科研之友
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摘要
El Nino-Southern Oscillation (ENSO) events are classically associated with a significant increase in the length of day (LOD), with positive mountain torques arising from an east-west pressure dipole in the Pacific driving a rise of atmospheric angular momentum (AAM) and consequent slowing of the Earth's rotation. The large 1982-1983 event produced a lengthening of the day of about 0.9 ms, while a major ENSO event during the 2015-2016 winter season produced an LOD excursion reaching 0.81 ms in January 2016. By evaluating the anomaly in mountain and friction torques, we found that (i) as a mixed eastern-central Pacific event, the 20152016 mountain torque was smaller than for the 1982-1983 and 1997-1998 events, which were pure eastern Pacific events, and (ii) the smaller mountain torque was compensated for by positive friction torques arising from an enhanced Hadley-type circulation in the eastern Pacific, leading to similar AAM-LOD signatures for all three extreme ENSO events. The 2015-2016 event thus contradicts the existing paradigm that mountain torques cause the Earth rotation response for extreme El Nino events.
- 出版日期2017-11-14
