Anne Sophie Daloz Director : Colin Jones The effects of increased horizontal resolution in simulating precipitation over Sub-Saharan Africa with GEM-LAM. Source : http://www.centre-cired.fr/forum/article Anne Sophie Daloz Director : Colin Jones

Why do we study Sub-Saharan Africa ? 1. Introduction Why do we study Sub-Saharan Africa ? Growing interests Burpee, Lafore, Lebel, Redelsperger, Chauvin … Droughts caused catastrophic period of starvation 70s et 80s in Sahel. Precipitation AEWs* Tropical cyclogenesis AEWs* Topography of Africa. In black, the Sub-Saharan region. http://www.junglephotos.com/africa/afmaps/afscimaps/africaelevationmap.shtml *AEW = African Easterly Wave

Precipitation mechanisms over Sub-Saharan Africa 1. Introduction Position and extreme migration of the ITCZ in red . Source : http://www.astrosurf/luxorion AEWs African Easterly Waves MCS Mesoscale Convective System ITCZ WAM West African Monsoon Topography of Africa. Source http://www.jungl ephotos.com/africa/afmaps/afscimaps/africaelevationmap.shtml Alizés chargés d4humdité , West African Monsoon Genesis : West Africa Inter Tropical Convergence Zone Area where easterlies of both hemisphere meet one another Convergent Flux Intense convection Important migration over Africa African Easterly Wave Easterly synoptic scale perturbations Genesis : Eastern Africa Mesoscale Convective Systems Majors Precipitating systems Regulated by AEWs ITCZ migration Strong gradient of T° and humidity io n /

1. Introduction Objectives Evaluate the effects of increased horizontal resolution of GEM-LAM* in simulating precipitation over Sub-Saharan Africa. *GEM-LAM = Global Environmental Multiscale Limited Area Model

1.0° GEM-LAM grid ; Katja Winger (2009) Data 2. Data & Methodology 1.0° GEM-LAM grid ; Katja Winger (2009) GEM* (LAM*) Horizontal resolution : 2º, 1º, 0.33°, 0.15° - Convective scheme: KF* - Vertical resolution : 53 levels - Top : 10 hPa TRMM* (3B42) Resolution : 0.25º 3 hourly Satellite data *GEM = Global Environmental Multiscale *LAM = Limited Area Model *KF = Kain-Fritsch *TRMM = Tropical Rainfall Measuring Mission Timesteps for the different runs : 0.15° = 450 sec 0. 33° = 900 sec 1.0° = 2700 sec 2.0° = 3600 sec The TRMM data and GEM integrations, have been interpolated in a common 1° grid and averaged over 1 day for 1998-2003.

Seasonal Mean (JAS*) of precipitation (mm/day) for 1979-2003. Areas of interest 2. Data & Methodology Seasonal Mean (JAS*) of precipitation (mm/day) for 1979-2003. Topography of Africa. Zone I : Longitude 20°W – 40°E Latitude 5°N-15°N Zone II : Longitude 20°W – 8°W Latitude 5°N-15°N *JAS = July, August, September

Seasonal Mean (JAS*) 4 integrations are capable to detect the general patterns such as : The center with less precipitation Peaks of convection (Atlantic coast, Cameroon & Ethiopia) 3. Results a) TRMM b) GEM-LAM 2.0° c) GEM-LAM 1.0° d) GEM-LAM 0.33° e) GEM-LAM 0.15° Precipitation (mm/day) 1998 - 2003 Zone I mm/day Latitude Longitude *JAS = July, August, September

Precipitation (Number of Very High Wet Days) 1999 – Zone II Seasonal Mean (JAS*) 3. Results Zone II (5°N – 15°N / 20°W – 8°W) Atlantic coast Very high wet days = PR > 20 mm a) TRMM b) GEM-LAM 2.0° c) GEM-LAM 1.0° d) GEM-LAM 0.33° e) GEM-LAM 0.15° Precipitation (Number of Very High Wet Days) 1999 – Zone II Latitude Longitude Maximum overestimate = 50 days = 70 % compared to TRMM

Time-Latitude diagrams of precipitation (mm/day) 1998 – 2003 Zone I Migration of the ITCZ The bias is decreasing with the augment of resolution in term of localization In term of intensity, an important bias remains for all the integrations 3. Results b) GEM-LAM 2.0° c) GEM-LAM 1.0° e) GEM-LAM 0.15° d) GEM-LAM 0.33° a) TRMM Time-Latitude diagrams of precipitation (mm/day) 1998 – 2003 Zone I Months Latitude Underestimate Overestimate Months Months Localization Intensity The ITCZ can be studied in term of - localization - intensity of the precipitation Underestimate of GEM 2° Overestimate of GEM 1° & GEM ST The better simulation of the migration to North seems to be for the stretched integration of GEM. Overestimate Overestimate Months Months

Hovmöller analysis (Time-Longitude) 3. Results Hovmöller = Study of easterly and westerly propagating systems , African wave Disturbances (AWD) The bias is decreasing with the augment of resolution in term of localization and intensity Time-Longitude diagrams of precipitation (mm/day) 1999 - Zone I a) TRMM b) GEM-LAM 2.0° c) GEM-LAM 1.0° d) GEM-LAM 0.33° e) GEM-LAM 0.15° mm/day

Conclusion Benefits of increased resolution in : - Representation of precip over the center of Sub-Saharan Africa - Interannual Variability could be a result of African Wave Disturbance & migration of the ITCZ. Significant bias in the areas of high convection (Atlantic & Ethiopia) - Incorrect representation of intensity of precipitation in the ITCZ - the convective trigger function of the KF scheme. Future plans - Changing the threshold in the convective trigger function of the KF scheme.

Thank you anne-sophie.daloz@cnrm.meteo.fr Colin Jones Louis-Philippe Caron Katja Winger Marko Markovic anne-sophie.daloz@cnrm.meteo.fr

Fraction of precipitation ( MJJAS)

TRMM/GPCP 1998-2003 a) GPCP et b) TRMM. Moyennes saisonnières (JAS) de la précipitation (mm/jour) pour 1998-2003 pour  a) GPCP et b) TRMM.