This paper analyzes the characteristics of super typhoons (STYs) over the western North Pacific (WNP) from 1965 to 2005 and describes the seasonal variability of STY activity. The relation between STY activity and...This paper analyzes the characteristics of super typhoons (STYs) over the western North Pacific (WNP) from 1965 to 2005 and describes the seasonal variability of STY activity. The relation between STY activity and the E1 Nifio-Southern Oscillation (ENSO) as well as the possible reason for the influence of the ENSO on STY activity are also investigated. The results showed that about one fifth of the tropical cyclones (TCs) over the WNP could reach the rank of STY. Most STYs appeared from July to November while there was a highest ratio between number of STYs and total number of TCs in November. Most STYs appeared east of the Philippine Sea. In E1 Nino years, affected by sea surface temperature (SST), monsoon trough and weak vertical wind shear, TC formation locations shifted eastward and there were more STYs than in La Nifia years when the affecting factors changed.展开更多
By using Season-reliant Empirical Orthogonal Function (S-EOF) analysis, three dominant modes of the spatial-temporal evolution of the drought/flood patterns in the rainy season over the east of China are revealed for ...By using Season-reliant Empirical Orthogonal Function (S-EOF) analysis, three dominant modes of the spatial-temporal evolution of the drought/flood patterns in the rainy season over the east of China are revealed for the period of 1960-2004. The first two leading modes occur during the turnabout phase of El Nino-Southern Oscillation (ENSO) decaying year, but the drought/flood patterns in the rainy season over the east of China are different due to the role of the Indian Ocean (IO). The first leading mode appears closely correlated with the ENSO events. In the decaying year of El Nino, the associated western North Pacific (WNP) anticyclone located over the Philippine Sea persists from the previous winter to the next early summer, transports warm and moist air toward the southern Yangtze River in China, and leads to wet conditions over this entire region. Therefore, the precipitation anomaly in summer exhibits a 'Southern Flood and Northern Drought' pattern over East China. On the other hand, the basin-wide Indian Ocean sea surface temperature anomaly (SSTA) plays a crucial role in prolonging the impact of ENSO on the second mode during the ENSO decaying summer. The Indian Ocean basin mode (IOBM) warming persists through summer and unleashes its influence, which forces a Matsuno-Gill pattern in the upper troposphere. Over the subtropical western North Pacific, an anomalous anticyclone forms in the lower troposphere. The southerlies on the northwest flank of this anticyclone increase the moisture transport onto central China, leading to abundant rainfall over the middle and lower reaches of the Yangtze River and Huaihe River valleys. The anomalous anticyclone causes dry conditions over South China and the South China Sea (SCS). The precipitation anomaly in summer exhibits a 'Northern Flood and Southern Drought' pattern over East China. Therefore, besides the ENSO event the IOBM is an important factor to influence the drought/flood patterns in the rainy season over the east of China. The third mode is positively correlated with the tropical SSTA in the Indian Ocean from the spring of preceding year(-1) to the winter of following year(+1), but not related to the ENSO events. The positive SSTA in the South China Sea and the Philippine Sea persists from spring to autumn, leading to weak north-south and land-sea thermal contrasts, which may weaken the intensity of the East Asia summer monsoon. The weakened rainfall over the northern Indian monsoon region may link to the third spatial mode through the 'Silk Road' teleconnection or a part of circumglobal teleconnection (CGT). The physical mechanisms that reveal these linkages remain elusive and invite further investigation.展开更多
Previous studies have revealed a significantly negative correlation between prior winter snow cover over the Tibetan Plateau (TPSC) and tropical cyclone genesis frequency (TCF) over the western North Pacific (WNP...Previous studies have revealed a significantly negative correlation between prior winter snow cover over the Tibetan Plateau (TPSC) and tropical cyclone genesis frequency (TCF) over the western North Pacific (WNP) in the following typhoon season. This study revisited this relationship based on long-term observational data. The results showed that the interannual correlation between TCF over the WNP and TPSC experienced a shift in the early 1990s. This correlation is significant during only 1993-2012 and is considerably weak during 1976-1992. The possible reasons causing the shift were examined further, and the results demonstrated that the central Pacific (CP) E1 Nifio-Southern Oscillation (ENSO) has played a vital role in intensifying the interannual relationship between TCF over the WNP and TPSC since the early 1990s. During 1993-2012, TPSC was negatively related to CP ENSO. When TPSC was higher than (lower than) normal, CP ENSO was often in its cold (warm) phase. Such a combination remarkably enhances the relationship of TPSC with the zonal land-sea thermal difference and thus with the summer monsoon over the WNE Additionally, it enhances the modulation of TPSC on the dynamical environments controlling TCF. As a result, the linkage between TPSC and TCF was significantly strengthened in this period. In sharp contrast, due to the weak relationship between TPSC and ENSO followed by the weak modulation of TPSC on the summer monsoon over the WNP and the dynamical environment during 1976-1992, the linkage between TPSC and TCF was weak during this time period. The results from additional dynamical diagnostic analyses further showed that during 1993-2012 CP ENSO modulated the barotropic energy conversion of zonal winds over the WNP, contributing to the intensified relationship between TPSC and TCF. These results will improve seasonal forecasting of tropical cyclone activity over the WNP.展开更多
During recent decades, more frequent flood-drought alternations have been seen in China as a result of global climate change and intensive human activities, which have sig- nificant implications on water and food secu...During recent decades, more frequent flood-drought alternations have been seen in China as a result of global climate change and intensive human activities, which have sig- nificant implications on water and food security. To better identify the characteristics of flood-drought alternations, we proposed a modified dry-wet abrupt alternation index (DWAAI) and applied the new method in the middle and lower reaches of the Yangtze River Basin (YRB-ML) to analyze the long-term spatio-temporal characteristics of dry-wet abrupt alterna- tion (DWAA) events based on the daily precipitation observations at 75 rainfall stations in summer from 1960 to 2015. We found that the DWAA events have been spreading in the study area with higher frequency and intensity since 1960. In particular, the DWAA events mainly occurred in May and June in the northwest of the YRB-ML, including Hanjiang River Basin, the middle reaches of the YRB, north of Dongting Lake and northwest of Poyang Lake. In addition, we also analyzed the impact of El Nifio Southern Oscillation (ENSO) on DWAA events in the YRB-ML. The results showed that around 41.04% of DWAA events occurred during the declining stages of La Nifia or within the subsequent 8 months after La Nina, which implies that La Nina events could be predictive signals of DWAA events. Besides, significant negative correlations have been found between the modified DWAAI values of all the rainfall stations and the sea surface temperature anomalies in the Nino3.4 region within the 6 months prior to the DWAA events, particularly for the Poyang Lake watershed and the middle reaches of the YRB. This study has significant implications on the flood and drought control and water resources management in the YRB-ML under the challenge of future climate change.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.s 40975038 and10735030)the State Key Development Program for Basic Research of China(973 Program)(Grant Nos.2006CB403603 and 2005CB422301)111 Project(Grant No.B07036)
文摘This paper analyzes the characteristics of super typhoons (STYs) over the western North Pacific (WNP) from 1965 to 2005 and describes the seasonal variability of STY activity. The relation between STY activity and the E1 Nifio-Southern Oscillation (ENSO) as well as the possible reason for the influence of the ENSO on STY activity are also investigated. The results showed that about one fifth of the tropical cyclones (TCs) over the WNP could reach the rank of STY. Most STYs appeared from July to November while there was a highest ratio between number of STYs and total number of TCs in November. Most STYs appeared east of the Philippine Sea. In E1 Nino years, affected by sea surface temperature (SST), monsoon trough and weak vertical wind shear, TC formation locations shifted eastward and there were more STYs than in La Nifia years when the affecting factors changed.
基金supported by the National Basic Research Program of China (973 Program) (No. 2012CB955604)the National Natural Science Foundation of China (Nos. 40975038, 40830106)+1 种基金the CMA Program (GYHY200906008)the 111 Project (B07036)
文摘By using Season-reliant Empirical Orthogonal Function (S-EOF) analysis, three dominant modes of the spatial-temporal evolution of the drought/flood patterns in the rainy season over the east of China are revealed for the period of 1960-2004. The first two leading modes occur during the turnabout phase of El Nino-Southern Oscillation (ENSO) decaying year, but the drought/flood patterns in the rainy season over the east of China are different due to the role of the Indian Ocean (IO). The first leading mode appears closely correlated with the ENSO events. In the decaying year of El Nino, the associated western North Pacific (WNP) anticyclone located over the Philippine Sea persists from the previous winter to the next early summer, transports warm and moist air toward the southern Yangtze River in China, and leads to wet conditions over this entire region. Therefore, the precipitation anomaly in summer exhibits a 'Southern Flood and Northern Drought' pattern over East China. On the other hand, the basin-wide Indian Ocean sea surface temperature anomaly (SSTA) plays a crucial role in prolonging the impact of ENSO on the second mode during the ENSO decaying summer. The Indian Ocean basin mode (IOBM) warming persists through summer and unleashes its influence, which forces a Matsuno-Gill pattern in the upper troposphere. Over the subtropical western North Pacific, an anomalous anticyclone forms in the lower troposphere. The southerlies on the northwest flank of this anticyclone increase the moisture transport onto central China, leading to abundant rainfall over the middle and lower reaches of the Yangtze River and Huaihe River valleys. The anomalous anticyclone causes dry conditions over South China and the South China Sea (SCS). The precipitation anomaly in summer exhibits a 'Northern Flood and Southern Drought' pattern over East China. Therefore, besides the ENSO event the IOBM is an important factor to influence the drought/flood patterns in the rainy season over the east of China. The third mode is positively correlated with the tropical SSTA in the Indian Ocean from the spring of preceding year(-1) to the winter of following year(+1), but not related to the ENSO events. The positive SSTA in the South China Sea and the Philippine Sea persists from spring to autumn, leading to weak north-south and land-sea thermal contrasts, which may weaken the intensity of the East Asia summer monsoon. The weakened rainfall over the northern Indian monsoon region may link to the third spatial mode through the 'Silk Road' teleconnection or a part of circumglobal teleconnection (CGT). The physical mechanisms that reveal these linkages remain elusive and invite further investigation.
基金supported by the China Meteorological Administration Special Public Welfare Research Fund(Grant No.GYHY201406001)National Key Basic Research Program of China(Grant No.2012CB956003)+1 种基金the National Natural Science Foundation of China(Grant No.41375093)supported in part by the Youth Elite Project of the CMA
文摘Previous studies have revealed a significantly negative correlation between prior winter snow cover over the Tibetan Plateau (TPSC) and tropical cyclone genesis frequency (TCF) over the western North Pacific (WNP) in the following typhoon season. This study revisited this relationship based on long-term observational data. The results showed that the interannual correlation between TCF over the WNP and TPSC experienced a shift in the early 1990s. This correlation is significant during only 1993-2012 and is considerably weak during 1976-1992. The possible reasons causing the shift were examined further, and the results demonstrated that the central Pacific (CP) E1 Nifio-Southern Oscillation (ENSO) has played a vital role in intensifying the interannual relationship between TCF over the WNP and TPSC since the early 1990s. During 1993-2012, TPSC was negatively related to CP ENSO. When TPSC was higher than (lower than) normal, CP ENSO was often in its cold (warm) phase. Such a combination remarkably enhances the relationship of TPSC with the zonal land-sea thermal difference and thus with the summer monsoon over the WNE Additionally, it enhances the modulation of TPSC on the dynamical environments controlling TCF. As a result, the linkage between TPSC and TCF was significantly strengthened in this period. In sharp contrast, due to the weak relationship between TPSC and ENSO followed by the weak modulation of TPSC on the summer monsoon over the WNP and the dynamical environment during 1976-1992, the linkage between TPSC and TCF was weak during this time period. The results from additional dynamical diagnostic analyses further showed that during 1993-2012 CP ENSO modulated the barotropic energy conversion of zonal winds over the WNP, contributing to the intensified relationship between TPSC and TCF. These results will improve seasonal forecasting of tropical cyclone activity over the WNP.
基金National Key Research and Development Program in China,No.2017YFA0603704National Natural Science Foundation of China,No.51339004
文摘During recent decades, more frequent flood-drought alternations have been seen in China as a result of global climate change and intensive human activities, which have sig- nificant implications on water and food security. To better identify the characteristics of flood-drought alternations, we proposed a modified dry-wet abrupt alternation index (DWAAI) and applied the new method in the middle and lower reaches of the Yangtze River Basin (YRB-ML) to analyze the long-term spatio-temporal characteristics of dry-wet abrupt alterna- tion (DWAA) events based on the daily precipitation observations at 75 rainfall stations in summer from 1960 to 2015. We found that the DWAA events have been spreading in the study area with higher frequency and intensity since 1960. In particular, the DWAA events mainly occurred in May and June in the northwest of the YRB-ML, including Hanjiang River Basin, the middle reaches of the YRB, north of Dongting Lake and northwest of Poyang Lake. In addition, we also analyzed the impact of El Nifio Southern Oscillation (ENSO) on DWAA events in the YRB-ML. The results showed that around 41.04% of DWAA events occurred during the declining stages of La Nifia or within the subsequent 8 months after La Nina, which implies that La Nina events could be predictive signals of DWAA events. Besides, significant negative correlations have been found between the modified DWAAI values of all the rainfall stations and the sea surface temperature anomalies in the Nino3.4 region within the 6 months prior to the DWAA events, particularly for the Poyang Lake watershed and the middle reaches of the YRB. This study has significant implications on the flood and drought control and water resources management in the YRB-ML under the challenge of future climate change.