Presentation on theme: "Chapter 7 Water and Atmospheric Moisture"— Presentation transcript:
1 Chapter 7 Water and Atmospheric Moisture Geosystems 6eAn Introduction to Physical GeographyRobert W. ChristophersonCharles E. Thomsen
2 Water and Atmospheric Moisture TOPICS:Adiabatic ProcessesAtmospheric Stability Clouds Fog
3 Adiabatic Processes Adiabatic processes Begins with a parcel of air Bouyancy caused initially by differences in (near) surface temperatureLess dense, warmer air rises, more dense, colder air sinks, after which…Ascending or descending air will undergo changes in temperature with no exchange of heat. This is an adiabatic process.
5 Adiabatic Processes Adiabatic processes Normal lapse rate: the average decrease in temperature with increasing altitudeEnvironmental lapse rate: the actual lapse rate at a particular place and timeAscending or descending air will undergo changes in temperature with no exchange of heat. This is an adiabatic process.Heat WAS exchanged = diabatic process.
7 Adiabatic Processes Dry adiabatic rate (DAR) Also called the Dry Adiabatic Lapse Rate (DALR)10 C°/ 1000 m5.5 F°/ 1000 ftLifting Condensation Level (LCL) is reached, then…Moist adiabatic rate (MAR)Also called the Wet Adiabatic Lapse Rate (WALR)6 C°/ 1000 m3.3 F°/ 1000 ft
11 Atmospheric Stability Stable and unstable atmospheric conditionsInvolves a parcel of air and its surrounding environment in the atmosphereStable atmosphere:A parcel of air is discouraged from risingKind of weather normally associated?Unstable atmosphere:A parcel of air is encouraged to rise
12 Unstable Atmosphere Parcel of air is encouraged to rise Examples of Stability Unstable Atmosphere Parcel of air is encouraged to riseFigure 7.20
13 Stable Atmosphere Parcel of air is discouraged from rising Examples of Stability Stable Atmosphere Parcel of air is discouraged from risingFigure 7.20
14 Atmospheric Stability To determine atmospheric stability:Compare the ELR with the DAR (or DALR) and MAR (or WALR)If ELR < MAR < DAR = STABLEIf ELR > DAR > MAR = UNSTABLEIf MAR < ELR < DAR = CONDITIONALLY UNSTABLE
15 Atmospheric Stability For example:We measure and find the ELR to be 12 Cº/ 1000 mWe know the DAR is 10 Cº/ 1000 m.We know the MAR is 6 Cº/ 1000 m.If ELR (12) > DAR (10) > MAR (6) then?If ELR > DAR > MAR = UNSTABLE
16 Atmospheric Stability If ELR is large (shallow slope), it will be to the left of both the DAR and MAR linesThis describes unstable atmospheric conditions!If ELR is small (steep slope), it will be to the right of both the DAR and MAR lines.This describes stable atmospheric conditions!
17 Atmospheric Temperatures and Stability ELRELRFigure 7.19
32 Fog Fog – a cloud layer at or very close to the surface formed when surface air temperatures and dewpt temperature are nearly identicalAdvection fog – warm, moist air layers moves over a cold surfaceEvaporation fog – dole air moves over warmer water bodyRadiation fog – loss of longwave radiation over moist surface
33 When warm, moist air moves over cooler body of water, what happens? Advection FogWhen warm, moist air moves over cooler body of water, what happens?Figure 7.25
34 Evaporation FogCold air lies over warmer body of water, and evaporation from water surface causes saturation and fog. Also, sea smoke = hazard.Figure 7.26
35 Radiation FogLoss of longwave radiation at night over moist surface causes saturation.Figure 7.28