Predictability using TIGGE database of a high impact weather event in the night of the Kenya airways crash in Douala Cameroon By David MONKAM, André LENOUO, Department of Physics, Faculty of Science, University of Douala, P.O. Box Douala, Cameroon André F. KAMGA ACMAD, Niamey, Niger and F. MKANKAM KAMGA. Department of Physics, Faculty of Science, University of Yaoundé, P.O. Box 812 Yaoundé, Cameroon

Outline Introduction Data Synoptic analysis of weather event - Convection indices - Mean fields - Simulation Conclusion

1. Introduction Figure 1: Topographic map of North Africa. Shading shows areas of elevation greater than 300 m above mean sea level. Highlands are designated by letters: A: Atlas highlands, E: Ethiopian highlands, C: Cameroon highlands, D: Darfur mountains, G: Guinea highlands, J: Jos Plateau, H: Hoggar highlands and V: Victoria highlands On the 5th of May 2007 at 00 h 05 local time, a Kenya Airways Boeing B crashed a few minutes after take off from the Douala (4.0° N, 9.7°E) international airport in Cameroon leading to the loss of more than one hundred lives. Cameroon is located between the latitudes 2°N and 13°N in central Africa (Fig.1)

The local climate in Douala is warm and wet, with strong instabilities favourable to the generation of thunderstorms and thunderbolts. Douala experiences African monsoon flow from early May to the end of September. Its geographical position close to the Cameroon highlands and the equatorial Atlantic Ocean (Gulf of Guinea) create interactions that shape the local climate including the monsoon. In this region, bad weather conditions are influenced by the West African monsoon system. (Sultan and Janicot, 2000 and Janicot and Sultan, 2001) Mindful of theses findings and of the geography of this area, we will : analyse the meteorological conditions prevailing in the night of the crash. examine the synoptic situation and the mean fields of meteorological parameters in connection with thunderstorms and thunderbolts formation from TIGGE database. also investigate the predictability of general circulation features related to the event using the ETA model (Black T., 1994).

2. Data Data used in this work are from the Interactive Grand Global Ensemble (TIGGE) of the Observing-system Research and Predictability EXperiment (THORPEX), available through the European Centre for Medium-Range Weather Forecasts (ECMWF) portal (http//tigge-portail.ecmwf.int/). Reanalyses wind and geopotential height data from the National Center for Environmental Prediction-National and the Center for Atmospheric Research (NCEP/NCAR) (Kalnay et al. 1996), Mean sea level surface pressure (MSLSP), geopotential height and total precipitation data from the European Center for Medium Range Weather Forecast (ECMWF) were obtained as daily mean interpolated onto 2.5°x2.5° grid maps for 4 th and 5 th May The twice-daily precipitation data of the Tropical Rainfall Measuring Mission (TRMM) were also obtained for the same period and spatial resolution. We also used upper-air soundings from the Douala radiosonde station. A postiori numerical weather prediction was carried out using the Eta model. Model run used the Kain-Fritsch (KF, 1993) convection scheme and NCEP Global Forecasting System (GFS) data at a spatial resolution of 32 km for initial and boundary conditions, starting on 04 May 2007, 0000 UTC.

Figure 2: Radiosondes of Douala international airport on the 4 th of May 2007 at 12 UTC and the 5 th of May 2007 at 00 UTC. The state curve of temperature is in black and the pseudo-adiabatic curve is in red line-point. 3.1 Convections indexes On 4 th May at 1200 UTC the value of CAPE was 3786 J/kg, higher than 3500 J/kg, which corresponds to the threshold for the development of thunderstorms. This is also confirmed by the showalter index (0 and 1 less than 2). Values of these indices associated to the instability between ground and 700 hPa as shown by the wind profile of figure 2, supported meteorological conditions favourable for storm development. 3. Synoptic analysis of weather event

3.2 Mean fields - In Fig.3a, at 1000 hPa, there is an area of high pressure associated with anticyclonic circulation over the south of Cameroon. This is favourable to the monsoon flow from the Atlantic Ocean. - At 300 hPa (Fig.3b) between 10°W and 20°E longitude, a well known feature called omega (Ω) configuration, which is a succession in the SW-NE direction of trough-anticyclone-trough is clearly visible. These features, which supported bad weather conditions over the region, are completely disorganized a few hours later (Figs. 3c,d) - In Fig.3c, at 1000 hPa, we still have the area of high pressure associated with anticyclonic circulation over the south of Cameroon, favourable to the monsoon flow from the Atlantic Ocean. -In Fig.3d, there is a low pressure at the Cameroon coast. We shall use this latter Figure 3: Wind and geopotential height at 1000 hPa and 300 hPa on the 4 th of May 2007 at 18 UTC (a and b) and on the 5 th of May 2007 at 00 UTC (c and d) from NCEP/NCAR. The structure in « » at 300 hPa has disappeared between 18 and 00 UTC.

3.3 Simulation -There is a zone of high pressure at the surface in the Guinea Gulf region on the ECMWF forecasts of SSP fields (Fig.4a) and Eta model simulation (Fig.4b). ==>This is favourable for monsoon influx. -There is good agreement between Eta model and ECMWF forecasts of SSP fields, but geopotential height structures are different. - The presence of low pressure at 300 hPa at the Cameroon coast (Fig.3d) and high pressure at the surface (Fig.4b) is favourable to the development of storm in this region. Figure 4: ECMWF and Eta model simulation of geopotential height at 300 hPa (continuous line) and sea surface pressure (discontinuous line) on the 5 th of May UTC.

-The spatial distribution of total precipitation exhibits a large disturbance zone over the Guinea Gulf. -There is also a good correlation between ECMWF, Eta model and TRMM precipitation. -The three models supported development of deep convection during the night of 4 may ETA model delimits the zone of precipitation correctly. Figure 5: Precipitations from ECMWF (a), sum on 3 hours, UTC on the 4 th of May 2007 of the precipitations simulated by ETA model (b) and precipitations from TRMM (c).

4. Conclusion Using convection indices and mean fields of several meteorological parameters, we have analysed the weather conditions related to the crash. Bad weather conditions characterized by a strong synoptic scale convective system prevailed during the night of the crash. Sounding data, ECMWF products on the TIGGE database, outputs of the ETA model and TRMM rainfall provided a basis for this study. A forecast up to one day in advance of the event was made. However, for better decision making in such a case, the forecast of the severity of this event is necessary. More research is needed to assess TIGGE products performance for such events.

Acknowledgement We thank WMO for the financial support to attend this symposium. Thank you very much for your attention!!!!!!!!!!!!!