Please finish reading Chapter 5 in Hartmann

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Hydrologic Cycle plus Surface Energy Budget
Wrap-Up

• Please finish reading Chapter 5 in Hartmann
• First exam Wednesday (Oct 2)
• Closed-book, closed-notes
• Review Ch 1-5 in Hartmann, plus class notes

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Surface Net SW Radiation

• Latitude
• Clouds
• Albedo

Source http//www.cdc.noaa.gov/ Reanalysis for
1968-1996
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Surface Net LW Radiation

• sTs4 (sfc temperature)
• Atmospheric emissivity (water vapor)
• Atmospheric temperature

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Sensible Heat Flux

• Water availability
• Tsfc Tair
• Net radiation

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Latent Heat Flux

• Generally greater than H over oceans
• Water availability
• Tsfc Tair
• Net radiation

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Ground Heat Flux (upward)

• Much smaller than H or LE
• Tsoil lags Tair
• Tibetan bullseye probably due to model error

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Surface Relative Humidity ()

• Ocean vs. land
• Atmospheric subsidence
• Soil moisture?

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The Hydrologic Cycle
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Earths Water Distribution
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Groundwater
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Atmospheric Waterannual mean precipitatble water
(mm)

• Mean 25 mm (1 inch)
• Mean precip rate is about 2.6 mm/day
• Residence time 9 days
• Very steady
• E P 2.6 mm/day

Source http//www.cdc.noaa.gov/ Reanalysis for
1968-1996
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January
Precipitation (mm/month)

• Very wet over tropics
• Seasonal shift (N/S)
• Monsoon regions
• Extremely dry subtropical highs
• Midlatitudes get more summer rain
• July rainfall looks like a map of forest cover

July
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Atmospheric Water Balance

• P-E Df fin - fout
• Net water import by atmosphere
• Water vapor is imported into the tropics and
  midlatitudes
• Water vapor is exported from the subtropics

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Sources of Atmospheric Water

• Water vapor is concentrated in the tropics
  (Clausius-Clapeyron Eqn)
• Evaporation from the sea surface depends on
  Rnet,T, u, and RH
• The greatest water source is in the subtropics,
  with near zero LE in the ITCZ

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Seasonal Hydrology

• Potential evap tracks temp and radiation
• Winter rain/summer dry climates on the US West
  Coast
• Summer rain climates in tropics

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Seasonal Hydrology (contd)

• Actual E is strongly limited by water
  availability in many places (E P rather than
  PE)
• Some midlatitude locations (e.g., Boston) have
  little seasonality in P, but strongly seasonal E

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Land-Ocean Transfers fluxes in cm/yr (adjusted
for area of land and ocean)

• Ocean transfers water to land in atmosphere
• Land returns this water in rivers
• Most precip over land (48/7564) is recycled
  water

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Precipitation Measurement

• Primary data on precipitation is a can with a
  stick

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Precipitation Measurement

• These gauges can work well without supervision in
  remote areas
• What about snow?
• Wind shielding Alter or Nipher shields
• Gauge catch is abysmal
• These are the ground truth by which radar and
  satellite products are judged!

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Precipitation Climatologies

• LW (1990) used spherical interpolation to
  estimate 0.5º precipitation from about 20,000
  gauge stations
• GPCC merges gauges with two kinds of satellite
  imagery to estimate precip on a 2.5 º grid

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Precipitation Climatologies (contd)

• Two climatologies agree that west is drier than
  east
• Many details are different
• Effects of resolution
• Where are the gauges?
• Land vs ocean
• Valleys vs mountains

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PRISM Climatology (SW Oregon)

• Start with gauge data and a digital elevation
  model
• Divide the region into topographic facets by
  slope and aspect
• Develop regression relationships between gauge
  catch at each station and elevation, for each
  prism facet
• Apply statistics to each gauge to make a map of
  precipitation

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Orographic Effects

• Rain gauges are where the people are (flatlands
  and valleys)
• Most precip falls where the people arent!
• Precipitation rates in the west are dominated by
  orographic effects

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PRISM Climatology

• Annual precip estimates (PRISM)

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European Centre for Medium-Range Weather
Prediction (ECMWF)
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ECMWF Forecast Model
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ECMWF Data Sources
Assimilation Cycle
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Radiosonde Locations (Vertical Profiles of T,
Td, u,v,w)
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