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William J. Gutowski, Jr. 1 Abayomi Abatan 1 Babatunde J. Abiodun 2 Joseph M. Prusa 3

West African Extreme Daily Precipitation in Observations and Stretched-Grid Simulations by CAM-EULAG. William J. Gutowski, Jr. 1 Abayomi Abatan 1 Babatunde J. Abiodun 2 Joseph M. Prusa 3 1 Iowa State University, Ames, IA 2 University of Cape Town, South Africa

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William J. Gutowski, Jr. 1 Abayomi Abatan 1 Babatunde J. Abiodun 2 Joseph M. Prusa 3

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  1. West African Extreme Daily Precipitation inObservations and Stretched-Grid Simulations by CAM-EULAG William J. Gutowski, Jr.1 Abayomi Abatan1 Babatunde J. Abiodun2 Joseph M. Prusa3 1Iowa State University, Ames, IA 2University of Cape Town, South Africa 3Teraflux Corp., Boca Raton, FL

  2. CAM-EULAG: Simulation • Cores: EULAG (stretched-grid & uniform), FV • Physics: CAM3 (same settings as for FV) • Experiment: AMIP-type, observed SSTs • Horizontal resolutions : • 2˚x2.5˚ [CAM-EULAG uniform; FV] • Stretched-grid (CEU-SG): 0.5˚ over West Africa • Vertical grid: 26 levels • Period: 1996 – 2007 (discard first two yr.)

  3. CAM-EULAG: Stretched Grid

  4. Extreme Precipitation: Observed & Simulated Behavior • Observation-Based Fields • Precip: TRMM (0.25˚) & GPCP (1˚) • Other fields: ERA-Interim Reanalysis • Analysis • Target region: West Africa (6N-16N, 5W-5E) • “Precipitation event” = Daily precip ≥ 0.0 mm at a grid point • Pool all “events” in the target region • Focus on precipitation intensity ≥ 99% • Focus on “widespread” events: ≥ 15 simultaneous daily extreme events

  5. CAM-EULAG: West Africa Annual Cycle(Abiodun et al., ActaGeophys., 2011) ERA-Interim +TRMM CEU - SG Region: 10 W – 10 E Precip [mm/d], 600 hPa Zonal Wind [dashes] Intertropical Discontinuity [solid line]

  6. Seasonal Average Precip.[mm/d] (6 N – 16 N, 5 W – 5 E)

  7. CAM-EULAG: PrecipitationDiurnal Cycle[mm/d] Stretched Grid (SG) Uniform TRMM Data: Diurnal Range ~ 2.5 – 9.5 mm/d Diurnal Max ~ 16-20 hr UCT (Lee et al., JGR, 2007) (Region: 10 W – 5 E) Hour of Day

  8. Monthly Timingof Extreme Precipitation

  9. Interannual Variability of Extreme Precipitation

  10. Composite Anomaly Meridional Wind JAS700 hPaDay Before ERA-Interim +TRMM CEU - SG 98 99 00 01 02 03 04 05 06 07

  11. Composite Anomaly Vertical WindExtreme Precipitation Days [mb/s] April –May -June Day of Events 1-Day before Events OBS. CEU

  12. Composite Anomaly Vertical WindExtreme Precipitation Days [mb/s] July - August - Sept. Day of Events 1-Day before Events OBS. CEU

  13. Spatial Simultaneity of Extremes April-May-June

  14. Spatial Simultaneity of Extremes July-August-Sept.

  15. Normalized Frequency vs. Intensity April-May-June

  16. Normalized Frequency vs. Intensity July-August-September

  17. % of Extremes as Consecutive-Day Events July-August-September

  18. Dirunal Cycle – CEU Extremes

  19. Dirunal Cycle – TRMM AMJ Extremes Mean Early Morning Max Mean Evening Max

  20. Dirunal Cycle – TRMM JAS Extremes Mean Early Morning Max Mean Evening Max

  21. TRMM: Squall Line (mm/hr)

  22. CEU: Stationary Convection (mm/hr) … and more persistent episodes of daily extremes

  23. SUMMARY • CAM-EULAG SG simulates well several aspects of mean climatology of West Africa, including diurnal cycle • CAM-EULAG SG simulates well some aspects of extreme precipitation • However, simulated extremes weaker than observations and are stationary • Extremes also tend to show daily persistence • Needed? • Resolution sufficient for squall lines • Or perhaps a super-parameterization approach can promote the needed propagation (M. Moncrieff, NCAR, pers. comm.)

  24. Thankyou!

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