A comparative study of winds and tidal variability in the mesosphere/lower-thermosphere region over Bulgaria and the UK

Abstract

Abstract. Meteor radars located in Bulgaria and the UK have been used to simultaneously measure winds in the mesosphere/lower-thermosphere region near 42.5°N, 26.6°E and 54.5°N, 3.9°W, respectively, over the period January 1991 to June 1992. The data have been used to investigate planetary waves and diurnal and semidiurnal tidal variability over the two sites. The tidal amplitudes at each site exhibit¯uctuations as large as 300% on time scales from a few days to the intra-seasonal, with most of the variability being at intra-seasonal scales. Spectral and cross-wavelet analysis reveals closely related tidal variability over the two sites, indicating that the variability occurs on spatial scales large compared to the spacing between the two radars. In some, but not all, cases, periodic variability of tidal amplitudes is associated with simultaneously present planetary waves of similar period, suggesting the variability is a consequence of non-linear interaction. Calculation of the zonal wave number of a number of large amplitude planetary waves suggests that during summer 1991 the 2-day wave had a zonal wave number of 3, but that during January±February 1991 it had a zonal wave number of 4.

Global structure, seasonal and interannual variability of the migrating semidiurnal tide seen in the SABER/TIMED temperatures (2002–2007)

“…A major advantage of the ground-based methods is their ability to study in detail seasonal, intraseasonal and interannual variability of the tides in the MLT at various geographic points (Bernard, 1981;Avery et al, 1989;Manson et al, 1990Manson et al, , 1999Clark and Salah, 1991;Vincent et al, 1998;Jacobi et al, 1999;Pancheva et al, 2000Pancheva et al, , 2002, as well as their vertical structure including vertical wavelengths and direction of propagation She et al, 2004;Yuan et al, 2008). A disadvantage of the ground-based methods is their inability to distinguish between global and local signatures and to provide only coarse information on spatial (latitudinal and longitudinal) structures of the tides.…”

Tidal variations of O<sub>2</sub> Atmospheric and OH(6-2) airglow and temperature at mid-latitudes from SATI observations

“…Jacobi et al, 1999;Pancheva et al, 2000Pancheva et al, , 2002Riggin et al, 2003;Forbes et al, 2004;Portnyagin et al, 2004) that have been used to study the tidal behaviour of the atmospheric winds. Studies of the influences of atmospheric tides on airglow emission and temperature using long-term, ground-based observations (e.g.…”

Sensitivity studies of the E region neutral response to the postmidnight diffuse aurora

“…Background winds and tides appear to have important effects on the wind structures, and tides are also known to vary significantly (e.g. Pancheva et al 2000;Beard et al, 1999;Canziani, 1994;Phillips and Briggs, 1991). Experiments were performed to determine the effects of introducing background winds and tides at different times relative to the time at which the auroral forcing is introduced, to investigate the effects of changes in the background winds in the presence of auroral forcing.…”

“…Manson et al, 2002;Forbes et al, 1994;Forbes and Vial, 1991), but propagating tides show great day to day variability in amplitude and phase (e.g. Pancheva et al, 2000;Beard et al, 1999;Canziani, 1994;Phillips and Briggs, 1991), so the amplitude and phase of the tides for a specific day and location is not well known, in the absence of direct measurements. The sensitivity of the neutral response to these changes in the amplitudes and phases of the propagating tides in the background winds is therefore explored in this paper, as well as the sensitivity of the response to the time when propagating tides are introduced relative to the time at which the auroral forcing becomes important.…”