Coronal magnetic field governs most of the coronal activities. Despite of its importance in solar atmosphere, there is no accurate method of measuring the coronal magnetic field. The current measurement methods of coronal magnetic fields depend on extrapolation of photospheric magnetic fields. There are different models to study the global structure of coronal magnetic field. The most commonly used models are PFSS model and magnetohydrodynamic (MHD) model.
In this thesis, we study the coronal magnetic field condition during major solar energetic particle (SEP) event of 23rd solar cycle by using the PFSS model. We use 114 SEP events observed by the SOHO/ERNE experiment in 1996-2010. In the beginning we identified 43 events that are relatively free from the disturbance caused by interplanetary coronal mass ejections (ICMEs). We examined these SEP events using IDL software developed by Lockheed Martin Solar and Astrophysics Lab (LMSAL). We produced plots of open coronal magnetic field of each events using SolarSoft. We also classified SEP events according to their number of connection points as events with; single connection point, double connection points and multiple connection points. Events with multiple connection points make up almost one third of the total events. These events show that the coronal magnetic connection are typically complicated and neighboring magnetic field lines in the solar wind can be magnetically connected to regions that are well separated in the low corona. We also found that the actual connection longitude (a longitude that takes in to account the coronal magnetic field) is most of the time is closer to the flare site associated with the event than the Parker spiral connection longitude. The Parker spiral longitudes, connection longitudes and flare longitudes are analyzed in detail by histograms. Finally, we chose two example events and analyzed them by using intensity-time profile of particles, plots of from LASCO CME catalog and plots produce by the SolarSoft. Based on our analysis we classified the example events into gradual and hybrid SEP events.
