A meteorological overview of the TRACE A period

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Abstract
General meteorological conditions over the South Atlantic basin during the Transport and Atmospheric Chemistry Near the Equator‐Atlantic (TRACE A) experiment period are described. TRACE A occurred during one of the longest continuous El Nino‐Southern Oscillation (ENSO) events of the twentieth century. Effects of this ENSO event included warmer than normal temperatures concurrent with a severe drought in southern Africa and warm, dry conditions over northeastern Brazil. Large‐scale flow patterns are described, and the TRACE A period is compared to climatological normals. Significant meteorological features affecting the TRACE A flights included a northward moving middle‐latitude cold frontal system over Brazil, eastward moving middle‐latitude frontal waves crossing the South Atlantic basin and southern Africa, and deep convection over central Africa. The Brazilian cold front helped induce organized convective systems which led to vertical transports of biomass burning related chemical species. A well‐defined middle‐latitude frontal wave was traversed during the transit flight from Rio de Janeiro to Johannesburg, along with the penetration of a tropopause fold of stratospheric air. Deep surface‐based mixed layers and frequent diurnal convection over central Africa were responsible for vertical transports over that continent. Middle‐latitude frontal waves that crossed the southern region of Africa slightly displaced the shear axes and col zones that often were present off the west coast of central Africa.