LAB 4 due this Friday, September 26 before class Meteo 003 9/24/14 LAB 4 due this Friday, September 26 before class

Terrain Effects on Rain Windward side of mountains makes air rise/enhances precipitation. Rain shadow on leeward sides RAIN SHADOW

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…

Visible Imagery What you see is what you get! Imagine yourself as the satellite in space, looking down. CLOUDS CLEAR

Infrared Imagery All about temperature! – Higher clouds are cooler, lower clouds warmer. Cold usually = bright in meteo-nation. Ground usually = dark LOW CLOUDS THE GROUND HIGHER CLOUD TOPS

Water Vapor Imagery Only good for upper troposphere – tells you nothing about the surface! MOIST DRY

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

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

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

Before Correction

After Correction

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

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 L H

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 Wind Direction Isobars Higher Pressure

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

Example State College, PA JULY JANUARY 5605 meters 500 mb 5375 meters level 5375 meters Colder Air Warmer Air Ground JULY JANUARY

Lab 4 – Due Friday at start of class 4.14 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, b 6.9 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