Geocoronal Hydrogen Observations Spanning Three Solar Minima

We have completed analysis of recent Fabry-Perot observations of upper atmospheric hydrogen during solar minimum conditions, establishing a baseline data set of three solar cycles. These data agree to within 10% uncertainties, and establish a reference data set of highly precise, consistently calibrated, thermospheric exospheric hydrogen column emission observations that can be used to compare with future observations. One of the potential diagnostics of global change in the upper atmosphere is exospheric hydrogen that is predicted to increase by on the order of 50-75% with a doubling of tropospheric methane. The reproducibility of the solar minimum hydrogen observations also confirms evidence for a mid-latitude solar cycle variation with higher intensities observed during solar maximum conditions. The solar cycle is a dominant source of natural variability in the upper atmosphere and must be accounted for when isolating potential signs of long-term change in the region. We present and discuss observations made with the Wisconsin H-alpha Mapper Fabry-Perot (WHAM) during solar cycle 23 from Kitt Peak, AZ and a comparison of the WHAM 1997 and 2006 solar minimum observations with those made from Pine Bluff Wisconsin during the 1985 solar minimum period.