STRATO-MESO-THERMOSPHERIC COUPLING AT MIDLATITUDES IN THE COURSE OF MIDWINTER STRAT-WARMINGS DURING DYANA

Wind observations in the meteor region carried out at the CNR radar station near Bologna (45-degrees-N; 12-degrees-E) in the winter of 1989-90 during the DYANA (DYnamics Adapted Network for the Atmosphere) project, give evidence of significant strato-meso-thermospheric coupling in the course of two strat-warmings recorded at the end of January and in mid-February 1990. Amplification of 10-12 day long-period waves just a few days before the temperature peak at the 10 hPa stratospheric level, and the strong phase variations of the semidiurnal tide (ST) in the 80-110 km region during the two separate events could be of interest for our knowledge of the evolution and influence of a strat-warming in the overall middle atmosphere. Possible interference processes and nonlinear mixing between planetary waves with different periodicities could account not only for aspects of wave amplification but also for the presence of subsidiary peaks of long period waves in the amplitude spectra of the observed zonal winds.