Effect of the Increase in Stratospheric Background Sulfate Aerosol on Stratospheric Temperature

Abstract

Balloon, lidar and satellite observations indicate that the concentration of stratospheric background sulfate aerosol is gradually and globally increasing due to anthropogenic and/or natural causes. By considering the above fact, this study investigates the extent to which the background aerosol increase can change the stratospheric temperature through the perturbation in radiative heating alone. The temperature change is evaluated with a seasonally-marched, fixed dynamical heating model, which prescribes tropospheric conditions and stratospheric dynamical heating. Radiative perturbation and hence temperature perturbation respond linearly to doubled and tripled background levels, the stratospheric loads of which are 0.0087 and 0.0174, respectively, at 0.55μm. The doubled background level yields radiative forcings of about -0.18, 0.03 and -0.15Wm^-2 for solar, terrestrial and net radiation, respectively. For the tripled background level, the middle and lower stratosphere in low latitudes warms by about 0.15K due primarily to the perturbation of terrestrial radiation with very weak annual oscillation. In high latitudes, on the other hand, the middle and lower stratosphere cools by about 0.15K due primarily to the perturbation of solar radiation with pronounced semiannual oscillation (maxima around solstice and minima around equinox) of about 0.1K. The causes of the latitudinal difference and the interhemispheric difference are described in relation to the background temperature and its seasonal march.