Provisionally Corrected Surface Wind Data, Worldwide Ocean-Atmosphere Surface Fields, and Sahellan Rainfall Variability

Abstract Worldwide ship datasets of sea surface temperature (SST), sea level pressure (SLP), and surface vector wind are analyzed for a July-September composite of five Sabelian wet years (1950, 1952, 1953, 1954, 1958) minus five Sahelian dry years (1972, 1973, 1982, 1983, 1984) (W – D). The results are compared with fields for a number of individual years and for 1988 minus 1987 (88 – 87); Sahelian rainfall in 1988 was near the 1951–80 normal, whereas 1987 was very dry. Before performing the analyses, an extensive study of the geostrophic consistency of trends in pressure gradients and observed wind was undertaken, motivated by the suggestion that changes in observational practice on board ships have introduced an upward trend in reported wind speed during the last 40 years. The results suggest that, during the period 1949–88, there is a mean increase in reported wind speed of about 16% that cannot be explained by trends in geostrophic winds derived from seasonal mean SLP. Estimates of the wind bias are ...