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Ann. Geophys., 16, 828-837, 1998
www.ann-geophys.net/16/828/1998/ doi:10.1007/s00585-998-0828-9 © European Geosciences Union 1998 |
The summertime 12-h wind oscillation with zonal wavenumber s = 1 in the lower thermosphere over the South Pole
1Institute for Experimental Meteorology, Obninsk, Russia
2Department of Aerospace Engineering Sciences, Campus Box 429, University of Colorado, Boulder, CO 80303-0429 USA
Abstract. Meteor radar measurements of winds near 95 km in four azimuth directions from the geographic South Pole are analyzed to reveal characteristics of the 12-h oscillation with zonal wavenumber one (s=1). The wind measurements are confined to the periods from 19 January 1995 through 26 January 1996 and from 21 November 1996 through 27 January 1997. The 12-h s=1 oscillation is found to be a predominantly summertime phenomenon, and is replaced in winter by a spectrum of oscillations with periods between 6 and 11.5 h. Both summers are characterized by minimum amplitudes (5–10 ms–1) during early January and maxima (15–20 ms–1) in November and late January. For 10-day means of the 12-h oscillation, smooth evolutions of phase of order 4–6 h occur during the course of the summer. In addition, there is considerable day-to-day variability (±5–10 ms–1 in amplitude) with distinct periods (i.e., ~5 days and ~8 days) which suggests modulation by planetary-scale disturbances. A comparison of climatological data from Scott Base, Molodezhnaya, and Mawson stations suggests that the 12-h oscillation near 78°S is s=1, but that at 68°S there is probably a mixture between s=1 and other zonal wavenumber oscillations (most probably s=2). The mechanism responsible for the existence of the 12-h s=1 oscillation has not yet been identified. Possible origins discussed herein include in situ excitation, nonlinear interaction between the migrating semidiurnal tide and a stationary s=1 feature, and thermal excitation in the troposphere.
Key words. Meteorology and atmospheric dynamics · Middle atmosphere dynamics · Thermospheric dynamics · Waves and tides
Citation: Portnyagin, Y. I., Forbes, J. M., Makarov, N. A., Merzlyakov, E. G., and Palo, S.: The summertime 12-h wind oscillation with zonal wavenumber s = 1 in the lower thermosphere over the South Pole, Ann. Geophys., 16, 828-837, doi:10.1007/s00585-998-0828-9, 1998.