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EAS 202 > 4: Forces, Pressure, and Fronts > Flashcards

4: Forces, Pressure, and Fronts Flashcards

1
Q

what is PGF

A
  • pressure gradient force: high to low pressure
  • pressure gradient arises due to the difference in pressure between two points
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2
Q

Coriolis Force

A

In Northern hemisphere: Coriolis force deflects moving objects to the right
In Southern hemisphere: the Coriolis force deflects moving objects to the left

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3
Q

What is Coriolis Force dependent on

A
  1. Dependent on latitude
    - zero at the equator
    - maximum at the poles
  2. Dependent on speed
    - greater for faster speeds
    - zero if the object is stationary
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4
Q

Frictional force

A

roughness of the surface slows down wind speed —> this produces eddies and turbulence
- lower wind speed near surface
-obstructions can also lower wind speed

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5
Q

Geostrophic winds

A

winds that result from an exact balance between the pressure gradient force and the coriolis force
- winds blow parallel to the isobars or contour lines above the level of friction

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6
Q

how are winds named

A

from their origin. Ex: east to west wind is called westerly

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7
Q

upper level winds

A

in the upper atmosphere, winds flow parallel to the contour lines in west to east direction
-contours decreases in height from south to north
- strong temperature gradient = strong height gradient = strong wind

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8
Q

relationship between geostrophic and gradient winds with contour lines

A
  • when contours are close together there wind and gradient is strong
  • geostrophic: straight
  • gradient: curved
  • when wind follows contour lines then there is a balance between the pressure gradient force and the Coriolis force
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9
Q

Surface winds

A
  • frictional drag at the surface slows the wind speed
  • slower wind speed means weaker Coriolis force therefore it no longer balances the pressure gradient force
  • wind flows across the isobars towards the low pressure, in low pressure systems it is toward the center and in high pressure systems it is outside of the system (outwards)
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10
Q

Vertical air motions in low and high pressure systems and what image

A
  • image 20
    Low pressure system/surface low: inward wind flow to the low pressure center (convergence) = rising air = upper level divergence (left) —> results in vertical cloud development and precipitation

High pressure system/surface high: outward wind flow because center is hight pressure (divergence) = sinking air (sucks it down) = upper level convergence —> results in clear sky and warm surface temperature

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11
Q

Source Regions of Air Masses in NA and what image

A

image 21
* Maritime: origiantes over the oceans; humid
* Continental: originates over continents; dry and tropical

  • Cold
  • Maritime polar (Pacific) air masses
  • Arctic air masses
  • Continental polar air masses
  • Maritime polar (Atlantic) air masses
  • Warm
  • Maritime tropical (Pacific) air masses
  • Continental tropical air masses
  • Maritime tropical (Gulf) air masses
  • Maritime tropical (Atlantic) air masses
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12
Q

Characteristics of North American Air Masses

A

try to recite image 22

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13
Q

What is a stationary front and what image

A
  • cold dense air and warm air separated by topography
  • No movement
  • Cold dense cP air butts up against the north-south Rocky Mountains
  • Milder mP on the western side of the Rockies
  • Surface wind blow parallel to front boundary in opposite direction
  • Do not produce significant precpitation
  • image 25
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14
Q

Cold and warm fronts and what images

A

Cold fronts: have cold air advancing and displacing warm air

Warm fronts: have cold air retreating and warm air overriding it

image 23 (top is cold) (bottom is warm)
image 24

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15
Q

What happens as a warm or cold front passes

A
  • Wind direction shifts clockwise
  • Temperature and dew point temperature are likely to change
  • Uplift of less dense air mass (warm) results in clouds, precipitation, and a drop in surface pressure
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16
Q

What are fronts characterized by on weather charts

A

characterized by a kink in contours

17
Q

What weather elements does a cold front affect and how does it work and what image

A
  • image 26
  • Cold, dry, stable, polar air replacing warm, moist, conditionally stable subtropical air
  • Sharp temperature fluctuation over a short distance
  • Change in the moisture characteristics
  • Change in wind direction
  • Clouds and precipitation pattern
18
Q

Characteristics of a cold front

A
  • Td and T will drop
  • Winds will veer clockwise (WNW to SSW)
  • Surface prssure is lowest under the front (in front of triangle)
  • Because of lifting, pressure falls and produces precipitation
19
Q

Type of Clouds of a Cold Front and ppt and what image

A
  • warm air is lifted ahead of the cold front
  • clouds and precipitation form just ahead of the front
  • primarily cumuliform clouds, sometimes stratiform
  • heavy precipitation and thunderstorms
  • image 27
20
Q

How does warm front operate

A
  • leading edge of warm, moist, subtropical air replaces retreating cold polar air
  • warm front moves at a slower speed
  • warm air overrides cold air creating frontal inversion (warm air on top of cold air) and cold air gradually retreats
  • image 28
21
Q

Characteristics of a warm front

A
  • T and Td will increase
  • Winds will veer clockwise (SSW to ESE)
  • Surface pressure lowest under the front
22
Q

Typse of clouds and ppt of a warm front and what image

A
  • clouds and precipitation form well ahead of the front
  • primarily stratiform clouds and sometimes cumuliform
  • extensive cloud cover
  • light, steady precipitation
  • image 29
23
Q

What is an occluded fornt

A
  • When cold fornt catches and overtakes the warm front
  • Represented by a purple line with triangles and semicircles
  • two main types of occlusions: cold type and warm type (most observed)
24
Q

what is a cold type occlusion and what image

A
  • cold front rapidly approaches the warm fornt and overtakes it
  • Warm air mass lifts off the ground
  • image 30
25
Q

Warm type occlusion and what image

A
  • Cold cP air ahead of warm front
  • Cool mP air following warm front
  • Cold front approaches the warm front
  • Mild, lighter mP air behind the cold front could not life the colder, heavier cP air off the ground so it will go over the warm air mass
  • image 31
26
Q

Weather conditions associated with occluded fronts

A

memorize image 32
* Temperature
* Pressure
* Clouds
* Precipitation
* Visibility
* Dew point

27
Q

Clouds before, during, and after passing in occluded fronts in the winter in NA

A

Before: Ci, Cs, As, NS
During: Ns, sometimes Tcu and Cb
After: Ns, As or scattered Cu

28
Q

Criteria to locate fronts

A
  • Large change in T over short distance aka packed isotherms
  • Large change it Td over short distance
  • Sudden change in wind direction and pressure
  • Cloud and precipitation pattern
  • Front located along troughline, along kink or bend

EAS 202 (14 decks)

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