Two‐dimensional simulation of Pinatubo aerosol and its effect on stratospheric ozone

Abstract

This paper presents time-dependent simulations of the response of the stratosphere to the injection into the atmosphere of massive amounts of sulfur during the eruption of Mt. Pinatubo (The Philippines) in June 1991. The study is based on a coupled two-dimensional chemical-dynamical-radiative model to which a microphysical model for sulfate aerosol formation and fate has been added. The study suggests that, during the first year (July 1991 to June 1992) following the volcanic eruption, the observed changes in the ozone amount integrated between 65øS and 65øN were caused primarily by changes in the meridional circulation (associated with heating by the volcanic cloud in the tropics) and in the photolysis rate of molecules such as ozone (associated with backscattering of light by the cloud). During the second year after the eruption, as the aerosol was dispersed at all latitudes and, in particular, reached the polar region, the largest contribution to ozone reduction resulted from the heterogeneous chemical conversion of N205 and C1ONO2 on the surface of the aerosol particles. The conversion of the latter compound, and hence the magnitude of the calculated ozone depletion, is highly dependent on the temperature in the lower stratosphere. Despite the fact that the surface area provided by aerosol particles decreased during the second year following the eruption, the calculated ozone depletion remained significant because the conversion of N9. O5 is insensitive to the aerosol surface area density for values larger than 1-10/zm2/cm 3 (depending on latitude). The predicted reduction in ozone at 20 km in March during the third year (July 1993 to June 1994) of the model integration is smaller by a factor of 2 than it was during the second year.

An Estimation of the Radiative Effect in the Stratosphere due to the Pinatubo Aerosol

“…The present study, however, demonstrated that the sense of the primary effect of the Pinatubo sulfate aerosol due to terrestrial radiation is a cooling in a narrow layer above the cross-over height of 18hPa (27km) and a warming in a widdddde layer below that height to 100hPa. The terrestrial warming due to the Pinatubo sulfate aerosol qualitatively agrees with those calculated by Young et al (1994), Tie et al (1994) and Pitari (1993), while the terrestrial cooling in the upper layer agrees with only that by Pitari (1993). This disagreement is thought to come mainly from the difference of aerosol heights, temperature profiles, and tropospheric conditions.…”

“…The tropospheric cooling and stratospheric warming due to solar radiation can be applied even when the temperature responses to the aerosol radiative heating, because the solar heating does not depend on the atmospheric conditions, except for ozone concentration, which decreases through the heterogeneous chemical reaction on the surface of the sulfate aerosol and through the vertical transport due to radiative heating perturbation (e.g., Tie et al, 1994;Grant et al, 1994). On the other hand, the result for the terrestrial radiation is valid only for the temperature used here because of its strong dependence on the local temperature.…”

“…The FDH model is, indeed, valid and useful to investigate the radiative effect alone, as in, for example, Fels (1985) and Pawson and Shine (1991), but the comparison with observed temperature needs some attention because the feedback effect of dynamics (and chemistry) is not necessarily small, particularly at high latitudes in winter. The incorporation of dynamical heating, which comes from heat flux due to meridional circulation and planetary and gravity waves, entails a two-dimensional model (e.g., Tie et al, 1994;Kinnison et al, 1994;Gerstel et al, 1995) or three-dimensional model (e.g., Rind et al, 1992;Pitari, 1993;Hansen et al, 1993), thus being beyond the scope of this paper. The evaluation, however, can be economically made, so long as the radiative perturbation is small enough, by adding the radiative heating perturbations obtained in this study as an external heating to on-line calculated heating in general circulation models (GCMs), which include no scattering process, as done by Graf et al (1992) and Graf et al (.1993) .…”

“…It also depends on other radiative properties and conditions such as single scattering albedo, composition and height of aerosol (Lacis et al, 1992;Lacis and Mishchenko, 1995). It is shown, for Pinatubo sulfate aerosol, that the major radiative effect is warming due to the absorption of terrestrial radiation from the troposphere, while the solar heating is a minor or negligible effect (Young et al, 1994;Tie et al, 1994).…”

“…Positive anomalies greater than 2 K could still be seen between 30°N and20°S in February 1992 (Kawamata et al, 1992). A significant decrease of NO2 (Perliski and Solomon, 1992;Koike et al, 1993) and 03 (Gleason et al, 1993;Tie et al, 1994) occurred through the heterogeneous chemical reactions on the sulfate aerosol surface (e.g., Brasseur and Granier, 1992).…”