Seasonal estimates of global atmospheric sea‐salt distributions

Abstract

Seasonal estimates of sea‐salt aerosol particle concentration distributions 15 m above the sea are presented on global contour maps. Measured data from a variety of sources relating atmospheric sea‐salt concentration to wind speed have been combined, yielding relationships of form C = exp (as + b), where C is sea‐salt concentration in micrograms per cubic meter and s is the horizontal wind speed in meters per second. These relationships, coupled with a Gaussian wind speed frequency distribution, allow us to calculate the atmospheric sea‐salt concentration accounting for the variance about mean wind speeds. We use monthly wind mean speed and variance information in 5° × 5° latitude/longitude squares over the world ocean to estimate the global sea‐salt aerosol particle mass distribution. The atmospheric sea‐salt concentrations in the northern hemisphere marine troposphere display a substantial seasonal dependence. The 3‐month seasonal average sea‐salt concentrations in this region differ by a factor of 2–3 between the boreal winter and summer, and the highest values are between 40 and 49 μg m−3. The seasonal variability of atmospheric sea‐salt concentrations in the high‐latitude southern hemisphere is much less than that in the northern hemisphere, varying by less than a factor of 2 between the austral winter and summer, and again the highest values are about 45 μg m−3. The equatorial areas have uniformly lower atmospheric sea‐salt concentrations than the high‐latitude regions. The monsoonal winds over the Indian Ocean produce sea‐salt concentrations in excess of 40 μg m−3 for the 3‐month boreal summer average.