CGER Reports

CGER’S SUPERCOMPUTER MONOGRAPH REPORT Vol.13

Simulations of the Stratospheric Circulation and Ozone during the Recent Past (1980–2004) with the MRI Chemistry-Climate Model

Kiyotaka Shibata [Meteorological Research Institute, Guest Investigator of NIES]
Makoto Deushi [Meteorological Research Institute]

This monograph is to describe the result of a middle-atmosphere ensemble simulation of the past 25 years from 1980 to 2004 using the chemistry-climate model (CCM) of the Meteorological Research Institute (MRI), taking into account observed forcings of sea-surface temperature, greenhouse gases, halogens, halons, volcanic aerosols, and solar irradiance variations. Five members with slightly different initial conditions are integrated in the ensemble simulation. The MRI-CCM dynamics module is a global spectral model truncated triangularly at a maximum wavenumber of 42 with 68 levels extending from the surface to 0.01 hPa (about 80 km) and a vertical spacing of 500m from 100 to 10 hPa. The chemistry module incorporates 51 species and 124 reactions including heterogeneous reactions. Multiple linear regression analysis with time lags for volcanic aerosols was performed on the zonal-mean quantities of the simulated result to separate the trend, the QBO, the El Chichón and Mount Pinatubo, the 11-year solar cycle, and the El Niño/Southern Oscillation (ENSO) signals. We hope that this research will contribute to increased accuracy in future predictions of ozone layer and related climate variations.

Figure 1 depicts the time evolution of the simulated total ozone for the entire period (1980 to 2004) together with the observed (TOMS/SBUV) total ozone for 1980 to 2001. The model simulates larger interannual variations in high northern latitudes than in high southern latitudes, similar to the observation data. The MRI-CCM reproduced the observed features in the ozone hole over the Antarctic: the area increases in size yearly beginning in the early 1980s, and eventually stabilizes beginning in the late 1990s.

Fig.1 Evolutions of the zonal-mean total ozone (DU) latitudinal distribution for the ensemble mean of the five members (upper) and the observation data (TOMS/SBUV) (lower).

Figure 2 illustrates the linear trend (K/decade) of the annual- and zonal-mean temperature of the ensemble-mean and the observation (ERA-40). The MRI-CCM produces a strong cooling band due to the increase in greenhouse gases, with two maxima exceeding 2.0 K/decade at the stratopause, very similar to that in the simulation. The trend of annual- and zonal-mean ozone (Fig.3) shows an intense decrease band at 2~5 hPa with maxima in the both middle latitudes, while there is a minimum decrease in the middle stratosphere in the tropics.

Fig.2 Latitude-pressure cross sections of the zonal-mean temperature linear trend (K/decade) from 200 to 0.1 hPa. Shading denotes the area of linear trend difference from zero at a 95% confidence level (t-test). Ensemble mean of the five members (left, contour interval is 0.25 K/decade) and the observation data (ERA-40) (right, contour interval 0.5 K/decade).
Fig.3 Latitude-pressure cross sections of the ozone linear trend (%/decade) from 200 to 0.1 hPa. Shading denotes the area of linear trend difference from zero at a 95% confidence level (t-test). The contour interval is 2%/decade. Ensemble mean of the five members (left) and observation data sets (TOMS/SBUV, upper right; SAGE I/II, lower right).