Meteo 003 9/24/14
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Transcript of Meteo 003 9/24/14
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Meteo 0039/24/14
LAB 4 due this Friday, September 26 before class
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Terrain Effects on Rain• Windward side of mountains makes air
rise/enhances precipitation.• Rain shadow on leeward sides
RAIN SHADOW
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Wind Direction
• In California – prevailing winds are westerly, so the central valley is in a rain shadow, as well as the CA/NV border.
• In Hawaii, prevailing winds are northeasterly, so… where would the rain shadow be? Remember what a NE wind means…
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Visible Imagery• What you see is what you get! Imagine
yourself as the satellite in space, looking down.
CLOUDSCLEAR
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Infrared Imagery• All about temperature! – Higher clouds are
cooler, lower clouds warmer. • Cold usually = bright in meteo-nation. Ground
usually = dark
HIGHER CLOUD TOPS
LOW CLOUDS THE GROUND
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Water Vapor Imagery
• Only good for upper troposphere – tells you nothing about the surface!
MOIST
DRY
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Radar Shortfalls• Precipitation from low clouds far away from
radar site can go unnoticed, the beam can overshoot due to the earth’s curvature and beam angle
• It will look as if there is nothing there
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A note about winds
• The pressure gradient force will always point towards lower pressure, regardless of which hemisphere you are in (perpendicular to isobars).
• What other two “forces” must we consider?
H L
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Sea Level Correction
• If you plotted actual station pressures, mountains would always have the lowest pressure, and coastal locations would always have the highest.
• We need to correct this.• Simplified way to do it:– For every 100m of elevation, you add 10mb of
pressure to correct to sea-level
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Before Correction
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After Correction
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Example of SLP Correction
• Allentown, PA– Elevation: 142 meters– Station pressure: 983 millibars
– Correction: (10mb/100m) = (x mb/150m)– X = 14.2mb
– Corrected pressure: 997.2 millibars
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Highs and Lows• For the feature to be analyzed, you need at
least one closed isobar contour • The example shows 5mb intervals, U.S. standard is 4mb, but any interval
may be used
LH
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Wind Reminder• Remember: The PGF is directed from high to
low pressure. With a moderate (medium) amount of friction and the Coriolis effect, the wind crosses isobars at (approximately) a 30 degree angle, toward lower pressure.
Lower Pressure
Higher Pressure
Wind Direction
Isobars
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Pressure Levels• Pressure surface elevation is proportional to
the average temperature of the column of air beneath it.
• Higher average temperature means higher pressure surfaces.
• So, the elevation of the 500mb pressure surface is higher at a warm, tropical location than a cold, polar location
• In the mid latitudes (like here in State College) the 500mb surface is higher in summer than in winter
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Example
• State College, PA
Ground JULY JANUARY
500 mb level
5605 meters
5375 meters
Warmer Air Colder Air
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Lab 4 – Due Friday at start of class4.14 a, b (draw an arrow showing wind direction)4.15 c (use dewpoint to get vapor pressure- just substitute dewpoint for temperature in the table)5.4 a, b, c 5.10 a, b 5.18 (Fig. 5.27 is helpful)6.2 a, b (draw AT LEAST 8 wind arrows on each)6.7 a, b6.9 a, c, d (you may use arrows instead of wind barbs if that’s easier for you- but make sure they point in the correct direction!)7.9 a, b