1. Testing the Effect of Domain Size on RegCM3’s Precipitation Output Over Southern Africa Anne Barrable¹ Mary-Jane Kgatuke² Chris Lennard¹ 1- University of Cape Town ; 2- South African Weather Service

2. Aims and Objectives  Establish the effect of different domain size and location on RegCM3 output.  Particularly examining precipitation in an agriculturally sensitive region.

3. Methods  Define 3 different domains over southern Africa including Madagascar.  Two domains chosen to overlap a common region, which formed the 3 rd domain…

4. Grid points: 43x32 Grid points: 18x18 Grid points: 64x44 SA Domain Common Domain SA + Madagascar

5. Methods  Define 3 different domains over southern Africa.  Examined February 1995, 1996, 1997.  11 th February anomalously wet day in study region –compared model between domains.

6. Model Parameters  60km grid.  Lambert Conformal projection.  NCEP reanalysis data.  Grell convection scheme using Fritsch & Chappell closure.

7. Results  Examined surface model precipitation data.  Daily precipitation averages. Comparison over common domain.  11 th February 1996. Comparison over common domain.

8. 199519971996 ?

9. Tropical Cyclone Josie was present in the Mozambique Channel for 5 days (9-14 Feb 1997)

10. SA Domain Common Domain SA + Madagascar Daily average Feb 1995

11. SA Domain Common Domain SA + Madagascar Daily average Feb 1996

12. SA Domain Common Domain SA + Madagascar Daily average Feb 1997

13. SA Domain Common Domain SA + Madagascar 11 th February 1996 ♠ Bloemfontein (11.5mm) ♣ Polokwane (10.4mm) ♦ Johannesburg (65.0mm) ♥ Van Reenen (74.2mm) ♠ ♣ ♦ ♥ ♥ ♥ ♦ ♦ ♣ ♣ ♠ ♠

14. General Conclusions  Summer and winter rainfall regions identified.  1996 wetter year corresponds to known La Nina year.  Different domains display different spatial precipitation characteristics.  Although not presented here, temperature (surface & 2m) showed a cold bias (3°).  Choice of domain location and size crucial w.r.t. topography AND synoptic systems.

15. Caveats and Model “Hitches”  Common domain too small; nudged by forcing data and did not allow the model to run freely.  Running smaller grid sizes (30km & 20km) did not work: 2 segmentation faults (even with time step at 20 seconds); 2 segmentation faults (even with time step at 20 seconds); 2 computer freezes; 2 computer freezes; 1 floating point exception error….Gave up! 1 floating point exception error….Gave up!  Stretched grid for smaller domains?

16. Caveats and Model “Hitches” cont…  Regrid for different grid size comparisons (in GrADS; already available in Ferret).  Map projection difficult to implement with precipitation. Map possibly shifted, particularly in SA- Madagascar domain. Map possibly shifted, particularly in SA- Madagascar domain.

17. Acknowledgments  Special thanks to Bill Gutowski for meaningful discussions of model results.  Thanks to Filippo Giorgi, his team, and the ICTP for allowing us the opportunity to learn and run RegCM”3”.