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Quick reminder : what is AMMA ?

Precipitation Validation Network in West Africa set up for AMMA Perspectives for Megha-Tropiques and GPM Michel Desbois et al. (LMD), Thierry Lebel et al. (IRD/LTHE) Abdou Ali et Abou Amani (AGRHYMET). Quick reminder : what is AMMA ?. What is available as pluviometric data over Sahel ?.

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Quick reminder : what is AMMA ?

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  1. Precipitation Validation Network in West Africa set up for AMMA Perspectives for Megha-Tropiques and GPMMichel Desbois et al. (LMD), Thierry Lebel et al. (IRD/LTHE)Abdou Ali et Abou Amani (AGRHYMET) Michel Desbois, Taipei, GPM GV meeting

  2. Quick reminder : what is AMMA ? Michel Desbois, Taipei, GPM GV meeting

  3. What is available as pluviometric data over Sahel ? Cilss network : 650 stations available several weeks after the rainy season CRA network : average of 280 stations available every 10 days SYN : average of 85 stations available each day Michel Desbois, Taipei, GPM GV meeting

  4. Summary on the kriging method used to create the areal rainfall for validation of satellite rainfall estimates Regression kriging method is used to estimate the mean areal rainfall for the three grids (0.5°x0.5°, 1°x1° and 2.5°x2.5°) from AGRHYMET rainfall data base (around 650 gauges on average) 2.      A drift model with quadratic component for the latitude and linear one for the longitude is used: the values of the coefficients a, b, c and d depend on the period (on the 10-day under consideration). There are estimated using the generalized least squares (GLS) in order to account for the spatial correlation of residuals. 3.      Also in order to account for the non-homogeneity of the drift coefficients in the Sahelian region, the studied area is divided in five regions. The central region between longitude 13°W and 10°E and latitude 12°N and 15°N. The different sides of this central region are considered separately. 4.      A nested variogram using two anisotropic exponential functions with an anisotropy coefficient of for the first structure (decorrelation distance = 0.2°) and 2/3 for the second structure nested (decorrelation distance = 3) is used. 5.      For details on the kriging method and raingauge data description used to compute the validation areal rainfall, see Ali et al., J. Appl. Meteo, 2005 (accepted). Michel Desbois, Taipei, GPM GV meeting

  5. Regional « supersites » are available for higher resolution studies Michel Desbois, Taipei, GPM GV meeting

  6. Supersites of Niamey and Djougou Michel Desbois, Taipei, GPM GV meeting

  7. Raingauge network – Mesoscale sitesAvailable data sets for 2004 • Niamey square degree • 33 recording rain gauges • Raw data 5 min, ~ from May to September (depends on the station) • Validated data: • 10-day periods - station and grid (krigging 5 km x5 km) • rainfall events (i.e. >30% rainy stations) - station and grid (krigging 5 km x5 km) North Benin 35 recording rain gauges Raw data 5 min, all over the year (with some missing data) Validated data: daily rainfall (stations) Gridded estimates are not available (yet) by lack of climatological knowledge Michel Desbois, Taipei, GPM GV meeting

  8. Example of large scale validation of a particular algorithm : SRA SRA means Sliding Rescaling Algorithm (Franck Chopin and Jean-Claude Bergès) It is based on the estimation of rainfall probability on MSG images (15minutes intervals, 3 km pixels), calibrated on coincidences with TRMM radar. A second step is to establish maps of « precipitation efficiencies » based on comparisons of monthly rainfall accumulation with rainfall probabilities Then, precipitation estimates can be provided at all time scales below one month (but errors need to be estimated) Michel Desbois, Taipei, GPM GV meeting

  9. Data and Experimentation area Input dataset:  Full flow of MSG/HRI  TRMM/PR from 3G68Land  GPCP 1° daily rainfall Validation dataset :  Dense raingauges network (IRD & AGRHYMET supplied) Experimentation Area :  A window on W-Africa from June to Sep. 2004 (25W to 25E and 5S to 20N) This is the AMMA West Africa Region Michel Desbois, Taipei, GPM GV meeting

  10. Example of Rainfall Probability Image Michel Desbois, Taipei, GPM GV meeting

  11. Collocation between Pr image and 2A25 TRMM data Michel Desbois, Taipei, GPM GV meeting

  12. Potential rainfall intensity 15th August 2004 Examples of Potential Intensity Image Mm/h Mm/h Michel Desbois, Taipei, GPM GV meeting

  13. Example of rainfall estimation image mm Michel Desbois, Taipei, GPM GV meeting

  14. mm Results for 3rd decade of August 2004 Krigged data set Number of stations SRA on area and space resolution of krigged data set SRA result Michel Desbois, Taipei, GPM GV meeting

  15. Third decade of August, 2004 GPCP 1DD raingauges Duration of rain (hours) SRA raingauges Michel Desbois, Taipei, GPM GV meeting

  16. Third decade of August 2004 Number of raingauges Absolute value difference between raingauges and SRA Michel Desbois, Taipei, GPM GV meeting

  17. Results for all the decades of 2004 are better for most of the indicators for SRA than for GPCP. But better validation fields are needed at smaller scales. Michel Desbois, Taipei, GPM GV meeting

  18. Present work for Amma is concentrated on giving results at smaller scales, for needs of soil moisture modelling and hydrology. Further validation will use the supersites of AMMA, which were already operated in 2004. Year 2005 will also be processed, as well as 2006 (the special observing period of AMMA, and 2007). After 2007, it is foreseen to maintain these supersites, in particular for the needs of Megha-Tropiques and GPM ground validation. It seems very difficult in Africa to establish and maintain validation sites in the definition of GPM, in particular with well calibrated rainfall radars. However, considering the crucial and specific problems of rainfall estimation in these regions of the world, the Megha-Tropiques science team is considering AMMA-type supersites as necessary for ground validation over these regions. (does GPM support this statement ?) Michel Desbois, Taipei, GPM GV meeting

  19. Perspectives of Megha-Tropiques (launch 2008-2009) nominal life time 3 years Michel Desbois, Taipei, GPM GV meeting

  20. ScaRaB : a wide band radiometer for radiative fluxes measurement (transversal scan, 40 km) • Saphir : a microwave water vapour sounder. 6 channels around 183.31 GHz. (transversal scan, 10 km) • Madras : a microwave imager • 5 channels 18, 23, 37, 89 and 157 GHz • (conical scan, <10 km to 40 km) • Marfeq is the radiofrequency part of this instrument Michel Desbois, Taipei, GPM GV meeting

  21. Michel Desbois, Taipei, GPM GV meeting

  22. 30 N 15 N 15 S 30 S Michel Desbois, Taipei, GPM GV meeting

  23. 2005 : new start of the scientific studies • 2004 : French mission team constituted : Michel Desbois (P.I.); Laurence Eymard (SAPHIR); Rémy Roca (mission); Nicolas Viltard (MADRAS); Michel Viollier (ScaRaB); Sophie Cloché (data bases) • January 2005 : 1st meeting of a preliminary French « science team » • April 2005 : Indo-French meeting of the mission teams in Bangalore (Indian team chaired by R. Narasimha, PI’s J. Srinivasan, M.S. Narayanan, participants P.C. Joshi, V.K. Agarwal, Kusuma Rao, members of SAC Ahmedabad, of ISRO HQ) • October 2005 : enlarged Indo-French meeting in Ahmedabad aimed to start common projects around missions Megha-Tropiques and Oceansat III (French altimeter Altika) Michel Desbois, Taipei, GPM GV meeting

  24. Preliminary list of actions • Actions devoted to algorithm developments • Satellite data bases for testing algorithms and processing procedures of the Megha-Tropiques instrumental package. • Microwave rain algorithm developments : adaptation and evaluation of TRMM-based algorithms; specific effort on the ice phase. • Combined geostationary - microwave algorithms. • Radiative fluxes retrievals at different space-time scales. • -Humidity retrievals in the perspective of SAPHIR. Michel Desbois, Taipei, GPM GV meeting

  25. Actions devoted to validation of satellite products • Precipitation retrieval validation (raingauges and radars) : sampling and scaling effects. • Validation for other quantities (ice microphysics, others…) • Intercomparisons of methods for water vapour determination (IR and MW sounders, GPS, … ) • General use of the AMMA campaigns and data bases for satellite validation studies • - Promoting specific campaigns for water vapour, clouds and radiative budget . Michel Desbois, Taipei, GPM GV meeting

  26. Actions devoted to MT sampling effects • Use of geostationary observations to simulate the MT sampling of convective systems and their life cycle. To be performed over Africa, India and Brazil. • Development of a simulator for MT from analyses / satellite observations to analyze the impact of MT orbit on the various fields retrieved (radiative budget, water vapour …) Michel Desbois, Taipei, GPM GV meeting

  27. Actions devoted to MT data scientific exploitation • Assimilation of microwave data including MT in forecast models. • Impact of dry subsidence areas in the subtropics on the global climate . • Upper tropospheric drying influences on monsoon cloud systems and hence on monsoon variability. • Construction of cloud climatology over the Indian ocean area. • Structure of mesoscale convective complexes/systems over Indian Monsoon Region. • Monsoon systems in India and Africa • Use of microwave emissivity in complement of VIS-IR data for land surface properties. • Cloud resolving models for Indian region using Microwave and radar data. Michel Desbois, Taipei, GPM GV meeting

  28. Conclusion • Numerous research subjects related to the satellite mission, but also to general tropical climate issues • Presently, not enough scientists between France and India to perform all this research • Mission teams in France and India look for a widening of the science community working on Megha-Tropiques related themes • Concerning ground validation, same tropical sites should be used for GPM and MEGHA-TROPIQUES Michel Desbois, Taipei, GPM GV meeting

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