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Geography 308 > Module 4 Wind > Flashcards

Module 4 Wind Flashcards

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1
Q

What is the major factor in the movement of air?

A

The pressure gradient force, this is the difference in pressure in two areas, where wind will wish to move to areas of low pressure

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2
Q

Describe what a horizontal pressure gradient force is and how it forms

A

A horizontal pressure gradient is when air moves to lower pressure area that’s cold, increasing it’s pressure, and then moves back to the area it came from as now the area it is in has a high pressure. This is a feedback loop. The reason why the cold area it moved to has a lower pressure is because since cold air sinks and warm air rises- theres more molecules of air aloft in warm air column than a cold air column causing a higher pressure over a warm air column than a cold one.

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3
Q

How do you measure air pressure?

A

a mercury barometer- weight of air pushes down on mercury forcing it up the tube and it’s pressure is what the air pressure is.
A aneroid barometer- a vaccum that when air pushes on it produces a pressure value for that force

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4
Q

Why do we set all station pressure data to sea level?

A

To avoid elevation interfering in the pressure measurements.

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5
Q

What are constant height charts?

A

charts that have different levels of pressure drawn at certain elevations.

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6
Q

What are isobaric charts

A

Is the same pressure mapped at different elevations, allows us to see how much height it takes for cold air/warm air to reach a certain pressure

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7
Q

Why does air flow not always move from high pressure systems to low pressure systems?

A

Because of another force acting on it that changes the direction of acceleration

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8
Q

What are the horizontal forces in the atmosphere?

A

Horizontal pressure gradient force
Coriolis force (or Coriolis effect)
Centripetal force (or Centripetal acceleration)
Friction

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9
Q

What are the vertical forces in the atmosphere?

A

Vertical pressure gradient force
Gravity

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10
Q

Does PGF cause movement of wind or direction?

A

Causes movement of wind

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11
Q

Whats the equation for PGF?

A

1/density multiplied by change in pressure over change in distance.

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12
Q

What’s the coriolis force?

A

Is the apparent force (as in not a real force but our view of it) that deflects free moving objects (not attached to the ground) from a straight line path

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13
Q

Describe why we see the coriolis force?

A

The earth rotates and we rotate with it, at the poles we rotate in a circle and don’t cover distance however on the thickest part of it we cover distance so its a translational movement. This is why when you fire something at the equator, since the equator is moving faster than the pole (in terms of covering distance) the projectile will move ahead of it (or to the east of it), changing the direction of it. The further north it travel the more curved path it’ll take because there’ll be higher difference in speeds between the equator and the poles. In the reverse, if you fire something from the poles it’ll go west because the equator is moving so fast east it’s left behind.

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14
Q

How does the Coriolis force work in the southern hemisphere?

A

In the southern hemisphere the same thing happens but the directions get flipped, so the projectile swerves left.

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15
Q

How does the coriolis force work when the projectile is shot from various location like in an east or west one?

A

Same thing if in the northern hemisphere the projectile will shift right, if the in southern it’ll shift left, as the shift will increase if there’s a high difference in latitude from where it shoot vs where it lands.

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16
Q

If you fired a projectile along the equator will the coriolis force affect it?

A

No because we’re at the equator, so it’s travel in the same direction as the same speed.

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17
Q

Does the coroilis force deflections increase with fast or slow wind speed?

A

It increases with fast wind speed- the wind travels faster to it’s direction resulting in a high deflection.

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18
Q

Whats the formula for the coriolis force?

A

The coriolis parameter multipled the velocity equals the coriolis force

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19
Q

If there is a curved wind but the coriolis force is not at play, what is responsible?

A

We need an excess force for this. this force is the centripedal force which causes air to curve, this happens through an imbalance between PGF and the Centripedal force, PGF wants air to circle around a low pressure and the centripedal force allows that air to curve, excess PGF force drives the turning of the wind. Get excess PGF force by reducing centripedal force through slowing the wind.

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20
Q

How does air flow around a low pressure area in the northern hemisphere?

A

counterclockwise and is called a cyclonic flow.

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21
Q

How does air flow around a high pressure system?

A

anticyclonically, here the air circulates clockwise (in the northern hemisphere). Since the PGF force isn’t driven to the center of the high pressure system, the coriolis force has to make it curve around it which means the wind speeds up in order for an increased coriolis force.

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22
Q

In the southern atmosphere how does air flow around a low pressure system? A high pressure system?

A

Air flows clockwise around a low pressure system and anticlockwise around a high pressure system

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23
Q

What forces act on wind close to the surface?

A

Frictional forces slow down wind, which causes wind above it to be further slowed down as the fast air is now moving over slow air

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24
Q

Whats the planetary boundary level?

A

The level in the atmopshere that is effected by frictional forces exerted by the ground, this is where wind speed changes with height.

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25
Q

What three forces are surface winds a sum of?

A

Pressure gradient force, coriolis force and friction

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26
Q

What are the three scales of motion?

A

Microscale (describes small scale turbulence) the mesoscale (medium turbulence would affect a city) and the synoptic scale (large scale turbulence)

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27
Q

How does microscale turbulence work?

A

This turbulence is a result of friction between the ground and the air, which then causes friction between slow moving air close to ground and air above, this friction then causes momentum towards slower moving air and the ground, which is what results in turbulence at the ground.

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28
Q

How does roughness length affect micro scale turbulence?

A

The rougher a surface is the slower the wind speed will be, the smoother it is the more turbulence from the wind you will experience as the wind will be faster. The point at which the wind speed is 0 is called the roughness length- for smooth surfaces this may be very small as air is fast, for rough surfaces this is very large as air is being dragged on by friction causing retardation of it and air layers above it.

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29
Q

Why is there a high win blowing on you near an ice rink, but little wind in a forest?

A

Because the roughness length of the ice rink is much smaller than that of the forest.

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30
Q

What is the laminar layer?

A

A smooth flowing layer of air which is above the stagnant layer of air, is slowed down minutely by the slow layer below it.

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31
Q

What is molecular viscosity?

A

Is friction between slow moving layers of air and fast moving layers of air. Not great at transferring momentum

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32
Q

How does the thickness of the laminar layer relate to turbulence?

A

If the turbulence is low, the laminar layer can be thick (as turbulence is what thins it) which results in very slow momentum transfer.

33
Q

What layer of air is above the laminar layer?

A

the turbulent layer

34
Q

Why is the turbulent layer good at transferring momentum?

A

Because in this layer air moves not only horixontally but also vertically

35
Q

How does turbulent layer transfer momentum?

A

By eddy viscosity

36
Q

What causes turbulent wind layers?

A

mechanical turbulence, convective turbulence, and atmospheric stability

37
Q

How does mechanical turbulence cause turbulent wind layers?

A

Rough surfaces, surfaces that have a bigger roughness length will cause greater turbulence when wind runs into them.
Strong winds- these winds will make bigger differences in wind layer which cause more friction and therefore more turbulence

38
Q

How does convective turbulence promote turbulence?

A

Strong surface heating- this creates rising air which means it increases in velocity in the vertical direction and therefore contribute to turbulence generation.

39
Q

How does atmospheric stabiloty promote turbulence?

A

If the atmosphere is unstable an air parcel will rise due to the fact it cools slower than ELR, so ELR is greater than SALR and DALR. This causes vertical motion and therefore turbulence,

40
Q

How does turbulence disperse molecules?

A

If the laminar layer contains a lot of a substance (ex water vapour) but then becomes turbulent due to turbulence the substance will will disperse in the whole air column due to vertical motion.

41
Q

Why do big lakes evaporate faster than wet lands?

A

Because in wet lands the roughness length is big due to friction so the stagnant layer is thick and won’t be affected by friction much and have no turbulence, however in an open pond the roughness length is much smaller so turbulence will be greater here, and the turbulent flow will pick up water molecules causing evaporation

42
Q

How are wind gusts a consequence of turbulence?

A

Due to turbulence we get strong period of wind and slow periods of wind- gusts and lulls, this is due to turbulence. Gusts are created by eddies (circular wind flows) that take strong winds from above and move them downwards, the lulls are do to upwards eddies. These affect our measurements of air flow as we can never get a consistant value when this happens.

43
Q

How are cars and planes affected by turbulence?

A

Turbulence creates gusty wind flows which affect the movement of them

44
Q

What is clear air turbulence?

A

turbulence that occurs in cloudless areas due to different speeds of wind aloft

45
Q

Why are non native plants bad to plant in the praries and how is that connected to turbulence

A

They lose water quickly and their soils erode quickly, this is because they have low rough surface lengths which cause the stagnant layer and laminar layer to be very small and momentum easily transferred to the surface which picks up water (evaporates) more and beats at soil eroding it.

46
Q

How does turbulence affect geomorpholgy?

A

Sand dunes are shaped according to the direction of turbulence. Wind also erodes bed rock.

47
Q

What is the main drive in mesoscale winds?

A

Thermal pressure systems

48
Q

What are shallow pressure systems?

A

Pressure systems that change from high to low the further you go up/down, cause by uneven surface heating which results in cold air columns and warm air columns. Wind flows between them- called thermal circulation.

49
Q

How is land/sea breeze an example of thermal circulation?

A

land heats up quicker than sea in the day time, causes air to go from sea to land as air is warmer and therefore lower pressure their.
An nightime- land cools faster creating a surface of high pressure, this land breeze then goes to the ocean with lower pressure surface air.

50
Q

How is florida an example of thermal circulation causing ppt?

A

Florida gets sea breezes from both sides, when the air masses collie it causes uplift and they cool into big clouds giving ppt and lightening.

51
Q

Explain mountain/valley breeze?

A

THe sun warms up the side of a mountain during the day which warms the air above it, this causes the warm air to travel upwards cooling as it does which forms a cloud.
At night the air cools, and flows downwards resulting in no cloud.

52
Q

What are katabatic winds?

A

A downslope flow, associated with cold, dense air that has formed by radiative cooling at high elevation (mountains, glacier)
cold glaciers, and mountains lose a lot of energy during the winter (strong radiative cooling), producing cold, dense air that pools in valleys, etc… Eventually that valley gets filled up with cold air, and it spills down the mountain, bringing a rush of strong, cold wind”

53
Q

Why is antartica the windiest contintent?

A

Due to katabatic winds- there’s a lot of glacier heres so a lot of cooling and therefore a lot of dense cold air that flows down mountains.

54
Q

What are chinook winds?

A

are warm dry winds caused by air that goes up a moutain, loses it’s moisture and then goes down the moutain.

55
Q

What are chinook winds driven by?

A

Large scale pressure systems such as synoptic scale pressure

56
Q

What is a monsoon?

A

a wind pattern that reverses seasonally, usually accompanied by changes in precipitation, these chnage sin ppt don’t have to be huge but there should be a distinct wet and dry season.

57
Q

What drives monsoons?

A

during summer months land air becomes hot and low pressure, breeze from high pressure cold ocean comes in and causes ppt.
In winter the land becomes much colder w high pressure and therefore flows to the low pressure warm ocean, causes a dry season as little ppt comes from this cold dry air.

58
Q

What are three factors that increase monsoon risk

A

Big continent, warm ocean, and high topography

59
Q

Where are monsoons more commonly found?

A

In the intertropical convergence zone the area where trade winds from the south and north converge and rise

60
Q

Can divergence and convergence produce low and high pressure centers?

A

Yes, when convergence (piling up of air at the surface) and divergence (air spreading out from top) are in balnce thers no highs or low,s but if divergence exceeds convergance than lows form as air is being lost and if convergance exceeds divergance than highs form as more air is being added. These aren’t surface pressure system as air is being added/ removed we have deep pressure systems.

61
Q

What are doldrums?

A

Is wind at the equator which has warm low pressure surfaces and high pressure wind aloft, because air rises her so much there’s a lot of ppt here and not much surface wind (CAUSE AIR’S BEING PUSHHED UPWARDS THROUGH HEATING) Called ITCZ, is a convergence zone for se and ne trade winds.

62
Q

Describe a hadley cell

A

Is a model that shows how thermal circulation moves air that is warm and low pressure upwards and to the poles.

63
Q

What are horse latitudes?

A

Latitues as 30 degrees to north and south pole, these are where air aloft from the equator converges due to the reducing circumference of the earth which then causes air to flow downwards towards the surface (causing a high pressure system)

64
Q

Where does the air from the horse latitudes flow accodring to the hadley cell model?

A

Back to the equator as it’s high pressure air going to the low pressure equatorial air.

65
Q

How does the Coriolis force effect air moving from the horse latitudes

A

The flow is deflected to the right (In the NH) which results in NE trade winds and in the south it will also deflect creating SE trade winds.

66
Q

Does all of the air in horse latitudes that sunk go the the equator?

A

No, some of the air goes poleward (according to the ferrel cell model) which then gets deflected due to the corilois effect and creates westerlie winds.

67
Q

What happens when the westerlies air travel more polewards?

A

They reach a polar front as the westerlies and the polar air collide, the westerlies air rises above it diverges and send air back to the equatorial and polewards.

68
Q

What happens to the polewards flow that come soff the polar front?

A

Forms a polar high due to convergence of air and sinking.

69
Q

Where do the polar easterlies come from?

A

Is the wind from the polar high being deflected east.

70
Q

What’s the jet stream?

A

Are fast moving air current at high altitudes that rap around the globe- include polar and subtropical jets

71
Q

Where do jet streams occur?

A

At the hadley cell and ferrel cell boundaries where theres a big difference between temperatures.

72
Q

How do jet streams form?

A

jet streams form through the pressure gradient betwen two air masses colliding from the cold dense pole air and the warm light subtropical air, this creates a polar jet flow which is deflected by the coriolis effect and therefore goes east, however it’s very fast as it’s also moving towards the pole and to squeeze itself into a small area it will travel faster.

73
Q

Why is the jet stream wavy

A

due to the increased corriolois force and heat and cool temps meeting which breaks down wind currents and makes them wavy.

74
Q

What are the waves in the jet stream called

A

rossby waves

75
Q

In the southern hemisphere why is there less rossby waves then in the northern?

A

Because there’s more continents there which disrupt the rossby waves

76
Q

How does the ITCZ shift?

A

It follows the sun, so when the sun is more on the south hemisphere it’‘l be ther if on north it’ll shift there, also will shift towards continents

77
Q

Why do pressure highs and lows move seasonally?

A

due to the itcz shifts

78
Q

What are consequnces of the itcz?

A

areas in it experience a lot of rainfall, areas in the subtropical highs experience little rainfall, and the midlatitudes are subject to highly variable conditions

Geography 308 (4 decks)

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