Notes for Meteorology 356
Friday, November 18, 2004
Elizabeth Winchester
Assignments
Read
through lightening link for Monday, particularly on thunder
Housekeeping
Midterm
2 on Wednesday, November 23
Topics:
á
Mediterranean
Climate
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Rainfall
Variability
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Diablo
Winds
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Tule
Fog
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Dynamic
& Thermal Lows
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Interpretation
of Weather Maps
Use
Scantron form 882
Diablo
Winds (Unfolding
Diablo Wind Pattern link)
3
forecasts shown on 500 mb charts
á
Show
Jet Stream, ridge, & trough
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Review
of dynamic pressure systems
3
forecasts shown on surface charts
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Show
pressure systems
á
Show
wind pattern which illustrates development of Diablo Wind Pattern
(dry, warm, clear weather)
Mediterranean
Climate
High
Temporal Variability of Rainfall
á
Average
rainfall not a good estimate of what it will be in a given year
á
High
degree of variability but amount of variability is not always the same
(can
be very extreme or less extreme)
Thunderstorms
Instability:
spontaneous motion of air up and down
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Stability
– air parcel finds itself colder than surrounding air; will sink
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Instability
– air parcel finds itself warmer than surrounding air; will rise
Ways
of Inferring Instability
see
examples on Simple Explanation of Instability link
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Dewpoint
temperatures: red & orange areas are prone to thunderstorms
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CAPE:
direct measure of instability (takes into account all aspects)
o
Deeper
colors show areas that are more likely to have severe storms
o
These
areas are the same as the red & orange areas on the dewpoint map
Example:
One air parcel is directly above an asphalt parking lot with
a temperature of approximately 75 degrees and the surrounding parcels are only
about 65 degrees
The warm parcel will rise and continue to rise as long as it
is warmer than the surrounding parcels; this can lead to large, tall
cumulonimbus clouds
Another
Way of Warming Air
Calorie:
amount of heat needed to raise temperature of water 1 degree
Latent Heat
á
At sea
level, warming is about 590 calories for each gram of water that condenses
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At
center of updraft, air is much warmer than surrounding air
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Air
does cool as it rises and expands, but not much
Development
of Thunderstorms
First
Stage
Cumulus:
relatively small water droplets; updrafts approximately 5 mph
Second
Stage
Cumulus
congestus: updrafts increase; clouds get higher than width; no precipitation
Final
Stage
Cumulonimbus: much larger; reaching top of troposphere
(13,000 feet); top made up of ice crystals and is smooth because ice interacts
differently with sunlight; precipitation: hail at top, falls and melts, comes
out at bottom as rain; both updrafts and downdrafts; lightening occurs