This paper analyzes the possible influence of boreal winter Arctic Oscillation/North Atlantic Oscillation （AO/ NAO） on the Indian Ocean upper ocean heat content in summer as well as the summer monsoonal circulation....This paper analyzes the possible influence of boreal winter Arctic Oscillation/North Atlantic Oscillation （AO/ NAO） on the Indian Ocean upper ocean heat content in summer as well as the summer monsoonal circulation. The strong interannual co-variation between winter 1000-hPa geopotential height in the Northern Hemisphere and sum- mer ocean heat content in the uppermost 120 m over the tropical Indian Ocean was investigated by a singular decom- position analysis for the period 1979-2014. The second paired-modes explain 23.8% of the squared covariance, and reveal an AO/NAO pattern over the North Atlantic and a warming upper ocean in the western tropical Indian Ocean. The positive upper ocean heat content enhances evaporation and convection, and results in an anomalous meridional circulation with ascending motion over 5°S-5°N and descending over 15°-25°N. Correspondingly, in the lower tro- posphere, significantly anomalous northerly winds appear over the western Indian Ocean north of the equator, imply- ing a weaker summer monsoon circulation. The off-equator oceanic Rossby wave plays a key role in linking the AO/NAO and the summer heat content anomalies. In boreal winter, a positive AO/NAO triggers a down-welling Rossby wave in the central tropical Indian Ocean through the atmospheric teleconnection. As the Rossby wave ar- rives in the western Indian Ocean in summer, it results in anomalous upper ocean heating near the equator mainly through the meridional advection. The AO/NAO-forced Rossby wave and the resultant upper ocean warming are well reproduced by an ocean circulation model. The winter AO/NAO could be a potential season-lead driver of the sum- mer atmospheric circulation over the northwestern Indian Ocean.展开更多
基金Supported by the National Natural Science Foundation of China(41375071)Project PE16010 of the Korea Polar Research Institute
文摘This paper analyzes the possible influence of boreal winter Arctic Oscillation/North Atlantic Oscillation （AO/ NAO） on the Indian Ocean upper ocean heat content in summer as well as the summer monsoonal circulation. The strong interannual co-variation between winter 1000-hPa geopotential height in the Northern Hemisphere and sum- mer ocean heat content in the uppermost 120 m over the tropical Indian Ocean was investigated by a singular decom- position analysis for the period 1979-2014. The second paired-modes explain 23.8% of the squared covariance, and reveal an AO/NAO pattern over the North Atlantic and a warming upper ocean in the western tropical Indian Ocean. The positive upper ocean heat content enhances evaporation and convection, and results in an anomalous meridional circulation with ascending motion over 5°S-5°N and descending over 15°-25°N. Correspondingly, in the lower tro- posphere, significantly anomalous northerly winds appear over the western Indian Ocean north of the equator, imply- ing a weaker summer monsoon circulation. The off-equator oceanic Rossby wave plays a key role in linking the AO/NAO and the summer heat content anomalies. In boreal winter, a positive AO/NAO triggers a down-welling Rossby wave in the central tropical Indian Ocean through the atmospheric teleconnection. As the Rossby wave ar- rives in the western Indian Ocean in summer, it results in anomalous upper ocean heating near the equator mainly through the meridional advection. The AO/NAO-forced Rossby wave and the resultant upper ocean warming are well reproduced by an ocean circulation model. The winter AO/NAO could be a potential season-lead driver of the sum- mer atmospheric circulation over the northwestern Indian Ocean.
