Solar irradiance variability during the October 2003 solar storm period

The extraordinary solar storms between 18 October 2003 and 5 November 2003 include over 140 flares, primarily from two different large sunspot groups. There were 11 large X-class flares during this period, including an X17 flare on 28 October 2003 and an X28 flare on 4 November 2003. The X28 flare is the largest flare since GOES began its solar X-ray measurements in 1976. The solar (full-disk) irradiance during these flares was observed by the instruments aboard the NASA Solar Radiation and Climate Experiment (SORCE) spacecraft and the NASA Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics ( TIMED) spacecraft. The total solar irradiance (TSI) dropped by unprecedented 0.34% during this period due to the dark, large sunspots. In addition, the TSI increased by 270 ppm during the X17 (4B optical) flare on 28 October, the first definitive measurement of a TSI flare event. The ultraviolet (UV) variations for this X17 flare range from a factor of about 50 shortward of 10 nm to about 10% for the Mg II 280 nm emission. One interesting result for the UV flare variations is that the broad wings of the H I Lyman-alpha (121.6 nm) emission increased by more than a factor of 2 during the X17 flare while the core of the Lyman-alpha emission only increased by 20%. Another interesting result is the time profile of the Si III 120.6 nm emission, which shows a sharp 1-minute long increase by a factor of 17 during the impulsive phase.