Solar EUV irradiance variability derived from terrestrial far ultraviolet dayglow observations

Remotely sensed ultraviolet emissions from the Earth's upper atmosphere are shown to mirror fluctuations in solar EUV irradiance during July 2002, including the overall increase and decrease as the Sun rotated, and episodic increases associated with multiple solar flares. The TIMED/ GUVI dayglow observations are used to derive a new quantity, Q(EUV)(GUVI), which is a measure of integrated solar EUV electromagnetic energy shortward of 45 nm. Both the absolute Q(EUV)(GUVI) values and their modulation by solar rotation agree well with the corresponding solar EUV energy estimated by the NRLEUV irradiance variability model. The Q(EUV)(GUVI) values do not support recent suggestions that the solar EUV irradiances estimated by the model of Hinteregger et al. be increased by a factor of four, nor even a factor of two.