Abstract
Using the Geophysical Fluid Dynamics Laboratory SKYHI GCM with a high vertical resolution and a recently improved radiative transfer code, we investigate the aerosol radiative forcing and the stratospheric temperature response for the June 15, 1991, Mount Pinatubo eruption. The investigation is carried out using an updated, comprehensive monthly and zonal-mean Pinatubo aerosol spectral optical properties data set. While the NIR solar spectral effects contribute substantially to the total stratospheric heating due to aerosols, over the entire global domain the longwave component exceeds the solar in causing a warming of the lower stratosphere (30-100 hPa). In contrast, the magnitude of the solar perturbation (increased reflection) in the overall surface-atmosphere radiative heat balance exceeds that due to the longwave (IR trapping effect). The troposphere affects the stratospheric radiative forcing, mainly because of the dependence of the reflected solar and upward longwave radiation on cloudiness, and this adds to the uncertainty in the calculation of the stratospheric temperature response. A four-member ensemble of 2-yr GCM integrations (June 1991 to May 1993) were performed using fixed SSTs and a cloud prediction scheme, one set with and another without the volcanic aerosols. The temperature of the tropical lower stratosphere increases by a statistically significant 3 K, which is almost 1 K less than in previous investigations that employed coarser vertical resolution in the stratosphere, but is still larger than observed. (Author)