冬季北太平洋多尺度水汽输送和大气河的变化特征及其与PDO和ENSO的联系

Multi-scale water vapor transportation and variation characteristics of atmospheric river over the North Pacific in winter and its relationship with PDO and ENSO

利用1950-2015年NCEP/NCAR大气再分析资料和NOAA海表面温度资料,通过回归分析和合成分析的方法研究了冬季北太平洋不同尺度水汽输送和大气河(Atmospheric River, AR)的变化特征及其与PDO、ENSO的联系。结果表明,在PDO正位相时期,时间平均的水汽输送将大量水汽从太平洋北部和中部地区输送到东北太平洋的阿拉斯加湾及北美西岸地区,同时将北太平洋副热带地区的水汽输送到热带地区;低频尺度的水汽输送主要是将水汽从北太平洋向低纬地区输送;天气尺度的水汽输送使得大量水汽在北太平洋中部风暴轴区域汇集;北太平洋AR中部和阿拉斯加及北美西岸地区的AR频率显著增强,热带太平洋AR中西部明显增强,而东部减弱并向西南方向移动延伸。在ENSO正位相时期,时间平均的水汽输送使得东北太平洋和热带太平洋地区降水异常增多;低频尺度的水汽输送导致北美西岸易发生极端降水事件;天气尺度的水汽输送与北太平洋风暴轴活动密切相关;北太平洋AR中西部有所减弱,但在其东部的北美西岸地区AR频率明显增强,热带太平洋AR中部地区显著增强,而在其东南部则明显减弱。PDO和ENSO处于不同位相下时对AR的影响表现出一定的非对称性,其中PDO对北太平洋AR的影响起主导作用,而ENSO对热带太平洋AR的影响起主导作用。

Based on the NCEP/NCAR reanalysis data and the monthly mean sea surface temperature data provided by NOAA from 1950 to 2015,the characteristics of multi-scale water vapor transportation and the Atmospheric Rivers(AR)in winter of North Pacific as well as their relationship with PDO were analyzed by regression analysis and composite analysis.Rresults show that when the PDO is in positive phase,the time-mean water vapor transportation component transports a large amount of water vapor from the northern and central Pacific to the Alaska Bay and west coast of North America region in the Northeast Pacific,and trosports the water vapor from the North Pacific subtropical region to the tropics.The low-frequency water vapor transportation component transports the water vapor southward from the North Pacific to the low latitudes region.The synoptic-scale water vapor transportation component makes a large amount of water vapor converge in the central North Pacific.Accordingly,the AR frequency in central North Pacific,Alaska and west coast of North America increases significantly,while the AR frequency strengthens in the northwestern part of the tropical Pacific and weakens in the eastern part.During the positive phase of ENSO,the time-mean water vapor transportation lead to the heavy precipitation in the Northeast Pacific and the tropical Pacific.The low-frequency water vapor transportation is conducive to the occurrence of extreme precipitation events in the west coast of North America.The distribution of the synoptic-scale water vapor transportation is closely related to the activities of storm track in the North Pacific.The North Pacific AR is weakened in the western-central part while strengthened in the eastern part,while the tropical Pacific AR is strengthened in the central part while weakened in the southeastern part.The impacts of PDO and ENSO during different phases on the AR show some asymmetry characteristics.PDO plays a leading role on the influence of AR in the North Pacific while ENSO on the AR in the tropical Pacific.