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Recent variations in geopotential height associated with West African monsoon variability

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Abstract

In the present study, the atmospheric circulation patterns associated with the seasonal West Africa (WA) monsoon (WAM) rainfall variability has been investigated. The observational rainfall data from the Climatic Research Unit (CRU) and atmospheric fields from the National Center for Environmental Prediction (NCEP) reanalysis 2, from 1979 to 2014, have been used. The rainfall variability extremes, classified as wet or dry years, are the outcomes of simultaneous 6-month SPI at the three rainfall zones, which shows increasing trends [Guinea Coast (GC = 0.012 year−1), Eastern Sudano Sahel (ESS = 0.045 year−1) and Western Sudano Sahel (WSS = 0.056 year−1) from Sen’s slope]; however, it is significant only in the Sahel region (α = 0.05 and α = 0.001 at ESS and WSS, respectively, from Mann–Kendall test). The vertical profile of the geopotential height (GpH) during the wet and dry years reveals that the 700 hPa anomalies show remarkable pattern at about 8°N to 13°N. This shows varying correlation with the zonal averaged vertically integrated moisture flux convergence and rainfall anomalies, respectively, as well as the oceanic pulsations indexes [Ocean Nino Index (ONI) and South Atlantic Ocean dipole index (SAODI), significant from t test], identified as precursors to the Sahel and GC rainfall variability respectively. The role of GpH anomalies at 700 hPa has been identified as the facilitator to the West African Westerly Jet’s input to the moisture flux transported over the WA. This is a new perspective of the circulation processes associated with WAM and serves as a basis for modeling investigations.

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Acknowledgements

The corresponding author acknowledges the postdoctoral fellowship granted him at the Institute of Atmospheric Physics, Center for Monsoon System Research supported by The Chinese Academy of Sciences President’s International Fellowship Initiative, CAS-PIFI, (GRANT No. 2016PE035). Appreciation also goes to the anonymous reviewers for their contributions.

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Authors and Affiliations

  1. Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China

    Ugochukwu K. Okoro, Wen Chen & Debashis Nath

  2. Atmospheric Physics Group, Department of Physics, Imo State University, P.M.B. 2000, Owerri, Nigeria

    Ugochukwu K. Okoro

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  1. Ugochukwu K. Okoro
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  2. Wen Chen
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Correspondence to Ugochukwu K. Okoro.

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Okoro, U.K., Chen, W. & Nath, D. Recent variations in geopotential height associated with West African monsoon variability. Meteorol Atmos Phys 131, 553–565 (2019). https://doi.org/10.1007/s00703-018-0593-6

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