The focus of the project is to investigate solar cyclic and climatic trends in geocoronal hydrogen using the Wisconsin long-term mid-latitude geocoronal emission record and the NCAR global mean model. The data have been acquired with two similarly designed ground-based Fabry-Perot Interferometers located in Wisconsin and Arizona. High signal-to-noise observations over solar cycle 23 have quantified a statistically significant solar cyclic influence on the geocoronal hydrogen column emission intensity. Observations from three solar minima (1985, 1997, 2006) agree to within 15% over most of the shadow altitude range. This project will continue the analysis of the Wisconsin northern hemisphere geocoronal data set now spanning three solar cycles to investigate solar cycle influences and to establish additional well-calibrated data sets for long-term comparisons into the future. The project includes an archival study to extend the Wisconsin data set backwards through reanalysis of observations taken in the 1970-80s using updated analysis techniques and the most recent Galactic background information from the Wisconsin H-alpha Mapper Fabry-Perot.
A seminal study by Roble and Dickinson [1989] used the NCAR global mean model of the mesosphere, thermosphere, and ionosphere to study the response of the middle and upper atmosphere to a doubling of carbon dioxide and methane. The results showed found an increase of 40-50% in upper thermospheric hydrogen in response to a doubling of methane. Additional studies with global mean model were carried out with historical time-dependent values of CO2 and solar UV fluxes to investigate the thermospheric density response to the solar cycle and to CO2 increases. This project will extend the model studies by adding historical concentrations of methane to the global mean model to investigate the magnitude of predicted solar cyclic and secular changes in thermospheric hydrogen over the 30-year period of the Wisconsin long-term mid-latitude data set. In order to facilitate comparison between these model predictions and the Wisconsin observations, output from the global mean model will be used as input to the LYAO_RT global resonance radiative transfer code to extend the hydrogen density profile into the exosphere and to calculate the corresponding hydrogen column emission intensity.
The project goal is to increase understanding of solar-terrestrial interactions, long-term variations, and lower-upper atmospheric coupling. The research would also result in the compilation of an observational dataset with high signal-to-noise ratios for past and future data and model comparisons.
