result in airflow parallel to the curved height contours
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12
Q

What happens to wind when isobars are curved?

A

the balance of forces must include centrifugal force (directed toward the centre of rotation)
- results in gradient wind around curved isobars

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13
Q

What wind forces are balanced in low pressure areas?

A

Fc (Coriolis) and Fcen (Centrifugal) balance Fp (pressure gradient force)

  • generates ‘gradient winds’ (curved around isobars)
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14
Q

What wind forces are balanced in high pressure areas?

A

Fp (gradient force) and Fcen (centrifugal) balance Fc (Coriolis)

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15
Q

What effect does friction have on wind?

A

creates drag in planet boundary layer (1.5km of air closest to surface)

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16
Q

What is the planet boundary layer, and when is it relevant?

A

the air within 1.5km of the planet’s surface
this is the area affected by drag

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17
Q

What are cyclones?

A
  • Low pressure areas at the surface with roughly enclosed isobars
  • air converges toward low P centers (cyclones)
  • ascending air, precipitation
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18
Q

What are anticyclones?

A
  • areas of high pressure with roughly enclosed isobars
  • air moves out from high pressure center, creates clear skies
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19
Q

What direction does are move in cyclones?

A

counterclockwise in N hemisphere
clockwise in S hemisphere

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20
Q

What direction does air move in anticyclones?

A

clockwise in N hemisphere
counterclockwise in S hemisphere

21
Q

What is the maximum amount of water the air can contain?

A

Differs depending on temperature!
(different saturation points)

21
Q

What 2 factors determine the amount of water vapour in the air?

A
  1. water supply/evaporation rate
  2. Temperature
22
Q

What is the difference between absolute humidity and specific humidity?

A
  • absolute humidity (vapour density) is the density of water vapour in g/m^3
    (changes with air volume)
  • specific humidity is the portion of air mass made of water vapour, expressed in g/kg
23
Q

What is the difference between specific humidity and mixing ratio?

A

specific humidity is the portion of air made up of water vapour (g/kg)

mixing ratio is the ratio of water vapour to dry air (g/kg)

24
Q

What is relative humidity?

A

the amount of water vapour in the air relative to the total amount that can be held at that temperature

25
Q

When is relative humidity highest?

A

in early morning, at the coolest time of day (ie at saturation point)

26
Q

What is the dew point temperature? (Td)

A

the temperature air must be cooled to in order to reach saturation of water vapour

27
Q

How do water droplets form and shrink?

A

condensation and evaporation

28
Q

What kind of process happens when a parcel of air is cooled to its dewpoint temperature?

A

a diabatic process where energy is gained/lost

29
Q

What is a diabatic process?

A

a process involving the addition/removal of energy from a system

  • ex when water condenses/evaporates it adds/removes energy from its surroudnings
30
Q

Where is nighttime loss of longwave radiation the greatest?

A

close to the surface

31
Q

What is fog?

A

surface cloud when air cools to dew point, gains moisture, or when cool/warm air are mixed

32
Q

When does cloud formation occur?

A

when a parcel of air is cooled to its dewpoint temperature

33
Q

What kind of process is cloud formation?

A

adiabatic
(as a result of air rising through the atmosphere, since as air rises it cools to dewpoint T)

34
Q

How does adiabatic warming/cooling occur in clouds?

A
  • dry adiabatic warming when air sinks/compresses/warms
  • drya diabatic cooling when air rises/expands/cools
35
Q

What is the dry adiabatic lapse rate? (DALR)

A
  • the rate of cooling/warming that occurs with a change in height (no energy exchange with other parcels of air)
  • equal to 9.8C / km)
36
Q

What is the saturated adiabatic lapse rate?

A
  • the rate of cooling with change in height for saturated parcels of air
  • condensation occurs since parcel is saturated, so a change in height also means energy is released into the environment)
  • 0.5 C/km
37
Q

between DALR and SALR, which is larger?

A

DALR

  • when saturation occurs (SALR), condensation releases heat into the environment, so SALR has a slower temp change
38
Q

What is the lifting condensation level?

A

LCL is the height at which rising parcels of air reach saturation (T = Tdew)
- the point where SALR applies and DALR stops applying

39
Q

What is the environmental Lapse Rate (ELR)?

A

the temperature profile of the atmosphere in terms of temperature changes with height (you can measure with a balloon)

40
Q

How does the ELR (environmental lapse rate) change throughout the say?

A

temperatures close to the surface change, but changes are smaller the higher you go

41
Q

What 4 mechanisms cause air to lift?

A
  • Orographic
  • Frontal
  • Convection
  • Convergence
42
Q

What is orographic uplift?

A
  • when air is deflected upwards by high terrain, it results in adiabatic cooling, promoting clouds and precipitation
  • creates rain shadow (no rain) on leeward side, while windward side is v wet
43
Q

What is frontal lifting?

A
  • when two masses of different densities converge (ex cold and warm)
  • warm air is lifted upward
  • most prominent in mid-latitudes, happens everywhere
44
Q

How is uplift caused by local convection?

A

when differential heating at surface causes warmer air to rise, expanding and forming clouds
- most prominent in prairies/low topography

45
Q

What is convergence uplift?

A
  • when air is forced to move horizontally and meets more air, some of it has to go up
  • adiabatic cooling, etc
  • not common in Canada, can happen on edges of mountain ranges
46
Q

What part of precipitation is explained by geography?

A

the temporal characteristics of precipitation (how/when it forms, due to orographic, frontal, convection uplift)

47
Q
A

Climate System (11 decks)

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