On the giant sea-salt particles in the atmosphere

Abstract

The vertical distribution of giant sea-salt particles in the 10-m layer over the sea surface, where humidity, eddy diffusivity, etc., sharply change with height, is analytically studied. A steady state with no horizontal gradient and with a logarithmic distribution of wind speed is assumed, but the vertical distributions of temperature and vapor pressure are taken into account in such a way that each droplet is assumed to instantaneously attain its equilibrium salinity for the environmental air at each level, and to remain as a droplet of supersaturated salt solution when the relative humidity is lower than 75%.

It is deduced that the vertical distribution of the number concentration of each class interval of mass of salt contained in a droplet should be approximately expressed by a straight line on a logarithmic diagram. Also, the logarithm of the ratio of the concentration of the particles at the sea surface and at the 10-m level is proportional to the two thirds power of the mass of salt, and inversely proportional to the wind speed at the 10-m level. The proportionality factor is approximately a function of the relative humidity at the 10-m level and a friction factor. This proportionality factor is calculated for various values of the variables and the effect of wind speed and relative humidity on the vertical distribution of particles is predicted.

When this result is applied to data of the concentration and the effective production rate of sea-salt particles at the 10-m level compiled in the previous paper, complicated features disappear to give very simple patterns of the production rate or the surface concentration of sea water droplets as a function of wind force and of mass of salt. This represents predicted processes of production of sea-salt particles at the ocean surface, and gives some agreement with the author's 1961 wind flume experiment.

Notes

1 The research in this paper was sponsored by the Atmospheric Sciences Program, National Science Foundation, NSF grant G 22292.