Gravity-wave momentum fluxes in the mesosphere over Ascension Island (8°  S, 14°  W) and the anomalous zonal winds of the semi-annual oscillation in 2002

Andrew Moss, Corwin Wright, Robin Davis, Nicholas Mitchell

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Abstract

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.
Original languageEnglish
Pages (from-to)323-330
JournalAnnales Geophysicae
Volume34
Issue number2
DOIs
Publication statusPublished - 3 Mar 2016

Keywords

  • Atmosphere
  • Gravity waves
  • Mesosphere
  • Wave-mean flow interaction

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