Dynamic changes in the outer ionosphere in the region of the ionospheric trough during an intense magnetic storm

VLF broadband measurements, RF diagnostic, electron density, and temperature measurements from the MAGION-3 satellite were used to study changes in the outer ionosphere during the intense, SSC associated magnetic storm on May 9, 1992. The MAGION-3 satellite as a part of the APEX Project was at this time in the midnight sector at altitudes between 1000 and 2000 km. Signatures of electron temperature peaks, whistler cut-offs, occurrence of different types of emissions, as well as pronounced equatorward edges of the plasma trough allowed us to estimate the equatorial plasmapause position. The inner plasmasphere shrank to values lower than L=2 during the main phase of this storm. The plasmapause position determined from the top-side ionosphere examination agrees well with in situ equatorial studies, except for during large and rapid changes in geomagnetic activity. The position, movement, and shape of the main ionospheric trough, and the waves occurring in this area, particularly the enhancement of broad band emission inside the plasmasphere during the recovery phase of a substorm, permit us to build a clearer view of the topside ionosphere during strong disturbances.