September 1999 SI Events: Ionospheric Response in Different MLT-Sectors.

N. PARTAMIES¹, K. KAURISTIE¹, P. EGLITIS² and M. USPENSKY¹
1) Finnish Meteorological Institute, Finland.
2) Swedish Institute of Space Physics, Uppsala Division, Sweden.

The September 1999 International Space Weather Campaign was arranged to study space weather events from their initiation at the sun to the impacts at the Earth. During the campaign the common aim of the numerous research groups was to collect as complete as possible dataset of ground-based and satellite observations for further analysis and modelling work. SuperDARN data naturally have an important role in the collected data set. In this study we analyse ionospheric effects of three SI events, which took place on September 12th, 15th and 22th at UT-times 0400, 2019, 1220, respectively (as defined from ground-based magnetometer data). In all these cases clear fast shocks were observed in the solar wind by ACE, WIND and IMP-8 satellites. On September 15th IMF Bz stayed positive before and after the shock, while the two other events were associated with negative IMF Bz. The study utilizes SuperDARN data together with recordings of several magnetometer chains (IMAGE, CANOPUS, GIMA, and Greenland). Special emphasis is given to Scandinavian observations which were made in different MLT-sectors (in the morning, evening and noon sectors) during the three events. Scandinavian observations are compared and contrasted with the data from other MLT-sectors and with the global SuperDARN convection patterns. In the presentation we discuss especially the ionospheric effects caused by the transient pressure pulses of the SIs. At first look magnetic response times seem to be nearly same at the different chains. More detailed analysis, however, reveals differences in the timing and pulse shapes between high and low latitude stations as well as between the dayside and the nightside stations. SuperDARN radars observed the SIs either as abrupt changes in the scattered power (in some cases also in the velocity) or as shifts in range of the maximum power regions. The characteristics of these signatures depends on the beam direction with respect to the ionospheric convection pattern. By careful analysis of these signatures we hope to resolve whether there exists some kind of systematic way for the ionosphere to respond to abrupt solar wind pressure changes.

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