Ionospheric response to the solar flare of 14 July 2000

We present our observations of the global ionospheric response to the X-class solar flare that started the Bastille Day storm on 14 June 2000. The observations were made using the Low-Resolution Airglow and Aurora Spectrograph (LORAAS) instrument on the Advanced Research and Global Observation Satellite (ARGOS). The ARGOS is in a Sun-synchronous orbit at 0230/1430 LT at approximately 840 km altitude. During the daytime the LORAAS observes the 911-Å emission; this emission is produced by radiative recombination of F region O⁺ and electrons. We simultaneously invert approximately one-half of an orbit of 911-Å limb scans (approximately 30-45 min of observing) using a tomographic inversion technique to produce dayside electron density maps in the orbit plane. We compare our observations of orbits immediately before and after the flare to the orbit in which the flare occurred. We observed a 41% increase in the average 911-Å brightness during the flare orbit compared to the orbits before and after the flare. This corresponds to an overall increase of electron density by ∼20%. This density enhancement has largely decayed by the next orbit. At altitudes near the F region peak, 250-450 km, the density enhancement has decayed to the preflare value. An enhancement of the electron densities at approximately –50° geomagnetic latitude has moved northward in the flare orbit, which may be indicative of enhanced meridional transport postflare. We compared our results to output from the SAMI-2 model, which was run for the flare study presents in the work of Meier et al. [2002].