The NCEP/NCAR global reanalysis data were used to analyze the interannual variation characteristics of the cross-equatorial flow (CEF) and its concurrent relationships with temperature and rainfall in China. The resul...The NCEP/NCAR global reanalysis data were used to analyze the interannual variation characteristics of the cross-equatorial flow (CEF) and its concurrent relationships with temperature and rainfall in China. The results indicated that CEF changes more in summer than in winter. As the main flow channel in summer, the Somali CEF changes in a way that does not markedly influence the changes in the CEF total except for winter. The summer CEF total has two sudden increases and one sudden decrease during the last century while the winter total has just one decrease. Long-period data show that the correlation between CEF and summer rainfall in China is not very significant, but is different before and after the 1970s, which is due to CEF's close links with the East Asia summer monsoon. Winter CEF's correlation with concurrent winter temperature in northern and southern China varies with the relationship between CEF and sea-level pressure in different areas.展开更多
Based on the daily rainfall datasets of 743 stations in China and the NCEP/NCAR monthly reanalysis data during the period of 1960-2003,the relationship between the anomalous extreme precipitation(EP) in the south of C...Based on the daily rainfall datasets of 743 stations in China and the NCEP/NCAR monthly reanalysis data during the period of 1960-2003,the relationship between the anomalous extreme precipitation(EP) in the south of China and atmospheric circulation in the Southern Hemisphere is analyzed.The phenomenon of opposite changes in the sea level pressure and geopotential height anomalies over the Ross Sea and New Zealand is defined as RN,and the index which describes this phenomenon is expressed as RNI.The results show that the RN has barotropic structure and the RNI in May is closely related to the June EP amount in the south of China(SCEP) and the East Asian summer monsoon(EASM).The positive correlations between the May RNI at each level and the June SCEP are significant,and the related simultaneous correlations between the RNI and the June SCEP are also positive,suggesting that the potential impact of RN on the SCEP persists from May to June.Therefore,RN in May can be taken as one of the predictive factors for the June SCEP.Furthermore,one possible physical mechanism by which the RN affects the June SCEP is a barotropic meridional teleconnection emanating from the Southern Hemisphere to the western North Pacific.展开更多
Based on gradient wind equations, including frictional force, and considering the effect of the movement of a tropical cyclone on wind speed, the Fujita Formula is improved and further simplified, and the numerical sc...Based on gradient wind equations, including frictional force, and considering the effect of the movement of a tropical cyclone on wind speed, the Fujita Formula is improved and further simplified, and the numerical scheme for calculating the maximum wind speed radius and wind velocity distribution of a moving tropical cyclone is derived. In addition, the effect of frictional force on the internal structure of the tropical cyclone is discussed. By comparison with observational data, this numerical scheme demonstrates great advantages, i.e. it can not only describe the asymmetrical wind speed distribution of a tropical cyclone reasonably, but can also calculate the maximum wind speed in each direction within the typhoon domain much more accurately. Furthermore, the combination of calculated and analyzed wind speed distributions by the scheme is perfectly consistent with observations.展开更多
A possible reason for the unreasonable simula- tion of maximum rainfall location, intensity and seasonal evolution over eastern China in CCM3 has been investigated. The analyses focus on the relationship between the s...A possible reason for the unreasonable simula- tion of maximum rainfall location, intensity and seasonal evolution over eastern China in CCM3 has been investigated. The analyses focus on the relationship between the simulated East Asian subtropical westerly jet biases and the seasonal evolution of rainbelt over eastern China. Comparisons of the simulated and observed precipitation distributions indicate that the simulated maximum rainfall location, intensity and seasonal evolution are inconsistent with reality. The simu- lated westerly jet center is located to the north of 40°N, which shifts eastward and northward and strengthens, com- pared with NCEP/NCAR reanalysis. The correlation analysis shows that there exists a significant positive correlation be- tween the maximum rainfall amount and zonal wind at 200 hPa over the Great Bend of the Huanghe River. Thus the simulated unrealistic heavy precipitation in the inland area of western China is related to the biases in the location and intensity of the East Asian subtropical westerly jet. Further analysis indicates that the temperature differences from south to north in the lower troposphere and the larger sensi- ble heating over the southeast Tibetan Plateau are responsi- ble for the westerly jet location and intensity biases. There- fore, much more attention should be paid to the accurate simulation of the surface heating near the Tibetan Plateau and the location and intensity of the East Asian subtropical westerly jet for the improvement of precipitation simulation over East Asia.展开更多
Diagnostic comparison of the East Asian subtropical jet （EASJ） and polar-front jet （EAPJ） in winter season is carried out by using the ERA-40 dataset. The large-scale circulation characteristics and synopticscale ...Diagnostic comparison of the East Asian subtropical jet （EASJ） and polar-front jet （EAPJ） in winter season is carried out by using the ERA-40 dataset. The large-scale circulation characteristics and synopticscale transient eddy activities （STEAs） associated with the EASJ and EAPJ are examined. The results show that the EASJ and EAPJ in the upper-level monthly mean data have no clear geographical border, while the distribution of the numbers of jet cores from the daily data exhibits a distinct boundary at the latitudes of the northern Tibetan Plateau. The two areas with large numbers of jet cores correspond to the EASJ and EAPJ regions. The analysis of STEAs over the East Asian region shows a spatial match of STEAs with the EASJ and EAPJ in winter： the strong EASJ is located within the weak southern branch of the STEA while the relatively weak EAPJ appears within the active northern branch of the STEA, indicating that the EAPJ is the jet coexisting with the STEA. Further analysis shows two anomalous modes of the winter EAPJ： the anomalous anticyclonic/cyclonic circulation and the weakened/strengthened local westerly wind. The large-scale circulation anomalies in the Northern Hemisphere related to the first mode are concentrated in the Eurasian mid to high latitudes, and are also influenced by the anomalous circulation in the upstream area. When the local westerly wind over the EAPJ region is weakened/strengthened, the westerly jet in the eastern part of the EASJ and that in the western Pacific region show opposite variations. The corresponding anomalous atmospheric circulation demonstrates the Eurasian （EU） pattern. The EAPJ anomalies are also closely linked with the STEA anomalies over East Asia. The anomalies in the northern branch of the STEA propagate as a wave train along its axis into the East Asian coastal waters, and then migrate eastward to the oceanic region. However, the ones near the southern branch are trapped over the eastern part of East Asia and its coastal waters at 200 hPa.展开更多
Pacific Decadal Oscillation (PDO) is a long-term ENSO-like variability of theNorth Pacific. It is the first principal component of EOF of the North Pacific SST. ENSO is thestrongest signal of annular change of global ...Pacific Decadal Oscillation (PDO) is a long-term ENSO-like variability of theNorth Pacific. It is the first principal component of EOF of the North Pacific SST. ENSO is thestrongest signal of annular change of global climate system. Empirical Mode Decomposition (EMD)method is applied to two types of indices. One type of index is the Pacific Decadal Oscillation(PDO) index that represents a long-term ENSO-like variability of the North Pacific. The other typeof indices such as Southern Oscillation (SO) index, Ninol+2 SST, Nino3 SST, Nino4 SST and Nino3.4SST represents ENSO. The relationship between two types of indices shows the temporalcharacteristics and relationships between the two phenomena. It is found that, for PDO, the goodcorrelations with ENSO only exist on the quasi-2-7-yr timescales and decadal and multi-decadaltimescales, suggesting that a close relationship between PDO and ENSO only exists among some specialintrinsic mode functions at lower frequency band.展开更多
The relationships between the 200-hPa westerly jet stream anomalies over the East Asian coastal waterwestern Pacific （WPJS）, and the oceanic surface heating and synoptic-scale transient eddy （STE） activity anomali...The relationships between the 200-hPa westerly jet stream anomalies over the East Asian coastal waterwestern Pacific （WPJS）, and the oceanic surface heating and synoptic-scale transient eddy （STE） activity anomalies over the North Pacific in wintertime are examined by using ERA-40 and NCEP/NCAR reanalysis data. The analysis demonstrates that the surface heating and the STE anomalies have different patterns, corresponding to the three WPJS anomalous modes, respectively. In the first WPJS anomalous mode, the WPJS main part shows no robust anomaly. The anomalous westerly wind, occurring over the mid-latitude central-eastern Pacific past the date line is associated with the anomalous heating presenting both in the tropical central-eastern Pacific past the date line and the center of the North Pacific basin. Meanwhile, the STE anomaly appears around the region of the anomalous zonal wind. The fluctuation in jet strength shown in the second WPJS mode is strongly related to the heating anomaly in the Kuroshio Current region and the STE anomaly in the jet exit region. The third mode demonstrates a northward/southward shift of the WPJS, which has a statistical connection with a south-north dipolar pattern of the heating anomaly in the western North Pacific separated at 35°N. Meanwhile, the STE spatial displacement is in conjunction with jet shifts in the same direction. The heating anomaly has a close connection with the atmospheric circulation, and thus changes the mid-latitude baroclinicity, leading to the STE anomaly, which then reinforces the WPJS anomaly via internal atmospheric dynamics.展开更多
基金Research on the Effect of Stratospheric Anomalies in North Pole on Weather and Climate of Asia and North Pacific–a key project of the Natural Science Foundation of China (40533016)
文摘The NCEP/NCAR global reanalysis data were used to analyze the interannual variation characteristics of the cross-equatorial flow (CEF) and its concurrent relationships with temperature and rainfall in China. The results indicated that CEF changes more in summer than in winter. As the main flow channel in summer, the Somali CEF changes in a way that does not markedly influence the changes in the CEF total except for winter. The summer CEF total has two sudden increases and one sudden decrease during the last century while the winter total has just one decrease. Long-period data show that the correlation between CEF and summer rainfall in China is not very significant, but is different before and after the 1970s, which is due to CEF's close links with the East Asia summer monsoon. Winter CEF's correlation with concurrent winter temperature in northern and southern China varies with the relationship between CEF and sea-level pressure in different areas.
基金National Basic Research Program of China (2004CB418300, 2010CB833406)National Natural Science Foundation of China (40675042, 40890054, 40871007)
文摘Based on the daily rainfall datasets of 743 stations in China and the NCEP/NCAR monthly reanalysis data during the period of 1960-2003,the relationship between the anomalous extreme precipitation(EP) in the south of China and atmospheric circulation in the Southern Hemisphere is analyzed.The phenomenon of opposite changes in the sea level pressure and geopotential height anomalies over the Ross Sea and New Zealand is defined as RN,and the index which describes this phenomenon is expressed as RNI.The results show that the RN has barotropic structure and the RNI in May is closely related to the June EP amount in the south of China(SCEP) and the East Asian summer monsoon(EASM).The positive correlations between the May RNI at each level and the June SCEP are significant,and the related simultaneous correlations between the RNI and the June SCEP are also positive,suggesting that the potential impact of RN on the SCEP persists from May to June.Therefore,RN in May can be taken as one of the predictive factors for the June SCEP.Furthermore,one possible physical mechanism by which the RN affects the June SCEP is a barotropic meridional teleconnection emanating from the Southern Hemisphere to the western North Pacific.
基金supported by the National Natural Science Foundation of China (NSFC) under Grant Nos. 40425009 and 40730953
文摘Based on gradient wind equations, including frictional force, and considering the effect of the movement of a tropical cyclone on wind speed, the Fujita Formula is improved and further simplified, and the numerical scheme for calculating the maximum wind speed radius and wind velocity distribution of a moving tropical cyclone is derived. In addition, the effect of frictional force on the internal structure of the tropical cyclone is discussed. By comparison with observational data, this numerical scheme demonstrates great advantages, i.e. it can not only describe the asymmetrical wind speed distribution of a tropical cyclone reasonably, but can also calculate the maximum wind speed in each direction within the typhoon domain much more accurately. Furthermore, the combination of calculated and analyzed wind speed distributions by the scheme is perfectly consistent with observations.
基金supported jointly by the National Natural Science Foundation of China(Grant No.40333026)the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No.ZKCX2-SW-210)
文摘A possible reason for the unreasonable simula- tion of maximum rainfall location, intensity and seasonal evolution over eastern China in CCM3 has been investigated. The analyses focus on the relationship between the simulated East Asian subtropical westerly jet biases and the seasonal evolution of rainbelt over eastern China. Comparisons of the simulated and observed precipitation distributions indicate that the simulated maximum rainfall location, intensity and seasonal evolution are inconsistent with reality. The simu- lated westerly jet center is located to the north of 40°N, which shifts eastward and northward and strengthens, com- pared with NCEP/NCAR reanalysis. The correlation analysis shows that there exists a significant positive correlation be- tween the maximum rainfall amount and zonal wind at 200 hPa over the Great Bend of the Huanghe River. Thus the simulated unrealistic heavy precipitation in the inland area of western China is related to the biases in the location and intensity of the East Asian subtropical westerly jet. Further analysis indicates that the temperature differences from south to north in the lower troposphere and the larger sensi- ble heating over the southeast Tibetan Plateau are responsi- ble for the westerly jet location and intensity biases. There- fore, much more attention should be paid to the accurate simulation of the surface heating near the Tibetan Plateau and the location and intensity of the East Asian subtropical westerly jet for the improvement of precipitation simulation over East Asia.
基金Supported by the National Natural Science Foundation of China under Grant Nos. 40775044 and 40730953the Natural Science Foundation of Jiangsu Province under Grant No. BK2008027
文摘Diagnostic comparison of the East Asian subtropical jet （EASJ） and polar-front jet （EAPJ） in winter season is carried out by using the ERA-40 dataset. The large-scale circulation characteristics and synopticscale transient eddy activities （STEAs） associated with the EASJ and EAPJ are examined. The results show that the EASJ and EAPJ in the upper-level monthly mean data have no clear geographical border, while the distribution of the numbers of jet cores from the daily data exhibits a distinct boundary at the latitudes of the northern Tibetan Plateau. The two areas with large numbers of jet cores correspond to the EASJ and EAPJ regions. The analysis of STEAs over the East Asian region shows a spatial match of STEAs with the EASJ and EAPJ in winter： the strong EASJ is located within the weak southern branch of the STEA while the relatively weak EAPJ appears within the active northern branch of the STEA, indicating that the EAPJ is the jet coexisting with the STEA. Further analysis shows two anomalous modes of the winter EAPJ： the anomalous anticyclonic/cyclonic circulation and the weakened/strengthened local westerly wind. The large-scale circulation anomalies in the Northern Hemisphere related to the first mode are concentrated in the Eurasian mid to high latitudes, and are also influenced by the anomalous circulation in the upstream area. When the local westerly wind over the EAPJ region is weakened/strengthened, the westerly jet in the eastern part of the EASJ and that in the western Pacific region show opposite variations. The corresponding anomalous atmospheric circulation demonstrates the Eurasian （EU） pattern. The EAPJ anomalies are also closely linked with the STEA anomalies over East Asia. The anomalies in the northern branch of the STEA propagate as a wave train along its axis into the East Asian coastal waters, and then migrate eastward to the oceanic region. However, the ones near the southern branch are trapped over the eastern part of East Asia and its coastal waters at 200 hPa.
基金This work is jointly supported by the National Natural Science Foundation of China under Grant Nos. 40233028, 40075017.
文摘Pacific Decadal Oscillation (PDO) is a long-term ENSO-like variability of theNorth Pacific. It is the first principal component of EOF of the North Pacific SST. ENSO is thestrongest signal of annular change of global climate system. Empirical Mode Decomposition (EMD)method is applied to two types of indices. One type of index is the Pacific Decadal Oscillation(PDO) index that represents a long-term ENSO-like variability of the North Pacific. The other typeof indices such as Southern Oscillation (SO) index, Ninol+2 SST, Nino3 SST, Nino4 SST and Nino3.4SST represents ENSO. The relationship between two types of indices shows the temporalcharacteristics and relationships between the two phenomena. It is found that, for PDO, the goodcorrelations with ENSO only exist on the quasi-2-7-yr timescales and decadal and multi-decadaltimescales, suggesting that a close relationship between PDO and ENSO only exists among some specialintrinsic mode functions at lower frequency band.
基金the National Natural Science Foundation of China under Grant Nos.40675041,40333026,and 40425009.
文摘The relationships between the 200-hPa westerly jet stream anomalies over the East Asian coastal waterwestern Pacific （WPJS）, and the oceanic surface heating and synoptic-scale transient eddy （STE） activity anomalies over the North Pacific in wintertime are examined by using ERA-40 and NCEP/NCAR reanalysis data. The analysis demonstrates that the surface heating and the STE anomalies have different patterns, corresponding to the three WPJS anomalous modes, respectively. In the first WPJS anomalous mode, the WPJS main part shows no robust anomaly. The anomalous westerly wind, occurring over the mid-latitude central-eastern Pacific past the date line is associated with the anomalous heating presenting both in the tropical central-eastern Pacific past the date line and the center of the North Pacific basin. Meanwhile, the STE anomaly appears around the region of the anomalous zonal wind. The fluctuation in jet strength shown in the second WPJS mode is strongly related to the heating anomaly in the Kuroshio Current region and the STE anomaly in the jet exit region. The third mode demonstrates a northward/southward shift of the WPJS, which has a statistical connection with a south-north dipolar pattern of the heating anomaly in the western North Pacific separated at 35°N. Meanwhile, the STE spatial displacement is in conjunction with jet shifts in the same direction. The heating anomaly has a close connection with the atmospheric circulation, and thus changes the mid-latitude baroclinicity, leading to the STE anomaly, which then reinforces the WPJS anomaly via internal atmospheric dynamics.
