Impact of X-Class Flares on the Polar Ionosphere

The ionospheric impact of X-class and large M-class flares has posed severe observational challenges for the ionosonde community. The very strong high frequency (HF) radio absorption associated with the X-class flares creates black-out conditions making ionosonde observations impossible. Similarly incoherent scatter radar (ISR) observations have generated only a few X-class flare impact observations because of limited duty cycle of these radars.

With the advent of the NSF Advanced Modular Incoherent Scatter Radar (AMISR) technology it has become possible to operate 24/7 with better than 10 minute cadence. The PFISR, located at Poker Flat, Alaska, has operated in such a mode since March 2007. This has provide a data base that has captured many X-class flares. The irradiance from a subset of these were also observed by the Extreme Ultraviolet Variability Experiment (EVE) on the NASA Solar Dynamics Observatory (SDO) satellite. Hence we are in a position to evaluate modeling approaches that describes E-region ionization via energetic photons as well as the subsequent ionization caused by these photoelectrons. A key issue remains, that associated with the Auger ionization process. This latter topic’s relevance will be described from the modeling and future observational needs point of view. The extension of this study into the central polar cap using Resolute Bay, Canada, AMISRs will be discussed.