• Introduction
• Model overview
• Ozone contribution from the stratosphere
• Ozone change in 1997 El Nino
• References

FIGURES

• Figure 1
• Figure 2
• Figure 3
• Figure 4
• Figure 5
• Figure 6
• Figure 7

1. Introduction
Tropospheric ozone is not only a principal green house effect gas, but also the most important chemical s. Understanding of present global distribution and budget of tropospheric ozone is very important for future prediction of atmospheric environment and climate. Stratospheric ozone is one of possible source of tropospheric ozone. Contribution of stratospheric ozone to the global budget of tropospheric ozone is, however, still uncertain. In this study, stratospheric effect on the distribution and budget of tropospheric ozone is analyzed using a 3D chemical model.

2. Model overview

The model used in this study has been developed by using the Center for Climate System Research/National Institute for Environmental Studies(CCSR/NIES) AGCM. This model is aimed at studying the global distribution and budget of tropospheric ozone and its precursors, and radiative effect of tropospheric ozone. The horizontal resolution is T21(5.6^ox5.6^o) with 32 layers in the vertical from the surface up to about 40 km altitude. In the present configuration of the model, the chemical component of the model predicts the concentration of 24 chemical species between the surface and approximately 20 km altitude, including 52 chemical reactions and 11 photolytic reactions. In this study, only ethane and ethene are considered as NMHCs trace gas. The model, however, can represent background chemistry of the troposphere. More detailed chemistry including biogenic NMHCs is now being implemented. The model also includes surface emission and wet/dry deposition. Surface emission data are mainly taken from Olivier et al., 1996. Detailed description will be discussed in Sudo et al.,(to be submitted).

3. Ozone contribution from the stratosphere

Figure 1 shows the percent contribution of stratospheric ozone to the tropospheric ozone distribution at the surface and 500 hPa for January and July.

Surface contribution is greater than 50% in the mid-high latitude in winter time and generally smaller than 10% in the polluted region in summer time, reflecting strong photochemical production of ozone. At 500 hPa altitude, contribution in the tropical region is small throughout a year because of intensive and deep convection, short life time of ozone associated with high humidity, and ozone chemical production due to lightning NO_x and biomass burning emission.
Figure 2 shows zonal averaged ozone contribution from the stratosphere. The similar seasonal variation as Figure 1 is seen.

Figure 3 indicates the effect of stratospheric ozone on seasonality of surface ozone concentration. Ozone from the stratosphere does not seem to control seasonality of surface ozone in these selected sites.

Tropospheric ozone budget in the model is seen in Table 1. Stratospheric ozone influx is relatively small compared to chemical production in the troposphere. The value of 636 TgO3/yr is within a range suggested in recent literatures(typically 400-1000 TgO3/yr).

4. Ozone change in 1997 El Nino

We conducted a simulation on the tropospheric ozone change in September and October 1997. Ozone enhancement in Indonesia during this period was reported in Fujiwara et al.,[1997], and elevated CO levels over Indonesia were also observed(Sawa et al., 1999). Satellite derived data from EP TOMS (Chandra et al., 1998) also indicates these changes(Figure 4).

In addition to the extensive forest fire event occurred in Indonesia, Meteorological changes in convection, humidity, precipitation, and transport from the stratosphere cold be big contributors to observed ozone change. In this simulation, SST data and ECMWF wind and temperature data of 1996, 1997 were used as nudging input to the GCM for a direct comparison to Chandra et al.,1998. Emission change due to extensive forest fire in Indonesia is not included in order to evaluate the effect of meteorological changes itself. Figure 5 shows simulated TCO(Tropospheric Column Ozone) anomaly corresponding to Figure 4. An asymmetrical dipole centered near the date line with TCO is well reproduced. It should be noted that simulated TCO enhancement in Indonesia is underestimated just because emission change associated with the extensive forest fire in Indonesia is not considered in this simulation.

Figure 6 shows the simulated difference of specific humidity (g/kg), ozone chemical lifetime change rate (%) between October 1997 and October 1996. It is clearly seen that chemical life time of ozone over Indonesian region is 2 or 3 times longer in October 1997 than in October 1996. This is just correspondig to much drier condition in Indonesia.

Figure 7 shows ozone concentration (ppbv) which originates in the stratosphere over Indonesian region for October 1997 and October of climatological run of the model. It is clear that more ozone intruded to the lower latitude from the mid latitude in both hemisphere in October 1997 compared to the climatological condition. This could be associated with low convective activity and low humidity in the Indonesian region during this period. These changes in humidity, convection and transport of stratospheric ozone consequently caused the tropospheric ozone change seen in Figure 5.

References

Chandra, S., J.R..Ziemke, W.Min and W.G. Read, Effects of 1997-1998 El Nino on tropospheric ozone and water vapor, Geophys. Res. Lett., 25, 3867-3870, 1998.

Fujiwara, M., K. Kita, S. Kawakami, T. Ogawa, N. Komala, S. Saraspriya, and A. Suripto, Tropospheric ozone enhancements during the Indonesian forest fire events in 1994 and in 1997 as revealed by ground-based observations, Geophys. Res. Lett., 26 , 2417-2420, 1999.

Olivier, J.G.J., Bouwman, A.F., Van der Maas, C.W.M., Berdowski, J.J.M, Veldt, C. Bloos, J.P.J., Visschedijk, A.J.H., Zandveld, P.Y.J., Haverlag, J.L, Description of EDGAR Version 2.0. A set of global emission inventories of greenhouse gases and ozone-depleting substances for all anthropogenic and most natural sources on a per country basis and on 1ox1o grid. RIVM/TNO report, December 1996. RIVM, Bilthoven, RIVM report nr. 771060 002. [TNO MEP report nr. R96/119], 1996.

Sawa, Y., H. Matsueda, Y. Tsutsumi, J. B. Jensen, H. Y. Inoue, and Y. Makino, Tropospheric carbon monoxide and hydrogen measurements over Kalimantan in Indonesia and northern Australia during October, 1997, Geoph. Res. Lett., 26 , 1389-1392, 1999.