West African convection regimes and their predictability from submonthly forecasts

  • N. VigaudEmail author
  • A. Giannini


Recurrent convection regimes are identified during the extended West African Monsoon (WAM) season (May–Nov) using a \(k-means\) clustering of 1980–2013 NOAA daily Outgoing Longwave Radiation (OLR), and are well reproduced in 1996–2015 ECMWF week-1 reforecasts despite systematic biases. One regime of broad drying across the Sahel in the early (May–Jun) and late (Oct) WAM is of particular interest regarding the prediction of onset date. This regime is associated with an anticyclonic cell along the Atlantic coast of West Africa leading to a weakened monsoon flow and subsiding anomalies across the Sahel. Teleconnections of this regime with the Indian monsoon sector are identified through modulations of the Walker circulation alongside relationships to MJO phase 3 more than 10 days in advance, when convection is enhanced over the Indian Ocean. Other regimes are associated with westward propagating anomalous convective cells along two distinct wave trains at \(15^\circ \hbox {N}\) and \(24^\circ \hbox {N}\) during the core (Jul–Sep) and late (Oct–Nov) WAM, respectively, and translate into wet anomalies transiting across the Sahel. A regime of broad Sahel wetting in the core WAM, more frequent since the 1990s, is related to global SST warming, agreeing with the observed recovery of Sahel rainfall. ECMWF skill in forecasting regime sequences decreases from week-1 to -4 leads, except in the case of the above-mentioned regime associated with early season dry spells, translating into the potential for skillful WAM onset date predictions. Our analysis suggests that sources of predictability include relationships to the MJO and the Indian monsoon sector, which need to be further examined to benefit subseasonal forecasting efforts in West Africa, and ultimately agricultural planning and food security across the Sahel.



The authors are grateful to the reviewers whose insightful comments helped improve the manuscript substantially, and to Seydou Traoré and Rémi Cousin for their assistance in computing local onset dates from TAMSAT merged daily rainfall estimates which were accessed from AGRHYMET Data Library ( The authors would like to acknowledge the financial support of the NASA SERVIR AST-2 NNX16AN29G grant as well as the use of forecasts from the S2S database recently published under the WWRP/WCRP S2S project ( Calculations were performed using IRI resources and S2S subsets archived in the IRI Data Library (IRIDL,, from which all other data were


  1. Bombardi R, Pegion K, Kinter J, Cash B, Adams J (2017) Sub-seasonal predictability of the onset and demise of the rainy season over monsoonal regions. Front Environ Sci 5:14. CrossRefGoogle Scholar
  2. Chauvin F, Roehrig R, Lafore J-P (2010) Intraseasonal variability of the Saharan heat low and its link with mid-latitudes. J Clim 23:2544–2561CrossRefGoogle Scholar
  3. Cheng X, Wallace J (2003) Regime analysis of the Northern Hemisphere winter-time 500 hPa height field: spatial patterns. J Atmos Sci 50:2674–2696CrossRefGoogle Scholar
  4. Diedhiou A, Janice S, Viltard A, de Felice P, Laurent H (1999) Easterly wave regimes and associated convection over West Africa and tropical Atlantic: results from the NCEP/NCAR and ECMWF reanalyses. Clim Dyn 15:795–822CrossRefGoogle Scholar
  5. Dinku T, Block P, Sharoff J, Hailemariam K, Osgood D, del Corral J, Cousin R, Thomson M (2014) Bridging critical gaps in climate services and applications in Africa. Earth Perspect 1:15. CrossRefGoogle Scholar
  6. Eltahir E, Gong C (1996) Dynamics of wet and dry years in West Africa. J Clim 9:1030–1042CrossRefGoogle Scholar
  7. Fitzpatrick R, Parker D, Marsham J, Knippertz P, Bain C (2015) The West African monsoon onset—a concise comparison of definitions. J Clim 28:8673–8694CrossRefGoogle Scholar
  8. Fitzpatrick R, Parker D, Marsham J, Knippertz P, Bain C (2016) On what scale can we predict the agronomic onset of the West African monsoon? Mon Weather Rev 144:1571–1589CrossRefGoogle Scholar
  9. Fontaine B, Louvet S (2006) Sudan-Sahel rainfall onset: definition of an objective index, types of years, and experimental hindcasts. J Geophys Res 111(D20103):1–14. CrossRefGoogle Scholar
  10. Funk C, Peterson P, Landsfeld M, Pedreros D, Verdin J, Rowland J, Romero B, Husak G, Michaelsen J, Verdin A (2014) A quasi-global precipitation time-series for drought monitoring. US Geological Survey Data Series 832:4Google Scholar
  11. Funk C, Peterson P, Landsfeld M, Pedreros D, Verdin J, Shukla S, Husak G, Rowland J, Harrison L, Hoell A, Michaelsen J (2015) The climate hazards infrared precipitation with stations-a new environmental record for monitoring extremes. Sci Data 2:150066. CrossRefGoogle Scholar
  12. Gadgil S, Rajeevan M, Nanjundiah R (2005) Monsoon prediction—why yet another failure? Curr Sci 88(9):1389–1400Google Scholar
  13. Giannini A (2015) Hydrology: climate change comes to the Sahel. Clim Dyn 18:303–320Google Scholar
  14. Giannini A, Saravanan R, Chang P (2003) Ocean forcing of Sahel rainfall on inter annual to interdecadal time scales. Science 302:1027–1030. CrossRefGoogle Scholar
  15. Huffman G, Bolvin D (2012) GPCP version 1.2 One-Degree Daily (1DD) precipitation dataset documentation. WDC-A, NCDC, AshevilleGoogle Scholar
  16. Huffman G, Adler R, Morrissey M, Bolvin D, Curtis S, Joyce R, McGavock B, Susskind J (2001) Global precipitation at one-degree daily resolution from multi-satellite observations. J Hydrometeorol 2:36–50CrossRefGoogle Scholar
  17. Huffman G, Adler R, Bolvin D, Nelkin E (2010) The TRMM multi-satellite precipitation analysis TMPA. In: Chapter 1 in satellite rainfall application for surface hydrology, pp 3-22 Eds Springer Verlag ISBN 978-90-481-2914-0Google Scholar
  18. Janicot S, Moron V, Fontaine B (1996) Sahel droughts and ENSO dynamics. Geophys Res Lett 23:515–518CrossRefGoogle Scholar
  19. Janicot S, Trzaska S, Poccard I (2001) Summer Sahel-ENSO teleconnection and decadal time scale SST variations. Clim Dyn 18(3–4):303–320CrossRefGoogle Scholar
  20. Janicot S, Mounier F, Hall N, Leroux S, Sultan B, Kiladis G (2009) Dynamics of the West African monsoon. Part IV: analysis of 25–90-day variability of convection and the role of the Indian monsoon. J Clim 22:1541–1565CrossRefGoogle Scholar
  21. Janicot S, Mounier F, Gervois S, Sultan B, Kiladis G (2010) Dynamics of the West African monsoon. Part V: the role of convectively coupled equatorial Rossby waves J Clim. CrossRefGoogle Scholar
  22. Janicot S, Caniaux G, Chauvin F, de Coetlogon G, Fontaine B, Hall N, Kiladis G, Lafore J-P, Lavaysse C, Lavender S, Leroux S, Marteau R, Mounier F, Philippon N, Roehrig R, Sultan B, Taylor CM (2011) Intraseasonal variability of the West African monsoon. Atmos Sci Lett 12(1):58–66CrossRefGoogle Scholar
  23. Joly M, Voldoire A (2009) Role of the Gulf of Guinea in the inter-annual variability of the West African monsoon: what do we learn from CMIP3 coupled simulations? Int J Clim 30(12):1843–1856Google Scholar
  24. Kanamitsu M, Ebisuzaki W, Woollen J, Yang S-K, Hnilo J, Fiorino M, Potter GL (2002) NCEP-DOE AMIP-2 reanalysis (R-2). Bull Atmos Meteorol Soc 77:1631–1643CrossRefGoogle Scholar
  25. Krishna Kumar K, Rajagopalan B, Hoerling M, Bates G, Cane M (2006) Unraveling the mystery of Indian monsoon failure during El Niño. Science 314(5796):115–119CrossRefGoogle Scholar
  26. Lavender S, Matthews A (2009) Response of the West African monsoon to the Madden-Julian Oscillation. J Clim 22:4097–4116CrossRefGoogle Scholar
  27. Le Barbé L, Lebel T, Tapsoba D (2003) Rainfall variability in West Africa during the years 1950–90. J Clim 15:187–202CrossRefGoogle Scholar
  28. Lebel T, Diedhiou A, Laurent H (2003) Seasonal cycle and interannual variability of the sahelian rainfall at hydrological scales, J Geophys Lett. CrossRefGoogle Scholar
  29. Liebmann B, Smith C (1996) Description of a complete (interpolated) Outgoing Longwave Radiation dataset. Bull Am Meteorol Soc 83:1631–1643Google Scholar
  30. Livezey R, Chen W (1983) Statistical field significance and its determination by Monte Carlo techniques. Mon Yea Rev 111:46–59CrossRefGoogle Scholar
  31. Losada T, Rodriguez-Fonseca B, Janicot S, Gervois S, Chauvin F, Ruti P (2010) A multi-model approach to the Atlantic Equatorial mode: impact on the West African monsoon. Clim Dyn 35(1):29–43CrossRefGoogle Scholar
  32. Maidment R, Grimes D, Black E, Tarnavsky E, Young M, Greatrex H, Allan R, Stein T, Nkonde E, Senkunda S, Alcantara E (2017) A new, long-term daily satellite-based rainfall dataset for operational monitoring in Africa. Sci Data 4:170063. CrossRefGoogle Scholar
  33. Marteau R, Moron V, Philippon N (2008) Spatial coherence of monsoon onset over Western and Central Sahel (1950–2000). J Clim 22:1331–1342Google Scholar
  34. Mathon V, Laurent H, Lebel T (2002) Mesoscale convective system rainfall in the Sahel. J Appl Meteorol 41:1081–1092CrossRefGoogle Scholar
  35. Matthews A (2004) Intraseasonal variability over tropical Africa during northern summer. J Clim 17:2427–2440CrossRefGoogle Scholar
  36. Michelangeli P, Vautard R, Legras B (1995) Weather regime occurence and quasi-stationarity. J Atmos Sci 52:1237–1256CrossRefGoogle Scholar
  37. Moron V, Plaut G (2003) The impact of El Niño-Southern Oscillation upon weather regimes over Europe and the North Atlantic during boreal winter. Int J Climatol 23:363–379CrossRefGoogle Scholar
  38. Mounier F, Janicot S, Kiladis G (2008) Dynamics of the West African monsoon. Part III: the quasi-biweekly zonal dipole. J Clim 21:1911–1928CrossRefGoogle Scholar
  39. Ramel R, Galle H, Messager C (2006) On the northward shift of the West African monsoon. Clim Dyn 26:429–440CrossRefGoogle Scholar
  40. Reynolds RW, Smith TM, Liu C, Chelton D, Casey K, Schlax M (2007) Daily high-resolution-blended analyses for sea surface temperature. J Clim 20:5473–5496CrossRefGoogle Scholar
  41. Roebber P (2009) Visualizing multiple measures of forecast quality. Weather Forecast 24:601–608CrossRefGoogle Scholar
  42. Rowell D (2013) Simulating SST teleconnections to Africa: What is the state of the art? J Clim 26:5397–5418CrossRefGoogle Scholar
  43. Sultan B, Janicot S (2000) Abrupt shift of the ITCZ over West Africa and intra-seasonal variability. Geophys Res Lett 27:3353–3356CrossRefGoogle Scholar
  44. Sultan B, Janicot S (2003) Dynamics of the West African monsoon. Part II: the preonset and onset of the summer monsoon. J Clim 16:3407–3427CrossRefGoogle Scholar
  45. Sultan B, Janicot S, Diedhiou A (2003) Dynamics of the West African monsoon. Part I: documentation of increased variability. J Clim 1(21):3389–3406CrossRefGoogle Scholar
  46. Sultan B, Correia S, Janicot S (2009) Medium-lead prediction of intraseasonal oscillations in West Africa. Weather Forecast 24:767–784CrossRefGoogle Scholar
  47. Taylor C (2008) Intraseasonal land-atmosphere coupling in the West African monsoon. J Clim 21:6636–6648CrossRefGoogle Scholar
  48. Taylor C, Parker D, Kalthoff N, Gaertner M, Philippon N, Bastin S, Harris P, Boone A, Guichard F, Agusti-Panareda A, Baldi M, Cerlini P, Descroix L, Douville H, Flamant C, Grandpeix J, Polcher J (2011) New perspectives on land-atmosphere feedbacks from the African Monsoon Multidisciplinary Analysis. Atmos Sci Lett 12:38–44CrossRefGoogle Scholar
  49. Vigaud N, Robertson A (2017) Convection regimes and tropical-midlatitude interactions over the Intra-American Seas from May to November. J Climatol Int 37:987–1000. CrossRefGoogle Scholar
  50. Vigaud N, Pohl B, Cretat J (2012) Tropical-temperate interactions over southern Africa simulated by a regional climate model. Dyn Clim 39:2895–2916. CrossRefGoogle Scholar
  51. Vigaud N, Lyon B, Giannini A (2016) Sub-seasonal teleconnections between convection over the Indian Ocean, East African long rains and tropical Pacific surface temperatures. Int J Climatol 3:1167–1180. CrossRefGoogle Scholar
  52. Vigaud N, Robertson A, Tippett M, Acharya N (2017) Subseasonal predictability of boreal summer monsoon rainfall from ensemble forecasts. Front Environ Sci 5:67. CrossRefGoogle Scholar
  53. Vigaud N, Ting M, Lee D-E, Barnston A, Kushnir Y (2018) Multiscale variability in North American summer maximum temperatures and modulations from the North Atlantic simulated by an AGCM. J Clim 31:2549–2562CrossRefGoogle Scholar
  54. Vitart F, Ardilouze C, Bonet A, Brookshaw A, Chen M, Codorean C, Deque M, Ferranti L, Fucile E, Fuentes M, Hendon H, Hodgson J, Kang H-S, Kumar A, Lin H, Liu G, Liu X, Malguzzi P, Mallas I, Manoussakis M, Mastrangelo D, MacLachlan C, McLean P, Minami A, Mladek R, Nakazawa T, Najm S, Nie Y, Rixen M, Robertson A, Ruti P, Sun C, Takaya Y, Tolstykh M, Venuti F, Waliser D, Woolnough S, Wu T, Won D-J, Xiao H, Zaripov R, Zhang L (2017) The Subseasonal to Seasonal (S2S) prediction project database. Bull Am Meteorol 98:163–173. CrossRefGoogle Scholar
  55. Vizy E, Cook K (2009) A mechanism for African monsoon breaks: Mediterranean cold air surges. J Geophys Res 114:1–19CrossRefGoogle Scholar
  56. Wheeler M, Hendon H (2004) An all-season real-time multivariate MJO index: development of an index for monitoring and prediction. Mon Weather Rev 132:1917–1932CrossRefGoogle Scholar
  57. World Meteorological Organization (2013), Sub-seasonal to Seasonal prediction, GenevaGoogle Scholar

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© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.International Research Institute for Climate and SocietyEarth Institute at Columbia UniversityNew YorkUSA

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