PLASMOIDS AS MAGNETIC-FLUX ROPES

Observational constraints on the magnetic topology and orientation of plasmoids is examined using a magnetic field model. We develop a magnetic flux rope model to examine whether principal axis analysis (PAA) of magnetometer signatures from a single satellite pass is sufficient to determine the magnetic topology of plasmoids and if plasmoid observations are best explained by the flux rope, closed loop, or large-amplitude wave picture. Satellite data are simulated by extracting the magnetic field along a path through our model of a magnetic flux rope. We then examine the results using PAA. We find that the principal axis directions (and therefore the interpretation of structure orientation) is highly dependent on several parameters including the satellite trajectory through the structure. Because of this we conclude that PAA of magnetometer data from a single satellite pass is insufficient to differentiate between magnetic closed loop and flux rope models. We also compare our model results to ISEE 3 magnetometer data of plasmoid events in various coordinate frames including principal axis and geocentric solar magnetospheric. We find that previously identified plasmoid events that have been explained as closed loop structures can also be modeled as flux ropes. We also searched the literature for previously reported flux rope and closed loop plasmoid events to examine if these structures had any similarities and/or differences. The results of our modeling efforts and examination of both flux rope and plasmoid events lead us to favor the flux rope model of plasmoid formation, as it is better able to unify the observations of various magnetic structures observed by ISEE 3.