Climate Dynamics

, Volume 52, Issue 5–6, pp 2903–2922 | Cite as

Understanding the summertime diurnal cycle of precipitation over sub-Saharan West Africa: regions with daytime rainfall peaks in the absence of significant topographic features

  • Edward K. VizyEmail author
  • Kerry H. Cook


Convection-permitting regional model output is analyzed to better understand the diurnal cycle of rainfall during the height of the West African summer monsoon. This investigation focuses on two regions, the western Bodélé of Chad and eastern Burkina Faso, that have a propensity for daytime rainfall, but why this occurs does not conform to our conventional understanding of being directly associated with the presence of significant topographic feature(s). The August diurnal cycle of rainfall for the Bodélé is characterized by an afternoon peak, with mesoscale convective systems (MCSs) originating within 500 km accounting for 80% of the afternoon precipitation. These MCSs are associated with a deepening of the monsoon trough over the western Sahara related to northern storm track African easterly wave (AEW) disturbance activity, combined with anomalous ridging over eastern Chad associated with cold pool outflow from convection that originates over the Marra Mountains the previous afternoon. These circulation features enhance the moist low-level southwesterly flow and increase instability over the Bodélé. Over Burkina Faso rainfall has a primary afternoon peak, and a secondary morning peak. MCSs account for 95% of the total rainfall. Morning rainfall is primarily due to MCSs forming over the Damergou Gap of Niger, while the afternoon rainfall is associated with MCSs that originate over the Damergou Gap as well as locally. While both types of MCSs are associated with an approaching southern storm track AEW disturbance, it is differences in northern storm track activity that helps explain why some MCSs originate over the Damergou Gap.


Diurnal cycle of precipitation West Africa Sahel Mesoscale convective system Cold pool outflow MCS genesis African easterly wave disturbance African easterly jet Inter-tropical front Convection permitting modeling 



This work was funded by NSF Award #1444505. The authors acknowledge the Texas Advanced Computing Center (TACC) at The University of Texas at Austin for providing HPC and database resources that have contributed to the research results reported within this paper. URL: The Grid Analysis and Display System software (GrADS) developed at COLA/IGES was used for generating the figures.


  1. Berry GJ, Thorncroft CD (2005) Case study of an intense African easterly wave. Mon Weather Rev 133:752–766. CrossRefGoogle Scholar
  2. Burpee RW (1972) The origin and structure of easterly waves in the lower troposphere of North Africa. J Atmos Sci 29:77–90.<0077:TOASOE>2.0.CO;2Google Scholar
  3. Carlson TN, Ludlam FH (1968) Conditions for the occurrence of severe local storms. Tellus 20:206–223. CrossRefGoogle Scholar
  4. Carlson TN, Benjamin SG, Forbes GS (1983) Elevated mixed layers in the regional severe storm environment: conceptual model and case studies. Mon Weather Rev 111:1453–1473.<1453:EMLITR>2.0.CO;2Google Scholar
  5. Chen F, Dudhia J (2001) Coupling an advanced land-surface/ hydrology model with the Penn State/NCAR MM5 modeling system. Part I: Model description and implementation. Mon Weather Rev 129:569–585.<0569:CAALSH>2.0.CO;2Google Scholar
  6. Christensen JH, Kumar KK et al (2013) Climate phenomena and their relevance for future regional climate change. In: Stocker TF, Qin D, Plattner GK, Tignor M, Allen SK, Boschung J, Nauels S, Xia Y, Bex V, Midgley PM (eds) Climate change (2013). The physical science basis. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change. Cambridge University Press, CambridgeGoogle Scholar
  7. Corfidi SF (2003) Cold pools and MCS propagation: forecasting the motion of downwind-developing MCSs. Weather Forecast 18:997–1017.<0997:CPAMPF>2.0.CO;2Google Scholar
  8. Crétat J, Vizy EK, Cook KH (2014) How well are daily intense rainfall events captured by current climate models over Africa? Clim Dyn 42:2691–2711. CrossRefGoogle Scholar
  9. Crétat J, Vizy EK, Cook KH (2015) The relationship between African easterly waves and daily rainfall over West Africa. Observations and regional climate simulations. Clim Dyn 44:385–404. CrossRefGoogle Scholar
  10. Dai A (2001) Global precipitation and thunderstorm frequencies. Part II: Diurnal variations. J Clim 14:1112–1128.<1112:GPATFP>2.0.CO;2Google Scholar
  11. Dee DP, Uppala SM, Simmons AJ et al (2011) The ERA-Interim reanalysis: configuration and performance of the data assimilation system. Q J Roy Meteorol Soc 137:553–597. CrossRefGoogle Scholar
  12. Dhonneur G (1973) Study of a line squall in Niger Bend. Bull Am Meteorol Soc 54:1075–1075Google Scholar
  13. Dhonneur G (1981) Les amas nuageux mobiles principale composante de la météorologie du Sahel. La Météorologie 27:75–82Google Scholar
  14. Diedhiou A, Janicot S, Viltard A, de Félice P, Laurent H (1999) Easterly wave regimes and associated convection over West Africa and the tropical Atlantic: results from the NCEP/NCAR and ECMWF reanalyses. Clim Dyn 15:795–822. CrossRefGoogle Scholar
  15. Dione C, Lothon M, Badiane D, Campistron B, Couvreux F, Guichard F, Salle S (2014) Phenomenology of Sahelian convection observed in Niamey during the early monsoon. Q J R Meteorol Soc 140:500–516. CrossRefGoogle Scholar
  16. Dudhia J (1989) Numerical study of convection observed during the winter monsoon experiment using a mesoscale two-dimensional model. J Atmos Sci 46:3077–3107.<3077:NSOCOD>2.0.CO;2Google Scholar
  17. Duvel JP (1990) Convection over tropical Africa and the Atlantic Ocean during northern summer. Part II: Modulation by easterly waves. Mon Weather Rev 118:1855–1868.<1855:COTAAT>2.0.CO;2Google Scholar
  18. Fink AH, Reiner A (2003) Spatiotemporal variability of the relation between African easterly waves and West African squall lines in 1998 and 1999. J Geophys Res 108:4332. CrossRefGoogle Scholar
  19. Fink AH, Vincent DG, Ermert V (2006) Rainfall types in the West African Sudanian zone during the summer monsoon 2002. Mon Weather Rev 134:2143–2164. CrossRefGoogle Scholar
  20. Flamant C, Chaboureau JP, Parker DJ, Taylor CA, Cammas JP, Bock O, Pelon J (2007) Airborne observations of the impact of a convective system on the planetary boundary layer thermodynamics and aerosol distribution in the intertropical discontinuity region of the West African Monsoon. Q J R Meteorol Soc 133:1175–1189. CrossRefGoogle Scholar
  21. Garcia-Carreras L, Marsham JH, Parker DJ, Bain CL, Milton S, Saci A, Salah-Ferroudj M, Ouchene B, Washington R (2013) The impact of convective cold pool outflows on model biases in the Sahara. Geophys Res Lett 40:1647–1652. CrossRefGoogle Scholar
  22. Gbambie ASB, Steyn DG (2012) Sea breezes at Cononou and their interaction with the West African monsoon. Int J Climatol 33:2889–2899. CrossRefGoogle Scholar
  23. Gounou A, Guichard F, Covreux F (2012) Observations of diurnal cycles over a West African meridional transect: pre-monsoon and full-monsoon. Bound Layer Meteorol 144:329–357. CrossRefGoogle Scholar
  24. Grams CM, Jones SC, Marsham JH, Parker DJ, Haywood JM, Heuveline V (2010) The Atlantic inflow to the Saharan heat low: observations and modelling. Q J Roy Meteorol Soc 136:125–140. CrossRefGoogle Scholar
  25. Hodges KI, Thorncroft CD (1997) Distribution and statistics of African mesoscale convective weather systems based on the ISCCP Meteosat imagery. Mon Weather Rev 125:2821–2837.<2821:DASOAM>2.0.CO;2Google Scholar
  26. Hong S-Y, Noh Y, Dudhia J (2006) A new vertical diffusion package with an explicit treatment of entrainment processes. Mon Weather Rev 134:2318–2341. CrossRefGoogle Scholar
  27. Hopsch SB, Thorncroft CD, Tyle KR (2010) Analysis of African easterly wave structures and their role in influencing tropical cyclogenesis. Mon Weather Rev 138:1399–1419. CrossRefGoogle Scholar
  28. Houze RA Jr (1993) Cloud dynamics. Academic, San DiegoGoogle Scholar
  29. Houze RA Jr (2012) Orographic effects on precipitating clouds. Rev Geophys 50:RG1001. CrossRefGoogle Scholar
  30. Hsieh J-S, Cook KH (2005) Generation of African easterly wave disturbances: relationship to the African easterly jet. Mon Weather Rev 133:1311–1327. CrossRefGoogle Scholar
  31. Hsieh J-S, Cook KH (2008) On the instability of the African easterly jet and the generation of African waves: reversals of the potential vorticity gradient. J Atmos Sci 65:2130–2151. CrossRefGoogle Scholar
  32. Joyce R, Janowiak J, Arkin PA, Xie P (2004) CMORPH: a method that produces global precipitation estimates from passive microwave and infrared data at high spatial and temporal resolution. J Hydrometeorol 5:487–503. 1525–7541(2004)005,0487:CAMTPG.2.0.CO;2Google Scholar
  33. Kain, JS (2004) The Kain–Fritsch convective parameterization: an update. J Appl Meteorol 43:170–181.<0170:TKCPAU>2.0.CO;2Google Scholar
  34. Laing AG, Fritsch JM (1993) Mesoscale convective complexes in Africa. Mon Weather Rev 121:2254–2263.<2254:MCCIA>2.0.CO;2Google Scholar
  35. Laing AG, Fritsch JM, Negri AJ (1999) Contribution of mesoscale convective complexes to rainfall in Sahelian Africa: estimates from geostationary infrared and passive microwave data. J Appl Meteorol 38:957–964.<0957:COMCCT>2.0.CO;2Google Scholar
  36. Laing AG, Carbone R, Levizzani V, Tuttle J (2008) The propagation and diurnal cycles of deep convection in northern tropical Africa. Q J Roy Meteorol Soc 134:93–109. CrossRefGoogle Scholar
  37. Laing AG, Trier SB, Davis CA (2012) Numerical simulation of episodes of organized convection in tropical northern Africa. Mon Weather Rev 140:2874–2886. CrossRefGoogle Scholar
  38. Laurent H, D’Amato N, Lebel T (1998) How important is the contribution of the mesoscale convective complexes to the Sahelian rainfall? Phys Chem Earth 23:629–633. CrossRefGoogle Scholar
  39. Le Barbé L, Lebel T (1997) Rainfall climatology of the HAPEX-Sahel region during the years 1950–1990. J Hydrol 188–189:43–73. CrossRefGoogle Scholar
  40. Marsham JH, Dixon N, Garcia-Carreras L, Lister G, Parker DJ, Knippertz P, Birch C (2013) The role of moist convection in the West African monsoon system—insights from continental-scale convection-permitting simulations. Geophys Res Lett 40:1843–1849. CrossRefGoogle Scholar
  41. Mathon V, Laurent H, Lebel T (2002) Mesoscale convective system rainfall in the Sahel. J Appl Meteorol 41:1081–1092.<1081:MCSRIT>2.0.CO;2Google Scholar
  42. Maurer V, Bischoff-Gauß I, Kalthoff N, Gantner L, Roca R, Panitz HJ (2016) Initiation of deep convection in the Sahel in a convection-permitting climate simulation for northern Africa. Q J R Meteorol Soc. (accepted author manuscript) Google Scholar
  43. Meehl GA, Stocker TF, Collins WD, Friedlingstein P et al (2007) Global climate projections. In: Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt KB, Tignor M, Miller HL (eds) Climate change 2007: the physical science basis. Contribution of working group I to the fourth assessment report of the intergovernmental panel on climate change. Cambridge University Press, CambridgeGoogle Scholar
  44. Mlawer EJ, Taubman SJ, Brown PD, Iacono MJ, Clough SA (1997) Radiative transfer for inhomogeneous atmosphere: RRTM, a validated correlated-k model for the longwave. J Geophys Res 102:16663–16682. CrossRefGoogle Scholar
  45. Mohr KI (2004) Interannual, monthly, and regional variability in the wet season diurnal cycle of precipitation in sub-Saharan Africa. J Clim 17:2441–2453.<2441:IMARVI>2.0.CO;2Google Scholar
  46. Mohr KI, Thorncroft CD (2006) Intense convective systems in West Africa and their relationship to the African easterly jet. Q J Roy Meteorol Soc 132:163–176. CrossRefGoogle Scholar
  47. Mohr KI, Zipser EJ (1996) Mesoscale convective systems defined by their 85-GHz ice scattering signature: size and intensity comparison over tropical oceans and continents. Mon Weather Rev 124:2417–2437.<2417:MCSDBT>2.0.CO;2Google Scholar
  48. Mohr KI, Famiglietti JS, Zipser EJ (1999) The contribution to tropical rainfall with respect to convective system type, size, and intensity estimated from the 85-GHz ice-scattering signature. J Appl Meteorol 38:596–606.<0596:TCTTRW>2.0.CO;2Google Scholar
  49. Nesbitt SW, Zipser EJ (2003) The diurnal cycle of rainfall and convective intensity according to three years of TRMM measurements. J Clim 16:1456–1475.<1456:TDCORA>2.0.CO;2Google Scholar
  50. Parker MD, Johnson RH (2004) Simulated convective lines with leading precipitation. Part II: Evolution and maintenance. J Atmos Sci 61:1656–1673.<1656:SCLWLP>2.0.CO;2Google Scholar
  51. Parker DJ, Burton RR, Diongue-Niang A, Ellis RJ, Felton M, Taylor CM, Thorncroft CD, Bessemoulin P, Tompkins AM (2005) The diurnal cycle of the West African monsoon circulation. Q J R Meteorol Soc 131(611):2839–2860. CrossRefGoogle Scholar
  52. Payne SW, McGarry MM (1977) The relationship of satellite inferred convective activity to easterly waves over West Africa and the adjacent ocean during phase III of GATE. Mon Weather Rev 105:413–420.<0413:TROSIC>2.0.CO;2Google Scholar
  53. Pearson KJ, Lister GMS, Birch CE, Allan RP, Hogan RJ, Woolnough SJ (2013) Modelling the diurnal cycle of tropical convection across the “Grey Zone”. Q J R Meteorol Soc 140:491–499. CrossRefGoogle Scholar
  54. Provod M, Marsham JH, Parker DJ, Birch CE (2016) A characterization of cold pools in the West African Sahel. Mon Weather Rev 144:1924–1934. CrossRefGoogle Scholar
  55. Redelsperger JL, Lafore JP (1988) A three-dimensional simulation of a tropical squall-line: convective organization and thermodynamic vertical transport. J Atmos Sci 45:1334–1356.<1334:ATDSOA>2.0.CO;2Google Scholar
  56. Reed RJ, Norquist DC, Recker EE (1977) The structure and properties of African wave disturbances as observed during Phase III of GATE. Mon Weather Rev 105:317–333.<0317:TSAPOA>2.0.CO;2Google Scholar
  57. Roca R, Louvet S, Picon L, Desbois M (2005) A study of convective systems, water vapour and top of the atmosphere cloud radiative forcing over the Indian Ocean using INSAT-1B and ERBE data. Meteor Atmos Phys 90:49–65. CrossRefGoogle Scholar
  58. Rotunno R, Klemp JB, Weisman ML (1988) A theory for strong, long-lived squall lines. J Atmos Sci 45:463–485.<0463:ATFSLL>2.0.CO;2Google Scholar
  59. Rowell DP, Milford JR (1993) On the generation of African squall lines. J Clim 6:1181–1193.<1181:OTGOAS>2.0.CO;2Google Scholar
  60. Shinoda MT, Okatani T, Saloum M (1999) Diurnal variations of rainfall over Niger in the West African Sahel: a comparison between wet and drought years. Int J Climatol 19:81–94.<81::AID-JOC350.3.0.CO;2-FGoogle Scholar
  61. Skamarock WC, Klemp JB, Dudhia J, Gill DO, Barker DM, Wang W, Powers JG (2005) A description of the advanced research WRF version 2. NCAR/TN-408 + STR [available from NCAR Information Services, P.O. Box 3000, Boulder, CO 80307]Google Scholar
  62. Taylor CM, Birch CE, Parker DJ, Dixon N, Guichard F, Nikulin G, Lister GMS (2013) Modeling soil moisture-precipitation feedback in the Sahel: importance of spatial scale versus convective parameterization. Geophys Res Lett 40:6213–6218. CrossRefGoogle Scholar
  63. Tetzlaff G, Peters M (1988) A composite study of early summer squall lines and their environment over West Africa. Meteorol Atmos Phys 38:153–163. CrossRefGoogle Scholar
  64. Thompson G, Rasmussen RM, Manning K (2004) Explicit forecasts of winter precipitation using an improved bulk microphysics scheme. Part I: Description and sensitivity analysis. Mon Weather Rev 132:519–542.<0519:EFOWPU>2.0.CO;2Google Scholar
  65. Trier SB, Skamarock WC, LeMone MA (1997) Structure and evolution of the 22 February 1993 TOGA COARE squall line: organization mechanisms inferred from numerical simulation. J Atmos Sci 54:386–407.<0386:SAEOTF>2.0.CO;2Google Scholar
  66. Vizy EK, Cook KH (2009) Tropical storm development from African easterly waves in the eastern Atlantic: a comparison of two successive waves using a regional model as part of NASA AMMA 2006. J Atmos Sci 66:3313–3334. CrossRefGoogle Scholar
  67. Vizy EK, Cook KH (2012) Mid-21st century changes in extreme events over northern and tropical Africa. J Clim 25:5748–5767. CrossRefGoogle Scholar
  68. Vizy EK, Cook KH (2017) Mesoscale convective systems and nocturnal rainfall over the West African Sahel: role of the inter-tropical front. Clim Dyn. Google Scholar
  69. Vizy EK, Cook KH, Crétat J, Neupane N (2013) Projections of a wetter Sahel in the 21st century from global and regional models. J Clim 26:4664–4687. CrossRefGoogle Scholar
  70. Vizy EK, Cook KH, Chimphamba J, McCusker B (2015) Projected changes in Malawi’s growing season. Clim Dyn 45:1673–1698. CrossRefGoogle Scholar
  71. Vondou DA (2012) Spatio-temporal variability of Western Central African convection from infrared observations. Atmosphere 3:377–399. CrossRefGoogle Scholar
  72. Vondou DA, Nzeukou A, Lenouo A, Kamga FM (2010) Seasonal variations in the diurnal patterns of convection in Cameroon–Nigeria and their neighboring areas. Atmos Sci Lett 11:290–300. CrossRefGoogle Scholar
  73. Weisman ML, Klemp JB (1982) The dependence of numerically simulated convective storms on vertical wind shear and buoyancy. Mon Weather Rev 110:504–520.<0504:TDONSC>2.0.CO;2Google Scholar
  74. Yang GY, Slingo J (2001) The diurnal cycle in the tropics. Mon Weather Rev 129:784–801.<0784:TDCITT>2.0.CO;2Google Scholar
  75. Zhang G, Cook KH, Vizy EK (2016a) The diurnal cycle of warm season rainfall over West Africa. Part I: Observational analysis. J Clim 29:8423–8437. CrossRefGoogle Scholar
  76. Zhang G, Cook KH, Vizy EK (2016b) The diurnal cycle of warm season rainfall over West Africa. Part II: Convection-permitting simulations. J Clim 29:8439–8454. CrossRefGoogle Scholar
  77. Zipser EJ (1977) Mesoscale and convective-scale downdrafts as distinct components of squall-line structure. Mon Weather Rev 105:1568–1589.<1568:MACDAD>2.0.CO;2Google Scholar

Copyright information

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

Authors and Affiliations

  1. 1.Department of Geological SciencesJackson School of Geosciences, The University of Texas at AustinAustinUSA

Personalised recommendations