1. A. Laing, 25 Oct 2006 Patterns of convection in Africa: Implications for prediction of precipitation Patterns of convection in Africa: Implications for prediction of precipitation Arlene Laing (NCAR/MMM) Societal need for improved precipitation of prediction in Africa (economy, health, water resource management, …).Societal need for improved precipitation of prediction in Africa (economy, health, water resource management, …). Prediction depends on improved understanding of initiation and evolution of organized convection Substantial fraction of organized convective events exhibits systematic propagation at regional to continental scales. Coherence behavior implies qualitative predictability beyond one or two days Long-term statistics of organized convection (from satellite, new radars, etc…) => role of regenerating convection in tropical cyclogenesis => Better understanding of water cycle at various scales, role of regenerating convection in tropical cyclogenesis => improve models, prediction

2. A. Laing, 25 Oct 2006 Seasonal & Diurnal Cycles Average Hourly Percentage of Cold Cloud, T bb < 253K Convection triggered daily in lee of high terrain Local & Propagating Convection Preferred zones of initiation and propagation Letters mark mountain peaks 0.5 1.0 1.5 Average Elevation (km) 0º – 20ºN 0.5 1.0 1.5 Average Elevation (km) 0º – 20ºN

3. A. Laing, 25 Oct 2006 Mean Diurnal Cycles Average frequency of cold cloud as function of longitude & time 0 6 12 18 12 6 propagation 0.6 1.2 10E20E30E40E Average elevation (km) 35S – 20S 35S-20S5S-15N 0 - 20N 0 6 12 18 12 6 20W10W010E20E30E40E Propagation Average Elevation (km) 5S – 15N +1+2 0 Propagation 0.5 1.0 1.5 20W10W010E20E 30E 40E Average Elevation (km) 0º – 20ºN 0 6 12 18 12 6 UTC Convection triggered daily by heating of elevated terrain Local diurnal heating maxima & propagating convection 16-31 Dec 200316-31 Oct 199916-30 June 1999 (Tbb< 233K)

4. A. Laing, 25 Oct 2006 Convection Episodes & Prediction Real-time propagation stats combined with climatology for short term forecasts (0-6hrs) of deep convection, precipitation Classify synoptic regime favoring frequent episodes of organized propagating convection. Aid in predicting high impact precipitation events Radar rainrates and lifecycle of convection => improve QPF Mean Median Span (km) 1062 700 Duration (h) 25.4 18.0 Phase Speed (m/s) 12.0 11.2 30 ms -1 7 ms -1 Tropical N. Africa (60deg longitude) ~5 episodes per day across zonal domain

5. A. Laing, 25 Oct 2006 Patterns of convective precipitation over W. Africa resemble those in specific regions around the World... specifically, environmental shear controls convective organization (c.f., US continent during summer - Moncrieff and Liu, 2006)

6. A. Laing, 25 Oct 2006 Data & Methods Meteosat-7 IR, 30min NCEP GFS Analyses May 1999 - March 2004 Reduced Dimension (Hovmoller) techniques. Cold cloud as proxy for precipitating convection Compute phase speeds, duration, span Compare with easterly wave statistics Examine large-scale influences 0 20W 20E 20S 20N 0 40E 0.6 1.2 0 Average Elevation (km) 35S - 20S Nov - Feb Autumn, Spring Autumn, Spring 0.5 1.0 1.5 20W10W010E20E30E 40E Average Elevation (km) 0 – 20N May - Aug