On the longitudinal structure of the transient day-to-day variation of the semidiurnal tide in the mid-latitude lower thermosphere - I. Winter season

The longitudinal structure of the day-to-day variations of semidiurnal tide amplitudes is analysed based on coordinated mesosphere/lower thermosphere wind measurements at several stations during three winter campaigns. Possible excitation sources of these variations are discussed. Special attention is given to a nonlinear interaction between the semidiurnal tide and the day-to-day mean wind variations. Data processing includes the S-transform analysis which takes into account transient behaviour of secondary waves. It is shown that strong tidal modulations appear during a stratospheric warming and may be caused by aperiodic mean wind variations during this event

Electric fields and meteor radar wind measurements near 95 km over South Pole

Meteor and auroral drift measurements by P. Prikryl et al. (Radio Sci., 21, 271, 1986) and theoretical estimates by G.C. Reid (Radio Sci., 18, 1028, 1983) suggest that sufficiently large electric fields may decouple meteor trail electron motions from that of the neutral gas, leading to erroneous measurement of the neutral wind during sufficiently disturbed conditions. In the present study, we seek evidence of such effects by comparing hourly meteor radar wind measurements V_N near 95 km over South Pole with overhead F-region drifts V, measured by the SuperDARN radar at Halley (76° S, 27° W). Within the parameter space of our data set, we find no relationship between V_1 and the zonal wavenumber s = 0 and s = 1 components of V_N, and only a weak relationship for the wind residuals from the combined s = 0 and s = 1 wind field. For the latter, an inferred wind residual of 5.8ms^ is implied for an F-region plasma drift of 1000ms^ (E-field &thkzp; 70mVm^). This value of 5.8 ms^ falls within the 2 to 20ms^ range of plasma drifts expected to be induced at 95km by F-region E-fields ranging between 20 and lOOmVm^ by G.C. Reid (ibid, 1983). Thus, we cannot discount the possibility that this inferred wind is actually a plasma drift. In any case, we conclude that electric field contamination of previous scientific analyses with this data set which focused on the s = 0 and s = 1 components of the wind field, are negligible. Future experimental and modeling work is required to ascertain the degree to which .E-field induced effects on winds inferred from advection of meteor trails exist under more extreme conditions, or perhaps over shorter time scales

Emerging pattern of global change in the upper atmosphere and ionosphere

In the upper atmosphere, greenhouse gases produce a cooling effect, instead of a warming effect. Increases in greenhouse gas concentrations are expected to induce substantial changes in the mesosphere, thermosphere, and ionosphere, including a thermal contraction of these layers. In this article we construct for the first time a pattern of the observed long-term global change in the upper atmosphere, based on trend studies of various parameters. The picture we obtain is qualitative, and contains several gaps and a few discrepancies, but the overall pattern of observed long-term changes throughout the upper atmosphere is consistent with model predictions of the effect of greenhouse gas increases. Together with the large body of lower atmospheric trend research, our synthesis indicates that anthropogenic emissions of greenhouse gases are affecting the atmosphere at nearly all altitudes between ground and space