Earth FUV Dayglow Response to the 20 January 2005 Solar Flare: TIMED and IMAGE 
Observations
	
Retherford, K. D., Gladstone, R., Solomon, S. C., Immel, T. J.


An X-class solar flare occurred on 20 January 2005 when the TIMED and IMAGE
spacecraft were both well positioned to observe the response of Earth's dayglow
emission intensity. Brightness enhancements during the flare relative to just
before were determined at tangent altitudes of peak emission viewed toward the
limb with TIMED. The TIMED observations were made at low solar zenith angles and
show flare enhancements of roughly 15%, 30%, 30%, and 60%, respectively, for OI
130.4 nm, OI 135.6 nm, N2 LBH Short, and N2 LBH Long modes of the TIMED/GUVI
instrument. However, GUVI observations of HI Lyman-alpha emission brightness do
not show a significant brightness change. This lack of change in HI Lyman-alpha
dayglow brightness is consistent with no significant change (<2%) in the solar
Lyman-alpha flux observed with TIMED/SEE. Enhancements of emissions produced by
photodissociation and photoelectron impact excitation sources are studied with
IMAGE observations following Immel et al., JGR, 2003. Simulations of dayglow
limb profiles to compare with the observations are produced using the NRLMSIS
atmosphere model, the IRI90 ionosphere model, the GLOW photoelectron model, and
the REDISTER radiative transfer model. The combined datasets enable a better
study of the airglow sources most affected by the EUV and x-ray components of
solar irradiance variability. We report our preliminary analysis of the response
of FUV dayglow emissions to this event.

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American Geophysical Union, Spring Meeting 2005