In this study,we evaluate the forecast skill of the subseasonal-to-seasonal(S2S)prediction model of the Beijing Climate Center(BCC)for the boreal summer intraseasonal oscillation(BSISO).We also discuss the key factors...In this study,we evaluate the forecast skill of the subseasonal-to-seasonal(S2S)prediction model of the Beijing Climate Center(BCC)for the boreal summer intraseasonal oscillation(BSISO).We also discuss the key factors that inhibit the BSISO forecast skill in this model.Based on the bivariate anomaly correlation coefficient(ACC)of the BSISO index,defined by the first two EOF modes of outgoing longwave radiation and 850-hPa zonal wind anomalies over the Asian monsoon region,we found that the hindcast skill degraded as the lead time increased.The ACC dropped to below 0.5for lead times of 11 days and longer when the predicted BSISO showed weakened strength and insignificant northward propagation.To identify what causes the weakened forecast skill of BSISO at the forecast lead time of 11 days,we diagnosed the main mechanisms responsible for the BSISO northward propagation.The same analysis was also carried out using the observations and the outputs of the four-day forecast lead that successfully predicted the observed northward-propagating BSISO.We found that the lack of northward propagation at the 11-day forecast lead was due to insufficient increases in low-level cyclonic vorticity,moistening and warm temperature anomalies to the north of the convection,which were induced by the interaction between background mean flows and BSISO-related anomalous fields.The BCC S2S model can predict the background monsoon circulations,such as the low-level southerly and the northerly and easterly vertical shears,but has limited capability in forecasting the distributions of circulation and moisture anomalies.展开更多
The Tibetan Plateau is a key factor for the pattern of the general circulation of the atmosphere (GCA) in eastern Asia. The pattern of the GCA after the uplift of the plateau is well known, while the pattern of the GC...The Tibetan Plateau is a key factor for the pattern of the general circulation of the atmosphere (GCA) in eastern Asia. The pattern of the GCA after the uplift of the plateau is well known, while the pattern of the GCA before the uplift of the plateau is lack of direct evidences. Based on the knowability of desert, a section recording wind directions across the Cretaceous northern hemisphere mid-low latitude desert belt is measured and the pattern of the GCA in the Cretaceous is revealed. The result shows that the eastern Asia was really controlled by the planetary circulation before the uplift of the plateau, i.e. westerlies in the north and northeast trades in the south. The convert belt between westerlies and trades had drifted northwards and southwards. The possibility of existence of paleo-monsoon is also dealt with and a possibly imposed paleo-monsoon is suggested.展开更多
基金supported by the National Basic Research Program of China (973 Program) (Grant No.2015CB453200)
文摘In this study,we evaluate the forecast skill of the subseasonal-to-seasonal(S2S)prediction model of the Beijing Climate Center(BCC)for the boreal summer intraseasonal oscillation(BSISO).We also discuss the key factors that inhibit the BSISO forecast skill in this model.Based on the bivariate anomaly correlation coefficient(ACC)of the BSISO index,defined by the first two EOF modes of outgoing longwave radiation and 850-hPa zonal wind anomalies over the Asian monsoon region,we found that the hindcast skill degraded as the lead time increased.The ACC dropped to below 0.5for lead times of 11 days and longer when the predicted BSISO showed weakened strength and insignificant northward propagation.To identify what causes the weakened forecast skill of BSISO at the forecast lead time of 11 days,we diagnosed the main mechanisms responsible for the BSISO northward propagation.The same analysis was also carried out using the observations and the outputs of the four-day forecast lead that successfully predicted the observed northward-propagating BSISO.We found that the lack of northward propagation at the 11-day forecast lead was due to insufficient increases in low-level cyclonic vorticity,moistening and warm temperature anomalies to the north of the convection,which were induced by the interaction between background mean flows and BSISO-related anomalous fields.The BCC S2S model can predict the background monsoon circulations,such as the low-level southerly and the northerly and easterly vertical shears,but has limited capability in forecasting the distributions of circulation and moisture anomalies.
基金the National Natural Science Foundation of China (Grant No. 49572113).
文摘The Tibetan Plateau is a key factor for the pattern of the general circulation of the atmosphere (GCA) in eastern Asia. The pattern of the GCA after the uplift of the plateau is well known, while the pattern of the GCA before the uplift of the plateau is lack of direct evidences. Based on the knowability of desert, a section recording wind directions across the Cretaceous northern hemisphere mid-low latitude desert belt is measured and the pattern of the GCA in the Cretaceous is revealed. The result shows that the eastern Asia was really controlled by the planetary circulation before the uplift of the plateau, i.e. westerlies in the north and northeast trades in the south. The convert belt between westerlies and trades had drifted northwards and southwards. The possibility of existence of paleo-monsoon is also dealt with and a possibly imposed paleo-monsoon is suggested.
