Wave motions in the lower thermosphere during the Energy Budget Campaign 1980 from three locations in the northern Hemisphere

Abstract

Simultaneous meteor radar wind observations were made at Budrio (Italy, 45° N), Sheffield (U.K., 53° N) and Stornoway (U.K., 58° N) during the Energy Budget Campaign (EBC), November–December 1980, in the altitude region between 75 and 115 km. Wind results are presented in terms of prevailing components and oscillations of different time scales: tidal (8, 12 and 24 h), gravity ((3÷6) h) and planetary ((2÷10) days) waves. The seasonal variation of the prevailing zonal components observed at the three stations in previous years shows the same maxima of Summer and Winter, as well as the equinoctial minima exhibited by the CIRA 1972 model for 50° N. The data show marked tidal activity with the semi-diurnal tide which exceeds in amplitude any other mode in the wind spectra. Tidal amplitudes recorded at Budrio appear significantly lower than those recorded at Sheffield and Stornoway. Variations of the amplitude of maxima of the semi-diurnal oscillation relative to the Budrio and Sheffield data show time scales generally greater than 5 days throughout the recording period. The diurnal and terdiurnal tides represent a small part of the total wind energy in the meteor zone and exhibit phases which disagree strongly at the quoted stations. The scatter in the hourly data is representative of small-scale wind disturbances due to internal gravity waves: at Budrio, by using the MEM method for individual day's data (November 23–24, 28–29, 1980), gravity waves with vertical wave-lengths of (20÷45) km, periods of 3.5, 4.5 and 6 h, and amplitudes of the order of 10 ms−1 have been observed. Long-period oscillations with periods in the (2÷10) day time interval have been identified in the wind patterns at Budrio and Sheffield, but the presence of planetary waves of quasi-2-day period was less significant than during a previous Summer 1980 run carried out at the same stations.