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Lecture 5Atmospheric Moisture &
Precipitation
Geog210Physical Geography
Professor Paluzzi
Water and Atmospheric MoistureWater and the Hydrosphere
Stages of Water
Humidity - Relative Humidity
Clouds
Fog
Water on EarthWorldwide equilibrium
97.22% - oceans
2.78% - fresh water77.14% of fresh water is in long term storage Glaciers
.333% - lakes, rivers, streams
Subsurface - groundwater 22%
Water Distribution50% of freshwater is contained in the 7 largest lakes Lake Baykal – located in southeast Siberia - largest freshwater reserve in the world
• 400 miles long, a mile deep
Earth’s Water
HydrologicCycle.swf
Land & Water HemisphereNot equally distributed
Northern HemisphereLand Dominates
Southern HemisphereWater dominates
Water Hemisphere Western parts of northern and
southern hemispheres
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Saline Lakes (Seas)¼ of 1% of surface water are in saline lakesShrinking Aral Sea
60% of the sea’s total volume has disappeared
Excessive utilization for irrigation led to the progressive drying of the sea.
Use of rivers feeding the sea for agricultural irrigation
Salinity increased from 10g/l to 40g/l
destroying animal and vegetation species
Saline Lakes (Seas)Surface area has decreased by 45% and water volume by 60%.complete separation into “small sea” and “large sea”
Economic and cultural damagesSevere shortage of water for 50 million peopleEnvironmental problem - ships
The Shrinking Aral Sea
Mosaic of satellite images, 1960 – 1994
• The Aral Sea on May 29, 1973 from Landsat-1
• The Aral Sea on August 19, 1987 from Landsat-4
• The Aral Sea on July 29, 2000 from Landsat-7
The Shrinking Aral Sea
1973 1987 2000
Saline Lakes (Seas)Caspian Sea – the worlds largest lake
Roughly the size of Montana
Ural and Volga Rivers feed the lake, but not rivers flow out
Upstream harvesting of water Less water reached the lake – evap.
leaving the salt
Threatening fishing industry
Continued to shrink until the late 1970’s
Recently – more rain Increased depth
Saline Lakes (Seas)Lake Balkhash – (Kazakstan) – fifteenth largest lake in the world
Roughly the size of Connecticut and Rhode Island combinedSeveral rivers feed the lake, but not rivers flow out
The Ili River – sediment (west)
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U.S. Saline LakesMono Lake, CA
Basin of Sierra Nevada
Formed about 3 million years ago
Mono Lake is the terminal point in a watershed fed from melting runoff.
U.S. Saline LakesGreat Salt Lake, UT
About 75 miles long, and 28 miles wide, and covers 1,700 square miles
Has a maximum depth of about 35 feet
Typically 3 to 5 times saltier than the ocean
Fish free, the largest aquatic critters are brine shrimp and brine flies
Three Stages of WaterSolid – as water cools, it contracts in volume (until 39°F) then expansion occurs
Solid Liquid (Freezing & Melting)
Ice cube tray
Frost heaves – Road/pavement damage
Solid GasSublimation Process of ice changing
directly to a gas
Gas -> directly to solid
Water attaches to icecrystals (frost)
Liquid Gas – evaporation/condensation
Hydrologic CycleWater moves among the ocean, atmosphere
and land
Evaporation
Precipitation
Transpiration from plants
Runoff
Sinks into soil
Recharge of groundwater
Hydrologic CyclePrecipitation: Particles of liquid water or ice that fall from the atmosphere and may reach the ground.
HumidityHumidity – water vapor in the air
The maximum quantity of moisture that can be held in the air depends on air temperature
A function of temperature
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HumidityRelative humidity - the ratio of water vapor in the air, compared to maximum water vapor possible
Tells us how close we are to saturation (100%)Dew point – temperature at which air becomes saturated Further cooling results in condensation (dew)
Temperature changesLower temperature relative humidity rises
Raise temperature relative humidity decreases
Relative Humidity
Actual Water Vapor in Air
Relative Humidity = Maximum water vapor possible X 100
in the air at that temperature
• Highest at dawn – when temperature is lowest
ie. Dew on car in the morning
• Lowest in late afternoon – temperatures highest
Moisture in the AtmosphereRelative humidity –
Highest at dawn – when temperature is lowest
Lowest in late afternoon – temperatures highest
Water Vapor
11 a.m.50%
Relative Humidity
Water Vapor
5 p.m. 20% Relative
Humidity
Warmer air = greater maximum water vapor possible
Cooler air = lesser maximum water vapor possible
Water Vapor
5 a.m. 100%
Relative Humidity
Maximum water-vapor
possible
Humidity InstrumentsHair Hygrometer
Human hair changes length based on humidity
Relative HumiditySling Hygrometer
2 thermometers1 – dry, records air temperature
2 – wet, records temperature that is lowered by the evaporation of the wet bulb High humidity – little evaporation
Low humidity – more evaporation
The Adiabatic ProcessAtmospheric pressure decreases with altitude, so:
As a parcel of air risespressure on the parcel decreases
air expands and cools
As a parcel of air descendspressure on the parcel increases
air is compressed and warms
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Adiabatic ProcessesDry adiabatic rate - rate at which rising air is cooled by expansion when no condensation is occurring:
5.5 F°/ 1000 ft
Moist adiabatic rateBetween 2.2°& 4.9° F°/ 1000 ft
Clouds and FogClouds – a great mass of moisture droplets
As air rising, it cools. When it reaches it’s dew point (saturation) further cooling results in moisture droplets forming through condensation
Cloud condensation nuclei – microscopic particles present in the atmosphere around which clouds form
Cloud Types and Identification
Figure 7.20
Altitude and shape are key to cloud id’ingLow Clouds – up to 6500’
Stratus, stratocumulus, nimbostratus
Middle Clouds – 6500’ to 20,000’Altostratus, altocumulus
High Clouds – 20,000’ to 43,000’Cirrus, cirrostratus, cirrocumulus
Vertically Developed Clouds – near surface to 43,000’
Cumulus, cumulonimbus
Cloud Types & Identification: Low
Stratus – uniform, featureless, greyUp to 6500’ – composed of water only
Cloud Types & Identification: LowStratocumulus – soft, gray, rounded masses, irregular shaped:
Up to 6500’ - water
Cloud Types & Identification: LowNimbostratus – up to 6500’: water :
Stratus clouds that yield rain
Gray, dark, low with drizzling rain
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Cloud Types & Identification: MiddleAltostratus – thin to thick, uniform gray sheet or layer – similar to stratus, except higher altitudes
Sun’s outline visible
6500’ – 20,000’ – Composition – ice and waterDangerous to aircraft – cause ice to buildup
Cloud Types & Identification: MiddleAltocumulus – patches of cotton balls, arranged in lines or groups
Often in front of a cold front, precede thunderstorms on hot, humid summer days
6500’ – 20,000’, ice & water
Cirrus – wispy, feathery, hair-like20,000’ – 43,000’ – icy composition
Indicate an incoming storm
Cloud Types & Identification: High
Cirrostratus – thin veil of sheets of ice crystals, milky, results in halos around the sun and moon.
Indicates precipitation will occur within 12-24 hours
Ice
Cloud Types & Identification: High
Cloud Types & Identification: HighCirrocumulus – dappled, puffy appearance
“Mackerel sky” – High altitude – 20,000 – 40,000’ feetAlmost exclusively Icy composition
Indicate incoming storms
Cirrocumulus differs from Cirrus and Cirrostratus in that it is rippled or subdivided into very small cloudlets
Cloud Types & Identification: VerticalCumulus – often called Fair Weather Clouds
Mostly detached clouds, generally dense and with sharp outlines
The sunlit parts of these clouds are mostly brilliant white.
Their base is relatively dark and nearly horizontal
may be composed solely of water droplets, super-cooled water droplets, ice crystals, snowflakes, ice pellets or a combination of all – Near surface to 43,000’
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Cloud Types & Identification: VerticalCumulonimbus – mushroomed shaped
Dense, heavy, lots of vertical development
Associated with dark thunderstorms and heavy showersThunderheads from surface to 43,000’
Upper air flow (wind) flattens the top
Cloud Types & IdentificationCumulonimbus Development – anvil shaped
Updraft/downdraft – lift and drop of water droplets and ice crystals creates static electricity charges, resulting in thunder/lightning
Generally occur in afternoon, as heat builds during day, but cold
fronts meeting the warm fronts push air vertical
FogFog – a cloud layer that is on the ground; visibility restricted to 1km or less
Tells us the air temperature and dew-point temperature are nearly identical and the air is saturated
Advection fogAdvection fog – forms when warm moist air moves over a cold surface
Evaporation fogEvaporation Fog – when cold air lies over warm water (lake, ocean surface, swimming pool)
Sea smoke
Upslope fogUpslope fog – warm, moist air flows to higher elevations along a hill or mountain
Adiabatic cooling
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Valley fogValley fog – cold air is denser than warm air, it occurs when cold air settles in the valleys when temperature meets the saturation point
Radiation fogRadiation fog – : formed when temperature of the air at ground level falls below dew point