夏季北太平洋洋中槽强度的年际变化及其与北美地面气温的关系

Interannual variation of tropical upper tropospheric trough over the Northern Pacific in summer and its relationship with surface air temperature over the North America

利用1979—2010年NCEP/NCAR再分析资料和特拉华大学地面气温资料,研究了夏季北太平洋洋中槽强度的年际变化特征、成因及其与北美地表气温的联系。结果表明,夏季北太平洋洋中槽强度存在明显的年际变化特征,并主要表现为准4 a和准5a的周期变化特征。进一步的分析表明,夏季北太平洋洋中槽强度与同期北美东南地区地表气温存在显著的负相关,当夏季北太平洋洋中槽强度异常偏强(弱)时,洋中槽下游的北美东南地区对流层中高层的位势高度异常降低(升高),对应于控制该地区的高压减弱(增强),从而使得该地区地表气温降低(升高)。此外,夏季热带印度洋海温异常对洋中槽的年际变化起了决定性的作用。当热带印度洋海温异常偏暖时,通过调节大气边界层相当位温,加热对流层大气,在热带印度洋东侧激发出东传的开尔文波,同时也使得北太平洋中东部位势高度异常升高,导致洋中槽的异常减弱。反之亦然。

Based on the NCEP / NCAR reanalysis and surface air temperature data recorded by University of Delaw are,the interannual variation of tropical upper tropospheric trough（ TUTT） over the northern Pacific in summer and its causes,together w ith its relationship w ith the surface air temperature over the North America,are investigated. Re-sults indicate that the TUTT experiences a marked interannual variation during the period of 1979—2010 w ith tw o main periodicities of quasi-4 and quasi-5 years. Results also show that the TUTT intensity is highly negatively correlated w ith the surface air temperature over the southeast part of North America. As the summer TUTT increases（ decreases） in intensity,the geopotential height in the upper-middle troposphere over southeast part of North America decreases（ increases）,thus the high w hich dominates over the southeast part of North America is correspondingly w eakened（ enhanced）,leading to a decrease（ an increase） in surface air temperature there. In addition,the interannual variation of TUTT is highly related to both the SST anomalies over the tropical Indian Ocean and SST anomalies over the tropical w estern Atlantic Ocean in summer,how ever,the former plays a dominant role. The increase of SST anomalies over the tropical Indian Ocean in summer w ould heat the overlying atmosphere and excite the eastw ard-propagating Kelvin w aves to east of the equatorial Indian Ocean,and cause increase in geopotential heights of middle and eastern Pacific,thus induce the w eak of TUTT intensity; and vice versa.