The Quasi-Two-Day Wave Event of January 1984 and Its Impact on the Mean Mesospheric Circulation

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  • 1 CSIRO Division of, Atmospheric Research, Adelaide 3195, Australia
  • | 2 Department of Physics, University of Adelaide, Adelaide 5001, Australia
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Abstract

Studies of the quasi-two-day wave show that it is a summertime phenomenon. In the summer of 1983–84 at Adelaide (35°S, 138°E), the main phase of the wave appeared as a pulse in mid-January which lasted about seven cycles (14 days). Coincident with the onset of the pulse a temporary but substantial change occured in the prevailing circulation throughout a deep layer of the upper mesosphere; a perturbation of more than 10 m s&−1 occurred in the northward flow, whereas the change in the zonal flow (about 30 m s−1 westward) actually caused a reversal of the prevailing eastward simulation above 84 km.

It is suggested that these changes in the prevailing circulation were a response to the wave pulse. A simple calculation is performed to estimate the anticipated response to the observed wave event; under plausible assumptions about the magnitude of mean and eddy dissipation processes, predicted circulation changes agree reasonably well with those observed.

It is concluded that such events have a substantial, if temporary, impact on the prevailing circulation in the upper mesospere and may be important in the transport of atmospheric constituents at these heights during summer.

Abstract

Studies of the quasi-two-day wave show that it is a summertime phenomenon. In the summer of 1983–84 at Adelaide (35°S, 138°E), the main phase of the wave appeared as a pulse in mid-January which lasted about seven cycles (14 days). Coincident with the onset of the pulse a temporary but substantial change occured in the prevailing circulation throughout a deep layer of the upper mesosphere; a perturbation of more than 10 m s&−1 occurred in the northward flow, whereas the change in the zonal flow (about 30 m s−1 westward) actually caused a reversal of the prevailing eastward simulation above 84 km.

It is suggested that these changes in the prevailing circulation were a response to the wave pulse. A simple calculation is performed to estimate the anticipated response to the observed wave event; under plausible assumptions about the magnitude of mean and eddy dissipation processes, predicted circulation changes agree reasonably well with those observed.

It is concluded that such events have a substantial, if temporary, impact on the prevailing circulation in the upper mesospere and may be important in the transport of atmospheric constituents at these heights during summer.

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