Atmos' Water Content

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Atmos. Water Content

• Collect Hmwk 1, answers posted on Monday

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Last Time

• Hydrological Cycle
• See diagram
• Transpiration- water vapor that is given off by
  plants
• Evapotranspiration- combines evaporation and
  transpiration effects
• Numbers 97 of water resources tied up in oceans

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Water Resources

• 97 in Oceans
• Fresh Water 0.09
• In Atmos 1/1000th of a percent
• A lot of importance though
• Where do we find this small percentage in the
  atmosphere?

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Water Vapor

• Water vapor in the vertical
• Since temp decreases with height (lapse rate 6.5
  deg C per km, 3.8 F per 1kft)
• Therefore water vapor content decreases with
  height
• mixing ratio drops off more dramatically with
  height than temperature
• Above 850 mb, water content drops off rapidly
• Most is contained between 1000-850 mb

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Water Content (cont)

• Where is the water mass on the earth?
• See handouts given in classNCAR Tech Memo-
  Distribution of Topographical Quantities 1995
• Winter cloud cover- in mid-latitudes over the
  oceans (both northern and southern hemisphere)
• India and Sahara less cloudy regions in winter,
  some subtropical regions as well

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Cloudiness (cont.)

• In summer, in mid-latitudes over ocean is still
  cloudy
• In summer the cloudiness in N.H. moves slightly
  northward
• July-August low cloudiness, major deserts, Saudi
  Arabia, Australia, Sahara
• Cloud cover over land 50

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Page 1.40

• Relative humidity with height ,averaged in
  latitudinal bands
• Features are fairly similar in both winter and
  summer
• Values greater than 70 represent the boundary
  layer, which makes sense
• In the S.H. boundary layer is fairly moist from
  equator to pole, N.H dries out around 30 N.trade
  wind deserts

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Function of land mass

• Function of the land
• N.H. 39 land, and 61 ocean
• S.H. 19 land, and 81 ocean
• Big land ocean dist asymmetry

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RH x-y plots

• Oceanic areas more humid, land masses are dry,
  except for the tropical rain forests
• Siberia in the summer is relatively humid
• SE US with humidity in the summer can be some of
  the most uncomfortable places in the world

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Figure 1.43- PW

• Precipitable Water (PW) The sum of the values of
  mixing ratio in a column of atmosphere
• Lots of PW near the equator where it is warmest
• In summer in N.H. high PW values reach the
  Southern US

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Figure 1.45

• Average precipitation over all longitudes for
  each latitude belt
• High amounts are found in the equatorial regions,
  where it is warmest (among other
  processes---ITCZ)
• Secondary maximums around 30 N and 30
  Smid-latitude jet streams are found here
• X-Y plot is the final diagrammore handouts
  coming in the near future when we discuss gen
  circ further

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Cloud Formation

• Dr. Lupos 3-legged stool example
• 3 things to get cloud
• Moisture
• Vertical motion (lift)
• Cloud Condensation Nuclei (CCN)
• Natural CCN
• Sea Salt, Sand/dirt, Bugs, Pollen, etc.
• Anthropogenic CCN
• Pollution Sources, etc.

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Cloud types

• Cloudiness impacts temperature- cloudy nights
  warmer than clear, for example
• High Clouds
• Cirrus-type clouds, ice crystals
• Middle Clouds
• Alto, ice crystals and supercooled droplets
• Low Clouds
• Main Precip producersNimbostratus (uniform
  sheet) vs. Cumulonimbus (convective heap)

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Precip Clouds (cont.)

• In N.H. nimbostratus dominate in winter,
  cumulonimbus dominate in warmer seasons
• Nimbostratus, are uniform with a large area of
  weak forcing, warm frontal (stratiform)
  precipitation
• Cumulonimbus can grow up to 60000 feet, severe
  thunderstorms, heavy convective precipitation,
  high albedo only snow is higherclimate impacts

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Drought

• Places that are typically moist, but can become
  dry over a long duration, 2003 was a recent
  drought locally
• 1988 was a widespread drought in the US
• Different types of drought
• Meteorological
• Agricultural
• Hydrological

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Drought (cont.)

• Basic drought equation precipitation minus
  evaporation
• If evaporation exceeds precip for quite a time,
  the result is a drought
• Meteorological drought compares P-E to climatology

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Palmer Index

• Rates a severity for drought
• Long term indexcannot tell you if you have had
  relief due to a month being rainy
• For more information
• www.drought.noaa.gov/palmer.html
• Also see the Drought Mitigation CenterUniversity
  of Nebraska-Lincoln
• www.drought.unl.edu/whatis/indicies.htm