Interplanetary Coronal Mass Ejections from MESSENGER Orbital Observations at Mercury 

Friday, 18 December 2015
Poster Hall (Moscone South)
Reka Moldovan Winslow1, Noé Lugaz1, Lydia C Philpott2, Nathan Schwadron3, Charles J Farrugia1, Brian J Anderson4 and Charles William Smith1, (1)University of New Hampshire Main Campus, Durham, NH, United States, (2)University of British Columbia, Department of Earth, Ocean and Atmospheric Sciences, Vancouver, BC, Canada, (3)University of New Hampshire Main Campus, Space Science Center, Durham, NH, United States, (4)Johns Hopkins University, Baltimore, MD, United States
We use observations from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, in orbit around Mercury, to investigate interplanetary coronal mass ejections (ICMEs) near 0.3 AU. MESSENGER, the first spacecraft since the 1980s to make in-situ measurements at distances < 0.5 AU, presents a unique opportunity for observing the innermost heliosphere. It also allows studies of ICME evolution as they expand and propagate outward, interacting with the solar wind. In order to catalog ICME events observed by MESSENGER, we design a strict set of selection criteria to identify them based on magnetic field observations only, since reliable solar wind plasma observations are not available from MESSENGER. We identify 61 ICME events observed by the MESSENGER Magnetometer between 2011 and 2014, and present statistical analyses of ICME properties at Mercury. In addition, using existing datasets of ICMEs at 1 AU we investigate key ICME property changes from Mercury to 1 AU. We find good agreement with previous studies for the magnetic field strength dependence on heliospheric distance, r. We have also established three different lines of evidence that ICME deceleration continues beyond the orbit of Mercury: 1) we find a shallow decrease with distance of ∼r−0.45 for the ICME shock speed from Mercury to 1 AU, 2) the average transit speed from the Sun to Mercury for ICMEs in our catalog is ∼20% faster than the average speed from the Sun to 1 AU, 3) the ICME transit time to 1 AU has a weaker dependence on the CME initial coronagraphic speed, as compared to what we predict based on our MESSENGER ICME catalog. Based on our results, future ICME propagation studies should account for ICME speed changes beyond Mercury’s heliocentric distances to improve ICME arrival time forecasting. Our ICME database will also prove particularly useful for multipoint spacecraft studies of recent ICMEs, as well as for model validation of ICME properties.