Extreme geomagnetic and optical disturbances over Irkutsk during the 2003 November 20 superstorm

Abstract

We study geomagnetic disturbances and aurora observed near Irkutsk (GEO: 52.2°, 104.5°) at mid-latitude observatories of the Institute of Solar-Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences (ISTP SB RAS) during the 2003 November 20 superstorm. Based on the data from the world network of magnetometers and on the magnetogram inversion technique, we found the auroral oval boundaries, the westward electrojet position, and calculated the parameters for the auroral electron energy distribution. We found a relationship of precipitations of energetic electrons (≥1keV) with the bursts of the Pi1B/Pi1c pulsations and intensity in the 557.7 nm emission and in the 360–410 nm spectral channel observed in the postmidnight sector within the period, when the auroral oval southern boundary lowered below the latitude of Irkutsk. The origin of the observed emissions at the middle latitude is related to electron precipitations in the main and equatorial parts of the westward electrojet. Modeling the ionosphere parameters showed that collision of oxygen atoms with thermal electrons and deactivation of excited nitrogen atom N(2D) at collisions with oxygen molecules make the main contributions to the 630 nm total intensity. During the addressed superstorm, two types of mid-latitude auroras were probably observed: diffuse aurora and/or type « d», as well as emission irregular variations typical of normal auroras related to the auroral energy particle precipitation.