Chapter 7 Transient Atmospheric Flows and Disturbances Part 1: Mid-Latitude Systems Part 2: Localized Systems Part 3: Major Tropical Disturbances

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Chapter 7Transient Atmospheric Flows and
DisturbancesPart 1 Mid-Latitude SystemsPart 2
Localized SystemsPart 3 Major Tropical
Disturbances
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Storms and the Landscape
Chapter 7 Part 1

• More limited than wind and pressure systems
• Involve flow of air masses and other atmospheric
  disturbances

• Immediate impacts
• Strong winds, uprooted trees
• Darkened skies
• Precipitation
• Maybe thunder and lightning
• Possible flooding
• Positive Long-term Impacts
• Water supply
• Plant growth

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Air Masses

• Air mass large parcel of air that has relatively
  uniform properties in the horizontal dimension
  and moves as an entity
• Three requirements
• Must be large
• Have uniform properties
• Distinct from surrounding air

Fig. 7-1
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• Source Regions areas on Earths surface suited
  to generate air masses
• Extensive
• Physically uniform
• Associated with stationary or anti-cyclonic air

• Continental or Maritime
• Latitude
• Affects
• Humidity
• Temperature
• Stability

• Fig. 7-2

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• Classification

First Letter Humidity indicator
Second Letter (capitalized) Temperature
indicator
Land or water
Latitude
c continental (dry)
E 0º ? 10º Equatorial T 10º ? 35º
Tropical P 55º ? 70º Polar A 70º ? 90º
Arctic / Antarctic
m maritime (moist)
Middle latitudes (35º ? 55º) not a major source
region
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Movement and Modification

• Movement promotes change
• Thermal modification
• Dynamic modification
• Moisture modification
• Movement changes the weather of regions the air
  mass moves through

• Movement and Modification
• Example Temperature Modification

Fig. 7-4
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North American Air Masses

• Maritime tropical (mT)
• Continental tropical (cT)
• Maritime polar (mP)
• Continental polar (cP)
• Arctic (C)

Figure 7-2
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Fronts

• Front zone of discontinuity between unlike air
  masses
• Rapid change in air properties
• Barrier between 2 air masses
• Most noticeable difference temperature change
• Fronts Lean
• Moves in the direction of the more active air mass

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• Fronts
• Warm Front

• Fig. 7-6

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• Fronts
• Cold Front

• Fig. 7-8

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Frontal Advance
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Stationary and Occluded Fronts

• Stationary front the common boundary between
  two air masses in a situation in which neither
  air mass displaces the other
• Occluded front a complex front formed when a
  cold front overtakes a warm front

• Symbols for Fronts on Weather Maps

Fig. 7-7
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Atmospheric Disturbances

• 2 types of disturbances
• Stormy
• Calm
• Common characteristics
• Smaller than general circulation components
• Migratory
• Short in duration
• Relatively predictable weather conditions

Source NOAA Photo Library http//www.photolib.noa
a.gov/collections.html
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• Midlatitude Disturbances
• Middle Latitudes (35º ? 55º)

• Battleground between tropical and polar air
  masses
• Midlatitude Cyclone
• Midlatitude Anticyclone

August 7, 2005
Source http//www.nnvl.noaa.gov/
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Atmospheric Disturbances

• Midlatitude Cyclone
• Large migratory low-pressure system occurring
  within the mid-latitudes
• Responsible for most day-to-day weather changes
• Bring precipitation to much of worlds population
• Circular wind pattern converges counterclockwise

mP
Figure 7-13
cP
mT
Note the shift in winds and location of
precipitation along frontal boundaries
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• Occlusion

• Fig. 7-15

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Lifecycle
Low developing
Stationary Front
Mature Stage
Cold front moves faster and catches up with warm
front
Occlusion
Dissipation-no warm air at surface
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• Polar Front Jet Stream
• Storms path

• Fig. 7-13

• Cyclogenesis
• Fig 7-14

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View from Space
Warm front
Wrap around precip west of low
Cold front
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Mid-latitude Cyclone 827a.m. 11-28-05
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Mid-latitude Cyclone 1247p.m. 11-28-05
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Surface Temperatures associated with
Mid-latitude cyclone (11-28-05)
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Atmospheric Disturbances

• Characteristics
• Upper air convergence
• Subsidence
• High surface pressure
• Diverging surface winds

• Midlatitude Anticyclone
• a migratory high-pressure cell of the
  midlatitudes
• Usually larger than midlatitude cyclones
• Travels as fast as, or slower than, midlatitude
  cyclones
• Prone to remain over the same area
• Cyclones and anticyclones alternate with each
  other in an irregular sequence

• Fig. 7-16

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Midlatitude Cyclones and Anticyclones
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• Relations of Cyclones and Anticyclones
• Often occur in next to each other in midlatitudes
• Anticyclone forms a cold front on its leading edge

• Locations of Anticyclones and Cyclones
• System of highs and lows, 35º to 70º of latitude
• East-West migration
• Dominates midlatitudes, especially in winter

• Fig. 7-18