Rainfall Patterns

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Rainfall Patterns

• Differential warming and cooling of water and
  land
• Temperate areas
• prevailing westerlies -gt wind comes off water on
  to land on the west coast
• Water tends to be warmer than land at Northern
  latitudes
• Wind coming off water cools, and tends to drop
  water as rain.
• British Columbia and Southern Chile
• Drenched with almost continual rains,
  particularly in the winter

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U.S. West Coast

• Oregon and Northern California
• Land is a bit warmer than the water in the
  summer.
• In the winter the land is cooler than the water,
• Southern California
• Land is almost always warmer than the ocean.
  Little rain results except in the high mountains.
• The westerlies here are thirsty

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Baja

• Not only is the land quite warm, the water is
  much colder
• Strong local winds pulling water away from the
  coast.
• Coriolis force
• Upwelling
• Water coming from the deep is both cold and
  nutrient rich.
• These factors, plus the latitude make Baja a very
  dry place

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Atacama desert

• Found in Northern Chile
• The land is much warmer than the water
• Found at 25º So. latitude.

0º
25º
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Air movement above 30º

• Surface air moves poleward from 30º to about 60º.
• Air moves from the pole toward 60º also
• the cell rises somewhere between 50º and 60º.
• Increased precipitation occurs where the air
  masses meet and rise.
• Jet stream influence
• U.S. air masses coming from the south often bring
  moisture from the Gulf.

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Major factors altering climatic patterns

• Tall Mountain Ranges
• Adiabatic cooling
• Rain shadow effect

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Major factors altering climatic patterns
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Major factors altering climatic patterns

• Tall Mountain Ranges
• Adiabatic cooling
• Rain shadow effect

• Large bodies of water (large lakes)

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Lake Effect Snow

• Buffalo, New York shattered its all-time 24-hour
  snowfall record when 38 in. of snow were measured
  at the airport on 9-10 December 1995.

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Large land masses

• Maritime climate of coastal areas is less extreme
  than that of inland areas (Continental climate).
• San Francisco and New York - approximately the
  same latitude.

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Monsoons

• Summer heat causes rising air masses.
• Air gets sucked off of the ocean to replace it.
• Air masses cool as they rise, drop large amounts
  of rain.
• Cherrapugi, India in July 1861
• Thunderstorms

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• Morning Sentinel July 28, 2005

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Microclimate factors Altitude

• 4ºC drop in temperature for every 1000 m increase
  in altitude ( 100 miles north)
• Causes
• Adiabatic cooling (causes condensation)
• Moist air cools more slowly -gt receives heat from
  condensation of water)
• More moist environment as altitude increases due
  to increased rainfall and decreased evaporation

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Causes - (cont)

• Atmospheric blanket

reradiates heat rapidly (rapid cooling at night)
More dense lower atmosphere More moisture to hold
heat
Bounces heat back
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Microclimate factors Aspect

• The most dramatic effects come in areas with some
  moisture stress.

South
North
Less direct rays, thus cooler, more moist
South facing slope
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Aspect and Temperature
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Microclimate factors Aspect
West Virginia

• Shrubs

Shrubs
Trees
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El Nino - La Nina
El Nino
La Nina
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Fig. 23-7
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El Nino
Normal year
Most dramatic El Nino - 1998
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El Nino effects
Text Fig 23.6
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