Abstract
Observations of the horizontal wind field over the South Pole were made during 1995 using a meteor radar. These data have revealed the presence of a rich spectrum of waves over the South Pole with a distinct annual occurrence. Included in this spectrum are long-period waves, whose periods are greater than one solar day, which are propagating eastward. These waves exhibit a distinct seasonal occurrence where the envelope of wave periods decreases from a period of 10 days near the fall equinox to a minimum of 2 days near the winter solstice and then progresses towards a period near 10 days at the spring equinox. Computation of the meridional gradient of quasi-geostrophic potential vorticity has revealed a region in the high-latitude upper mesosphere which could support an instability and serve as a source for these waves. Estimation of the wave periods which would be generated from an instability in this region closely resembles the observed seasonal variation in wave periods over the South Pole. These results are consistent with the hypothesis that the observed eastward propagating long-period waves over the South Pole are generated by an instability in the polar upper mesosphere. However, given our limited data set we cannot rule out a stratospheric source. Embedded in this spectrum of eastward propagating waves during the austral winter are a number of distinct wave events. Eight such wave events have been identified and localized using a constant-Q filter bank. The periods of these wave events ranges from 1.7 to 9.8 days and all exist for at least 3 wave periods. Least squares analysis has revealed that a number of these events are inconsistent with a wave propagating zonally around the geographic pole and could be related to waves propagating around a dynamical pole which is offset from the geographic pole. Additionally, one event which was observed appears to be a standing oscillation.Key words. Meteorology and atmospheric dynamics (Middle atmospheric dynamics; waves and tides).
Highlights
In November 1994 initial work began to install a meteor radar at Amundsen-Scott station, South Pole
We have presented evidence from observations over the South Pole taken with a meteor radar that clearly show a strong seasonal variation in the periods and intensity of eastward propagating long period waves
The upper mesospheric meteor wind observations over the South Pole presented have indicated a signi®cant seasonal variation in wave activity which occurs in this region
Summary
In November 1994 initial work began to install a meteor radar at Amundsen-Scott station, South Pole. A second continuous period of observations occurred from November 21 1996 to January 27, 1997 These meteor radar measurements are the ®rst continuous measurements of the mesosphere and lowerthermospheric horizontal wind ®eld over the South Pole and as a result have provided a picture of the dynamical structure in this region which was previously unknown. Palo et al.: Transient eastward-propagating long-period waves observed over the South Pole strong 12 and 24 h westward propagating oscillations observed during the summer (Hernandez et al, 1993; Forbes et al, 1995; Portnyagin et al, 1997b). These waves have a period greater than one solar day. We will discuss the meteor system and its limitations, describe the seasonal occurrence of waves over the South Pole and ®nally conclude with a discussion of the observed transient long-period wave events over the South Pole
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