Relativistic electrons are an important space weather hazard, being a major source of radiation damage to satellites and posing a risk to humans in space. We use approximately 20 years of data from the US Global Positioning System (GPS) satellite NS41 to determine the characteristics of the geomagnetic storms that lead to the largest relativistic electron fluxes in GPS orbit. The largest CME-driven events are associated with the solar wind having negative excursions of the IMF Bz with minimum values of ~-14 nT two hours prior to zero epoch, defined as the time of the minimum in the Dst index and strong Dst minima, reaching ~-130 nT at zero epoch. In contrast, events driven by high speed solar wind streams (HSSs) are associated with smaller negative excursions of IMF Bz with minimum values of ~-4 nT two hours prior to zero epoch and moderate Dst minima, reaching ~-60 nT at zero epoch. Compared with HSS-driven events, peak E = 2.0 MeV fluxes associated with CME-driven events are larger by factors of 1.3 at L=4.5 and 2.4 at L=6.5. Both the CME- and HSS-driven events are associated with enhancements in the solar wind number density and pressure prior to zero epoch. Following zero epoch the solar wind number density and pressure become low and substorm activity is enhanced for several days.

Instrumentation was deployed in the Antarctic Peninsula region to monitor conditions occurring in the region of near-space surrounding the Earth. The opportunity was taken to link into a NASA satellite mission occurring at the same time and with similar goals - to study the dynamics of the Earth-Sun system at a location where the two systems are finely balanced. The experiments have been used to interpret the changes in plasma composition at the same point in space due to solar weather events. A refurbished VLF Doppler receiver was installed at Rothera to measure plasmaspheric electron concentration. The electron number density was determined from analysis of the 15 minute integration providing group delay times, Doppler shift and arrival bearing of whistler-mode signals, of man-made transmissions, from MSK format transmitters from north east America. If you would like more information about the VLF Doppler receiver data that is still being routinely collected at Rothera please contact the UK Polar Data Centre at the British Antarctic Survey.