Equatorial aerosol-ozone structure and variations as observed by balloon-borne backscattersondes since 1995 at Natal, Brazil (6°S)

Simultaneous aerosol and ozone profiles have been measured near Natal, Brazil (6.07°S, 35.34°W) in an irregular but continuing effort since 1995 using balloon‐borne backscattersondes. This study introduces the primary features of the data set and our preliminary interpretation. Although measurements from ground level to ∼32 km are made, the results reported here focus on the free troposphere (FT). An apparent clear annual cycle in the occurrence of FT aerosol layers is observed, which peaks during the biomass burning season, similar to the previously reported annual cycle in tropical ozone layers. A majority of the layers occurring during the burning season contain enhancements of both aerosol and ozone. The comparatively low amounts of aerosol backscatter enhancements found in the FT layers indicate that any aerosols originating in the much higher concentrations of the planetary boundary layer (PBL) must have been greatly reduced in backscatter before they were observed in the soundings. In general, the FT backscatter profile over Natal can be described as displaying a background or baseline character that is frequently perturbed by layers of various concentrations and thicknesses. Although only the last stages of the Pinatubo volcanic aerosol decay were observed, a curious multiple‐step reduction in the aerosol was seen in the profiles near 20 km. Because the soundings were conducted with varying regularity in a limited time period, current interpretation of results can only be considered tentative.