Using observed and reanalysis datasets,the South China Sea summer monsoon（SCSSM） onset process is analyzed in each year from 1997 to 2014.Regional mean（5-20°N,110-120°E） 850 hPa zonal wind,precipitation,...Using observed and reanalysis datasets,the South China Sea summer monsoon（SCSSM） onset process is analyzed in each year from 1997 to 2014.Regional mean（5-20°N,110-120°E） 850 hPa zonal wind,precipitation,and SST are used as indices to describe SCSSM onset.Three distinct onset types are identified：among the 18 years studied,nine are normal onset years,which are characterized by a well-established westerly wind and associated precipitation over the South China Sea（SCS）;eight are intermittent onset years,in which monsoon precipitation does not occur continuously following the establishment of the westerly wind over the SCS;and one year,2014,is a delayed onset year,in which the western Pacific subtropical high dominates over the SCS after the seasonal transition and prevents the monsoon onset.A comparison of the first two types suggests that a positive SST gradient in the northern Indian Ocean and local SST warming in the SCS are two key factors in the normal SCSSM onset type.With regard to the influence of the El Nino-Southern Oscillation background,there are four late onset years（1997,1998,2007,and 2010） that coincide with El Nino events,but only two early-onset years（1999 and 2012） out of the six years featuring La Nina events.Further analysis suggests that the zonal thermal contrast across the Indian and western Pacific oceans modulates monsoon onset in La Nina years.展开更多
The analyses of conductivity-temperature-depth (CTD) temperature and salinity data of R/V (Research Vessel) 'Shiyan 3' and R/V 'Kexue 1' observed during the South China Sea Monsoon Experiment (SCSMEX) ...The analyses of conductivity-temperature-depth (CTD) temperature and salinity data of R/V (Research Vessel) 'Shiyan 3' and R/V 'Kexue 1' observed during the South China Sea Monsoon Experiment (SCSMEX) were made to describe the vertical structure and variation of sea temperature and salinity in the upper layer of northern South China Sea (SCS) before and after the summer monsoon onset.The stratification of the upper-layer water in northern SCS is more obvious in late April than July.Isotherm distribution at some sections forms a wave-shaped structure with obvious thermal trough and ridge.High surface temperature water was observed off northwest of Luzon Island in late April.The formation of a mixed layer in the surface layer northwest of Luzon Island is prominent in July.Water on the northern SCS continental shelf has obviously turned much fresher in July than April due to the effects of discharge from Zhujiang River and Guangdong coastal waters.展开更多
基金jointly funded by the National Basic Research Program of China[grant number 2014CB953904]Strategic Priority Research Program of the Chinese Academy of Sciences[grant number XDA11010402]+1 种基金National Natural Science Foundation of China[grant numbers 41305068,41405091,41305065,and 91337110]China Postdoctoral Science Foundation[2013M541011]
文摘Using observed and reanalysis datasets,the South China Sea summer monsoon（SCSSM） onset process is analyzed in each year from 1997 to 2014.Regional mean（5-20°N,110-120°E） 850 hPa zonal wind,precipitation,and SST are used as indices to describe SCSSM onset.Three distinct onset types are identified：among the 18 years studied,nine are normal onset years,which are characterized by a well-established westerly wind and associated precipitation over the South China Sea（SCS）;eight are intermittent onset years,in which monsoon precipitation does not occur continuously following the establishment of the westerly wind over the SCS;and one year,2014,is a delayed onset year,in which the western Pacific subtropical high dominates over the SCS after the seasonal transition and prevents the monsoon onset.A comparison of the first two types suggests that a positive SST gradient in the northern Indian Ocean and local SST warming in the SCS are two key factors in the normal SCSSM onset type.With regard to the influence of the El Nino-Southern Oscillation background,there are four late onset years（1997,1998,2007,and 2010） that coincide with El Nino events,but only two early-onset years（1999 and 2012） out of the six years featuring La Nina events.Further analysis suggests that the zonal thermal contrast across the Indian and western Pacific oceans modulates monsoon onset in La Nina years.
基金the Project"South China Sea Monsoon Experiment"Guangdong Provincial Natural Science Foundation (Project No.021566)
文摘The analyses of conductivity-temperature-depth (CTD) temperature and salinity data of R/V (Research Vessel) 'Shiyan 3' and R/V 'Kexue 1' observed during the South China Sea Monsoon Experiment (SCSMEX) were made to describe the vertical structure and variation of sea temperature and salinity in the upper layer of northern South China Sea (SCS) before and after the summer monsoon onset.The stratification of the upper-layer water in northern SCS is more obvious in late April than July.Isotherm distribution at some sections forms a wave-shaped structure with obvious thermal trough and ridge.High surface temperature water was observed off northwest of Luzon Island in late April.The formation of a mixed layer in the surface layer northwest of Luzon Island is prominent in July.Water on the northern SCS continental shelf has obviously turned much fresher in July than April due to the effects of discharge from Zhujiang River and Guangdong coastal waters.
