滤除ENSO信号前后夏季热带印度洋海盆尺度海温距平对西太平洋副热带高压的不同影响

Impacts of tropical Indian Ocean sea surface temperature anomalies on the variation of western Pacific subtropical high in the summer: Dependent and independent of ENSO

中文关键词:  西太平洋副热带高压  印度洋海盆尺度模  厄尔尼诺  开尔文波  非绝热加热

英文关键词:Western Pacific Subtropical High  Indian Ocean basin-wide mode  El Niño  Kelvin wave  Diabatic heating

中文摘要:

      使用NCEP/NCAR再分析资料、哈得来海表温度和中国国家气候中心的西太平洋副热带高压（西太副高）特征指数，对比分析了ENSO背景下的夏季印度洋海盆尺度模（Indian Ocean basin mode，IOBM）与独立于ENSO的纯IOBM（pure Indian Ocean basin mode，IOBM_P）对西太副高的影响机理。结果表明，滤除前期ENSO信号后，西北太平洋上为海温负距平，并在其西北侧强迫出Gill型反气旋。另外，印度洋与海洋性大陆间存在西高东低的海温距平梯度，印度洋正、负海温距平激发出的赤道开尔文波影响至海洋性大陆西部地区，强迫出的异常大气环流关于赤道基本对称。加之此时中国南海至西北太平洋地区降水偏弱，潜热释放偏少，从而非绝热冷却，导致西太副高异常偏强、偏南。而在前期厄尔尼诺的影响下，次年夏季印度洋与海洋性大陆地区均有利于出现海温正距平，开尔文波的影响偏强、偏东，强迫出的异常环流偏向北半球，通过“埃克曼抽吸”和非绝热冷却在对流层低层制造出异常负涡度进而影响西太副高，使其明显偏强、偏西、偏南。由于IOBM_P在2和8年周期上对西太副高的影响最明显，而ENSO信号中主要是3—7 a的短周期振荡，因此，ENSO背景下的印度洋变暖对西太副高的遥强迫实际包含了来自热带中太平洋的3—7 a周期信号的滞后影响和印度洋地区局地变化特别是2和8年周期变化的作用。这些结果为人们深入理解西太副高变化规律和做出有效预报提供了线索。

英文摘要:

      Using the NCEP/NCAR reanalysis dataset, the Hadley sea surface temperature (SST) data and the western Pacific Subtropical High (WPSH) indexes provided by the National Climate Center (NCC) of China, different impacts of Indian Ocean (IO) SST anomalies (SSTA) dependent and independent of ENSO on the variation of summertime WPSH are investigated. It is demonstrated that when the preceding El Niño signal is removed from the SSTA, SST is warmer than normal in the IO but cooler in the Maritime Continent (MC) in the summer. An anomalous anticyclonic circulation appears to the northwest of the cold SSTA center. At the same time, warm IO SSTA trigger Kelvin waves that mainly affect the region west of the MC. The abnormal atmospheric circulations are roughly symmetrical about the equator in the western Pacific. Meanwhile, the abnormal cooling over the South China Sea and the northwestern Pacific caused by less latent heat release leads to the intensification and southwestward expansion of the WPSH. However, in the context of early El Niño, warm SSTA appear over both the IO and MC, resulting in stronger eastward propagation of Kelvin waves and enhanced circulation anomalies north of the equator. The diabatic cooling and the Ekman pumping generate abnormal negative vorticity in the lower troposphere, which is favorable for the intensification and southwestward expansion of the WPSH. Moreover, in the background of ENSO condition, the WPSH is forced to vary by remote IO SSTA, which actually include both the lagging effects of signals with a short period of 3-7 years from the central-east Pacific and simultaneous impacts of local SSTA with 2 year and 8 year periodic oscillations from the tropical India Ocean. These results are helpful for better understanding and predicting variations of the WPSH.