Sea-Salt Particles in the Middle Troposphere over the Tropical Pacific Ocean

Abstract

   During the INSTAC-I flight campaign, aerosol number-size distribution was measured in the middle troposphere at 4 - 5 km altitude from 0°N to 34°N by using an optical counter. Aerosol particles were also collected for electron microscopic examinations. Two features of spatial distribution of aerosols were observed over the tropical areas. Sulfuric acid was detected in the particles with a wide size range where the concentrations showed uniform spatial distribution with low values. On the other hand, high aerosol concentrations in which sea-salt particles were dominant instead of sulfuric acid were observed intermittently with space and found to be associated with the existence of convective clouds. The upward transport of sea-salt particles through convective clouds is considered to be responsible for high particle concentrations in the middle tropical troposphere. This suggests that the vertical transport of sea-salt particles would influence the microphysical properties of clouds in the middle and upper troposphere.