By using a nine-level atmospheric general circulation model developed at the Institute of Atmospheric Physics (IAP 9L AGCM), two sets of numerical experiments are carried out to investigate the influence of the Mascar...By using a nine-level atmospheric general circulation model developed at the Institute of Atmospheric Physics (IAP 9L AGCM), two sets of numerical experiments are carried out to investigate the influence of the Mascarene high (MH) and Australian high (AH) over the southern subtropics upon the East Asian summer monsoon circulation and summer precipitation in East Asia. The use of ensemble statistics is adopted to reduce the simulation errors. The result shows that with the intensification of MH, the Somali low-level jet is significantly enhanced together with the summer monsoon circulation in the tropical Asia and western Pacific region. Furthermore, the anticyclonic anomaly in the tropical western Pacific to the east of the Philippines may induce a weak East-Asia-Pacific teleconnection pattern. In the meantime, geopotential height in the Tropics is enhanced while it is reduced over most regions of mid-high latitudes, thus the northwestern Pacific subtropical high at 500 hPa extends southwestward, resulting in more rainfall in southern China arid less rainfall in northern China. A similar anomaly pattern of the atmospheric circulation systems is found in the experiment of the intensification of AH. On the other hand, because the cross-equatorial currents associated with AH are much weaker than the Somali jet, the anomaly magnitude caused by the intensification of AH is generally weak, and the influence of AH on summer rainfall in China seems to be localized in southern China. Comparison between the two sets of experiments indicates that MH plays a crucial role in the interactions of general atmospheric circulation between the two hemispheres.展开更多
Based on the reanalysis data fromNCEP/NCAR and other observational data, interannualvariability of Mascarene high (MH) and Australian high (AH) from 1970 to 1999 is examined. It is shown that interannual variability o...Based on the reanalysis data fromNCEP/NCAR and other observational data, interannualvariability of Mascarene high (MH) and Australian high (AH) from 1970 to 1999 is examined. It is shown that interannual variability of MH is dominated by the Antarctic oscillation (AAO), when the circumpolar low in the high southern lati-tudes deepens, the intensity of MH will be intensified. On the other hand, AH is correlated by AAO as well as El Nio and South Oscillation (ENSO), the intensity of AH will be inten-sified when El Nio occurs. Both correlation analysis andcase study demonstrate that summer rainfall over East Asia is closely related to MH and AH. When MH intensifies from boreal spring to summer (i.e. from austral autumn to winter)there is more rainfall over regions from the Yangtze Rivervalley to Japan, in contrast, less rainfall is found over south-ern China and western Pacific to the east of Taiwan, andmost of regions in mid-latitudes of East Asia. Compared with MH, the effect of AH on summer rainfall in East Asia is lim-ited to localized regions, there is more rainfall over southern China with the intensification of AH. The results in this study show that AAO is a strong signal on interannual time-scale, which plays an important role in summer rainfall over East Asia. This discovery is of real importance to revealing the physical mechanism of interannual variability of EastAsian summer monsoon and prediction of summer precipi-tation in China.展开更多
基于NCEP/NCAR再分析资料,分析西北太平洋热带辐合区上升运动(ITCZω)与越赤道气流和澳大利亚高压之间的关系,并给出了三者在2003、2007年淮河流域强降水的异常特征。结果表明越赤道气流对西北太平洋ITCZω的影响主要反映在对其强度的影...基于NCEP/NCAR再分析资料,分析西北太平洋热带辐合区上升运动(ITCZω)与越赤道气流和澳大利亚高压之间的关系,并给出了三者在2003、2007年淮河流域强降水的异常特征。结果表明越赤道气流对西北太平洋ITCZω的影响主要反映在对其强度的影响,对其位置的影响不明显。总体上来说,925 h Pa上各支越赤道气流强度与西北太平洋ITCZω强度的相关性都要好于850 h Pa;ITCZω强度与澳大利亚高压强度的相关只在对流层低层可以通过95%的信度检验。2003、2007年淮河流域强降水期间,90°E及以东的越赤道气流偏弱;澳大利亚高压强度也偏弱;对应ITCZω偏弱、偏南;2003、2007年90°E、105°E、150°E附近越赤道气流的强度较多年平均都要偏弱,2007年125°E附近越赤道气流的强度较多年平均也较弱;2007年ITCZω偏弱的程度要大于2003年;2007年南半球冷空气偏弱持续的时间虽然长于2003年,但偏弱的程度却小于2003年。展开更多
基金supported by the National Natural Science Foundation of China under Grant Nos.40233027,40075020 and 40221503
文摘By using a nine-level atmospheric general circulation model developed at the Institute of Atmospheric Physics (IAP 9L AGCM), two sets of numerical experiments are carried out to investigate the influence of the Mascarene high (MH) and Australian high (AH) over the southern subtropics upon the East Asian summer monsoon circulation and summer precipitation in East Asia. The use of ensemble statistics is adopted to reduce the simulation errors. The result shows that with the intensification of MH, the Somali low-level jet is significantly enhanced together with the summer monsoon circulation in the tropical Asia and western Pacific region. Furthermore, the anticyclonic anomaly in the tropical western Pacific to the east of the Philippines may induce a weak East-Asia-Pacific teleconnection pattern. In the meantime, geopotential height in the Tropics is enhanced while it is reduced over most regions of mid-high latitudes, thus the northwestern Pacific subtropical high at 500 hPa extends southwestward, resulting in more rainfall in southern China arid less rainfall in northern China. A similar anomaly pattern of the atmospheric circulation systems is found in the experiment of the intensification of AH. On the other hand, because the cross-equatorial currents associated with AH are much weaker than the Somali jet, the anomaly magnitude caused by the intensification of AH is generally weak, and the influence of AH on summer rainfall in China seems to be localized in southern China. Comparison between the two sets of experiments indicates that MH plays a crucial role in the interactions of general atmospheric circulation between the two hemispheres.
基金the National Key Basic Development Program (Grant No. G1998040900Part I) and the National Natural Science Foundation of China (Grant Nos. 40125014 and 40075020)
文摘Based on the reanalysis data fromNCEP/NCAR and other observational data, interannualvariability of Mascarene high (MH) and Australian high (AH) from 1970 to 1999 is examined. It is shown that interannual variability of MH is dominated by the Antarctic oscillation (AAO), when the circumpolar low in the high southern lati-tudes deepens, the intensity of MH will be intensified. On the other hand, AH is correlated by AAO as well as El Nio and South Oscillation (ENSO), the intensity of AH will be inten-sified when El Nio occurs. Both correlation analysis andcase study demonstrate that summer rainfall over East Asia is closely related to MH and AH. When MH intensifies from boreal spring to summer (i.e. from austral autumn to winter)there is more rainfall over regions from the Yangtze Rivervalley to Japan, in contrast, less rainfall is found over south-ern China and western Pacific to the east of Taiwan, andmost of regions in mid-latitudes of East Asia. Compared with MH, the effect of AH on summer rainfall in East Asia is lim-ited to localized regions, there is more rainfall over southern China with the intensification of AH. The results in this study show that AAO is a strong signal on interannual time-scale, which plays an important role in summer rainfall over East Asia. This discovery is of real importance to revealing the physical mechanism of interannual variability of EastAsian summer monsoon and prediction of summer precipi-tation in China.
文摘基于NCEP/NCAR再分析资料,分析西北太平洋热带辐合区上升运动(ITCZω)与越赤道气流和澳大利亚高压之间的关系,并给出了三者在2003、2007年淮河流域强降水的异常特征。结果表明越赤道气流对西北太平洋ITCZω的影响主要反映在对其强度的影响,对其位置的影响不明显。总体上来说,925 h Pa上各支越赤道气流强度与西北太平洋ITCZω强度的相关性都要好于850 h Pa;ITCZω强度与澳大利亚高压强度的相关只在对流层低层可以通过95%的信度检验。2003、2007年淮河流域强降水期间,90°E及以东的越赤道气流偏弱;澳大利亚高压强度也偏弱;对应ITCZω偏弱、偏南;2003、2007年90°E、105°E、150°E附近越赤道气流的强度较多年平均都要偏弱,2007年125°E附近越赤道气流的强度较多年平均也较弱;2007年ITCZω偏弱的程度要大于2003年;2007年南半球冷空气偏弱持续的时间虽然长于2003年,但偏弱的程度却小于2003年。
