RESULTS Frontier Newsletter No.13 Jan.2001

Study of the Possible Impacts of Global Warming on the Winter Cyclone Activity over the East Asia-Pacific Region with a High-resolution AGCM

Dr.Quanzhen Geng(Global Warming Research Program),Dr.Masato Sugi(Meteorological Research Institute)

Fig.1 : Cyclone density in winter
Fig.1 : Cyclone density in winter

(a) NCEP ; (b) T106 control ; (c) difference between the global warming run and the control run.Unit is in cyclones /4.5 ‹~4.5 ‹lon ]lat / season.

One of the research goals of the Global Warming Research Program is to give a reliable estimation of the impacts of global warming on the weather and climate events. With the high- resolution AGCM (T 106 )of Japan Meteorological Agency (JMA),this study investigates the possible changes of the extratropical cyclones due to enhanced greenhouse gases and sulfate aerosols.

Two 20 - yr experiments are performed with the AGCM,that is,the control run (CTL)and the time- slice global warming run (GWR).In the control run,the atmos- phere is forced by the observed SST and sea- ice of 1979 - 1998 .In the global warm- ing run,the atmosphere is forced by the monthly mean anomalies of SST and sea-ice obtained from a transient climate change experiment with the GFDL coupled ocean- atmosphere model with a low- resolution of R 15 .The equivalent amounts of CO 2 and sulfate aerosol concentrations at about year 2050 ,as used in the GFDL R 15 model,are prescribed.

The cyclone activity appeared in the high- resolution AGCM is analyzed using an objective cyclone detection and tracking algorithm.Cyclone density,cyclone tracks, moving speed,deepening rate,and intensity are examined and compared with that ana- lyzed form the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research(NCAR) reanalysis data of the same period from 1979 to 1998 .Figs.1 a- b show that the simu- lated cyclone activity is very similar to that analyzed from the NCEP reanalysis data. Encouraged by the good performance of the model in reproducing the cyclone climatol- ogy,we go a step further to use the model to investigate the possible impacts of global warming on the cyclone activity.

As shown in Fig.1 c,the cyclone density (the number of cyclones appeared in a unit area in one season)in winter over the East Asia- Pacific region exhibits a remarkable reduction due to enhanced greenhouse gases and sulfate aerosols.Further analysis shows that the cyclone intensity,moving speed and deepening rate are weakened at the beginning of the Pacific storm track.This will be expected to have a strong influence on the weather and climate events in winter over the East Asian countries such as Japan, Korea,and north and northeast China.For the whole Northern Hemispheric extratrop- ics (20 - 80 KN),the cyclone density in win- ter decreases about 10 %.

With the high- resolution climate model, we are now extending our research to inves- tigate the impacts of global warming on other weather systems,such as the Baiu front.

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