Infrared Greybody Emissivity and Visible Albedo of High Altitude Semitransparent Cloud

Abstract

Infrared greybody emissivity of high altitude semitransparent cloud at anvil-head accompanying large scale convective cloud system and the relationship to the visible albedo was estimated from GMS-1 radiation measurements. Generally we can not estimate the greybody emissivity of semitransparent cloud like cirrus from the only satellite radiation measurement because satellite observations do not directly give the cloud top temperature which is needed for estimate of the greybody emissivity. However, the greybody emissivity of semitransparent cloud can be easily estimated under the condition that the temperature of the anvil may be approximately equal to that of the core of the system. Seventeen examples satisfying nearly the condition were picked out from imageries of GMS-1 (22 Sept. 1979) in the tropical region. The author could estimate the greybody emissivity of many semitransparent clouds from the only radiation measurement of the satellite. Obtained relationships between cloud greybody emissivity and the visible albedo showed radiative character between the theoretical relationships for the cloud of long ice cylinders and that of spherical droplets. In addition, it showed that the greybody emissivity of semitransparent cloud increases more quickly than the albedo with increasing of the optical thickness.