Solar Cycle Influences Seen in Ground-based Geocoronal Hydrogen Measurements

Type Journal Article
Names S. M. Nossal, E. J. Mierkiewicz, F. L. Roesler, J. Bishop, L. M. Haffner, R. J. Reynolds
Publication AGU Spring Meeting Abstracts
Volume 31
Pages 07
Date May 1, 2006
Library Catalog NASA ADS
Abstract Long term observations of geocoronal hydrogen offer potential to contribute to our understanding of vertical coupling processes affecting hydrogen-containing species. For example, models predict a 40-75% increase in exospheric hydrogen associated with a doubling of tropospheric concentrations of carbon dioxide and methane [Roble, AGU meeting, Spring 2005; Roble and Dickinson, 1989; Ehhalt, 1986]. Understanding the influence of the solar cycle on the upper atmosphere is required to isolate signatures of natural variability from those due to human-caused change. Mid-latitude ground-based Fabry-Perot Interferometer observations of geocoronal hydrogen fluorescence emissions by Wisconsin observers now span more than two decades and include observations taken near Madison, Wisconsin, as well as more recent observations from the Kitt Peak Observatory, near Tucson Arizona. Observations of thermospheric + exospheric Balmer-alpha column emissions by the Wisconsin H- alpha Mapper (WHAM) Fabry-Perot (Kitt Peak, Arizona) show a statistically significant solar cycle variation over solar cycle 23 with intensities at midrange shadow altitudes approximately 45% higher during solar maximum compared with solar minimum conditions. The higher signal-to-noise WHAM observations corroborate suggestions of a solar cycle trend in observations of Balmer-alpha emissions from Wisconsin over solar cycle 22. Geocoronal hydrogen column emissions are a function of both the vertical density structure and the incoming solar UV radiation, both of which change over the course of the solar cycle. Multiple scattering of solar Lyman line radiation below the Earth's shadow complicates the analysis of the observations requiring the use of detailed data/forward modeling comparisons to retrieve geophysical information such as the hydrogen column abundance from the observations [Bishop, 1999; Bishop et al., 2004]. We will discuss our previous solar minimum observations and plans for observations during the upcoming solar minimum period, including the challenges and strategies associated with comparing data taken with different, but similarly designed, instruments at different mid-latitude observatories. We will also discuss work in progress on parameter definitions in the forward modeling technique, tested in terms of sensitivity under differing observing applications (e.g. lone station measurements versus coincident measurements acquired by several independent instruments).
Tags 0310 Airglow and aurora, 0325), 0328 Exosphere, 0355 Thermosphere: composition and chemistry, 1610 Atmosphere (0315, 1650 Solar variability (7537)
UW-Madison Astronomy Home