1 NWS-COMET Hydrometeorology Course 15 – 30 June 1999 Meteorology Primer

2 Peter A. Stamus Research Associate - Senior Meteorologist NOAA/Forecast Systems Laboratory and CSU/Cooperative Institute for Research in the Atmosphere (CIRA) (fax)

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 Structure Fun facts Standard atmosphere –Very long term average for mid-latitudes –Average surface pressure 1013 mb –Average surface temperature 59 o F 1/2 of the mass of the atmosphere (500 mb) below 6 km (3.7 miles)

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6 Atmosphere Structure Fun facts Lapse rate (decrease in temperature in the vertical) Troposphere: +15 o C (at sfc) to ~ -50 o C (at 10 km) -6.5 o C / km

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8 Water vapor in the atmosphere The most important parameter we attempt to measure and forecast. Clouds Precipitation Energy Transfer

9 Evaporation and Condensation

10 Evaporation and Condensation Evaporation –Fast molecules escape, slower remain cooling process Condensation –Slower molecules collide, form droplets, droplets fall, faster molecules remain warming process

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

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13 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

14 Saturation Vapor Pressure

15 Relative Humidity and Dew Point Pressure at 1000 mb Parcel A Parcel B T = 10 o C (50 o F) e s = 12.3 mb e = 12.3 mb T = 20 o C (68 o F) e s = 23.7 mb e = 12.3 mb RH = (e / e s ) x 100 = 100%RH = (e / e s ) x 100 = 52% Therefore: T d = 10 o C 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.

16 Energy Budget Incoming solar Emitted long-wave Transfer with latitude Long-term balance

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19 Energy Transfer with latitude

20 Daily and Seasonal Energy Balance

21 Lab 1 Basic Surface Features/Moisture

22 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, but smaller horizontal variations produce winds and weather systems

23 Pressure and terrain

24 Pressure and volume

25 Pressure and volume (cont.)

26 Typical 500 mb map

27 Lab 2 3-D Atmospheric Structure

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

29 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

30 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

31 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

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35 Typical Flow

36 Idealized surface flow

37 Lab 3 Wind