Thermospheric Neutral Temperature Response to Auroral and Solar EUV Energy Input

A Fabry-Perot imager (FPI) has been installed at Syowa Station, Antarctica since 2001 in order to study short-term thermospheric response to auroral activities and long-term variability of the polar-thermospheric circulation. In this paper variations in thermospheric neutral temperature derived from the FPI observation are compared with solar EUV flux and auroral activity. The FPI is equipped with a stabilized Fabry-Perot interferometer with a clear aperture of 150 mm, a special optical system designed for the etalon, and a back-illuminated CCD camera. Spacing of the etalon is periodically checked by a fringe image of frequency-stabilized He-Ne laser emission. The etalon controller and the laser are kept in a thermostatic chamber to avoid temperature drift. The FPI acquired approximately 50,000 images on 71 nights from March 31, 2001 to October 16, 2001. The interference fringe images of OI 557.7 nm and OI 630.0 nm emissions were alternatively obtained every minute with an exposure time of 30 sec. Reference images of the laser and dark images were acquired every 30 min. Horizontal distributions of thermospheric wind and temperature are derived from the fringe images of the auroral emissions. Temporal drift of the etalon spacing is corrected using the laser fringe images. To derive absolute values of wind speed the absolute spacing of the interferometer must be known with an accuracy of 10E-8. The spacing can be determined with the accuracy from the known wavelengths of auroral and laser emissions and the orders of interference determined from differences among average fringe peak positions of the these emissions. Temporal variations of the neutral temperature and wind in the F-region were compared with the solar EUV flux data obtained by SOHO and all-sky auroral image data simultaneously acquired with the FPI data. The daily average temperatures correlate with the solar EUV flux for the time scales of a few days to several months. For faster temperature increases with the time scales of hours to a few days local auroral energy input seems to be a predominant energy source. Acknowledgment: Solar EUV flux data are provided by the CELIAS/SEM experiment onboard SOHO.