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Anomalously strong westward winds during the first phase of the equatorial mesospheric semi-annual oscillation (MSAO) have been attributed to unusual filtering conditions producing exceptional gravity-wave fluxes. We test this hypothesis using meteor-radar measurements made over Ascension Island (8° S, 14° W). An anomalous wind event in 2002 of −85.5 ms−1 occurred simultaneously with the momentum fluxes of high-frequency gravity waves reaching the largest observed westward values of −29 m2 s−2 and strong westward wind accelerations of −510 ms−1 day−1. However, despite this strong wave forcing during the event, no unusual filtering conditions or significant increases in wave-excitation proxies were observed. Further, although strong westward wave-induced accelerations were also observed during the 2006 MSAO first phase, there was no corresponding simultaneous response in westward wind. We thus suggest that strong westward fluxes/accelerations of high-frequency gravity waves are not always sufficient to produce anomalous first-phase westward MSAO winds and other forcing may be significant.
- Gravity waves
- Wave-mean flow interaction
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- Department of Electronic & Electrical Engineering - Royal Society University Research Fellow
- Centre for Climate Adaptation & Environment Research (CAER) - Co-Director
Person: Research & Teaching, Core staff