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NWS-COMET Hydrometeorology Course 15 – 30 June 1999

NWS-COMET Hydrometeorology Course 15 – 30 June 1999. Meteorology Primer. Presented by: Pete Stamus Tues, Wed, 15-16 June 1999 Hydromet 99-2. Peter A. Stamus Research Associate - Senior Meteorologist NOAA/Forecast Systems Laboratory and

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NWS-COMET Hydrometeorology Course 15 – 30 June 1999

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  1. NWS-COMETHydrometeorology Course15 – 30 June 1999 Meteorology Primer Presented by: Pete Stamus Tues, Wed, 15-16 June 1999 Hydromet 99-2

  2. Peter A. Stamus Research Associate - Senior Meteorologist NOAA/Forecast Systems Laboratory and CSU/Cooperative Institute for Research in the Atmosphere (CIRA) 303-497-6100 303-497-7262 (fax) stamus@fsl.noaa.gov

  3. Purpose of the primer • Basic understanding of meteorological processes. • Starting point for the rest of Hydromet • To give you a semester-long Introduction to Meteorology course in 8 hours.

  4. Atmosphere StructureFun facts • Standard atmosphere • Very long term average for mid-latitudes • Average surface pressure 1013 mb • Average surface temperature 59 oF • 1/2 of the mass of the atmosphere (500 mb) below 6 km (3.7 miles)

  5. Atmosphere StructureFun facts • Lapse rate (decrease in temperature in the vertical) Troposphere: +15 oC (at sfc) to ~ -50 oC (at 10 km) -6.5 oC / km

  6. Water vapor in the atmosphereThe most important parameter we attempt to measure and forecast. • Clouds • Precipitation • Energy Transfer

  7. Evaporation and Condensation

  8. Evaporation and Condensation • Evaporation • Fast molecules escape, slower remain cooling process • Condensation • Slower molecules collide, form droplets, droplets fall, faster molecules remain warming process

  9. Evaporation and Condensation (cont.) • The Evaporation/Condensation process transfers heat energy to the atmosphere • Latent Heat of Condensation

  10. Evaporation and Condensation (cont.)Fun facts • Wind enhances evaporation • Warm water evaporates faster than cool water • Air temperature effects evaporation rate • Cool air, slower molecules, condensation more likely, slows evaporation • Warm air can hold more water vapor before saturation than cold air

  11. Saturation Vapor Pressure

  12. Relative Humidity and Dew Point Parcel B Parcel A Pressure at 1000 mb T = 10 oC (50 oF) es = 12.3 mb e = 12.3 mb T = 20 oC (68 oF) es = 23.7 mb e = 12.3 mb RH = (e / es) x 100 = 100% RH = (e / es) x 100 = 52% Therefore: Td = 10 oC for Parcel B Dew point = Temperature to which air must be cooled at constant pressure to reach saturation. It is a measure of the air’s actual water vapor content. Relative Humidity is a measure of the degree of saturation of the air.

  13. Energy Budget • Incoming solar • Emitted long-wave • Transfer with latitude • Long-term balance

  14. Energy Transfer with latitude

  15. Daily and Seasonal Energy Balance

  16. Lab 1 Basic Surface Features/Moisture

  17. Atmospheric Pressure • Pressure = total weight of air above • Air is compressible, so gravity concentrates most air molecules near the surface • Atm pressure decreases with height rising air cools, sinking air warms • Greatest pressure variation in vertical, butsmallerhorizontal variations produce winds and weather systems

  18. Pressure and terrain

  19. Pressure and volume

  20. Pressure and volume (cont.)

  21. Typical 500 mb map

  22. Lab 2 3-D Atmospheric Structure

  23. Wind • Differential heating of land/ocean leads to pressure differences in the atmosphere • Pressure differences are forces that lead to atmospheric motions

  24. Wind (cont.) • Newton’s Laws of Motion • First Law: Objects at rest remain at rest and objects in motion remain in motion, provided no force acts on the object • Second Law: Force equals mass times the acceleration produced F = ma • To determine wind direction and speed, need to know the forces that affect horizontal movement of the air

  25. Wind (cont.) • Forces that lead to the wind • pressure gradient force (PGF) • Coriolis force (C) • centripetal force (c) • gravity (g) -- doesn’t effect horizontal motions • friction (F) Net Force = PGF + C + c + g + F • If these forces add to zero, then (1) The air remains at rest; or, (2) The air remains in motion along a straight path at a constant speed

  26. Wind (cont.) • pressure gradient force (PGF) • Moves air from higher pressure to lower pressure • Coriolis force (C) • Apparent force due to the Earth’s rotation • Acts to turn wind to the right in the Northern Hemisphere • centripetal force (c) • Inward directed, keeps parcels rotating around pressure centers • gravity (g) • Always acts downward; vertical motions only • friction (F) • Acts opposite to the direction of motion; retards motion

  27. Typical Flow

  28. Idealized surface flow

  29. Lab 3 Wind

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