Intercomparison of stable isotopes in precipitation simulated by GCMs with GNIP survey over East Asia

Using the isotope enabled ECHAM4,GISS E and HadCM3 GCMs,the spatial distribution of mean δ18 O in precipitation,mean seasonality and the correlations of δ18 O in precipitation with temperature and precipitation amount are analyzed.The simulated results are in agreement with stable isotopic features by GNIP observations.Over East Asia,the distribution of δ18 O in precipitation is of marked latitude effect and altitude effect.The latitude effect is covered by the continent effect in some regions.The largest seasonality of δ18 O in precipitation appears in eastern Siberia controlled by cold high pressure,and the smallest seasonality is in the western Pacific controlled by the subtropical high.Relatively weak seasonality appears in middle latitudes where oceanic and continental air masses frequently interact.However,three GCMs show significant systematic lower δ18 O for inland mid-high latitudes than GNIP data,which is related to the used isotopic scheme in GCMs.Temperature effect occurs mainly in inland mid-high latitudes.The higher the latitude and the closer the distance to inland is,then the stronger the temperature effect.Amount effect occurs mainly in low-mid latitudes and monsoon areas,with the strongest effect in low-latitude coasts or islands.However,three GCMs provide virtually non-existent amount effect in arid regions over Central Asia.The enrichment action of stable isotopes in falling raindrops under a cloud base,which is enlarged by these modes,is responsible for such a result.A significant difference between spatial distributions of δ18 O statistics by GCMs simulations and by GNIP observations is that the standard deviation of GCMs statistics is greater than that of GNIP statistics.In contrast,by comparing parallel time series at a single station,the standard deviations of GCMs simulations are smaller than that of GNIP observations.