NEW APPLICATION OF THE OPERATIONAL SOUNDER HIRS IN DETERMINING A CLIMATOLOGY OF SULFURIC-ACID AEROSOL FROM THE PINATUBO ERUPTION

The high-resolution infrared radiation sounder (HIRS) has been used to retrieve sulphuric acid aerosol from the June 15, 1991, eruption of Mount Pinatubo (15.1 degrees N, 120.4 degrees E). The aerosol climatology retrieved includes latitudinal distributions of column density and monthly global mass loadings from May 1991 to Autumn 1993. The method of retrieval utilizes the sensitivity of one of the HIRS channels situated at 8.3 mu m to the aerosol; The retrieved transmission at 8.3 mu m is related to the column density via the specific absorption coefficient. A second channel at 12.5 mu m, which is relatively insensitive to the aerosol, is used to remove other variations in the signal at 8.3 mu m. In July 1991, latitudinal distributions of column density show the aerosol confined to the tropics with the bulk of the aerosol mass located south of the equator. By May 1993 the aerosol has returned to a preeruption level in the tropics. The transport of aerosol to southern latitudes is shown to be more rapid than to northern latitudes. Monthly global mass loadings are estimated to be 15 Mt (megatons) in July 1991, rising to 21 Mt by September 1991, later dropping to 16 Mt by July 1992, and returning to preeruption values by October 1993. The results derived in this paper should prove useful for climate models attempting to study the global impact of the Pinatubo eruption.