Response of the East Asian summer monsoon（EASM） rainfall to external forcing（insolation,volcanic aerosol,and greenhouse gases） is investigated by analysis of a millennium simulation with the coupled climate model ...Response of the East Asian summer monsoon（EASM） rainfall to external forcing（insolation,volcanic aerosol,and greenhouse gases） is investigated by analysis of a millennium simulation with the coupled climate model ECHO-G.The model reproduces reasonably realistic present-day EASM climatology.The simulated precipitation variation in East Asia over the last millennium compares favorably with the observed and proxy data.It is found that the features and sensitivity of the forced response depend on latitude.On the centennial-millennial time scale（CMTS）,the extratropical precipitation closely follows the variation of the effective radiative forcing（insolation plus radiative effects of volcanic aerosols）.The subtropical precipitation is less sensitive but the differences of this variable between the Medieval Warm Period（MWP） and Little Ice Age（LIA） remain significant.The tropical rainfall is insensitive to the external forcing.It is also found that the precipitation variations in the extratropics and subtropics are in phase on the CMTS,while they are anti-correlated on the interannual time scale.The intertropical convergence zone（ITCZ） and subtropical precipitation are anti-correlated on the CMTS,so are they on the interannual time scale.These findings suggest that the proxy data in the extratropical East Asia more sensitively reflect the EASM variations,and this has important implications on interpretation of paleo-proxy records.展开更多
The Maritime Continent（MC） is under influences of both the tropical Pacific and the Indian Ocean. Anomalous convective activities over the MC have significant impacts on the East Asian summer monsoon（EASM） and cli...The Maritime Continent（MC） is under influences of both the tropical Pacific and the Indian Ocean. Anomalous convective activities over the MC have significant impacts on the East Asian summer monsoon（EASM） and climate in China. In the present study, the variation in convective activity over the MC in boreal summer and its relationship to EASM anomalies are investigated based on regression analysis of NCEP–NCAR reanalysis and CMAP [Climate Prediction Center（CPC） Merged Analysis of Precipitation] data, with a focus on the impacts of ENSO and the Indian Ocean Dipole（IOD）. The most significant interannual variability of convective activity is found over 10°S–10°N, 95°–145°E, which can be roughly defined as the key area of the MC（hereafter, KMC）. Outgoing longwave radiation anomaly（OLRA） exhibits 3- to 7-yr periodicities over the KMC, and around 70% of the OLRA variance can be explained by the ENSO signal. However, distinct convection and precipitation anomalies still exist over this region after the ENSO and IOD signals are removed. Abnormally low precipitation always corresponds to positive OLRA over the KMC when negative diabatic heating anomalies and anomalous cooling of the atmospheric column lead to abnormal descending motion over this region. Correspondingly, abnormal divergence occurs in the lower troposphere while convergence occurs in the upper troposphere, triggering an East Asia–Pacific/Pacific–Japan（EAP/PJ）-like anomalous wave train that propagates northeastward and leads to a significant positive precipitation anomaly from the Yangtze River valley in China to the islands of Japan. This EAP/PJ-like wave pattern becomes even clearer after the removal of the ENSO signal and the combined effects of ENSO and IOD, suggesting that convective anomalies over the KMC have an important impact on EASM anomalies. The above results provide important clues for the prediction of EASM anomalies and associated summer precipitation anomalies in China.展开更多
National Meteorological Information Center （NMIC） rainfall data and NCEP/NCAR daily circulation reanalysis data are employed to establish the onset-pentad time index of the spring persistent rains （SPR） and the de...National Meteorological Information Center （NMIC） rainfall data and NCEP/NCAR daily circulation reanalysis data are employed to establish the onset-pentad time index of the spring persistent rains （SPR） and the decay-pentad time index of the South China Sea （SCS） sub-high. These indexes are used to study the relationship between the factors in SPR period and their relations to the circulation and precipitation of the East Asian summer monsoon （EASM）. Results show that, the summer rainfall over southeastern China decreases when SPR onset is late. For then EASM strengthens and the cyclonic circulation around the Tibetan Plateau （TP） strengthens, which makes abnormal anti-cyclonic circulation （cyclonic convergent circulation weakens） appear over southeastern China. When the decay of SCS sub-high delays, abnormal flood prevails over the middle and lower reaches of the Yangtze River （MLYR） and to the south. That is mainly caused by EASM weakening while SCS sub-high strengthening, then the abnormal southwesterly over South China and the abnormal northerlies of anti-cyclonic circulation around the TP converge over the Yangtze Valley. The two indexes have high correlations with multivariate ENSO index （MEI） in March, indicating that the climate abnormity in East Asia is related to global climate abnormity tightly. The two time indexes are independent of each other, which is favorable for the prediction of the anomalies of the circulation and precipitation of EASM. From this point of view, we must take the global climate background into account when we analyze and predict the East Asian summer circulation and precipitation.展开更多
东亚夏季风强度的变化与中国雨带和旱涝分布密切相关。为了做好东亚夏季风强度的短期气候预测,采用小波分析、Lanczos滤波器、交叉检验等方法,研究了东亚夏季风强度的多尺度变化特征,在年际与年代际尺度上分别寻找了它在前冬海温场、200...东亚夏季风强度的变化与中国雨带和旱涝分布密切相关。为了做好东亚夏季风强度的短期气候预测,采用小波分析、Lanczos滤波器、交叉检验等方法,研究了东亚夏季风强度的多尺度变化特征,在年际与年代际尺度上分别寻找了它在前冬海温场、200 h Pa纬向风场上的前兆信号,并利用最优子集回归建立了东亚夏季风强度的多尺度统计物理预测模型。结果表明:东亚夏季风强度存在准4年、准13年和准43年的周期振荡。年际尺度上,前冬赤道东太平洋(10°N^10°S,160°W^80°W)海温与东亚夏季风强度有最强的显著负相关,且它与东亚夏季风强度在200 h Pa纬向风场上的前兆信号有较强的负相关;年代际尺度上,南半球60°S与35°S附近200 h Pa纬向风之差与东亚夏季风强度有最强的显著正相关,且它与东亚夏季风强度在热带印度洋、低纬度东南太平洋、低纬度南大西洋的海温及亚洲副热带200 h Pa纬向风等前兆信号有强的正相关。通过探讨这两个前兆因子对东亚夏季风强度的预测意义,揭示了他们影响东亚夏季风强度年际和年代际变化的可能物理过程。所建立的东亚夏季风强度多尺度最优子集回归预测模型,不仅对东亚夏季风强度的年际变化具有较好的预测能力,而且对异常极值年份也具有一定的预测能力。展开更多
基金Supported by the National Basic Research Program of China under Grant Nos.2010CB950102,2010CB833404,and 2011CB403301the Innovation Project of Chinese Academy of Sciences under Grant Nos.KZCX2-YW-337 and NIGLAS2010XK02the National Natural Science Foundation of China under Grant Nos.40871007,40890054,and 40672210
文摘Response of the East Asian summer monsoon（EASM） rainfall to external forcing（insolation,volcanic aerosol,and greenhouse gases） is investigated by analysis of a millennium simulation with the coupled climate model ECHO-G.The model reproduces reasonably realistic present-day EASM climatology.The simulated precipitation variation in East Asia over the last millennium compares favorably with the observed and proxy data.It is found that the features and sensitivity of the forced response depend on latitude.On the centennial-millennial time scale（CMTS）,the extratropical precipitation closely follows the variation of the effective radiative forcing（insolation plus radiative effects of volcanic aerosols）.The subtropical precipitation is less sensitive but the differences of this variable between the Medieval Warm Period（MWP） and Little Ice Age（LIA） remain significant.The tropical rainfall is insensitive to the external forcing.It is also found that the precipitation variations in the extratropics and subtropics are in phase on the CMTS,while they are anti-correlated on the interannual time scale.The intertropical convergence zone（ITCZ） and subtropical precipitation are anti-correlated on the CMTS,so are they on the interannual time scale.These findings suggest that the proxy data in the extratropical East Asia more sensitively reflect the EASM variations,and this has important implications on interpretation of paleo-proxy records.
基金National Natural Science Foundation of China(41330425)China Meteorological Administration Special Public Welfare Research Fund(GYHY201406024)Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘The Maritime Continent（MC） is under influences of both the tropical Pacific and the Indian Ocean. Anomalous convective activities over the MC have significant impacts on the East Asian summer monsoon（EASM） and climate in China. In the present study, the variation in convective activity over the MC in boreal summer and its relationship to EASM anomalies are investigated based on regression analysis of NCEP–NCAR reanalysis and CMAP [Climate Prediction Center（CPC） Merged Analysis of Precipitation] data, with a focus on the impacts of ENSO and the Indian Ocean Dipole（IOD）. The most significant interannual variability of convective activity is found over 10°S–10°N, 95°–145°E, which can be roughly defined as the key area of the MC（hereafter, KMC）. Outgoing longwave radiation anomaly（OLRA） exhibits 3- to 7-yr periodicities over the KMC, and around 70% of the OLRA variance can be explained by the ENSO signal. However, distinct convection and precipitation anomalies still exist over this region after the ENSO and IOD signals are removed. Abnormally low precipitation always corresponds to positive OLRA over the KMC when negative diabatic heating anomalies and anomalous cooling of the atmospheric column lead to abnormal descending motion over this region. Correspondingly, abnormal divergence occurs in the lower troposphere while convergence occurs in the upper troposphere, triggering an East Asia–Pacific/Pacific–Japan（EAP/PJ）-like anomalous wave train that propagates northeastward and leads to a significant positive precipitation anomaly from the Yangtze River valley in China to the islands of Japan. This EAP/PJ-like wave pattern becomes even clearer after the removal of the ENSO signal and the combined effects of ENSO and IOD, suggesting that convective anomalies over the KMC have an important impact on EASM anomalies. The above results provide important clues for the prediction of EASM anomalies and associated summer precipitation anomalies in China.
基金Supported by the National"973"Program under No.2006CB403600the National Natural Science Foundation of China Project under Nos.40475027,40220503,and 40523001.
文摘National Meteorological Information Center （NMIC） rainfall data and NCEP/NCAR daily circulation reanalysis data are employed to establish the onset-pentad time index of the spring persistent rains （SPR） and the decay-pentad time index of the South China Sea （SCS） sub-high. These indexes are used to study the relationship between the factors in SPR period and their relations to the circulation and precipitation of the East Asian summer monsoon （EASM）. Results show that, the summer rainfall over southeastern China decreases when SPR onset is late. For then EASM strengthens and the cyclonic circulation around the Tibetan Plateau （TP） strengthens, which makes abnormal anti-cyclonic circulation （cyclonic convergent circulation weakens） appear over southeastern China. When the decay of SCS sub-high delays, abnormal flood prevails over the middle and lower reaches of the Yangtze River （MLYR） and to the south. That is mainly caused by EASM weakening while SCS sub-high strengthening, then the abnormal southwesterly over South China and the abnormal northerlies of anti-cyclonic circulation around the TP converge over the Yangtze Valley. The two indexes have high correlations with multivariate ENSO index （MEI） in March, indicating that the climate abnormity in East Asia is related to global climate abnormity tightly. The two time indexes are independent of each other, which is favorable for the prediction of the anomalies of the circulation and precipitation of EASM. From this point of view, we must take the global climate background into account when we analyze and predict the East Asian summer circulation and precipitation.
文摘东亚夏季风强度的变化与中国雨带和旱涝分布密切相关。为了做好东亚夏季风强度的短期气候预测,采用小波分析、Lanczos滤波器、交叉检验等方法,研究了东亚夏季风强度的多尺度变化特征,在年际与年代际尺度上分别寻找了它在前冬海温场、200 h Pa纬向风场上的前兆信号,并利用最优子集回归建立了东亚夏季风强度的多尺度统计物理预测模型。结果表明:东亚夏季风强度存在准4年、准13年和准43年的周期振荡。年际尺度上,前冬赤道东太平洋(10°N^10°S,160°W^80°W)海温与东亚夏季风强度有最强的显著负相关,且它与东亚夏季风强度在200 h Pa纬向风场上的前兆信号有较强的负相关;年代际尺度上,南半球60°S与35°S附近200 h Pa纬向风之差与东亚夏季风强度有最强的显著正相关,且它与东亚夏季风强度在热带印度洋、低纬度东南太平洋、低纬度南大西洋的海温及亚洲副热带200 h Pa纬向风等前兆信号有强的正相关。通过探讨这两个前兆因子对东亚夏季风强度的预测意义,揭示了他们影响东亚夏季风强度年际和年代际变化的可能物理过程。所建立的东亚夏季风强度多尺度最优子集回归预测模型,不仅对东亚夏季风强度的年际变化具有较好的预测能力,而且对异常极值年份也具有一定的预测能力。
