High Latitude Ionospheric Impact of the April 1997 Solar Flare and Coronal Mass Ejection

On April 7, 1997, the EIT and LASCO instruments on NASA's Solar and Heliospheric Observatory (SOHO) recorded a solar flare and a coronal mass ejection (CME). The solar matter and shock wave associated with these events propagated in the solar wind to Earth on April 10-11, 1997. This page presents ground based measurements of ionospheric activity associated with the solar flare and coronal mass ejection. All data on this page were taken with the Sondrestrom incoherent scatter radar. For a comprehensive survey of data from all NASA instruments that observed this event, see http://www-spof.gsfc.nasa.gov/istp/event.apr97.

Preliminary Results

The radar data presented below are the result of a preliminary analysis. Two plots that display data from the radar are presented below

Time Line of Electron Density

On April 7, 1997, scientists from NASA's ISTP (IOnternational Solar Terrestrial Physics) program observed a flare and a coronal mass ejection. Several episodes of auroral activity were triggered by the arrival of mass ejecta, and the shock that preceded it, to the Earth between late April 10 and early April 11. The Sondrestrom radar operated in a three position mode between 16 UT on April 10 and 16 UT on the 11th. The following shows the electron density, electron temperature, and ion temperature as functions of altitude and time.

Electrodynamic Properties

The Sondrestrom radar sampled the arc that intensified with the expansion that started at ~2220 UT on April 10. Enhancements in Hall and Pedersen conductances and Joule heating were observed around 23 UT. The radar also sampled the region in the vicinity of the arc system that intensified near the poleward edge of the oval at 0355 UT on April 11. The intensification followed the expansion onset of 0300 UT. Note the rotation in the electric field from northward to westward as the as the region of high Hall and Pedersen conductances (~20 mho) was transversed at ~0400 UT. Moderate values of electric field, conductances, and Joule hetaing followed the arc intensification.