Radial Evolution of Stream Interaction Regions and Sector Boundaries in the Inner Heliosphere: Observations and MHD Simulations
Monday, 15 December 2014
The data that the MESSENGER probe collected while in cruise phase from Earth to Mercury provide a unique opportunity to investigate the radial evolution of solar wind structures between ~0.3 and 1 AU. While no solar wind plasma data were available from the spacecraft, the heliospheric magnetic field measurements were taken during the cruise phase. We have collected MESSENGER and OMNI data from a number of Carrington rotations between 2008 and 2010 when the probe was in radial conjunction with Earth to minimize the aging of the structure between the observation times at MESSENGER and L1. During these rotations MESSENGER was between ~0.3 and 0.5 AU from Sun. In this presentation we use the high-resolution heliospheric version of the Lyon-Fedder-Mobarry (LFM) magnetohydrodynamic (MHD) model (LFM-helio) driven by the latest generation of Wang-Sheeley-Arge (WSA) coronal solutions. We investigate the radial development of a number of major structures in observations and in our model. We compare the strength of magnetic field compressions as a function of the coronal boundary variables (solar wind speed, density and temperature) and study the complexity of sector boundary crossings at different heliospheric distances. In many cases the crossings become more complex (multiple crossings within a few hours to days) between MESSENGER and L1; in other cases, the crossings are already complex at MESSENGER. In addition, in some cases short periods (a few hours to a day) of predominantly radial field magnetic field are observed. In many of these cases there is a question as to whether the observed structures exist in the corona (and if so whether they are reproduced by WSA) or are produced as the solar wind progresses toward Earth. We attempt to investigate these issues by imposing additional perturbations on top of the WSA coronal solutions, track their evolution and consider whether the observations can be reproduced.