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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