Climate Dynamics

, Volume 38, Issue 5–6, pp 965–983 | Cite as

The role of the Indian monsoon onset in the West African monsoon onset: observations and AGCM nudged simulations

  • Emmanouil Flaounas
  • Serge Janicot
  • Sophie Bastin
  • Rémy Roca
  • Elsa Mohino


In spring the inland penetration of the West African Monsoon (WAM) is weak and the associated rainband is located over the Guinean coast. Then within a few days deep convection weakens considerably and the rainband reappears about 20 days after over the Sahel, where it remains until late September signalling the summer rainy season. Over the period 1989–2008 a teleconnection induced by the Indian monsoon onset is shown to have a significant impact on the WAM onset, by performing composite analyses on both observational data sets and atmospheric general circulation model simulations ensembles where the model is nudged to observations over the Indian monsoon sector. The initiation of convective activity over the Indian subcontinent north of 15°N at the time of the Indian monsoon onset results in a westward propagating Rossby wave establishing over North Africa 7–15 days after. A back-trajectory analysis shows that during this period, dry air originating from the westerly subtropical jet entrance is driven to subside and move southward over West Africa inhibiting convection there. At the same time the low-level pressure field over West Africa reinforces the moisture transport inland. After the passage of the wave, the dry air intrusions weaken drastically. Hence 20 days after the Indian monsoon onset, convection is released over the Sahel where thermodynamic conditions are more favourable. This scenario is very similar in the observations and in the nudged simulations, meaning that the Indian monsoon onset is instrumental in the WAM onset and its predictability at intraseasonal scale.


West African monsoon onset Indian monsoon onset Dry-air intrusions Madden-Julian Oscillation Atmospheric general circulation models Nudging 



The authors are grateful to Laurent Li (LMD) for making available his LMDz nudged simulations and to Hélène Brogniez (LATMOS) for providing the data on the back-trajectories. We are also thankful to the Climate Diagnostics Center (NOAA, Boulder, CO) and to the NCEP for the OLR data. Based on French initiative, AMMA was built by an international scientific group and is currently funded by a large number of agencies, especially from France, UK, US and Africa. It has been the beneficiary of a major financial contribution from the European Community’s Sixth Framework Research Programme. Detailed information on scientific coordination and funding is available on the AMMA International website


  1. Brandt P, Caniaux G, Bourles B, Lazar A, Dengler M, Funk A, Hormann V, Giordani H, Marin F (2010) Equatorial upper-ocean dynamics and their interaction with the West African monsoon. Atmos Sci Lett (Special issue on AMMA, submitted)Google Scholar
  2. Camberlin P, Fontaine B, Louvet S, Oettli P, Valimba P (2010) Climate adjustments over Africa accompanying the Indian Monsoon onset. J Clim 23(8):2047–2064CrossRefGoogle Scholar
  3. Chauvin F, Roehrig R, Lafore JP (2010) Intraseasonal variability of the Saharan heat low and its link with midlatitudes. J Clim 23:2544–2561CrossRefGoogle Scholar
  4. De Coëtlogon G, Janicot S, Lazar A (2010) Intraseasonal variability of the ocean-atmosphere coupling in the Gulf of Guinea during boreal spring and summer. Q J R Meteor Soc. doi: 10.1002/qj.554
  5. Dee DP, Uppala S (2009) Variational bias correction of satellite radiance data in the ERA-Interim reanalysis. QJR Meteorol Soc 135:1830–1841CrossRefGoogle Scholar
  6. Flaounas E, Janicot S, Bastin S, Roca R (2011) The West African Monsoon onset in 2006: sensitivity to surface albedo, orography, SST and synoptic scale dry-air intrusions using WRF. In revision to Climate DynamicsGoogle Scholar
  7. Flatau MK, Flatau PJ, Rudnick D (2001) The dynamics of double monsoon onsets. J Clim 14:4130–4146CrossRefGoogle Scholar
  8. Hagos SM, Cook KH (2007) Dynamics of the West African monsoon jump. J Clim 20:5264–5284CrossRefGoogle Scholar
  9. Hourdin F, Musat I, Bony S, Braconnot P, Codron F, Dufresne JL, Fairhead L, Filiberti MA, Friedlingstein P, Grandpeix JY, Krinner G, LeVan P, Li ZX, Lott F (2006) The LMDZ4 general circulation model: climate performance and sensitivity to parametrized physics with emphasis on tropical convection. Clim Dyn 27:787–813CrossRefGoogle Scholar
  10. Huffman GJ, Adler RF, Morrissey MM, Curtis S, Joyce R, McGavock B, Susskind J (2000) Global precipitation at 1 degree daily resolution from multi-satellite observations. J Hydrometeorol 2:36–50CrossRefGoogle Scholar
  11. Janicot S, Sultan B (2001) Intra-seasonal modulation of convection in the West African monsoon. Geophys Res Lett 28:523–526CrossRefGoogle Scholar
  12. Janicot S, Thorncroft C et al (2008) Large scale overview of the summer monsoon over the summer monsoon in West Africa during the AMMA field experiment in 2006. Ann Geophys 26:2569–2595CrossRefGoogle Scholar
  13. Janicot S, Mounier F, Hall NMJ, Leroux S, Sultan B, Kiladis GN (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
  14. Lavaysse C, Flamant C, Janicot S, Parker DJ, Lafore JP, Sultan B, Pelon J (2009) Seasonal evolution of the West African heat low: a climatological perspective. Clim Dyn. doi: 10.1007/s00382-009-0553-4
  15. Lavender SL, Matthews AJ (2009) Response of the West African monsoon to the Madden-Julian Oscillation. J Clim 11:4097–4116CrossRefGoogle Scholar
  16. Liebmann B, Smith C (1996) Description of a complete (interpolated) outgoing longwave radiation dataset. Bull Am Meteor Soc 106:1275–1277Google Scholar
  17. Madden RA, Julian PR (1994) Observations of the 40–50 tropical oscillation–a review. Mon Weather Rev 122:814–837CrossRefGoogle Scholar
  18. Maloney ED, Shaman J (2008) Intraseasonal variability of the West African monsoon and Atlantic ITCZ. J Clim 21:2898–2918CrossRefGoogle Scholar
  19. Matthews AJ (2004) Intraseasonal variability over tropical Africa during northern summer. J Clim 17:2427–2440CrossRefGoogle Scholar
  20. Mohino E, Janicot S, Douville H, Li L (2011) Impact of summer MJO on West Africa using nudged climate simulations. In revision to Climate DynamicsGoogle Scholar
  21. Okumura Y, Xie SP (2004) Interaction of the Atlantic equatorial cold tongue and the African monsoon. J Clim 17:3589–3602CrossRefGoogle Scholar
  22. Pai DS, Nair RM (2009) Summer monsoon onset over Kerala: New definition and prediction. J Earth Syst Sci 118:123–135CrossRefGoogle Scholar
  23. Pierrehumbert RT, Roca R (1998) Evidence for control of Atlantic subtropical humidity by large scale advection. Geophys Res Lett 25:4537–4540CrossRefGoogle Scholar
  24. Pohl B, Janicot S, Fontaine B, Marteau R (2009) Implication of the Madden-Julian oscillation in the 40-day variability of the West African Monsoon. J Clim 22:3769–3785CrossRefGoogle Scholar
  25. Ramel R, Gallee H, Messager C (2006) On the northward shift of the West African monsoon. Clim Dyn 26. doi: 10.1007/s00,382–005–0093–5
  26. Roca R, Lafore JP, Piriou C, Redelsperger JL (2005) Extratropical dry-air intrusions into the West African monsoon midtroposphere: an important factor for the convective activity over the Sahel. J Atmos Sci 62:390–407CrossRefGoogle Scholar
  27. Rodwell MJ, Hoskins BJ (1996) Monsoons and the dynamics of deserts. Q J R Met Soc 122:1385–1404CrossRefGoogle Scholar
  28. Rodwell MJ, Hoskins BJ (2001) Subtropical anticyclones and summer monsoons. J Clim 14:3192–3211CrossRefGoogle Scholar
  29. Sijikumar S, Roucou P, Fontaine B (2006) Monsoon onset over Sudan-Sahel: simulation by the regional scale model MM5. Geophys Res Lett 33:L03814. doi: 10.1029/2005GL024819
  30. Sultan B, Janicot S (2000) Abrupt shift of the ITCZ over West Africa and intra-seasonal variability. Geophys Res Lett 27:3353–3356CrossRefGoogle Scholar
  31. Sultan B, Janicot S (2003) The West African monsoon dynamics. Part II: the “preonset” and “onset” of the summer monsoon. J Clim 16:3389–3406CrossRefGoogle Scholar
  32. Vizy EK, Cook KH (2009) A mechanism for African monsoon breaks: mediterranean cold air surges. J Geophys Res 114: D01104. doi: 10.1029/2008JD010654

Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Emmanouil Flaounas
    • 1
  • Serge Janicot
    • 2
  • Sophie Bastin
    • 3
  • Rémy Roca
    • 4
  • Elsa Mohino
    • 5
    • 6
  1. 1.LATMOS/IPSL, Université Pierre et Marie CurieParis cedex 05France
  2. 2.LOCEAN/IPSL, IRD, Université Pierre et Marie CurieParisFrance
  3. 3.LATMOS/IPSL, CNRS, Université Pierre et Marie CurieParisFrance
  4. 4.LMD/IPSL, CNRS, Université Pierre et Marie CurieParisFrance
  5. 5.LOCEAN/IPSL, CNRS, Université Pierre et Marie CurieParisFrance
  6. 6.Universidad de SevillaSevillaSpain

Personalised recommendations