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Intro to Physical Geography > Pressure and Winds > Flashcards

Pressure and Winds Flashcards

1
Q

What is pressure?

A

The weight of the atmosphere

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2
Q

How is pressure measured?

A

millibars

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3
Q

What are isobars?

A

Isobars connect points of equal pressure

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4
Q

What do circles in isobars represent?

A

The circles represent cells of high & low pressure

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5
Q

What might cause pressure variation across the surface of the earth?

A

Uneven heating of earth’s surface

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6
Q

What are the 4 types of surface pressure conditions across the surface of the earth?

A

Thermal Lows and Highs and Dynamic Lows and Highs

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7
Q

What is thermal Low pressure and what is it caused by?

A

Thermal Low Pressure is caused by SURFACE HEATING. Warm air rises (convection) as it expands & becomes less dense than surrounding air creating a Thermal Low at surface

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8
Q

Where might thermal low pressure occur on a very large scale? (hint: where is there heating on a very large scale?)

A

At the equator. There is more direct sunlight on the equator than any other place, and the equator receives 2.5 times more energy than the poles

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9
Q

What is thermal high pressure?

A

When air cools, it contracts, becomes denser than surrounding air and sinks, creates a Thermal High at surface

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10
Q

Where does thermal high pressure happen on a large scale?

A

The poles

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11
Q

What are dynamic highs in lows and where do they occur?

A

They are changing and moving, and occur in the mid-latitudes

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12
Q

What causes winds?

A

Differences in pressure across space

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13
Q

What are the three physical forces that act on wind?

A
  1. pressure gradient force
  2. Coriolis Force (Effect)
  3. Friction
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14
Q

What is the pressure gradient force (PGF)

A

It is perpendicular to isobars. PGR causes air to flow from high low

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15
Q

What does the spacing of isobars indicate in relation to PGF?

A

The spacing of isobars indicates strength of PGF

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16
Q

What does closely spaced isobars mean?

A

Steeper pressure gradient (closely spaced) = stronger wind

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17
Q

What kind of winds are driven mainly by PGF?

A

Most local and many regional scale winds

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18
Q

Land and Sea Breezes are one example of local winds. How do Land and Sea Breezes form?

A

Local Winds: Land & Sea Breezes (PGF) form because of land/water differences in temperature and pressure

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19
Q

What are sea breeze conditions in the daytime?

A

Look at picture on slide number 14 on powerpoint

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20
Q

What are sea breeze conditions in the nighttime?

A

Look at picture on slide number 15 on powerpoint

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21
Q

What is the basic reason for land-sea breezes?

A

Differential heating of land and water (remember? land heats up and cools down faster)

This difference in temp. creates pressure differences and thus breezes

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22
Q

What is another type of local winds?

A

Mountain-Valley Breezes

23
Q

Will mountian-valley breezes go up or down the mountain during the day

A

Valleys heat up, so air rises upslope

24
Q

What happens to mountain-valley breezes during the night?

A

Radiational cooling at night causes colder denser air to sink by gravity

25
Q

Where do regional-scale winds occur?

A

Regional-scale winds (a little bigger than local-scale) occur over large areas at the scale of mountain ranges rather than a single mountain (local)

26
Q

What are cold katabatic winds?

A

Cold, dense air flows down slope due to gravity
(just like water!).

Often very strong winds as high as 100 mph

Winds often channel, converge, and compress, like streams into a very strong “river” of air

27
Q

What is some evidence of katabatic winds?

A
  1. pattern of snow exposing ridges and building up on the lee side, and 2. the streamers of new frozen sea ice
28
Q

What is polynya?

A

Pockets of open water

29
Q

What are other regional-scale winds beside katabatic winds?

A

Chinooks, Santa Ana Winds

30
Q

What are chinooks?

A

Warm, Dry Wind: Chinooks occur on dry “leeward side” of the Rocky Mts., warm by compression and are called “snow eaters”– they melt or evaporate snow (sublimation)

31
Q

What are the effects of Chinooks?

A
  • Wood may split due to extreme dryness
  • Fire hazards are increased—May cause violent grass or forest fires, or cause small fires to spread.
  • irritability, sleeplessness
  • Susceptible people may get migraine headaches or suffer nervous disorders
  • Psychologically, some people feel “better”
32
Q

What are Santa Ana Winds (Devil Winds)?

A

Warm dry winds affecting coastal S CA esp. in fall.

  • Strong H Press. Over US west/sw = cool, dry, “heavy” air
  • Flows H to L
  • air heats by compression (~5°F /1000 ft.) as air descends coast mountains
33
Q

What are some negative effects of Santa Ana Winds?

A

Dust, Heat, Fire!

34
Q

What are some positive effects of Santa Ana Winds?

A
  • Surfers love them because they make big waves.
  • Increased ocean circulation near shore = nutrients, fish
  • Blows off smog over LA Basin
35
Q

In summary what are the wind associated with Pressure Gradient Force (PGF)?

A 
Local scale
•Land-Sea breezes
•Mountain-Valley breezes 
Regional scale
•Cold Katabatic winds, e.g., Mistral and Bora
•Warm winds, e.g., Chinooks, Santa Anas
36
Q

What is the Coriolis force?

A

Coriolis is not actually a force, but an “apparent” DEFLECTION due to the rotation of the earth…

37
Q

Dos the earth rotate faster at the equator or the poles?

A

Earth rotates faster at equator than at the poles

38
Q

Why is the Coriolis effect important?

A

Its important to pilots because if they take a direct path to a location, say NYC, they would end up completely off course (like Des Moines)

39
Q

Where does the Coriolis effect deflect winds to?

A

The right in Northern Hemisphere

The left in the Southern Hemisphere

40
Q

What is the effect of Coriolis like at the equator? At the poles?

A

Effect of Coriolis is ZERO at the Equator

Strongest at Poles!

41
Q

How does the Coriolis Force affect the PGF and what does it create?

A

It balances the PGF and sometimes creates “Geostrophic” winds

42
Q

What do geostrophic winds do?

A

“Geostrophic” winds flow parallel to the isobars in the upper Troposphere ……NOT at surface because FRICTION

43
Q

What acts upon surface winds?

A

Friction

44
Q

What does friction do?

A

Friction SLOWS down atmospheric motion AT SURFACE where there is roughness

45
Q

How does friction affect the coriolis effect?

A

Friction slightly overrides the coriolis force and causes wind at the SURFACE to flow across isobars at an angle, but always from H to L

46
Q

What does friction cause surface winds to do?

A

Friction causes surfaces wind to spiral forming

Dynamic Low and High pressure “cells”.

47
Q

What are anticyclones?

A

High pressure cells

48
Q

What are cyclones?

A

Low pressure cells

49
Q

Where do these high and low pressure cells created by surface winds travel?

A

These cells TRAVEL across the mid-lats from W to E!

50
Q

What are the two rules for pressure cells?

A
  1. Surface Flow is ALWAYS OUT of Highs and IN to Lows (Remember flow High to Low like water)
  2. Spirals are opposite in Northern and Southern Hemispheres
51
Q

What happens to air in a cyclone?

A

Low pressure converges air at the surface

52
Q

What happens to air in an anticyclone?

A

High pressure diverges air at the surface

53
Q

What are some examples of Katabatic winds?

A

Mistral and Bora

Intro to Physical Geography (27 decks)

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