Investigation of the atmospheric circulation anomalies associated with extreme rainfall events over the Coastal West Africa


1 Assistant Lecturer, College of Atmospheric Sciences, Nanjing University of Information Science and Technology, Nanjing, Jiangsu, China

2 Assistant Lecturer, Uganda National Meteorological Authority, Kampala, Uganda

3 Assistant Lecturer, Department of Meteorology and Hydrology, Myanmar

4 Assistant Lecturer, Department of Meteorology, South Eastern Kenya University, Kitui, Kenya


This study investigates the atmospheric circulation associated with extreme rainfall events over the coastal West Africa. The rainfall data of this study were obtained from the Global Precipitation Climatology Centre (GPCC), spanning from 1981 to 2010. The atmospheric datasets were also obtained from the ERA-Interim reanalysis. The study employed the Z-Index to categorize dry and wet years into seven distinct grades. The analyses focused on the summer monsoon rainfall season experienced in July to September (JAS). The extreme drought years were identified to be 1982 and 1983, while extreme wet years were pointed out to be 1999 and 2007. The area of study was dominated by anomalous westerly moisture transport, characterized by convergence at low level during wet years. The major source of moisture over the study area is Atlantic Ocean. Dry and wet years are characterized by positive and negative low-level geopotential height anomalies, respectively. Although the results of this study do not give a diagnosis of the reported rainfall variability, the information herein can be useful in the monitoring and update of seasonal forecasts. Accurate and reliable seasonal forecasting is beneficial in that it helps us minimize loss of lives and destruction of property.


Main Subjects

Barreiro, M., Giannini, A., Chang, P. and Saravanan, R., 2004, On the role of the South Atlantic atmospheric circulation in tropical Atlantic variability, in: Wang, C., Xie, S. P. and J. A. Carton (Eds.), Earth's Climate, American Geophysical Union, Washington, D. C. doi: 10.1029/147GM08. Bordi, I., Frigio, S., Parenti, P., Speranza, A. and Sutera, A., 2001, The analysis of the standardized precipitation index in the Mediterranean area, Regional patterns, Annali Di Geofisica, 44, 979-993. DOI: 10.4401/ag-3550.
Camberlin, P., Janicot, S. and Poccard, I., 2001, Seasonality and atmospheric dynamics of the teleconnection between African rainfall and tropical sea-surface temperature, Atlantic vs. ENSO, Int. J. Climatol., 21, 973-1005.doi: 10.1002/joc.673.
Cook, K., 2008, The mysteries of Sahel droughts, Nature Geosci., 1, 647-648.
Dai, A., Trenberth, K. E. and Qian, T., 2004, A global dataset of Palmer drought severity index for 1870-2002, Relationship with soil moisture and effects of surface warming, J. Hydrometeorol., 5, 1117-1130, doi:
Dee, D. P., Uppala, S. M., Simmons, A. J., Berrisford, P., Poli, P., Kobayashi, S., Andrae, U., Balmaseda, M. A., Balsamo, G., Bauer, P., Bechtold, P., Beljaars, A. C. M., van de Berg, L., Bidlot, J., Bormann, N., Delsol, C., Dragani, R., Fuentes, M., Geer, A. J., Haimberger, L., Healy, S. B., Hersbach, H, Hólm, E.V., Isaksen, L., Kållberg, P., Köhler, M., Matricardi, M., McNally, A. P., Monge-Sanz, B. M., Morcrett, J. J., Park, B. K., Peubey, C., de Rosnay, P., Tavolato, C., Thépaut, J. N. and Vitart, F., 2011, The ERA-interimreanalysis, Configuration and performance of the data assimilation system, Q. J. R, Meteorol. Soc., 137, 553-597, doi:10.1002/qj.828.
Folland, C. K., 1983, Regional-scale interannual variability of climate, a north-west European perspective, Meteorol. Mag., 112, 163-183.
Gadgil, S. and Rao, P. R. S., 2000, Farming strategies for a variable climate-a challenge, Curr. Sci., 78, 1203- 1215.
Hamilton, R. and Archbold, J., 1945, Meteorology of Nigeria and adjacent territory, Q. J. R. Meteorol. Soc., 71, 231-264, doi: 10.1002/qj.49707130905.
Hirst, A. and Hastenrath, S., 1983, Atmosphere-ocean mechanisms of climate anomalies in the Angola-tropical Atlantic Sector, J. Phys. Oceanogr., 13, 1146-1157, doi:<1146:AOMOCA>2.0.CO;2.
Ininda, J. M., 1995, Numerical simulation of the influence of sea surface temperature anomalies on the East African seasonal rainfall, Ph.D. Thesis, University of Nairobi, Kenya.
Janowiak, J. E., 1988, An investigation of 
interannual rainfall variability in Africa, J. Climate, 1, 240-255, doi:<0240:AIOIRV>2.0.CO;2.
Kalnay, E., Kanamitsu, M., Kistler, R., Collins, W., Deaven, D., Gandin, L., Iredell, M., Saha, S., White, G., Woollen, J., Zhu, Y., Leetmaa, A., Reynolds, B., Chelliah, M., Ebisuzaki, W., Higgins, W., Janowiak, J., Mo, K. C., Ropelewski, C., Wang, J., Jenne, R. and Joseph, D., 1996, The NCEP/NCAR 40-Year Reanalysis Project, Bull. Amer. Meteor. Soc., 77, 437-470, doi:<0437:TNYRP>2.0.CO;2.
Keenlyside, N. S. and Latif, M., 2007, Understanding equatorial Atlantic interannual variability, J. Climate, 20, 131-142, doi:
Koumare, I., 2014, Temporal/spatial distribution of rainfall and the associated circulation anomalies over West Africa, Pakistan, J. Meteorol., 10, 1-11.
Le Barbe, L., Lebel, T. and Tapsoba, D., 2002, Rainfall variability in West Africa during the years 1950-90, J. Climate, 15, 187-202, doi:<0187:RVIWAD>2.0.CO;2
Leonard, M. and Matthew, F., 2014, The impact of the Atlantic cold tongue on West African monsoon onset in regional model simulations for 1998-2002, Int. J. Climatol., 35, 275-287. doi: 10.1002/joc.3980.
McKee, T. B, Doesken, N. J. and Kleist, J., 1993, The relationship of drought frequency and duration to time scales, 8th Conference on Applied Climatology, 17th-22nd January 1993, Anaheim, California.
McSweeney, C., New, M., Lizcano, G. and Lu, X., 2010, The UNDP climate change country profiles improving the accessibility of observed and projected climate information for studies of climate change in developing countries, Bull. Amer. Meteorol. Soc., 91, 157-166, doi:
Nicholson, S. E. and Grist, J. P., 2001, A conceptual model for understanding rainfall variability in the West African Sahel on interannualand interdecadaltimescales, Int. J. Climatol., 21, 1733-1757, doi: 10.1002/joc.648.
Nicholson, E. and Websterb, J., 2007, A physical basis for the interannual variability of rainfall in the Sahel, Q. J. R. Meteorol. Soc., doi: 10.1002/qj.104.
Nicholson, S., 2008,The intensity, location and structure of the tropical rain belt over West Africa as factors in interannual variability, Int. J. Climatol., 28, 1775-1785.DOI: 10.1002/joc.1507. Nicholson, S., 2009, A revised picture of the structure of the “monsoon” and land ITCZ over West Africa,Clim. Dyn., 32, 1155-1171, doi:10.1007/s00382-008-0514-3.
Nnamchi, H. C. and Li, J., 2010, Influence of the South Atlantic Ocean dipole on West African summer precipitation, J. Climate, 24, 1184-1197, doi:
Ogwang, B. A., Guirong, T. and Haishan, C., 2012, Diagnosis of September - November drought and the associated circulation anomalies over Uganda, Pakistan J. Meteorol., 9, 11-24. Okoola, R. E., 1999, A diagnostic study of the East African monsoon circulation during the northern hemisphere spring season, Int. J. Climatol., 19, 143-169, doi: 10.1002/(SICI)1097-0088(199902)19:2<143::AID-JOC342>3.0.CO;2-U.
Polo, I., Rodriguez‐Fonseca, B., Losada, T. and Garcia‐Serrano, J., 2008, Tropical Atlantic variability modes (1979-2002). Part I: Time‐evolving SST modes related to West African rainfall, J. Climate, 21, 6457-6475, doi:10.1175/2008JCI2607.1.
Rodriguez-Fonseca, B., Janicot, S., Mohino, E., Losada, T., Bader, J., Caminade, C., Chauvin, F., Fontaine, B., Garcia-Serrano, J., Gervois, S., Joly, M., Polo, I., Ruti, P., Roucou, P. and Voldoire, A., 2010, Interannual and decadal SST-forced responses of the West African monsoon, Atmos. Sci. Lett.,12, 67-74, doi: 10.1002/asl.308.
Rouault, M., Servain, J., Reason, C., Bourlès, B. and Fauchereau, N., 2009, 
Extension of PIRATA in the tropical south‐east Atlantic, an initial one‐year experiment, Afri. J. Mar. Sci., 31, 63-71, doi: 10.2989/AJMS.2009.
Rufus, E., Yixuan, S. and Shaowen, S., 2013, Tropospheric circulation features during wet and dry years over West Africa, J. Meteorol. Rel. Sci., 4, 3-15.
Sultan, B. and Janicot, S., 2003, The West African monsoon dynamics, Part II: the “Preonset” and “Onset” of the summer monsoon, J. Climate, 16, 3407-3427, doi:<3407:TWAMDP>2.0.CO;2.
Tan, G., Zhaobo, S. and Chen, H., 2003, Diagnosis of summer time floods/droughts and their atmospheric circulation anomalies over north China, ACTA Meteorol. Sinica, 17, 257-273. Walsh, J. and Mostek, A., 1980, A quantitative analysis of meteorological anomaly patterns over the United States, 1900-1977, Mon. Weather Rev., 108, 615-630, doi:<0615:AQAOMA>2.0.CO;2.
Ward, M. N., 1998, Diagnosis and short-lead time prediction of summer rainfall in tropical North Africa at interannual and multi-decadal time scales, J. Climate, 11, 3167-3191, doi:<3167:DASLTP>2.0.CO;2. Xie, S.-P. and Carton, J. A., 2004, Tropical Atlantic variability, patterns, mechanisms, and impacts, in: Wang, C., Xie, S. P. and Carton, J. A. (Eds), Earth's Climate, American Geophysical Union, Washington, D.C., doi: 10.1029/147GM07.