Regional Climate Modeling Simulations of the West African Climate System

1. Regional Climate Modeling Simulations of the West African Climate System Gregory S. Jenkins, Amadou Gaye, Bamba Sylla LPASF AF20

2. 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).

3. 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

4. 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).

5. 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?

6. Convection Parameterizations

7. Biases in Zonal winds from convective parameterization

8. 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)

9. 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.

10. RegCM/Observations comparison for Temperature

11. RegCM/Observation comparison for Temperature

12. Annual cycle of Temperature (Observed and RegCM)-1993-2000 R = 0.92 R = 0.88

13. RegCM/Observation comparison for Precipitation (1993-2000)

14. RegCM/Observation comparison for Precipitation (1993-2000)

15. Annual cycle of Precipitation (Observed and RegCM)-1993-2000 R=0.956 R=0.976

16. NCEP/RegCM 700 hpa/200 hPa wind comparison

17. Dry(1997)/Wet (1999) Year comparison

18. Dry(2002)/Wet (1999) Year comparison

19. RegCM Spectral Signature of Easterly waves (V component)

20. RegCM Spectral Signature of Easterly waves (U component)

21. 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).

22. 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) RegCM data

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