Hydrologic Cycle PDF

Atmospheric Moisture 3 states of water Solid (Ice) -Liquid (water) -Gas (water vapor) Latent heat is absorbed when water changes to: Evaporation Melting Sublimation Latent heat is released when water changes to: Freezing Condensation Deposition ...

Atmospheric Moisture 3 states of water Solid (Ice) -Liquid (water) -Gas (water vapor) Latent heat is absorbed when water changes to: Evaporation Melting Sublimation Latent heat is released when water changes to: Freezing Condensation Deposition  Most water in oceans Hydrosphere 97.5% Realm of Most fresh water in water in all glaciers its forms Much more ground-water than fresh surface water Very little in atmos-phere at any one time Hydrologic Cycle: Represents flow of water among land, ocean & atmosphere Condensation & precipitation Evaporation Runoff Infiltration Humidity Amount of water vapor in the air Humidity varies dramatically all over Earth Warm air can hold much more water vapor than cold air Specific Humidity SH = mass of water (SH) – actual quantity vapor / mass of total of water vapor in air air Specific SH tends to be much higher in tropical regions (warm air parcels Humidity, are larger, can hold more water) Latitude & Temp SH closely correlated to temp, by latitude Saturation Specific Humidity Saturation – when air can hold no more H 2O↑ When SH = Saturation SH Increases geometrically with temperature Dew Point Temp at which air, when cooled, becomes saturated Temperature Provides measure of actual moisture in air Curve is same as for saturation specific humidity Also, a measure of human comfort Dew point temp > 70°F considered oppressive Relative What TV weather forecasters mean by “humidity” H2O↑ in air compared to max H2O↑at that temp Humidity Relative Humidity RH = 100 X (SH / (RH) Saturation SH) RH can change by: 50% RH means air evaporation - has ½ max H2O↑ at condensation - that temp change in temp.  As air rises, it expands and cools Adiabatic Air parcels cool at predictable rate as they rise: Process Unsaturated (no condensation) Dry adiabatic lapse rate (DAR)- 10°C/1000m At lifting condensation level, saturation occurs Saturated (condensation occurring, heat released) Cloud forms as parcel rises Moist adiabatic lapse rate – 4-9°C/1000m Use 5°C/1000m as estimate of Moist adiabatic rate Precipitation Can form in two ways: In warm clouds, water droplets condense - Droplets collide and coalesce into larger droplets In cold clouds, ice crystals form & grow - May form by deposition or by freezing supercooled water Ice may or may not melt on way down to Earth’s surface Precipitation Processes Air expands & cools as it rises, but… What makes it rise? 4 processes help air to rise and drive precipitation Orographic precipitation Convective precipitation Frontal precipitation Convergence Orographic Precipitation Moist air forced by wind over mountains As air is lifted, condensation & precipitation occur Air passes mtn top & descends leeward side This air is compressed and warms with no precipitation The dry, leeward side is called a Rainshadow Convective Air pockets warm at surface & rise rapidly Precipitation As they rise, they cool, first at DALR 10°C/1000m If ELR is high, air bubble stays warmer & rises Bubble reaches dew point temp → condensation Condensation forms clouds, releases heat Air cools at MALR, averaging 5°C/1000m Bubble cooling much slower than surrounding air Bubble pushes high into troposphere Types of Precipitation Precipitation – liquid or solid water crystals that fall from atmosphere to ground Types: Rain – reaches ground as liquid water Snow – flakes created by deposition in clouds Sleet/Freezing Rain Rain falling through freezing air Hail – formed in updrafts of thunderstorms