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GEOPHYSICAL RESEARCH LETTERS, VOL. 31, L06110, doi:10.1029/2003GL018729, 2004

Observations of solar cyclical variations in geocoronal Hα column emission intensities

S. M. Nossal

Department of Physics, University of Wisconsin, Madison, Wisconsin, USA


F. L. Roesler

Department of Physics, University of Wisconsin, Madison, Wisconsin, USA


E. J. Mierkiewicz

Department of Physics, University of Wisconsin, Madison, Wisconsin, USA


R. J. Reynolds

Department of Astronomy, University of Wisconsin, Madison, Wisconsin, USA


Abstract

Observations of thermospheric + exospheric Hα column emissions by the Wisconsin Hα Mapper (WHAM) Fabry-Perot (Kitt Peak, Arizona) over the 1997–2001 rise in solar cycle 23 show a statistically significant solar cyclical variation. The higher signal-to-noise WHAM observations corroborate suggestions of a solar cycle trend in the Hα emissions seen in Wisconsin observations over solar cycle 22. Here we compare WHAM 1997 and 2000–2001 winter solstice geocoronal Hα observations toward regions of the sky with low galactic emission. The observed variation in geocoronal hydrogen column emission intensities over the solar cycle is small compared with variations in hydrogen exobase densities. Higher Hα emissions are seen during solar maximum periods of the solar cycle. At a mid range shadow altitude (3000 km), WHAM geocoronal Hα intensities are about 45% higher during solar maximum than during solar minimum.

Received 26 September 2003; accepted 9 February 2004; published 20 March 2004.

Index Terms: 0310 Atmospheric Composition and Structure: Airglow and aurora; 0355 Atmospheric Composition and Structure: Thermosphere—composition and chemistry; 0394 Atmospheric Composition and Structure: Instruments and techniques; 1650 Global Change: Solar variability.

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Citation: Nossal, S. M., F. L. Roesler, E. J. Mierkiewicz, and R. J. Reynolds (2004), Observations of solar cyclical variations in geocoronal Hα column emission intensities, Geophys. Res. Lett., 31, L06110, doi:10.1029/2003GL018729.