Stratospheric temperature increases due to Pinatubo aerosols

Northern hemisphere stratospheric temperatures at 30 and 50 mb beginning in June 1991 are compared with 20‐year (1965–1984) and 26‐year (1964–1989) monthly means. Significant temperature increases are shown in July, August, September, and October for latitudes from approximately 30°N to the equator. In September and October, +2σ to +3σ deviations are observed for large areas between the equator and 30°N, with temperature increases as high as +3.5°C occurring at some locations. The monthly averaged zonal mean 30‐mb temperatures at 20°N in September and October were approximately 2.5°C higher than the 26‐year mean, with some daily zonal mean increases of almost 3°C. Higher values occurred equatorward of 20°N. We believe these warmings are due to absorption of radiation by the new aerosols produced from the June eruptions of the volcano Pinatubo (15.1°N, 120.4°E) in the Philippines. We also expect stratospheric warmings to be occurring simultaneously at southern latitudes, especially from the equator to about 20°S, based on satellite and lidar measurements of the locations of the new aerosol layers. These localized temperature increases should decrease in magnitude and become more global as the cloud disperses globally and spreads in altitude.