Regional Climate Modeling Simulations of the West African Climate System

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Regional Climate Modeling Simulations of the West
African Climate System

• Gregory S. Jenkins, Amadou Gaye, Bamba Sylla
• LPASF AF20

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Rational for Regional models

• Why use regional climate models for West Africa.
• Orography (Guinea highlands, Jos Plateau)
• Lakes (Lake Chad)
• Coastline
• Important physical and meteorological Gradients
  (vegetation, precipitation, temperature).
• Mesoscale forcing for precipitation (easterly
  waves, squall lines, mesoscale convective
  complexes, non squall clusters).

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Regional Climate Modeling Approach

• Drive regional climate model with observations at
  lateral boundaries.
• Identify biases in regional climate model using
  present-day observations.
• Drive regional climate model GCM data for
  present-day (1980-1984) at lateral boundaries.
• Identify and Compare biases to regional climate
  model driven by observations.
• Drive regional climate model with GCM data for
  2090-2094.
• Compare regional climate model changes to GCM
  21st and 20th century result

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Errors associated with regional climate models

• Parameterizations - convection, land-atmosphere,
  clouds)
• Biases (cold, warm, wet, dry)
• Internal model variability (Eg. Does the model
  represent easterly waves correctly).
• Lateral Boundary conditions (GCM errors)
• Climate sensitivity of regional climate model (
  how much warming for 1 W/m2 of GHG forcing).

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Questions associated with regional climate models

• Can we quantify the individual and collective
  errors in regional model simulations?
• Can we quantify the error associated with lateral
  boundary conditions?
• Can we address the added value associated with
  regional climate models?

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Convection Parameterizations
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Biases in Zonal winds from convective
parameterization
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Current Status

• 60 km Regional Climate model simulation for West
  Africa (25W-25E, 3N-27N).
• Driven at lateral boundaries by NCEP reanalysis.
• Phase I 1993-2002 (Done)
• Phase II. 1982-1993 (Running)
• Phase III. 1972-1982 (April, 2004)

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Capacity Building and Regional climate Modeling

• 21 year simulation- download 54 Gigabytes from
  US.
• 1 Gigabyte download (6-18 hours).
• 10 year RegCM simulation uses approximately 50
  Gigabytes.
• Need to invest infrastructures in Africa for
  long-term research. Costs are not prohibitive
  currently.
• Internet getting better.

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RegCM/Observations comparison for Temperature
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RegCM/Observation comparison for Temperature
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Annual cycle of Temperature (Observed and
RegCM)-1993-2000
R 0.92
R 0.88
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RegCM/Observation comparison for Precipitation
(1993-2000)
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RegCM/Observation comparison for Precipitation
(1993-2000)
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Annual cycle of Precipitation (Observed and
RegCM)-1993-2000
R0.956
R0.976
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NCEP/RegCM 700 hpa/200 hPa wind comparison
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Dry(1997)/Wet (1999) Year comparison
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Dry(2002)/Wet (1999) Year comparison
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RegCM Spectral Signature of Easterly waves (V
component)
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RegCM Spectral Signature of Easterly waves (U
component)
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Preliminary Summary

• RegCM does a good job in simulating West African
  Climate
• Precipitation (annual cycle captured)
• Temperature (annual cycle captured but cold bias
  in Guinea)
• AEJ, TEJ captured
• African Easterly waves (3-5 day and 6-9 day AEWs
  captured).

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RegCM data

• Saved every 6 hours surface fields, 12 hours
  meteorological fields.
• Available at diurnal, monthly timescales.

• Temperature (max, min, mean)
• Precipitation, evaporation, soil moisture,
  atmospheric moisture,
• Radiation - shortwave, longwave ,net, cloud
  fractions
• Dynamic field (u,v, SLP, geo-potential heights)

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Plans

• Finish RegCM/NCEP simulations.
• Begin driving RegCM with CSM data.