The daily precipitation data at 720 sta- tions over China for the 1957―2003 period during summer (May―August) are used to investigate the summer subseasonal long-cycle droughts-floods abrupt alternation (LDFA) pheno...The daily precipitation data at 720 sta- tions over China for the 1957―2003 period during summer (May―August) are used to investigate the summer subseasonal long-cycle droughts-floods abrupt alternation (LDFA) phenomenon and a long-cycle droughts-floods abrupt alternation index (LDFAI) in the middle and lower reaches of the Yangtze River (MLYRV) is defined to quantify this phenomenon. The large-scale atmospheric circula- tion features in the anomalous LDFA years are ex- amined statistically. Results demonstrate that the summer droughts-to-floods (DTF) in the MLYRV usually accompany with the more southward western Pacific subtropical high (WPSH), negative vorticity, strong divergence, descending movements develop- ing and the weak moisture transport in the low level, the more southward position of the South Asia high (SAH) and the westerly jets in the high level during May―June, but during July―August it is in the other way, northward shift of the WPSH, positive vorticity, strong convergence, ascending movements and strong moisture transport in the low level, and the northward shift of the SAH and the westerly jets in the high level. While for the summer floods-to-droughts (FTD) in the MLYRV it often goes with the active coldair mass from the high latitude, positive vorticity, strong convergence, ascending movement develop- ing and the strong moisture transport in the low level, and the SAH over the Tibetan Plateau in the high level, but during July―August it is often connected with the negative vorticity, strong divergence, de- scending movements developing and the weak moisture transport in the low level, the remarkable northward shift of the WPSH, the SAH extending northeastward to North China and the easterly jets prevailing in the high level over the MLYRV. In addi- tion, the summer LDFA in the MLYRV is of significant relationship with the Southern Hemisphere annual mode and the Northern Hemisphere annual mode in the preceding February, which offers some predictive signals for the summer LDFA foreca展开更多
Seven large-scale low-frequency rainfall regimes (LFRRs) in summertime are identified for China in a 10-dimensional phase space by using a 40-year daily precipitation dataset. Corresponding to the local extrema of obs...Seven large-scale low-frequency rainfall regimes (LFRRs) in summertime are identified for China in a 10-dimensional phase space by using a 40-year daily precipitation dataset. Corresponding to the local extrema of observed probability density in phase space, the LFRRs are characterized by the persistence and transitions that reflect the spread and jump features of low-frequency rainfall centers. The LFRRs are generally consistent with summer monsoon rainbelts on the intraseasonal timescale, and there exist the preferred transition relationships between the LFRRs. Four LFRRs’ transition modes (LFRRTMs), which are the dominant components of the interannual and intraseasonal variability of sum- mer rainfall in China, are further induced. Analyses of atmospheric circulation system show that the anomalies of the subtropical high over the western Pacific (SHWP) and blockings in mid-high latitudes, the low-latitude circulation anomalies, and the wavetrains over the East Asia-Pacific region (EAPWs), play crucial roles in the occurrence and transitions of the LFRRs. Moreover, the evolution of the SHWP and blockings, the distribution and movement of the EAPWs, and the intraseasonal variability of the East Asian-Pacific jet stream may be principal factors of the formations of the LFRRTMs.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.40523001 and 40221503)the National Basic Research Program of China(Grant No.2004CB418303).
文摘The daily precipitation data at 720 sta- tions over China for the 1957―2003 period during summer (May―August) are used to investigate the summer subseasonal long-cycle droughts-floods abrupt alternation (LDFA) phenomenon and a long-cycle droughts-floods abrupt alternation index (LDFAI) in the middle and lower reaches of the Yangtze River (MLYRV) is defined to quantify this phenomenon. The large-scale atmospheric circula- tion features in the anomalous LDFA years are ex- amined statistically. Results demonstrate that the summer droughts-to-floods (DTF) in the MLYRV usually accompany with the more southward western Pacific subtropical high (WPSH), negative vorticity, strong divergence, descending movements develop- ing and the weak moisture transport in the low level, the more southward position of the South Asia high (SAH) and the westerly jets in the high level during May―June, but during July―August it is in the other way, northward shift of the WPSH, positive vorticity, strong convergence, ascending movements and strong moisture transport in the low level, and the northward shift of the SAH and the westerly jets in the high level. While for the summer floods-to-droughts (FTD) in the MLYRV it often goes with the active coldair mass from the high latitude, positive vorticity, strong convergence, ascending movement develop- ing and the strong moisture transport in the low level, and the SAH over the Tibetan Plateau in the high level, but during July―August it is often connected with the negative vorticity, strong divergence, de- scending movements developing and the weak moisture transport in the low level, the remarkable northward shift of the WPSH, the SAH extending northeastward to North China and the easterly jets prevailing in the high level over the MLYRV. In addi- tion, the summer LDFA in the MLYRV is of significant relationship with the Southern Hemisphere annual mode and the Northern Hemisphere annual mode in the preceding February, which offers some predictive signals for the summer LDFA foreca
基金This work was jointly supported by the National Natural Science Foundation of China （Grants Nos. 40135020 and 40375025） and the Ministry of Science and Technology of China （Grant No. 2002ccd00100）.
文摘Seven large-scale low-frequency rainfall regimes (LFRRs) in summertime are identified for China in a 10-dimensional phase space by using a 40-year daily precipitation dataset. Corresponding to the local extrema of observed probability density in phase space, the LFRRs are characterized by the persistence and transitions that reflect the spread and jump features of low-frequency rainfall centers. The LFRRs are generally consistent with summer monsoon rainbelts on the intraseasonal timescale, and there exist the preferred transition relationships between the LFRRs. Four LFRRs’ transition modes (LFRRTMs), which are the dominant components of the interannual and intraseasonal variability of sum- mer rainfall in China, are further induced. Analyses of atmospheric circulation system show that the anomalies of the subtropical high over the western Pacific (SHWP) and blockings in mid-high latitudes, the low-latitude circulation anomalies, and the wavetrains over the East Asia-Pacific region (EAPWs), play crucial roles in the occurrence and transitions of the LFRRs. Moreover, the evolution of the SHWP and blockings, the distribution and movement of the EAPWs, and the intraseasonal variability of the East Asian-Pacific jet stream may be principal factors of the formations of the LFRRTMs.
