Atmospheric water cycle and moisture fluxes in the West African monsoon: mean annual cycles and relationship using NCEP/NCAR reanalyses

摘要

Atmospheric water (Precipitation minus Evaporation, P-E) and moisture fluxes from the NCEP/NCAR and observed rainfall data from the Climatic Research Unit are analyzed over the West African Monsoon region (WAM: 5°N–20°N; 18°W–18°E) on the period 1968–1998. The main results show that 1) P-E averaged over the 15°N–20°N belt in July–September (JAS) is a better proxy of observed rainfall in Sudan-Sahel (12°N–18°N) than NCEP/NCAR rainfall in this reanalysis; 2) part of the moisture fluxes vertically integrated in the layers 1000–300 hPa or 1000–925 hPa advected into WAM originate from the Mediterranean sea and Central Africa; 3) their interannual March–April and JAS variations, especially north of 20°N, present significant relationship with Sahelian P-E in JAS; 4) at more local scales moisture advections and convergences are also significantly associated with observed Sudan-Sahel rainfall and, in wet (dry) situations, with a clear dominance of westerly (easterly) anomalies in the moisture flux south of 15°N.