LOWER THERMOSPHERIC NEUTRAL WINDS AT SONDRE-STROMFJORD - A SEASONAL ANALYSIS

Data obtained by Sondre Stromfjord incoherent scatter radar during rec ent Lower Thermospheric Coupling Study (LTCS) campaigns have been anal yzed to examine seasonal changes in high-latitude lower thermosphere n eutral winds. Data included in this study were obtained with a 2x160 m u s multipulse as well as with higher-resolution multipulse and altern ating code techniques and were analyzed with different auto correlatio n function (ACF) fitting routines. We report neutral wind results obta ined during LTCS experiments with the new acquisition and analysis sys tem and compare these results with those acquired using earlier versio ns of the software. We investigate the effects of different assumption s in the ACF fitting program on the data return and quality. Wind resu lts are intercompared to examine average seasonal structure and variab ility. Strong semidiurnal oscillations characterize high-latitude lowe r thermospheric winds at 105 km irrespective of season; however, summe r amplitudes are nearly a factor of 2 greater than those observed duri ng winter. Average winter winds appear to have more variability than t hose deduced for summer. Equinox winds at fall and spring show similar oscillations but are nearly reversed in phase. At 115 km, diurnal osc illations grow and their amplitudes often exceeds typical semidiurnal amplitudes. Tidal amplitudes observed in radar data are compared with the predictions of several models, including National Center for Atmos pheric Research thermosphere-ionosphere-general-circulation model (TIG CM) [Roble et al., 1988], global scale wave model (GSWM) [Hagan et al. , 1994], and Forbes-Vial model (FV91) [Forbes and Vial, 1991]. These c omparisons suggest that theoretical predictions significantly underest imate tidal amplitudes calculated from Sondrestrom incoherent scatter radar measurements.