The summertime 12-h wind oscillation with zonal wavenumber s = 1 in the lower thermosphere over the South Pole

• Published in: Annales Geophysicae
• Main Authors: Portnyagin, Y. I., Forbes, J. M., Makarov, N. A., Merzlyakov, E. G., Palo, S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer Verlag 1998
• Subjects: article; Verlagsveröffentlichung; Molodezhnaya; Scott Base; South Pole; South pole
• Online Access: https://doi.org/10.1007/s00585-998-0828-9; https://noa.gwlb.de/receive/cop_mods_00037279; https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00037233/angeo-16-828-1998.pdf; https://angeo.copernicus.org/articles/16/828/1998/angeo-16-828-1998.pdf

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