本文利用观测和再分析资料,通过奇异值分解(Singular Value Decomposition,SVD)分析,发现北极涛动(Arctic Oscillation,AO)是显著影响中国夏季降水年际异常的前冬中高纬大气环流变异的主模态。AO在冬季发展成熟,在春季衰亡,在夏季发生...本文利用观测和再分析资料,通过奇异值分解(Singular Value Decomposition,SVD)分析,发现北极涛动(Arctic Oscillation,AO)是显著影响中国夏季降水年际异常的前冬中高纬大气环流变异的主模态。AO在冬季发展成熟,在春季衰亡,在夏季发生位相反转。AO会导致华北、东北、长江中下游和华南夏季降水异常呈现三极型分布。伴随正位相的AO,在黄海至日本海上空的异常低压伴随的东北风异常引起华北和东北水汽通量异常辐散及降水减少,而西北太平洋的异常高压不仅增强其北侧的西南风水汽输送,和北部异常低压共同作用导致长江中下游水汽通量异常辐合及降水增加,而且使得华南水汽通量异常辐散,降水减少。因此,本文发现的前冬AO模态与我国夏季三极型异常降水分布的关系可为我国夏季旱涝预测提供一个重要的中高纬前期因子。展开更多
基于1980-2017年京津冀地区定时观测资料、欧亚陆面积雪资料、欧洲中期天气预报中心(European Centre for Medium-range Weather Forecasts,ECMWF)再分析资料,美国国家环境预报中心/大气研究中心(NCEP/NCAR)再分析资料以及英国哈德莱中...基于1980-2017年京津冀地区定时观测资料、欧亚陆面积雪资料、欧洲中期天气预报中心(European Centre for Medium-range Weather Forecasts,ECMWF)再分析资料,美国国家环境预报中心/大气研究中心(NCEP/NCAR)再分析资料以及英国哈德莱中心提供的海冰密集度资料,分析了秋季10-11月京津冀霾日频数年际变率与同期欧亚积雪的物理联系,并通过气候统计诊断和敏感性试验探讨了积雪异常影响京津冀10-11月霾日频数年际变率的可能机理。结果表明,10-11月京津冀霾日频数年际变率与同期东欧-西伯利亚平原地区(记为R Eu;50°~60°N,40°~80°E)积雪厚度和积雪覆盖度均呈现显著的正相关关系。R Eu积雪正异常与其西北侧的挪威海-巴伦支海海域以及北欧到东欧地区上空大气冷源密切联系,该冷源可激发一个自上述区域途经R Eu一直到东北亚的准正压大尺度纬向Rossby波列来调制影响京津冀霾日频数年际变率的关键环流系统,即东北亚异常反气旋。上述异常环流背景下,京津冀地区对流层低层为偏南风异常所控制,稳定大气层结易于建立,边界层高度偏低、地面风速偏弱且相对湿度偏高。该环境条件有利于霾天气发生发展,使得同期霾日偏多。作为预测信号,当前期9月楚科奇海-西波弗特海海冰偏少(多)时,10-11月京津冀霾日可能偏多(少)。展开更多
The features of large-scale circulation, storm tracks and the dynamical relationship between them were examined by investigating Rossby wave breaking （RWB） processes associated with Eastern Pacific （EP） and Centra...The features of large-scale circulation, storm tracks and the dynamical relationship between them were examined by investigating Rossby wave breaking （RWB） processes associated with Eastern Pacific （EP） and Central Pacific （CP） E1-Nifio. During EP E1-Nino, the geopotential height anomaly at 500 hPa （Z500） exhibits a Pacific-North America （PNA） pattern. During CP EI-Nifio, the Z500 anomaly shows a north positive-south negative pattern over the North Pacific. The anomalous distributions of baroclinicity and storm track are consistent with those of upper-level zonal wind for both EP and CP EI-Nino, suggesting impacts of mean flow on storm track variability. Anticyclonic wave breaking （AWB） oczurs less frequently in EP EI-Nino years, while cyclonic wave breaking （CWB） occurs more frequently in CP EI-Nino years over the North Pacific sector. Outside the North Pacific, more CWB events occur over North America during EP Ei-NiNo. When AWB events occur less frequently over the North Pacific during EP EI-Nino, Z500 decreases locally and the zonal wind is strengthened （weakened） to the south （north）. This is because AWB events reflect a monopoie high anomaly at the centroid of breaking events. When CWB events occur more frequently over the North Pacific under CP EI-Nino conditions, and over North America under EP EI-Nino condition, Z500 increases （decreases） to the northeast （southwest）, since CWB events are related to a northeast-southwest dipole Z500 anomaly. The anomalous RWB events act to invigorate and reinforce the circulation anomalies over the North Pacific-North America region linked with the two types of EI-Nino.展开更多
In this study, we used the NCAR CAM3.0 model to study the climate effects of both decadal global Sea Surface Temperature(SST) changing and the increasing aerosol concentration in East Asia in boreal spring. In the dec...In this study, we used the NCAR CAM3.0 model to study the climate effects of both decadal global Sea Surface Temperature(SST) changing and the increasing aerosol concentration in East Asia in boreal spring. In the decadal SST changing experiment, a prominent sea surface cyclone anomaly occurred west of the Northwest Pacific warming SST. The cyclone anomaly is conductive to anomalous rising motion and more rainfall over the Northwest Pacific and southeast coast areas of China, but less rainfall in central China. Caused by the only aerosol concentration increasing, the change of climate in East Asia is totally different from that induced by the regime shift of SST around 1976/77 with the same model. The sulfate and black carbon aerosol concentrations were doubled respectively and synchronously in East Asia(20?–50?N, 100?–150?E) to investigate the climate effects of these two major aerosol types in three experiments. The results show that, in all three aerosol concentration changing experiments, the rainfall during boreal spring increases in North China and decreases in central China. It's worth noting that in the DTWO experiment, the rainfall diminishes in central China while it increases in the north and southeast coast areas of China, which is similar to observations. From the vertical profile between 110?E and 120?E, it is found that sulfate and black carbon aerosols first change the temperature of lower troposphere owing to their direct radiative effect, and then induce secondary meridional circulation anomaly through the different dynamic mechanisms involved, and at last generate precipitation and surface temperature anomalous patterns mentioned above.展开更多
With the homogeneity-adjusted surface air temperature (SAT) data at 312 stations in eastern China for 1979-2008 and the Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS) nighttime light d...With the homogeneity-adjusted surface air temperature (SAT) data at 312 stations in eastern China for 1979-2008 and the Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS) nighttime light data, the spatial heterogeneities of the SAT trends on different scales are detected with a spatial filtering (i.e. moving spatial anomaly) method, and the impact of urbanization in eastern China on surface warming is analyzed. Results show that the urbanization can induce a remarkable summer warming in Yangtze River Delta (YRD) city cluster region and a winter warming in Beijing-Tianjin-Hebei (BTH) city cluster region. The YRD warming in summer primarily results from the significant increasing of maximum temperature, with an estimated urban warming rate at 0.132-0.250℃ per decade, accounting for 36%-68% of the total regional warming. The BTH warming in winter is primarily due to the remarkable increasing of minimum temperature, with an estimated urban warming rate at 0.102-0.214℃ per decade, accounting for 12%-24% of the total regional warming. The temporal-spatial differences of urban warming effect may be attributed to the variation of regional climatic background and the change of anthropogenic heat release.展开更多
Recent studies have found a connection between Indian Ocean Basin Warming and the anomalous Northwest Pacific Anticyclone(ANPWA) during El Ni?o decaying year.This study focuses on the necessary condition for this conn...Recent studies have found a connection between Indian Ocean Basin Warming and the anomalous Northwest Pacific Anticyclone(ANPWA) during El Ni?o decaying year.This study focuses on the necessary condition for this connection by using observation and numerical simulation.The seasonal transition of the Indian Ocean sea surface wind is critical to the climatic effect of Indian Ocean Basin Warming.When the South Asian Summer Monsoon reaches its peak,the background wind becomes desirable for basin warming,which then affects the climate in the Northwest Pacific.Via the Kelvin waves and Ekman divergence,the wind anomalies exist in the lower atmosphere east of the Indian Ocean warm Sea Surface Temperature(SST) anomalies,and intensify and sustain the ANWPA throughout the El Nio decaying summer.This impact plays an important role in the inter-annual variability of the East Asian Summer Monsoon.展开更多
Both the tropical Indian and tropical Pacific Oceans are active atmosphere-ocean interactive regions with robust interannual variability, which also constitutes a linkage between the two basins in the mode of variabil...Both the tropical Indian and tropical Pacific Oceans are active atmosphere-ocean interactive regions with robust interannual variability, which also constitutes a linkage between the two basins in the mode of variability. Using a global atmosphereocean coupled model, we conducted two experiments(CTRL and PC) to explore the contributions of Indian Ocean interannual sea surface temperature(SST) modes to the occurrence of El Ni?o events. The results show that interannual variability of the SST in the Indian Ocean induces a rapid growth of El Ni?o events during the boreal autumn in an El Ni?o developing year. However, it weakens El Ni?o events or even promotes cold phase conversions in an El Ni?o decaying year. Therefore, the entire period of the El Ni?o is shortened by the interannual variations of the Indian Ocean SST. Specifically, during the El Ni?o developing years, the positive Indian Ocean Dipole(IOD) events force an anomalous Walker circulation, which then enhances the existing westerly wind anomalies over the west Pacific. This will cause a warmer El Ni?o event, with some modulations by ocean advection and oceanic Rossby and Kelvin waves. However, with the onset of the South Asian monsoon, the Indian Ocean Basin(IOB) warming SST anomalies excite low level easterly wind anomalies over the west tropical Pacific during the El Ni?o decaying years. As a result, the El Ni?o event is prompted to change from a warm phase to a cold phase. At the same time, an associated atmospheric anticyclone anomaly appears and leads to a decreasing precipitation anomaly over the northwest Pacific. In summary, with remote forcing in the atmospheric circulation, the IOD mode usually affects the El Ni?o during the developing years, whereas the IOB mode affects the El Ni?o during the decaying years.展开更多
By applying the OLR and wind data,rainfall data and the Madden and Julian Oscillation(MJO)index,the paper deals with intraseasonal oscillation features and inter-annual differences of the South China Sea(SCS)summer mo...By applying the OLR and wind data,rainfall data and the Madden and Julian Oscillation(MJO)index,the paper deals with intraseasonal oscillation features and inter-annual differences of the South China Sea(SCS)summer monsoon,distribution of its LF circulation and convection fields and rainfall,and path of summer monsoon ISO spreading,as well as impact of tropical Indo-MJO on SCS summer monsoon ISO during 1979-2008.It is found that(1)there are three intraseasonal oscillations of the SCS summer monsoon Intraseasonal Oscillation(ISO)in summer(from May to August)in the climate normal.The SCS summer monsoon ISO goes through six phases(exclusive of weak phase)at every complete fluctuation:developing,the strongest,weakening,restraining,the weakest,and recovering.Due to tropical LC convection spreading to the east and north, the LR convection and circulation fields in the 1st-3rd and 4th-6th phases present the anti-phase in the Arabian Sea-West Pacific latitudinal band.Its corresponding rain bands in the 1st-3rd and 4th-6th phases also present anti-phase roughly.The rain band,mainly in tropical regions in the south of 20°N,moves eastward with LR convection shifting eastward,while the rain band moves northward with LR convection shifting northward in East Asia(EA)subtropical regions in the north of 20°N.(2) The SCS summer monsoon ISO presents significant inter-annual variations in intensity.There are three stronger monsoon in- traseasonal oscillations in summer in the strong SCS monsoon ISO year.The first two oscillations from the tropical Indian Ocean ISO spread northward to the Bay of Bengal first,and then to the South China Sea(SCS)along the 10°-20°N latitudinal band.They are strengthened there and stimulate the ISO moving to the north to form the tropical Indo-ISO.Finally they spread to South China(SC)by relay way in the longitude-latitude direction.Moreover,in the weaker SCS summer monsoon ISO,the oscillation weakens greatly and irregularly in intensity with the weaker ISO spreading in the longitude-latitude direction.In average conditions,the tropical Indian ISO spreads to the SCS by about 20 days(one half ISO periods).(3)MJO1(the first modal of MJO index provided by the CPC)averaged value in the 1st-2nd pentads of April has the negative correlation with the SCS monsoon ISO intensity.The tropical Indo-MJO is slightly stronger in the subsequent May to August when it is more active in the 1st-2nd pentads of April,and the ISO also spreads strongly to the SCS,so that the SCS summer monsoon ISO strengthens.Conversely,the SCS summer monsoon ISO weakens.The abnormal MJO in the 1st-2nd pentads of April contributes to a certain theory basis for us to predict the subsequent SCS summer monsoon ISO intensity and analyze the related regions'abnormal rainfall.展开更多
The response of ENSO frequency to the increasing CO2 concentration and associated mechanism are examined with outputs of four coupled climate models (GFDL/CM2.0,CNRM/CM3,IPSL/CM4 and INM/CM3.0) submitted to the IPCC F...The response of ENSO frequency to the increasing CO2 concentration and associated mechanism are examined with outputs of four coupled climate models (GFDL/CM2.0,CNRM/CM3,IPSL/CM4 and INM/CM3.0) submitted to the IPCC Fourth Assessment Report (IPCC AR4).Results reveal a significant change of ENSO frequency as response to the increasing CO2 concentration.However,such a change exhibits an evident model dependence.The ENSO frequency tends to increase in GFDL/CM2.0 and CNRM/CM3 models and decreases in IPSL/CM4 and INM/CM3.0 models.The model dependence is found to be determined by how the model climatological background state of the tropical Pacific responds to the increasing CO 2 concentration.It is demonstrated that the change of zonally-and vertically-averaged climatological background upper ocean temperature gradient between the equator and off-equator is crucially responsible for the ENSO frequency change.As response to the increasing CO 2 concentration,the climatological background temperature gradient is increased in GFDL/CM2.0 and CNRM/CM3 models and decreased in IPSL/CM4 and INM/CM3.0 models.In terms of the recharge-discharge oscillator theory for ENSO,the increased (decreased) climatological background temperature gradient between the equator and off-equator induces a faster (slower) exchange of oceanic heat content between the equator and off-equator,thus giving rise to a shorter (longer) ENSO timescale and a higher (lower) ENSO frequency.展开更多
文摘本文利用观测和再分析资料,通过奇异值分解(Singular Value Decomposition,SVD)分析,发现北极涛动(Arctic Oscillation,AO)是显著影响中国夏季降水年际异常的前冬中高纬大气环流变异的主模态。AO在冬季发展成熟,在春季衰亡,在夏季发生位相反转。AO会导致华北、东北、长江中下游和华南夏季降水异常呈现三极型分布。伴随正位相的AO,在黄海至日本海上空的异常低压伴随的东北风异常引起华北和东北水汽通量异常辐散及降水减少,而西北太平洋的异常高压不仅增强其北侧的西南风水汽输送,和北部异常低压共同作用导致长江中下游水汽通量异常辐合及降水增加,而且使得华南水汽通量异常辐散,降水减少。因此,本文发现的前冬AO模态与我国夏季三极型异常降水分布的关系可为我国夏季旱涝预测提供一个重要的中高纬前期因子。
文摘基于1980-2017年京津冀地区定时观测资料、欧亚陆面积雪资料、欧洲中期天气预报中心(European Centre for Medium-range Weather Forecasts,ECMWF)再分析资料,美国国家环境预报中心/大气研究中心(NCEP/NCAR)再分析资料以及英国哈德莱中心提供的海冰密集度资料,分析了秋季10-11月京津冀霾日频数年际变率与同期欧亚积雪的物理联系,并通过气候统计诊断和敏感性试验探讨了积雪异常影响京津冀10-11月霾日频数年际变率的可能机理。结果表明,10-11月京津冀霾日频数年际变率与同期东欧-西伯利亚平原地区(记为R Eu;50°~60°N,40°~80°E)积雪厚度和积雪覆盖度均呈现显著的正相关关系。R Eu积雪正异常与其西北侧的挪威海-巴伦支海海域以及北欧到东欧地区上空大气冷源密切联系,该冷源可激发一个自上述区域途经R Eu一直到东北亚的准正压大尺度纬向Rossby波列来调制影响京津冀霾日频数年际变率的关键环流系统,即东北亚异常反气旋。上述异常环流背景下,京津冀地区对流层低层为偏南风异常所控制,稳定大气层结易于建立,边界层高度偏低、地面风速偏弱且相对湿度偏高。该环境条件有利于霾天气发生发展,使得同期霾日偏多。作为预测信号,当前期9月楚科奇海-西波弗特海海冰偏少(多)时,10-11月京津冀霾日可能偏多(少)。
基金jointly supported by the National Natural Science Foundation of China(Grant No.41275068)the Special Fund for Meteorology Research in the Public Interest(Grant No.GYHY201106017)the 973 Program(Grant No.2010CB428504)
文摘The features of large-scale circulation, storm tracks and the dynamical relationship between them were examined by investigating Rossby wave breaking （RWB） processes associated with Eastern Pacific （EP） and Central Pacific （CP） E1-Nifio. During EP E1-Nino, the geopotential height anomaly at 500 hPa （Z500） exhibits a Pacific-North America （PNA） pattern. During CP EI-Nifio, the Z500 anomaly shows a north positive-south negative pattern over the North Pacific. The anomalous distributions of baroclinicity and storm track are consistent with those of upper-level zonal wind for both EP and CP EI-Nino, suggesting impacts of mean flow on storm track variability. Anticyclonic wave breaking （AWB） oczurs less frequently in EP EI-Nino years, while cyclonic wave breaking （CWB） occurs more frequently in CP EI-Nino years over the North Pacific sector. Outside the North Pacific, more CWB events occur over North America during EP Ei-NiNo. When AWB events occur less frequently over the North Pacific during EP EI-Nino, Z500 decreases locally and the zonal wind is strengthened （weakened） to the south （north）. This is because AWB events reflect a monopoie high anomaly at the centroid of breaking events. When CWB events occur more frequently over the North Pacific under CP EI-Nino conditions, and over North America under EP EI-Nino condition, Z500 increases （decreases） to the northeast （southwest）, since CWB events are related to a northeast-southwest dipole Z500 anomaly. The anomalous RWB events act to invigorate and reinforce the circulation anomalies over the North Pacific-North America region linked with the two types of EI-Nino.
基金supported by the National Key Program for Developing Basic Science(Nos.2010CB428504,2012 CB956002)the National Natural Science Foundation of China(Nos.40906005,41105059,41065005,41176004,GYHY201106017,GYHY201206027)the National Key Technologies R&D Program of China(No.2009BAC 51B01)
文摘In this study, we used the NCAR CAM3.0 model to study the climate effects of both decadal global Sea Surface Temperature(SST) changing and the increasing aerosol concentration in East Asia in boreal spring. In the decadal SST changing experiment, a prominent sea surface cyclone anomaly occurred west of the Northwest Pacific warming SST. The cyclone anomaly is conductive to anomalous rising motion and more rainfall over the Northwest Pacific and southeast coast areas of China, but less rainfall in central China. Caused by the only aerosol concentration increasing, the change of climate in East Asia is totally different from that induced by the regime shift of SST around 1976/77 with the same model. The sulfate and black carbon aerosol concentrations were doubled respectively and synchronously in East Asia(20?–50?N, 100?–150?E) to investigate the climate effects of these two major aerosol types in three experiments. The results show that, in all three aerosol concentration changing experiments, the rainfall during boreal spring increases in North China and decreases in central China. It's worth noting that in the DTWO experiment, the rainfall diminishes in central China while it increases in the north and southeast coast areas of China, which is similar to observations. From the vertical profile between 110?E and 120?E, it is found that sulfate and black carbon aerosols first change the temperature of lower troposphere owing to their direct radiative effect, and then induce secondary meridional circulation anomaly through the different dynamic mechanisms involved, and at last generate precipitation and surface temperature anomalous patterns mentioned above.
基金supported by the National Basic Research Program of China (2010CB428504)
文摘With the homogeneity-adjusted surface air temperature (SAT) data at 312 stations in eastern China for 1979-2008 and the Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS) nighttime light data, the spatial heterogeneities of the SAT trends on different scales are detected with a spatial filtering (i.e. moving spatial anomaly) method, and the impact of urbanization in eastern China on surface warming is analyzed. Results show that the urbanization can induce a remarkable summer warming in Yangtze River Delta (YRD) city cluster region and a winter warming in Beijing-Tianjin-Hebei (BTH) city cluster region. The YRD warming in summer primarily results from the significant increasing of maximum temperature, with an estimated urban warming rate at 0.132-0.250℃ per decade, accounting for 36%-68% of the total regional warming. The BTH warming in winter is primarily due to the remarkable increasing of minimum temperature, with an estimated urban warming rate at 0.102-0.214℃ per decade, accounting for 12%-24% of the total regional warming. The temporal-spatial differences of urban warming effect may be attributed to the variation of regional climatic background and the change of anthropogenic heat release.
基金supported by the National Key Program for Developing Basic Science(Grant Nos.2010CB428504&2012CB956002)National Natural Science Foundation of China(Grant Nos.40906005,41105059,41275069,GYHY201106017&GYHY201206038)the National Key Technologies R&D Program of China(Grant No.2009BAC51B01)
文摘Recent studies have found a connection between Indian Ocean Basin Warming and the anomalous Northwest Pacific Anticyclone(ANPWA) during El Ni?o decaying year.This study focuses on the necessary condition for this connection by using observation and numerical simulation.The seasonal transition of the Indian Ocean sea surface wind is critical to the climatic effect of Indian Ocean Basin Warming.When the South Asian Summer Monsoon reaches its peak,the background wind becomes desirable for basin warming,which then affects the climate in the Northwest Pacific.Via the Kelvin waves and Ekman divergence,the wind anomalies exist in the lower atmosphere east of the Indian Ocean warm Sea Surface Temperature(SST) anomalies,and intensify and sustain the ANWPA throughout the El Nio decaying summer.This impact plays an important role in the inter-annual variability of the East Asian Summer Monsoon.
基金supported by the National Basic Research Program of China(Grant Nos.2010CB428504,2012CB956002)the National Natural Science Foundation of China(Grant Nos.40906005,41105059,41065005,GYHY2011-06017,GYHY201306027)+1 种基金the National Key Technologies R&D Program of China(Grant No.2009BAC51B01)the Jiangsu Collaborative Innovation Center for Climate Change
文摘Both the tropical Indian and tropical Pacific Oceans are active atmosphere-ocean interactive regions with robust interannual variability, which also constitutes a linkage between the two basins in the mode of variability. Using a global atmosphereocean coupled model, we conducted two experiments(CTRL and PC) to explore the contributions of Indian Ocean interannual sea surface temperature(SST) modes to the occurrence of El Ni?o events. The results show that interannual variability of the SST in the Indian Ocean induces a rapid growth of El Ni?o events during the boreal autumn in an El Ni?o developing year. However, it weakens El Ni?o events or even promotes cold phase conversions in an El Ni?o decaying year. Therefore, the entire period of the El Ni?o is shortened by the interannual variations of the Indian Ocean SST. Specifically, during the El Ni?o developing years, the positive Indian Ocean Dipole(IOD) events force an anomalous Walker circulation, which then enhances the existing westerly wind anomalies over the west Pacific. This will cause a warmer El Ni?o event, with some modulations by ocean advection and oceanic Rossby and Kelvin waves. However, with the onset of the South Asian monsoon, the Indian Ocean Basin(IOB) warming SST anomalies excite low level easterly wind anomalies over the west tropical Pacific during the El Ni?o decaying years. As a result, the El Ni?o event is prompted to change from a warm phase to a cold phase. At the same time, an associated atmospheric anticyclone anomaly appears and leads to a decreasing precipitation anomaly over the northwest Pacific. In summary, with remote forcing in the atmospheric circulation, the IOD mode usually affects the El Ni?o during the developing years, whereas the IOB mode affects the El Ni?o during the decaying years.
基金supported by Special Fund for the Meteorological Scientific Research of Public Sector(Grant No.GYHY200806004)National Basic Research Program of China (Grant No.2012CB956001)
文摘By applying the OLR and wind data,rainfall data and the Madden and Julian Oscillation(MJO)index,the paper deals with intraseasonal oscillation features and inter-annual differences of the South China Sea(SCS)summer monsoon,distribution of its LF circulation and convection fields and rainfall,and path of summer monsoon ISO spreading,as well as impact of tropical Indo-MJO on SCS summer monsoon ISO during 1979-2008.It is found that(1)there are three intraseasonal oscillations of the SCS summer monsoon Intraseasonal Oscillation(ISO)in summer(from May to August)in the climate normal.The SCS summer monsoon ISO goes through six phases(exclusive of weak phase)at every complete fluctuation:developing,the strongest,weakening,restraining,the weakest,and recovering.Due to tropical LC convection spreading to the east and north, the LR convection and circulation fields in the 1st-3rd and 4th-6th phases present the anti-phase in the Arabian Sea-West Pacific latitudinal band.Its corresponding rain bands in the 1st-3rd and 4th-6th phases also present anti-phase roughly.The rain band,mainly in tropical regions in the south of 20°N,moves eastward with LR convection shifting eastward,while the rain band moves northward with LR convection shifting northward in East Asia(EA)subtropical regions in the north of 20°N.(2) The SCS summer monsoon ISO presents significant inter-annual variations in intensity.There are three stronger monsoon in- traseasonal oscillations in summer in the strong SCS monsoon ISO year.The first two oscillations from the tropical Indian Ocean ISO spread northward to the Bay of Bengal first,and then to the South China Sea(SCS)along the 10°-20°N latitudinal band.They are strengthened there and stimulate the ISO moving to the north to form the tropical Indo-ISO.Finally they spread to South China(SC)by relay way in the longitude-latitude direction.Moreover,in the weaker SCS summer monsoon ISO,the oscillation weakens greatly and irregularly in intensity with the weaker ISO spreading in the longitude-latitude direction.In average conditions,the tropical Indian ISO spreads to the SCS by about 20 days(one half ISO periods).(3)MJO1(the first modal of MJO index provided by the CPC)averaged value in the 1st-2nd pentads of April has the negative correlation with the SCS monsoon ISO intensity.The tropical Indo-MJO is slightly stronger in the subsequent May to August when it is more active in the 1st-2nd pentads of April,and the ISO also spreads strongly to the SCS,so that the SCS summer monsoon ISO strengthens.Conversely,the SCS summer monsoon ISO weakens.The abnormal MJO in the 1st-2nd pentads of April contributes to a certain theory basis for us to predict the subsequent SCS summer monsoon ISO intensity and analyze the related regions'abnormal rainfall.
基金supported by the National Natural Science Foundation of China (Grant Nos.40730953 and 40425009)Natural Science Foundation of Jiangsu Province (Grant No.BK2008027)
文摘The response of ENSO frequency to the increasing CO2 concentration and associated mechanism are examined with outputs of four coupled climate models (GFDL/CM2.0,CNRM/CM3,IPSL/CM4 and INM/CM3.0) submitted to the IPCC Fourth Assessment Report (IPCC AR4).Results reveal a significant change of ENSO frequency as response to the increasing CO2 concentration.However,such a change exhibits an evident model dependence.The ENSO frequency tends to increase in GFDL/CM2.0 and CNRM/CM3 models and decreases in IPSL/CM4 and INM/CM3.0 models.The model dependence is found to be determined by how the model climatological background state of the tropical Pacific responds to the increasing CO 2 concentration.It is demonstrated that the change of zonally-and vertically-averaged climatological background upper ocean temperature gradient between the equator and off-equator is crucially responsible for the ENSO frequency change.As response to the increasing CO 2 concentration,the climatological background temperature gradient is increased in GFDL/CM2.0 and CNRM/CM3 models and decreased in IPSL/CM4 and INM/CM3.0 models.In terms of the recharge-discharge oscillator theory for ENSO,the increased (decreased) climatological background temperature gradient between the equator and off-equator induces a faster (slower) exchange of oceanic heat content between the equator and off-equator,thus giving rise to a shorter (longer) ENSO timescale and a higher (lower) ENSO frequency.
