The 11-year solar cycle, the Sun's rotation, and the middle stratosphere in winter. Part II: Response of planetary waves

The effect of the 11-year solar cycle on the response of planetary wavenumb ers 1 and 2 at 10 and 30 hPa in winter to solar activity oscillations on th e time scale of the Sun's rotation (27.2 day) is discussed in terms of stat istical spectral analysis. The three oscillations studied are the 27.2 d (p eriod of the Sun's rotation), 25.3 d (periodicity caused by modulation of t he 27.2 d stratospheric response by annual atmospheric variation), and 54.4 d (doubled period of the solar rotation). A significant effect of the 11-y ear solar cycle is found for the 54.4 d periodicity in planetary wavenumber 1, and for the 27.2 and 25.3 d periodicities in planetary wavenumber 2. Th e effect of the 11-year solar cycle is expressed in the evident differences between the amplitudes of responses of planetary waves at maximum and mini mum of the solar cycle: the amplitudes are much larger at high than at low solar activity. The 11-year modulation of planetary wave activity is most p ronounced at mid-latitudes, mainly at 40-60 degreesN, where the observed va riability of planetary waves is large. The results obtained are in good agr eement with results of the recent modeling study by Shindell et al. (Scienc e 284 (1999) 305). (C) 2001 Elsevier Science Ltd. All rights reserved.