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T ropical A pplications of M eteorology using SAT ellite data

Analysing Climate Trends in African Rainfall using Satellite Data. Ross Maidment r.i.maidment@pgr.reading.ac.uk TAMSAT Research Group, University of Reading Supervisors: Dr David Grimes and Dr Richard Allan. T ropical A pplications of M eteorology using SAT ellite data. Overview.

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T ropical A pplications of M eteorology using SAT ellite data

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  1. Analysing Climate Trends in African Rainfall using Satellite Data Ross Maidment r.i.maidment@pgr.reading.ac.uk TAMSAT Research Group, University of Reading Supervisors: Dr David Grimes and Dr Richard Allan Tropical Applications of Meteorology using SATellite data

  2. Overview Introduction Aims of my research The TAMSAT methodology to estimate rainfall Validation of rainfall estimates in Uganda Meteosat satellite data 6. Initial results – Ethiopia 7. Future work and Conclusions Tropical Applications of Meteorology using SATellite data

  3. 1. Introduction • Most of the African continent is economically dependent on rain fed agriculture, therefore changes in expected rainfall patterns can have serious consequences, both economically and from a humanitarian point of view • However, future predictions must be based on a secure knowledge of the present rainfall climate • The current African rainfall climatology is poorly understood, mainly due to inadequate ground based observations GPCC: Gauge locations – 2007, March - May Tropical Applications of Meteorology using SATellite data

  4. Introduction Cont... Satellite based rainfall data sets exist but many, such as the TRMM based algorithms only cover short time periods Those covering longer time periods, such as the widely used GPCP product tend to be a blend of different satellite sensors and gauge data, the proportions of which vary from year to year This makes these data sets unsuitable for climate studies as it is impossible to extract meaningful trends and statistics when biases vary interanually Tropical Applications of Meteorology using SATellite data

  5. Overview Introduction Aims of my research The TAMSAT methodology to estimate rainfall Validation of rainfall estimates in Uganda Meteosat satellite data 6. Initial results – Ethiopia 7. Future work and Conclusions Tropical Applications of Meteorology using SATellite data

  6. 2. Aims of my research • 1. To create TARCAT (TAMSAT African Rainfall Climatology And Time-series), a temporally homogeneous 30 year rainfall time-series and climatology for all of sub-Saharan Africa using the TAMSAT approach to rainfall estimation • 2. Analyse this data set to better understand temporal trends and statistics that describe the rainfall climate • 3. Evaluate model data to increase confidence in future predictions Tropical Applications of Meteorology using SATellite data

  7. Overview Introduction Aims of my research The TAMSAT methodology to estimate rainfall Validation of rainfall estimates in Uganda Meteosat satellite data 6. Initial results – Ethiopia 7. Future work and Conclusions Tropical Applications of Meteorology using SATellite data

  8. 3. TAMSAT Methodology • The TAMSAT approach to rainfall estimation is based entirely on Meteosat Thermal Infra-Red imagery to identify precipitating cumulonimbus clouds (deep convection) Tropical Applications of Meteorology using SATellite data

  9. Using Meteosat TIR imagery, identify optimum cloud top • temperature threshold Tt distinguishing between rain and no rain TAMSAT Methodology Cont... • Calculate Cold Cloud Duration (CCD) for each pixel (length of time • cloud top is colder than Tt ) • Estimate rainfall total as rain = a0 + a1 CCD • a0, a1, Tt are calibrated using local gauges from historic data • Calibration parameters vary in space and time (i.e. local calibration) • Resolution: Temporal – 10 days (1 dekad), Spatial – 0.05° (sat. pixel) Tropical Applications of Meteorology using SATellite data

  10. TAMSAT Operational Product Tropical Applications of Meteorology using SATellite data

  11. Overview Introduction Aims of my research The TAMSAT methodology to estimate rainfall Validation of rainfall estimates in Uganda Meteosat satellite data 6. Initial results – Ethiopia 7. Future work and Conclusions Tropical Applications of Meteorology using SATellite data

  12. 4. Rainfall Validation in Uganda Validating rainfall products against spatially interpolated gauge data (res: 0.5° x 0.5°) Period of study: 2001 to 2005 for first rainy season (Feb – June) Figure: spatially averaged dekadal rainfall ERA-40 ERA-Interim TAMSAT RFE 2.0 GPCP Tropical Applications of Meteorology using SATellite data

  13. Rainfall Validation in Uganda Cont... Temporal variability using 2003 and 2004 data Tropical Applications of Meteorology using SATellite data

  14. Overview Introduction Aims of my research The TAMSAT methodology to estimate rainfall Validation of rainfall estimates in Uganda Meteosat satellite data 6. Initial results – Ethiopia 7. Future work and Conclusions Tropical Applications of Meteorology using SATellite data

  15. 5. Meteosat TIR data • Meteosat archive spans 30 years, 1980 to present, giving complete African coverage every 30 minutes (First Generation) and every 15 minutes post June 2006 (Second Generation) • Problems with the TIR archive: • 1. Archive isn’t complete, with some gaps from one slot • up to several days (these gaps will be interpolated) Tropical Applications of Meteorology using SATellite data

  16. Meteosat TIR data - Problems OK < 6 hours < 36 hours > 36 hours Tropical Applications of Meteorology using SATellite data

  17. Meteosat TIR data - Problems 2. Change in satellite sensor introducing artificial temporal discontinuities in time-series - Timeline of warmest/brightest pixel over a ‘cloud free’ region of the Equatorial Atlantic to detect sudden changes: Tropical Applications of Meteorology using SATellite data

  18. Meteosat TIR data - Problems Satellite (Meteosat 2 – 9) Daily warmest pixel – warm ocean scene Tropical Applications of Meteorology using SATellite data

  19. Meteosat TIR data - Problems Satellite (Meteosat 2 – 9) Daily warmest pixel – warm ocean scene MET-7 MET-8/9 MET-6 MET-7 Tropical Applications of Meteorology using SATellite data

  20. Meteosat TIR data - Problems Other problems: 3. Changes in data format from MFG (OpenMTP) to MSG (Native) 4. Corrupt images (missing pixels, lines and whole images) 5. Failure in reading the header of some OpenMTP files 6. Change in radiance definition from ‘spectral’ to ‘effective’ radiance in May 2008 7. Using data obtained from the EUMETSAT archive that is from the non-prime satellite Tropical Applications of Meteorology using SATellite data

  21. Overview Introduction Aims of my research The TAMSAT methodology to estimate rainfall Validation of rainfall estimates in Uganda Meteosat satellite data 6. Initial results – Ethiopia 7. Future work and Conclusions Tropical Applications of Meteorology using SATellite data

  22. 6. Initial results - Ethiopia Why Ethiopia? - TAMSAT involved in joint project (with IRI, Columbia University and NMA, Ethiopia) based on Ethiopia and funded by Google (Dinku et al 2011) - Complex and interesting rainfall climate Have compared (so far): TAMSAT GPCP ERA-Interim Tropical Applications of Meteorology using SATellite data

  23. Initial Results – Ethiopia Cont... Tropical Applications of Meteorology using SATellite data

  24. Initial Results – Ethiopia Cont... Mean dekadal rainfall Tropical Applications of Meteorology using SATellite data

  25. Initial Results – Ethiopia Cont... Period: 1989 – 2009 Tropical Applications of Meteorology using SATellite data

  26. Initial Results – Ethiopia Cont... 6 Month & Annual Running Mean – Mean Monthly Rainfall Tropical Applications of Meteorology using SATellite data

  27. Initial Results – Ethiopia Cont... TARCAT – Trend during 1983-2009 period Tropical Applications of Meteorology using SATellite data

  28. Overview Introduction Aims of my research The TAMSAT methodology to estimate rainfall Validation of rainfall estimates in Uganda Meteosat satellite data 6. Initial results – Ethiopia 7. Future work and Conclusions Tropical Applications of Meteorology using SATellite data

  29. 7. Future work and Conclusions • Complete TARCAT and extend study to all of Africa • Main interests: • trends over the last 30 years • changes in length and start of wet season • changes in wet/dry regimes • changes in frequency of extreme events • Evaluate model data • The TAMSAT methodology and the Meteosat archive provides the opportunity to create a unique and consistent data set that can enhance our current understanding of the African rainfall climate and hopefully increase our confidence in future predictions Tropical Applications of Meteorology using SATellite data

  30. Thank you for your time Photo courtesy NASA Earth Observatory Tropical Applications of Meteorology using SATellite data

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