南大西洋副热带偶极子(South Atlantic Subtropical Dipole;SASD)为南大西洋海洋与大气相互作用的主要模态。它的空间型为海表面温度异常呈现东北-西南偶极子分布。当SASD指数大于1,为SASD正事件,小于-1,为负事件。根据1960-2016年HadIS...南大西洋副热带偶极子(South Atlantic Subtropical Dipole;SASD)为南大西洋海洋与大气相互作用的主要模态。它的空间型为海表面温度异常呈现东北-西南偶极子分布。当SASD指数大于1,为SASD正事件,小于-1,为负事件。根据1960-2016年HadISST(Hadley Center Global Sea Ice and Sea Surface Temperature)数据,本文鉴别出57年中共发生6次正事件和9次负事件。SASD存在显著的5~8年周期的年际变化特征。本文进一步利用1992-2016年ECCO2(Estimating the Circulation and Climate of the Ocean,PhaseⅡ)模式数据,根据温度倾向方程分别诊断了SASD西南极和东北极的混合层温度变化。诊断结果表明,SASD的年际变化主要来自于表面热力强迫项的年际变化。考虑到表面热力强迫项主要由短波辐射项控制,SASD的年际变化最终来源于短波辐射项的年际变化。展开更多
基于1961—2015年黄土高原57个基准站逐月降水资料,计算标准化降水指数(SPI),将其作为旱涝指标研究4月黄土高原旱涝异常年环流特征及其前期外强迫信号。结果表明:(1)当500 h Pa乌拉尔山至中国新疆高压脊偏强、东亚大槽偏深,700 h Pa黄...基于1961—2015年黄土高原57个基准站逐月降水资料,计算标准化降水指数(SPI),将其作为旱涝指标研究4月黄土高原旱涝异常年环流特征及其前期外强迫信号。结果表明:(1)当500 h Pa乌拉尔山至中国新疆高压脊偏强、东亚大槽偏深,700 h Pa黄土高原及其以东南风偏弱,700 h Pa中国东部至日本温度偏低,中国东部到日本以东洋面西风急流南压加强时,黄土高原易旱,反之易涝。(2) 4月北半球中高纬度150°W—180°E区域异常涝年阻塞出现次数多于异常旱年。(3)南印度洋偶极子(SIOD)或西南印度洋海温可以作为4月旱涝的前期强迫信号,4月SPI与前一年12月SIOD存在显著负相关关系。(4)黄土高原旱涝对SIOD正负位相异常的响应主要反映在500 h Pa乌拉尔山高压脊、东亚大槽以及700 h Pa贝加尔湖至中国东北以及乌拉尔山的环流差异上。展开更多
From the synopical CTD sections in the WOCE PR11 repeated cruises, the South Pacific Subtropical Mode Water (SPSTMW) has been identified in the region of the Tasman Front Extension (TFE) around 29?S to the east of Aus...From the synopical CTD sections in the WOCE PR11 repeated cruises, the South Pacific Subtropical Mode Water (SPSTMW) has been identified in the region of the Tasman Front Extension (TFE) around 29?S to the east of Australia. In the depth range of 150-250 m, the SPSTMW appears as a thermostad with vertical temperature gradient lower than 1.6℃(100 m)-1 and a tem- perature range of 16.5-19.5℃ and as a pycnostad with PV lower than 2×10-10 m-1 s-1 and a potential density range of 25.4-26.0 kg m-3. Like the subtropical mode waters in the North Atlantic and North Pacific, the formation of the SPSTMW is associated with the convective mixing during the austral wintertime as manifested from the time series of the Argo floats. And cold water entrains into the mixed layer with the deepening mixed layer from September to the middle of October. During the wintertime formation process, mesoscale eddies prevailing in the TFE region play an important role in the SPSTMW formation, and have a great effect on the SPSTMW distribution in the next year. The deeper (shallower) mixed layer in wintertime, consistent with the depressed (uplifted) permanent thermocline, is formed by the anticyclonic (cyclonic) eddies, and the substantial mode water thicker than 50 m is mainly found in the region of the anticyclonic eddies where the permanent thermocline is deeper than 450 m.展开更多
The sea surface height anomaly(SSHA) signals leading the fall Indian Ocean Dipole(IOD) are investigated. The results suggest that, prior to the IOD by one year, a positive SSHA emerges over the western-central tropica...The sea surface height anomaly(SSHA) signals leading the fall Indian Ocean Dipole(IOD) are investigated. The results suggest that, prior to the IOD by one year, a positive SSHA emerges over the western-central tropical Pacific(WCTP), which peaks during winter(January-February-March, JFM), persists into late spring and early summer(April-May-June, AMJ), and becomes weakened later on. An SSHA index, referred as to SSHA_WCTP, is defined as the averaged SSHA over the WCTP during JFM. The index is not only significantly positively correlated with the following-fall(September-October-November, SON) IOD index, but also is higher than the autocorrelation of the IOD index crossing the two different seasons. The connection of SSHA_ WCTP with following-summer rainfall in China is then explored. The results suggest that higher(lower) SSHA_ WCTP corresponds to increased(reduced) rainfall over southern coastal China, along with suppressed(increased) rainfall over the middle–lower reaches of the Yangtze River, North China, and the Xinjiang region of northwestern China. Mechanistically, following the preceding-winter higher(lower) SSHA_WCTP, the South Asia High and the Western Pacific Subtropical High are weakened(intensified), which results in the East Asian summer monsoon weakening(intensifying). Finally, the connection between SSHA_WCTP and El Ni?o-Southern Oscillation(ENSO) is analyzed. Despite a significant correlation, SSHA_WCTP is more closely connected with summer rainfall. This implies that the SSHA_WCTP index in the preceding winter is a more effective predictor of summer rainfall in comparison with ENSO.展开更多
文摘南大西洋副热带偶极子(South Atlantic Subtropical Dipole;SASD)为南大西洋海洋与大气相互作用的主要模态。它的空间型为海表面温度异常呈现东北-西南偶极子分布。当SASD指数大于1,为SASD正事件,小于-1,为负事件。根据1960-2016年HadISST(Hadley Center Global Sea Ice and Sea Surface Temperature)数据,本文鉴别出57年中共发生6次正事件和9次负事件。SASD存在显著的5~8年周期的年际变化特征。本文进一步利用1992-2016年ECCO2(Estimating the Circulation and Climate of the Ocean,PhaseⅡ)模式数据,根据温度倾向方程分别诊断了SASD西南极和东北极的混合层温度变化。诊断结果表明,SASD的年际变化主要来自于表面热力强迫项的年际变化。考虑到表面热力强迫项主要由短波辐射项控制,SASD的年际变化最终来源于短波辐射项的年际变化。
文摘基于1961—2015年黄土高原57个基准站逐月降水资料,计算标准化降水指数(SPI),将其作为旱涝指标研究4月黄土高原旱涝异常年环流特征及其前期外强迫信号。结果表明:(1)当500 h Pa乌拉尔山至中国新疆高压脊偏强、东亚大槽偏深,700 h Pa黄土高原及其以东南风偏弱,700 h Pa中国东部至日本温度偏低,中国东部到日本以东洋面西风急流南压加强时,黄土高原易旱,反之易涝。(2) 4月北半球中高纬度150°W—180°E区域异常涝年阻塞出现次数多于异常旱年。(3)南印度洋偶极子(SIOD)或西南印度洋海温可以作为4月旱涝的前期强迫信号,4月SPI与前一年12月SIOD存在显著负相关关系。(4)黄土高原旱涝对SIOD正负位相异常的响应主要反映在500 h Pa乌拉尔山高压脊、东亚大槽以及700 h Pa贝加尔湖至中国东北以及乌拉尔山的环流差异上。
基金This study was supported by the Chinese Natural Science Foundation of China(NSFC)(Nos.40276009 and 90411010)
文摘From the synopical CTD sections in the WOCE PR11 repeated cruises, the South Pacific Subtropical Mode Water (SPSTMW) has been identified in the region of the Tasman Front Extension (TFE) around 29?S to the east of Australia. In the depth range of 150-250 m, the SPSTMW appears as a thermostad with vertical temperature gradient lower than 1.6℃(100 m)-1 and a tem- perature range of 16.5-19.5℃ and as a pycnostad with PV lower than 2×10-10 m-1 s-1 and a potential density range of 25.4-26.0 kg m-3. Like the subtropical mode waters in the North Atlantic and North Pacific, the formation of the SPSTMW is associated with the convective mixing during the austral wintertime as manifested from the time series of the Argo floats. And cold water entrains into the mixed layer with the deepening mixed layer from September to the middle of October. During the wintertime formation process, mesoscale eddies prevailing in the TFE region play an important role in the SPSTMW formation, and have a great effect on the SPSTMW distribution in the next year. The deeper (shallower) mixed layer in wintertime, consistent with the depressed (uplifted) permanent thermocline, is formed by the anticyclonic (cyclonic) eddies, and the substantial mode water thicker than 50 m is mainly found in the region of the anticyclonic eddies where the permanent thermocline is deeper than 450 m.
基金jointly supported by the Strategic Project of the Chinese Academy of Sciences(Grant No.XDA11010401)the National Basic Research Program of China(973 Program,Grant Nos.2012CB417403 and 2015CB453202)
文摘The sea surface height anomaly(SSHA) signals leading the fall Indian Ocean Dipole(IOD) are investigated. The results suggest that, prior to the IOD by one year, a positive SSHA emerges over the western-central tropical Pacific(WCTP), which peaks during winter(January-February-March, JFM), persists into late spring and early summer(April-May-June, AMJ), and becomes weakened later on. An SSHA index, referred as to SSHA_WCTP, is defined as the averaged SSHA over the WCTP during JFM. The index is not only significantly positively correlated with the following-fall(September-October-November, SON) IOD index, but also is higher than the autocorrelation of the IOD index crossing the two different seasons. The connection of SSHA_ WCTP with following-summer rainfall in China is then explored. The results suggest that higher(lower) SSHA_ WCTP corresponds to increased(reduced) rainfall over southern coastal China, along with suppressed(increased) rainfall over the middle–lower reaches of the Yangtze River, North China, and the Xinjiang region of northwestern China. Mechanistically, following the preceding-winter higher(lower) SSHA_WCTP, the South Asia High and the Western Pacific Subtropical High are weakened(intensified), which results in the East Asian summer monsoon weakening(intensifying). Finally, the connection between SSHA_WCTP and El Ni?o-Southern Oscillation(ENSO) is analyzed. Despite a significant correlation, SSHA_WCTP is more closely connected with summer rainfall. This implies that the SSHA_WCTP index in the preceding winter is a more effective predictor of summer rainfall in comparison with ENSO.
