HR: 17:45h
AN: SA14A-08    [Abstracts]
TI: Day-to-Day Variability of the F-layer at Sunrise
AU: * David, M
EM: michael@sim2.cass.usu.edu
AF: Utah State University, Center for Atmospheric and Space Sciences, 4405 Old Main Hill, Logan, UT 84322-4405 United States
AU: Sojka, J J
EM: fasojka@sojka.cass.usu.edu
AF: Utah State University, Center for Atmospheric and Space Sciences, 4405 Old Main Hill, Logan, UT 84322-4405 United States
AU: Schunk, R W
EM: schunk@cc.usu.edu
AF: Utah State University, Center for Atmospheric and Space Sciences, 4405 Old Main Hill, Logan, UT 84322-4405 United States
AU: Holt, J M
EM: jmh@haystack.edu
AF: MIT Haystack Observatory, Off Route 40, Westford, MA 01886 United States
AB: Using a 30-day continuous incoherent scatter radar (ISR) data base from Millstone Hill and the Utah State University Time Dependent Ionospheric Model (TDIM), we investigate the day-to-day variability in the rate of increase of the electron densities as the ionosphere enters sunrise. The data shows this variability to be quite large. Rishbeth et al [1995] studied the F-layer at sunrise and showed that there is a seasonal dependence, which was explained as a consequence of seasonal variation in the atomic to molecular ratio of the neutral atmosphere in the F2-layer. The month-long data base used in this study extends from 4 October to 4 November 2002. The observations provide full electron density, electron temperature, ion temperature, and vertical ion drift profiles throughout the F-layer. Using the TDIM ionospheric model, simulations are carried out to find the source of the marked day-to-day differences in the sunrise response of the F-layer at the Millstone Hill location. Possible drivers of this variability include the temperature and drift variation as well as neutral density and ratio effects, the latter being associated with geomagnetic forcing of the thermosphere. The role of pre-dawn conditioning of the ionosphere is also considered.
DE: 2427 Ionosphere/atmosphere interactions (0335)
DE: 2443 Midlatitude ionosphere
DE: 2467 Plasma temperature and density
SC: SPA-Aeronomy [SA]
MN: 2004 AGU Fall Meeting