Persistent heavy rainfall events in South China can be divided into pre-and post-monsoon-onset events according to the onset of the South China Sea Summer Monsoon. In this study, daily rainfall data from 174 stations ...Persistent heavy rainfall events in South China can be divided into pre-and post-monsoon-onset events according to the onset of the South China Sea Summer Monsoon. In this study, daily rainfall data from 174 stations in South China and daily NCEP/NCAR reanalysis data are used to investigate pre-monsoon-onset events. The synoptic characteristics of pre-monsoon-onset heavy rainfall events are examined in detail. It is found that 21 heavy rainfall cases happened in the pre-monsoon period between 1961 and 2005. Among them, more than 60% of the events happened under a saddle pattern circulation. Using a case study, the role of the saddle field is investigated and slantwise vorticity development （SVD） theory is applied to diagnose the mechanisms for heavy rainfall development. It is found that a low-level saddle field and low-level jets result in the accumulation of warm moist air in the lower troposphere over South China and provide the necessary unstable conditions for heavy rainfall development. The existence of a saddle field plays an important role in maintaining these unstable conditions. The slantwise movement of the isentropic surface over South China can increase local vorticity and lead to strong vertical motion, which then triggers heavy rainfall.展开更多
PM2.5 and total suspended particulate （TSP） samples were collected at Lijiang, southeastern Tibetan Plateau, China. Sixteen elements （Al, Si, S, K, Ca, Cr, Mn, Ti, Fe, Ni, Zn, As, Br, Sb, Pb and Cu） were analyzed ...PM2.5 and total suspended particulate （TSP） samples were collected at Lijiang, southeastern Tibetan Plateau, China. Sixteen elements （Al, Si, S, K, Ca, Cr, Mn, Ti, Fe, Ni, Zn, As, Br, Sb, Pb and Cu） were analyzed to investigate their elemental compositions during the pre-monsoon period. The results showed that Ca was the most abundant element in both PM2.5 and TSP samples. The enrichment factors （EFs） ofSi, Ti, Ca, Fe, K and Mn were all below 10 for both PM2.5 and TSP, and these elements also had lower PM2.5/TSP ratios （0.32-0.34）, suggesting that they were mainly derived from crustal sources. Elements Cu, Zn, S, Br and Sb showed strong enrichment in PM2.5 and TSP samples, with their PM2.5/TSP ratios ranging from 0.66 to 0.97, indicating that they were enriched in the fine fractions and influenced by anthropogenic sources. Analysis of the wind field at 500 hPa and calculations of back trajectories indicated that Al, Si, Ca, Ti, Cr, Mn and Fe can be influenced by transport from northwestern China during the dust-storm season, and that S, K, Ni, Br and Pb reached high concentrations during westerly transport from south Asia. Combined with the principle component analysis and correlation analysis, elements of PM2.5 samples were mainly from crustal sources, biomass burning emissions and regional traffic-related sources.展开更多
The evident effects of the thermal anomalies over the Tibetan Plateau (TP) and its vicinities are summarized and discussed in this paper. By the singular value decomposition (SVD) technique and numerical simulations o...The evident effects of the thermal anomalies over the Tibetan Plateau (TP) and its vicinities are summarized and discussed in this paper. By the singular value decomposition (SVD) technique and numerical simulations of the effect of the snow depth anomaly over the TP, it is shown that the snow depth anomaly, especially in winter, is one of the factors innuencing precipitation in China, and the winter snow anomaly is more important than the spring one. The relations between the sensible heat anomaly over the TP and the intensity of the South China Sea summer monsoon (SCSSM) are studied, too, and two key areas of the sensible heat anomaly over the TP are found. The relationships between the South Asia High (SAH) and the precipitation in the years with typical droughts or floods in the mid to lower valleys of the Yangtze River (MLVYR) and North China are investigated in some detail. It is found that not only the intensity of the SAH over the TP, but also the 100-hPa height in a large area influences the precipitation in the above two regions. The effects of the SAH on the onsets of the tropical Asian summer monsoon (TASM) including the SCSSM and the tropical Indian summer monsoon (TISM) are studied as well. It is found that the onset times of both the SCSSM and the TISM are highly dependent upon the latitudinal position of the SAH center.展开更多
基金supported by the National Natural Science Foundation of China under Grant No. 40730951the National Basic Research Program of China (973 Program) under Grant No. 2009CB421404
文摘Persistent heavy rainfall events in South China can be divided into pre-and post-monsoon-onset events according to the onset of the South China Sea Summer Monsoon. In this study, daily rainfall data from 174 stations in South China and daily NCEP/NCAR reanalysis data are used to investigate pre-monsoon-onset events. The synoptic characteristics of pre-monsoon-onset heavy rainfall events are examined in detail. It is found that 21 heavy rainfall cases happened in the pre-monsoon period between 1961 and 2005. Among them, more than 60% of the events happened under a saddle pattern circulation. Using a case study, the role of the saddle field is investigated and slantwise vorticity development （SVD） theory is applied to diagnose the mechanisms for heavy rainfall development. It is found that a low-level saddle field and low-level jets result in the accumulation of warm moist air in the lower troposphere over South China and provide the necessary unstable conditions for heavy rainfall development. The existence of a saddle field plays an important role in maintaining these unstable conditions. The slantwise movement of the isentropic surface over South China can increase local vorticity and lead to strong vertical motion, which then triggers heavy rainfall.
基金supported by the Natural Science Foundation of China(NSFC40925009 and 40801028)projects from the Chinese Academy of Sciences(Nos.0929011018,KZCX2-YW-BR-10 and KZCX2-YW-148)the Ministry of Science & Technology (2009IM030100)
文摘PM2.5 and total suspended particulate （TSP） samples were collected at Lijiang, southeastern Tibetan Plateau, China. Sixteen elements （Al, Si, S, K, Ca, Cr, Mn, Ti, Fe, Ni, Zn, As, Br, Sb, Pb and Cu） were analyzed to investigate their elemental compositions during the pre-monsoon period. The results showed that Ca was the most abundant element in both PM2.5 and TSP samples. The enrichment factors （EFs） ofSi, Ti, Ca, Fe, K and Mn were all below 10 for both PM2.5 and TSP, and these elements also had lower PM2.5/TSP ratios （0.32-0.34）, suggesting that they were mainly derived from crustal sources. Elements Cu, Zn, S, Br and Sb showed strong enrichment in PM2.5 and TSP samples, with their PM2.5/TSP ratios ranging from 0.66 to 0.97, indicating that they were enriched in the fine fractions and influenced by anthropogenic sources. Analysis of the wind field at 500 hPa and calculations of back trajectories indicated that Al, Si, Ca, Ti, Cr, Mn and Fe can be influenced by transport from northwestern China during the dust-storm season, and that S, K, Ni, Br and Pb reached high concentrations during westerly transport from south Asia. Combined with the principle component analysis and correlation analysis, elements of PM2.5 samples were mainly from crustal sources, biomass burning emissions and regional traffic-related sources.
基金the Chinese Academy of Sciences(ZKCX2-SW-210)the National Natural Science Foundation of China under Grant Nos.40175021 and 40233037.
文摘The evident effects of the thermal anomalies over the Tibetan Plateau (TP) and its vicinities are summarized and discussed in this paper. By the singular value decomposition (SVD) technique and numerical simulations of the effect of the snow depth anomaly over the TP, it is shown that the snow depth anomaly, especially in winter, is one of the factors innuencing precipitation in China, and the winter snow anomaly is more important than the spring one. The relations between the sensible heat anomaly over the TP and the intensity of the South China Sea summer monsoon (SCSSM) are studied, too, and two key areas of the sensible heat anomaly over the TP are found. The relationships between the South Asia High (SAH) and the precipitation in the years with typical droughts or floods in the mid to lower valleys of the Yangtze River (MLVYR) and North China are investigated in some detail. It is found that not only the intensity of the SAH over the TP, but also the 100-hPa height in a large area influences the precipitation in the above two regions. The effects of the SAH on the onsets of the tropical Asian summer monsoon (TASM) including the SCSSM and the tropical Indian summer monsoon (TISM) are studied as well. It is found that the onset times of both the SCSSM and the TISM are highly dependent upon the latitudinal position of the SAH center.
