Effect of the 14 July 2000 solar flare on Earth's FUV emissions

[1] An X-class solar flare occurring on 14 July 2000 (Bastille Day) marked the initiation of events which led to a powerful geomagnetic storm on 15 July. At the time of the flare the NASA-IMAGE spacecraft was near apogee and observed a global-scale transient increase in far ultraviolet ( FUV) emissions of the thermosphere in both the N-2 Lyman-Birge-Hopfield (LBH) band and the O I 135.6-nm line and also in geocoronal emissions of H I at 121.6-nm. Comparison with the solar x-ray flux measured by GOES 10 shows the delayed response of the FUV emissions compared to the peak in x-rays. This lag is attributed to a later peak in EUV emissions, which drive the photoelectron flux in the energy range which is, in turn, most effective in producing N2 LBH and O I 135.6-nm emissions. Measurements of solar EUV input by Solar and Heliospheric Observatory (SOHO) Charge, Element, and Isotope Analysis System (CELIAS)/Solar Extreme-UltraViolet Monitor (SEM) confirm the close correlation between solar EUV and terrestrial FUV emissions. A comparison of the flare-time variation in the signal in each channel of the instrument allows one to ( 1) determine the variation in resonantly scattered solar emissions and ( 2) differentiate between emissions created through photodissociation by solar EUV and those driven by terrestrial photoelectron impact. The latter provides a means for positively identifying the dayglow emissions observed in the SI-12 instrument.