Georg-August-Universität Göttingen, Institut für Astrophysik, Göttingen, Germany
Radiation hazards by intense solar energetic particle events (SEPs) pose a serious threat to satellite systems, aircraft crews and astronauts. To help better understanding the dependence of intense SEP fluxes on the location of the onset site of their solar drivers, a specific study has been carried out taking into account the magnetic connection to the associated CME and its plane of the sky speed.
The NOAA solar proton event list „Solar Proton Events Affecting the Earth Environment (http://www.swpc.noaa.gov/ftpdir/indices/SPE.txt), classified by the NOAA space weather scales was investigated for the time period after launch of ACE in order to be able to analyze the solar wind plasma and IMF conditions measured near Earth orbit at event onset.
The whole NOAA proton event list comprised 252 events from April 1976 to June 2013, for which integrated 5 minutes averages of the various GOES proton flux measurements at energies > 10 MeV had reached three consecutive values of 10 pfu or above. Events which occurred temporarily connected have been treated in this study as one single event.
The time period with information on major SEP events provided by the list, together with the solar wind data, span the period November 1997 to March 2012, with 105 SEP entries. These events were then compared with information on CMEs and flares listed in the SOHO LASCO CME catalogue.
Taking into account times with missing SOHO data and events without determined CME speeds,the established SEP event list includes 81 proton events and a total of 100 associated CMEs. For these events the proton flux data for energies >10 MeV measured by the GOES satellites were used to determine the characteristic proton event parameters, such as peak flux, event duration and the number of total measured protons per event. The parameters of solar activity were compiled from the SOHO/LASCO CME catalogue.
The source regions of the CMEs were identified using images and movies of the SOHO/LASCO/EIT and MDI, SDO/AIA and HMI, and STEREO/SECCHI instruments. Solar wind data from the ACE and in a few cases as substitutes, from the WIND satellites were used to determine the two-dimensional (in longitude) and three-dimensional magnetic connection (the real solar wind source region) to the Sun at the onset of the solar proton events.
Results for the dependence of the intensities of the particle events on the location of the CME onset sites, their lateral expansions and outward plane of the sky propagation speeds are presented and the implications are discussed for the development of state-of-the-art forecast capabilities.
Part of this work was funded by the European Union in the FP7-Project eHEROES (Environment for Human Exploration and RObotic Experimentation in Space). The University of Göttingen led eHEROES Task 3.6 “Source region, acceleration mechanisms and interplanetary propagation of SEPs”, as part of eHEROES Work Package 3 ”Solar and Space Events and their Evolution“.
The achievements of this task are summarised through the eHEROES deliverable D3.5 „Source region, acceleration mechanisms and interplanetary propagation of SEPs”, available at www.affects-fp7.eu
services/eheroes-seps/. Contributing partners to D3.5 were UCL, UCT, LPI. Volker Bothmer acknowledges support of the CGAUSS (Coronagraphic German And US Solar Probe Plus Survey) project for WISPR by the German Space Agency DLR under grant 50 OL 1601.