The Origin of Trade-Wind Orographic Shower Rains

Abstract

The purpose of the work reported here was to learn more about rain formation through a study of the extensive Project Shower and other data on the physics and the chemistry of rains. Most of the observations used have been published. It is demonstrated that the water and chloride content of orographic shower rains in Hawaii can be roughly computed from the observed amounts of sea-salt aerosols and water vapor in the sub-cloud layer over the sea, assuming wet adiabatic ascent of the air. From this and several other relationships among the properties of the air and rains, it is tentatively concluded that the showers originate within especially moist parcels of air which are carried into the orographic cloud by the trade winds, and which were previously formed in the sub-cloud layer over the windward sea. Specific suggestions are made for testing the degree to which potential shower-forming air may be identified over the sea, or the windward shore prior to rain formation.