Temporal and spatial characteristics of Saharan dust outbreaks

Temporal and spatial characteristics of moderate to heavy northern African aerosol outbreaks over the North Atlantic Ocean for the period of January 1989 through December 1992 are presented using NOAA's advanced very high resolution radiometer (AVHRR) aerosol optical thickness (AOT) data. The episodic nature of the transport and deposition of northern African aeolian material as well as the intra-annual variability of these aerosol outbreaks is detailed. Saharan dust outbreaks are generally observed within relatively well-defined zonal corridors that are approximately 10 degrees wide latitude. The latitude of these westward outbreaks progresses from south to north during the first 6-7 months of a year. After reaching its northernmost extent ((-) 20 degrees-25 degrees N) around August, the area of aerosol outbreaks then moves southward. The first six months of a year are the most active in terms of aerosol outbreak frequency and spatial extent. The annual peak in outbreak activity occurs most frequently during the months of February through April. The annual westward mass flux of northern African aeolian material over the North Atlantic during the years detailed in this study range from an annual minimum of 130 Mt for 1990 to an annual maximum of 460 Mt for 1991. These fluxes are not supplied in a steady fashion. Approximately 50% of the annual westward mass flux of northern African aerosols is transported during 20% of a given year. The annual mass fluxes presented in this study are found to be consistent with other independent estimates of the westward mass flux of northern African aerosols. The relationship of these aerosol loadings to sub-Saharan rainfall is consistent as well with earlier observations. Aerosol loadings are also presented and compared to regional sedimentation rates. The impact of the transport and deposition of this aeolian material on marine biogeochemical cycles of the North Atlantic is addressed briefly with the calculation of the annual mass flux of various nutritive species. Lastly, the continued development of the National Oceanographic and Atmospheric Admini- stration's AVHRR AOT observations and analyses may lead to a North African aeolian emission system analog useful in the geologic sedimentary record.