The Effect of Solar Radiation Absorption in the Tropical Troposphere

Abstract

Data from an experiment to measure the upward and downward components of solar radiation from aircraft during the Barbados Oceanographic and Meteorological Experiment (BOMEX) have been analyzed in the present study. Two groups of results were found. In the cloud-free tropical troposphere: 1) Absorption of solar radiation in the entire troposphere can be twice as large as previous estimates of 13% given by Manabe and Strickler. Comparison of observed heating rates to calculations shows that the increase in attenuation may be due to non-gaseous constituents in the atmosphere. 2) The vertical profile of solar radiative heating was particularly variable in the lowest layers while in the mean, the profile suggests a slight maximum near 700 mb. 3) In using the solar radiation observations of this study in an energy budget of the tropics a hypothesis regarding a nighttime maximum of precipitation in the tropical regions was formed. Findings from a radiative study of certain cloud type cases show (i) selective vertical absorption in stratocumulus acts to destabilize the clouds' environment; (ii) large cumulus or cumulonimbus clouds occasionally decrease the solar insolation reaching the surface to only 3% of that incoming at cloud top; and (iii) cirrus clouds are possible stabilizing mechanisms in the tropical environment since they act to warm the local environment at high altitudes while suppressing solar warming from cloud base to surface.