The seasonal cycle in the lower troposphere over West Africa from sounding observations

Chidong Zhang, Phoebe Woodworth, Guojun Gu

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35 Scopus citations


In situ sounding observations from selected sites in West and Central Africa were used to document the seasonal cycle in the lower troposphere associated with the annual migration of precipitation. The main purpose of this exercise is to provide a description of the seasonal cycle free of the errors and biases of numerical models, which can be substantial in this region. Many features in the circulation typically associated with the West African Monsoon (WAM) exist through almost the entire seasonal cycle in the region. The low-level easterly jet, known as the African Easterly Jet during the monsoon season, remains prominent and closely related to the rain band in other phases of the seasonal cycle, even when the rain band is located near the equator. The surface southerly monsoon onshore flow penetrates through the rain band in the entire season cycle. The depth of the southerly surface monsoon flow undergoes a seasonal variation, and is greatest during the peak season of the monsoon. A unique feature is a low-level (∼ 700 hPa) northerly flow penetrating through the rain band in various phases of the seasonal cycle. Risking possible biases of land-bound sounding data, these observations are synthesized into a schematic describing the salient features in the low-level circulation associated with the rain band in different phases of the seasonal cycle. This synthesized circulation pattern in West Africa is in contrast to the traditional conceptual circulation pattern associated with the marine ITCZ and other monsoon systems. The results from this study call for more research attention to the low-level meridional circulation for a full understanding of the dynamics of the WAM. This study also advocates the study of the WAN to be conducted in a broad context of the seasonal cycle in the region and in comparison to the marine ITCZ.

Original languageEnglish (US)
Pages (from-to)2559-2582
Number of pages24
JournalQuarterly Journal of the Royal Meteorological Society
Issue number621
StatePublished - Oct 1 2006


  • Meridional circulation
  • Precipitation
  • West African Monsoon

ASJC Scopus subject areas

  • Atmospheric Science


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