INTRODUCTION TO THE HYDROLOGIC CYCLE

      
Hydrologic Cycle Image credit: National Weather Service (2005) Jetstream: An Online School for Weather http://www.srh.weather.gov/srh/jetstream/atmos/hydro.htm

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B. EVAPORATION: TRANSFER MOISTURE INTO THE ATMOSPHERE

Affected by:

• amount of available water

• sunlight

• temperature

• water vapor content of the air

  • saturation curve

• wind

Global Average Evaporation Rate 1988-2000 Based on NCEP-R2 Data Set

Image credit: NASA/GSFC (2007) Global Modeling and Assimilation Office http://gmao.gsfc.nasa.gov/research/merra/climate.php

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C. HUMIDITY: MOISTURE IN THE ATMOSPHERE

• Vapor pressure: weight of the molecules of water vapor (mb)

  • saturation vapor pressure

• Mixing ratio: grams of water vapor per kilogram of air (g/kg)

• saturation mixing ratio      

• Relative humidity: ratio of the water vapor content of the air to the water vapor capacity of the air

  • content: the actual amount of water vapor present

  • capacity: the maximum amount of water that can be maintained in a gaseous state given the air temperature

Image credit: NASA/JPL (2006) New Global Maps Made from AIRS Data. http://airs.jpl.nasa.gov/News/Features/FeaturesNewGlobalMaps/   

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D. PRECIPITATION: TRANSFER MOISTURE OUT OF THE ATMOSPHERE

Image credit: ©Michael Collier. Image source: Earth Science World Image Bank http://www.earthscienceworld.org/images Stratocumulous clouds, Monument Valley, Arizona

• Condensation

  • clouds

  • fog

• Dew point temperature

• Cooling mechanisms

• radiation cooling (contact cooling)

• uplift

• Precipitation

  • collision-coalescence process

  • Bergeron ice crystal process

• Global precipitation patterns       

Image credit: National Weather Service Climate Prediction Center (2002) NOAA, Mean annual precipitation 1979-1995. http://www.cpc.ncep.noaa.gov/products/precip/CWlink/wayne/annual.precip.html

Image credit: National Weather Service Climate Prediction Center (2002) NOAA, Mean annual precipitation 1979-1995. http://www.cpc.noaa.gov/products/precip/realtime/clim/annual/monthly/annual.html

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E. SUMMARY

• Hydrologic cycle

• Evaporation: sunlight, temperature, humidity, wind

  • saturation curve

• Humidity: vapor pressure, mixing ratio, relative humidity

• relative humidity varies with air temperature and water vapor content

• Condensation: dew point temperature, clouds, fog

• Precipitation

Image credit: Ralph F. Kresge, NOAA Photo Library, Historic NWS Collection http://www.photolib.noaa.gov/historic/nws/wea02054.htm