Observations of Geocoronal H-Alpha Emission Intensities Over Changing Solar Geophysical Conditions

We will present observations of thermospheric exospheric hydrogen H-alpha emissions taken by the Wisconsin H-alpha Mapper Fabry-Perot (WHAM) during the time period of 1997 through 2001. WHAM has acquired more than 37,000 spectra to date over about 100 nights. These observations span from near solar minimum through solar maximum conditions. The WHAM Fabry-Perot is located at the Kitt Peak Observatory near Tucson, Arizona and is remotely operable from Wisconsin. WHAM\u27s resolving power is sufficient for the retrieval of the geocoronal H-alpha emission intensity, but not for the resolution of the line profile. The resolution, precision and high signal-to-noise of the WHAM Fabry-Perot facilitate the separation of the terrestrial emission from the galactic emission. Variability in the WHAM geocoronal H-alpha observations over the rise of the solar cycle is limited to within about 35% with higher emissions observed during solar maximum conditions. This result is consistent with observed limits to the variability over the past solar cycle made using similarly designed Fabry-Perot instruments, but with photomultiplier detection, from midlatitude Wisconsin and Haleakala observing sites. These data are also consistent with comparisons made between winter solstice zenith observations taken during the early 1990\u27s from Wisconsin (NSF-CHARM campaign) and WHAM zenith observations