RADAR OBSERVATIONS OF HIGH-LATITUDE LOWER-THERMOSPHERIC AND UPPER-MESOSPHERIC WINDS AND THEIR RESPONSE TO GEOMAGNETIC ACTIVITY (ALASKA)

Observations made by the Chatanika, Alaska, incoherent scatter radar during the summer months of 1976 to 1981 are analyzed to obtain high resolution lower-thermospheric neutral winds. Average winds and their tidal components are presented and compared to previous observational and model results. The winds are dominated by strong semi-diurnal fluctuations, although diurnal oscillations are also present. Neutral winds for three different levels of geomagnetic activity are compared with NCAR Thermospheric General Circulation Model (TGCM) results for three different steady-state levels of magnetospheric forcing. During geomagnetically active intervals, neutral winds above 100 km develop an enhanced zonal component in the morning sector, in agreement with TGCM predictions.;Observations of upper-mesospheric neutral winds made during two energetic Solar Proton Events (SPEs) by the Poker Flat, MST radar are presented. The tidal response to steady-state forcing distributions appropriate to the altered ozone heating profiles and Joule heat source generated by the July 13, 1982 SPE is simulated using a classical tidal model. These forcing distributions result in altered tidal velocity components at high altitude and latitude in the steady-state. Model results are compared with observations and time dependent behavior is discussed.;These results allow the low-altitude limits of magnetospheric coupling to the neutral atmosphere to be determined. Lower-thermospheric neutral winds are coupled to the ion convection driven by typical magnetospheric forcing above about 100 km. Coupling to lower atmospheric levels does not occur except during intervals of extreme disturbance of the magnetosphere-ionosphere-thermosphere system which are also accompanied by dramatically increased ionization in the high-latitude mesosphere, such as SPEs.;Upper-mesospheric neutral wind observations obtained by the Poker Flat, Alaska Mesosphere-Stratosphere-Troposphere (MST) radar during the summer months of 1980 to 1982 are investigated statistically for evidence of variations due to geomagnetic activity. Cross-correlation and spectral analyses show that no consistent and significant causal relationship exists between neutral winds at upper-mesospheric heights and the occurrence of geomagnetic activity during typical events. Indications of variations in the intensity of neutral turbulence during active intervals are presented.