Abstract
The regional climate model (MAR) is used to perform a simulation of the year 1992 over West Africa. It is shown that MAR is able to simulate the main features of the rainy regime over West Africa and especially the discontinuous seasonal progression of the West African Monsoon along the year. One particular feature that is reasonably well reproduced is the abrupt shift of the rain band from 5° to 10°N at the end of June (also called “monsoon jump”). This study suggests that such a phenomenon is associated with the shift of the Saharan heat low between two favourite positions: one being over the Sahelian area (10–15°N) and the other over the Saharan area (20–25°N). These two favourite locations of the heat low are linked to the spatial distribution of surface albedo over West Africa that drives the spatio-temporal location of the surface temperature maxima. A detailed analysis of this “monsoon jump” is performed and the causes of the strong decrease in precipitation that precedes the northward shift of the rain band are also investigated.
Similar content being viewed by others
References
Adler RF, Huffman GJ, Chang A, Ferraro R, Xie P, Janowiak J, Rudolf B, Schneider U, Curtis S, Bolvin D, Gruber A, Susskind J, Arkin P, Nelkin E (2003) The Version-2 Global Precipitation Climatology Project (GPCP) monthly precipitation analysis (1979–present). J Hydrometeorol 4:1147–1167
Ati OF, Stinger CJ, Oladipo EO (2002) A comparison of methods to determine the onset of the growing season in the northern Nigeria. Int J Climatol 22:731–742
Bechtold P, Bazile E, Guichard F, Mascart P, Richard E (2001) A mass flux convection scheme for regional and global models. Q J R Meteorol Soc 127:869–886
Brasseur O (2001) Development and application of a physical approach to estimating wind gusts. Mon Weather Rev 129:5–25
Brasseur O, Tricot C, Ntezimana V, Gallée H, Schayes G (1998) Importance of the convective adjustment scheme in the simulation of the diurnal cycle of convective activity in Africa. In: Demarée GJ Alexandre, De Dapper M (eds) Proceedings of the international conference. Tropical climatology, meteorology and hydrology, pp 299–312
Cassano JJ, Box JE, Bromwich DH, Li L, Steffen K (2001) Evaluation of polar MM5 simulations of Greenland’s atmospheric circulation. J Geophys Res 106:867–890
De Ridder K (1997) Land surface processes and the potential for convective precipitation. J Geophys Res 102:30085–30090
De Ridder K, Gallée H (1998) Land surface-induced regional climate change in Southern Israel. J Appl Meteorol 37:1470–1485
Eltahir EAB, Gong C (1996) Dynamics of wet and dry years in West Africa. J Climate 9:1030–1042
Emanuel KA (1995) On thermally direct circulations in moist atmospheres. J Atmos Sci 52:1529–1534
Fletcher NH (1962) Physics of rain clouds. Cambridge University Press, Cambridge
Fontaine B, Philippon N, Camberlin P (1999) An improvement of June–September rainfall forecasting in the Sahel based upon region April–May moist static energy content (1968–1997). Geophys Res Lett 26:2041–2044
Fouquart Y, Bonnel B (1980) Computation of the solar heating of the Earth’s atmosphere: a new parameterization. Beitr Phys Atmos 53:35–62
Gallée H (1995) Simulation of the mesocyclonic activity in the Ross Sea. Antarctica Mon Weather Rev 123:2051–2069
Gallée H, Schayes G (1994) Development of a three-dimensional meso gamma primitive equations model. Katabatic winds simulation in the area of Terra Nova Bay. Antarctica Mon Weather Rev 122:671–685
Gallée H, Moufouma-Okia W, Brasseur O, Dupays I, Marbaix P, Messager C, Ramel R, Lebel T (2004) A high resolution simulation of a West African rainy season using a regional climate model. J Geophys Res 109, DOI 10.1029/2003JD004020
Gu G, Adler RF (2004) Seasonal evolution and variability associated with the West African Monsoon system. J Climate 17:3364–3377
Huffman GJ et al (1997) The Global Precipitation Climatology Project (GPCP) combined precipitation data set. Bull Am Meteor Soc 78:5–20
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 KC, Ropelewski C, Wang J, Roy Jenne, Dennis Joseph (1996) The NCEP/NCAR 40-year reanalysis project. B Am Meteorol Soc 77(3):437–471
Kessler E (1969) On the distribution and continuity of water substance in atmospheric circulation. Meteorol Monogr, vol 10, No. 32, AMS
Le Barbé L, Lebel T, Tapsoba D (2002) Rainfall variability in West Africa during the years 1950–90. J Climate 15:187–202
Lebel T, Diedhiou A, Laurent H (2003) Seasonal cycle and interannual variability of the Sahelian rainfall at hydrological scales. J Geophys Res, 108(D8), DOI 10.1029/2001JD001580
Legates DR, Willmott CJ (1990) Mean seasonal and spatial variability in gauge-corrected global precipitation. Int J Climatol 10:11–127
Levkov L, Rockel B, Kapitza H, Raschke E (1992) 3D mesoscale numerical studies of cirrus and stratus clouds by their time and space evolution. Beitr Phys Atmos 65:35–57
Lin YL, Farley RD, Orville HD (1983) Bulk parametrization of the snow field in a cloud model. J Appl Meteorol 22:1065–1092
Marbaix P, Gallée H, Brasseur O, Van Ypersele JP (2003) Lateral boundary conditions in regional climate models: a detailed study of the relaxation procedure. Mon Weather Rev 131:461–479
Matthews AJ (2004) Intraseasonal variability over Tropical Africa during Northern Summer. J Climate 17:2427–2440
Messager C, Gallée H, Brasseur O (2004) Precipitation sensitivity to regional SST in a climate simulation during the West African monsoon for two dry years. Climate Dyn 22:249–266
Meyers MP, DeMott PJ, Cotton WR (1992) New primary ice-nucleation parameterizations in an explicit cloud model. J Appl Meteorol 31:708–721
Morcrette JJ (1984) Sur la paramétrisation du rayonnement dans les modèles de la circulation générale atmosphérique. Ph.D. thesis, univ. des Sci. et Tech. de Lille, Lille, France. Thèse de Doctorat d’Etat, 373 pp
Reynolds RW, Smith MT (1995) A high-resolution global sea surface temperature climatology. J Climate 8:1571–1583
Sultan B, Janicot S (2000) Abrupt shift of the ICTZ over West Africa and intra-seasonal variability. Geophys Res Lett 27:3353–3356
Sultan B, Janicot S (2003) The West African Monsoon dynamics. Part II: the preonset and onset of the summer monsoon. J Climate 16:3407–3427
Thorncroft CD, Blackburn M (1997) On the maintenance of the African Easterly Jet. Q J R Meteorol Soc 123:763–786
Willmott CJ, Robenson SM (1995) Climatologically aided interpolation (CAI) of terrestrial air temperature. Int J Climatol 15:221–229
Zheng X, Eltahir EAB (1998) The role of vegetation in the dynamics of West African monsoons. J Climate 11:2078–2096
Acknowledgments
All major computations were realised with IDRIS computing resources. The authors thank the NCEP, ECMWF, UDEL institutions for their datasets. The GPCP merged analysis of pentad precipitation is created at the CPC of NOAA. Thanks to Bernard Fontaine and Frederic Hourdin for useful discussions and comments. We also thank the two anonymous reviewers for their help in improving this paper. This research was in part supported by the AMMA international program.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Ramel, R., Gallée, H. & Messager, C. On the northward shift of the West African monsoon. Clim Dyn 26, 429–440 (2006). https://doi.org/10.1007/s00382-005-0093-5
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00382-005-0093-5