The first leading modes of the interannual variations in low-level circulation over the North and South Pacific are the Northern Oscillation （NO） and Southern Oscillation （SO）,which are oscillations in sea level pressure anomalies （SLPAs）between the eastern and western Pacific Ocean.The second leading modes are the North Pacific Oscillation （NPO） and the Antarctic Oscillation （AAO）,which reflect oscillations between the subtropics and the high and middle latitudes.The transition chains of these four oscillations were investigated using the National Centers for Environmental Prediction-National Center for Atmospheric Research （NCEP-NCAR） reanalysis data.The general pattern of the transition chain between the NO and NPO was from the negative phase of the NO （NO-） to the positive phase of the NPO （NPO＋）,then from NO＋ to NPO-to NO-.The whole transition chain took about 4-6 years.The general pattern and period of the transition between the SO and AAO were similar to those between the NO and NPO.In addition,the transition chains between the NO and NPO,and the SO and AAO,were almost simultaneous.The transition chains of the four oscillations were found to be closely connected,with the eastward propagations of SLPAs occurring along both sides of the Equator.
利用1971—2016年大连地区逐日降水量观测资料和NCEP/NCAR(National Centers for Environmental Prediction/National Center for Atmospheric Research)再分析月平均资料,对2013年7月大连地区降水异常偏多的成因进行了诊断分析。结果表明:2013年7月欧亚中高纬地区维持两脊一槽环流型,乌拉尔山和鄂霍次克海高压异常偏强,贝加尔湖附近低槽稳定维持造成冷空气频繁南下;同时,高空西风急流位置偏北偏强,西太平洋副热带高压明显偏西偏北,东亚夏季风偏强,有利于来自孟加拉湾、南海和西北太平洋的暖湿水汽沿副热带高压外围持续向大连地区输送,冷暖空气在大连地区交汇,形成水汽的异常辐合区,造成大连地区降水异常偏多。高能舌、不稳定层结、异常偏强的上升运动、高空辐散及低空辐合为大连地区降水异常偏多提供了有利的热力和动力条件。
