Simulations with the MesoNH model from 27 August 2005 to 29 August 2005 (6UTC) performed by Meteo-France CNRM Nicole Asencio See powerpoint comments associated to each slide.

Rain Observations Area c Aug 28 12UTC Aug 28 18UTC Aug 29 00UTC Aug 29 06UTC Mcs Tracking derived from Meteosat IR Aug 27 12UTC See: Date Observation/satellite

m Numerical set-up 10km model Non-hydrostatic Mesonh model microphysic with ice convective scheme KAFR Simulations 27 August 28 August29 August Start and coupling= Arpege Ano27 Start and coupling= Arpege Ano28 Start and coupling= Arpege Tropiques Start and coupling= ECMWF Tno28 Eno28 Orography 6utc 0utc

24-hour rain validation 6h-6h 27 August Arpege start=27/08

24-hour rain validation 6h-6h 28 August Arpege Tropiques start=28/08Arpege start=28/08 Arpege start=27/08 ECMWF start=28/08

hourly rain validation: Niger sites 28/08 18:00 29/08 08:00 Arpege Tropiques start=28/08Arpege start=28/08 ECMWF start=28/08Arpege start=27/08

hourly rain validation: Benin sites 28/08 18:00 28/08 18:00 Arpege Tropiques start=28/08Arpege start=28/08 ECMWF start=28/08Arpege start=27/08

IWV time evolution ( compared to O. Bock plots) 27/08 00:00 30/08 00:00 Arpege start=27/08 Arpege start=28/08 Arpege Tropiques start=28/08 ECMWF start=28/08

2-meter Temperature time evolution ( compared to O. Bock plots) 27/08 00:00 30/08 00:00 Arpege start=27/08 Arpege start=28/08 Arpege Tropiques start=28/08 ECMWF start=28/08

Pressure (first model level) time evolution ( compared to O. Bock plots) 27/08 00:00 30/08 00:00 Arpege start=27/08 Arpege start=28/08 Arpege Tropiques start=28/08 ECMWF start=28/08

For these coarse resolution mesoscale runs using a convective parameterization, surface rainfall is a misleading parameter for the evaluation of the simulations scenarii. The model could represent MCS systems but with no associated rain at the ground. On an other side, rain could be generated by the convection parametrization and no MCS are present in the simulation (for example Sahel areas). The time evolutions at Niamey, Gao and Djougou do not allow to discriminate the simulations To evaluate the simulations scenarii, we choose to represent the time-evolution of The following model convective parameters (instantaneous outputs of the model every hour) vertical velocity 500m above ground level water content integrated on the column of the hydrometeors above the 0° Celsius level (i.e. for the cold Mesonh microphysic Ice + Graupel + Snow) The Brightness Temperature derived from model variables is a very expensive calculation and it gives a similar result compared to the hydrometeors content. The advantage is that it can be compared to observables, the Meteosat IR product.

Simulations scenario evaluation: lower levels Arpege Tropiques start=28/08 Arpege start=28/08 ECMWF start=28/08Arpege start=27/08 The Nigerian MCS are represented

Simulations scenario evaluation: upper levels ECMWF start=28/08Arpege start=27/08 Arpege start=28/08Arpege Tropiques start=28/08

Initial states: TEJ at 200hPa Arpege Tropiques Arpege ECMWF 28 August UTC m/s

Initial states: AEJ at 700hPa Arpege Tropiques Arpege ECMWF 28 August UTC m/s

Initial states: Integrated water Content Arpege Tropiques Arpege ECMWF 28 August UTC mm

Conclusions and Perspectives The simulation with Arpege-Tropiques analysis gives the best scenario (two MCS over Nigeria) but the systems propagate too slowly and do not cross over Benin at 06UTC on 29th August. We will perform a new simulation with the Mesonh two_way nesting method: - a 4km or 5km horizontal model nested within the 10km model - this high resolution model explicitly resolves the convection so we expect to better represent the propagation of the two systems over Nigeria. The ECMWF Mesonh simulation and the BOLAM simulations starting one day before give a similar scenario : a system over Niger rather than over Nigeria. Supplementary diagnosis will be performed to evaluate the main differences between the analysis.

Comments of the slides: Slide 2: top-left:The first MCS system (green) starts on 27 August over northern Centre Afrique country. Middle-left: a second system (light green) starts on 28 August near northern part of the Jos Plateau Bottom-left: the two previous systems merge together before crossing Benin country. Two other systems (blue and orange) start near Niamey. Top-right: the merged systems go on over the sea. The two new systems (blue and orange) grow. Middle right: only one system (blue) is active and crosses the Burkina Faso country. Slide3 : A wide domain has been chosen in order to represent the systems propagation and life cycle when the simulations start on 27 August and on 28 August.The simulations end at 6UTC to calculate 24 hour-accumulated rain from 6UTC to 6UTC for comparisons with CPC rainfall product. Slide4 : Too much precipitation over Sahel areas. If we consider only the blue to red colours : over the eastern part (Tchad, Centre Afrique ) and the western part of the domain, the accumulated rain is encouraging. Slide5: Some great differences with the representation of the systems in the simulations. 24-h accumulated rainfall is consistent with the evolution of the systems, that seem to propagate too slowly in the different simulations. Too much precipitation over Sahel areas. If we consider only the blue to red colours :only the ECMWF simulation gives a good amount of precipitation over the northern Benin (blue colour) but the accumulated rain over Nigeria is not well represented. Slide6: These evolutions should be compared with the figure 3a of « the water Cycle First case study. » report. Only the ECMWF and Arpege 27 simulations give some rain over Niger sites The comparisons are not good at this small loacl scale. Slide7: These evolutions should be compared with the figure 3b of « the water Cycle First case study. » report. Only Arpege Tropiques simulation gives some rain at the beginning of the period. The comparisons are not good at this small local scale : temporal evolution and amount.

Slide 8: Simulations are relatively close to the observations at Niamey and Djougou: values and evolution Some differences between the simulations, for Gao ECMWF simulation departs significantly from the other ones. Slide 9: Simulations are close to the observations at Niamey and Djougou: values and evolution Differences between the simulations could be related to different cloud covers in areas where it did not rain. Slide 10: Simulations are relatively close to the observations at Niamey and Djougou: evolution but values are different also because the ground of the model Is higher than the station level ( a few mb I.e. a few tens of meter) Some differences between the simulations. These time evolution diagnosis do not allow to clearly discriminate the simulations. Slide 12 : To evaluate the scenario of the two days, we represent the hourly evolution of the vertical velocity greater than 0.25m/s at 500 meters above ground level. Light Blue colour= hourly locations during the morning (1-11UTC) of the first day of the simulation Dark blue for the afternoon (13-24UTC) of the first day grey colour= morning (1-11UTC) of the second day, Black and grey= afternoon (13-24UTC) of the second day. Green colour= during the third day ( only Ano27 gets this colour). Midday = red colour. A zoom of the simulation domain ( hashed zone=orography at 600m) Arpege simulation starting on 27 August (bottom-right): the system propagates from Centre Afrique to Nigeria but slows down during the 29 August day (green colour) Arpege simulation starting on 28 August (top-right): The second system over the northern part of Joss plateau is not represented Arpege-Tropiques simulation starting on 28 August (top-left) : well represents two systems moving to Benin ECMWF simulation starting on 28 August (bottom-left) : the scenario is not good. A system near Niamey is represented and nothing over Nigeria.

Slide13: To evaluate the scenario of the two days, we represent the hourly evolution of the vertical integration of all the cold hydrometeors ( ice + snow + graupel) greater than 1.5 mm. A zoom of the simulation domain ( hashed zone=orography at 600m) The diagnosis with the brightness temperature lower than 200K give a similar result. Compare this diagnosis with the previous one at the lower levels: two more systems are represented near Tchad Lake and over Soudan country whose signature does not appear on the 500m vertical velocity field. Apege and Arpege Tropiques simulations seem to represent a good scenario but the systems are too late and do not cross over Benin at 06UTC 29 August. Slide 14: A weak difference between TEJ ECMWF analysis and from Arpege ones. Slide 15: The AEJ is stronger on the eastern part of the domain for Arpege Analyses compared to ECMWF analyse. Slide 16: A great difference with less humidity in the ECMWF over northern Nigeria, southern Niger and Centre Africa country where the MCS is located at this time. The differences between the Arpege analysis are not significant. The different scenarii between Arpege Tropiques and Arpege simulations seem to be explained more by the differences in the dynamics rather than by the differences in the humidity fields.