Observations of the High-Latitude Ionospheric Response to the Onset of the April 2002 Storm

The high-latitude incoherent scatter radars at Sondrestrom, Greenland, and Longyearbyen, Svalbard, observed detailed ionospheric behavior during the initial shock, occurring near 11:00 UT on April 17, and the onset of the geomagnetic storm. During this period, the Sondrestrom radar observed extreme electric field enhancements in excess of 120 mV/m. The direction of the electric field at Sondrestrom indicates the measurements are located in the sunward convection region of the dawn and pre-noon sector. These large electric fields subsequently produced very high levels of Joule heating rates (greater than 80 mW/m2), extreme ion heating events (in excess of 3500 K), aurorally enhanced electron temperatures and current-driven instabilities leading to extreme electron temperatures in the lower E region (in excess of 2000 K). Additionally the F-region meridional neutral wind response and E region neutral winds are inferred. Concurrent observations on Svalbard, in the post-noon and dusk sector, also indicate enhanced F- and E-region ion and electron temperatures. Though the ionospheric response observed by the radars are determined locally, electric field enhancements estimated by AMIE runs during this period of the storm suggest that these effects may, in fact, occur over a much larger region.