Improving solar wind modeling at Mercury: Incorporating transient solar phenomena into the WSA-ENLIL model

Tuesday, 16 December 2014
Ryan M. Dewey1, Daniel N. Baker2, Brian J Anderson3, Mehdi Benna4, Catherine L Johnson5, Haje Korth6, Daniel J Gershman7, George C Ho6, William E McClintock8, Dusan Odstrcil9, Lydia C Philpott5, Jim M Raines10, David Schriver11, James A Slavin10, Sean C Solomon12, Reka M Winslow13 and Thomas Zurbuchen14, (1)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (2)University of Colorado, Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (3)Johns Hopkins University, Baltimore, MD, United States, (4)NASA - GSFC, Greenbelt, MD, United States, (5)University of British Columbia, Department of Earth, Ocean and Atmospheric Sciences, Vancouver, BC, Canada, (6)Johns Hopkins Univ/APL, Laurel, MD, United States, (7)NASA Goddard Space Flight Center, Heliophysics Sci. Div., Greenbelt, MD, United States, (8)Univ Colorado, Boulder, CO, United States, (9)George Mason University Fairfax, Computational and Data Sciences, Fairfax, VA, United States, (10)University of Michigan Ann Arbor, Ann Arbor, MI, United States, (11)University of California Los Angeles, Los Angeles, CA, United States, (12)Columbia University of New York, Palisades, NY, United States, (13)University of British Columbia, Vancouver, BC, Canada, (14)Univ Michigan, Ann Arbor, MI, United States
Coronal mass ejections (CMEs) and other transient solar phenomena play important roles in magnetospheric and exospheric dynamics. Although a planet may only occasionally interact with the products of these events, such transient phenomena can result in departures from the background solar wind that often involve more than an order of magnitude greater ram pressure and interplanetary electric field applied to the magnetosphere. For Mercury, an order of magnitude greater ram pressure can push the magnetopause to the planet’s surface, exposing the surface directly to the solar wind. In order to understand how the solar wind interacts with Mercury’s magnetosphere and exosphere, previous studies have used the Wang-Sheeley-Arge (WSA)-ENLIL solar wind modeling tool to calculate basic and composite solar wind parameters, such as solar wind velocity (V) and Alfvén Mach number (MA) at Mercury’s orbital location. This model forecasts only the background solar wind, however, and does not include these transient events. The Cone extension permits the inclusion of CMEs and other phenomena, and thus enables characterization of the effect of strong solar wind perturbations on the Mercury system. The Cone extension is predicated on the assumption of constant angular and radial velocities of ejecta to integrate them into the WSA-ENLIL coupled model. Comparisons of the model results with the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft observations indicate that the WSA-ENLIL-Cone model more accurately forecasts total solar wind conditions at Mercury and has greater predictive power for magnetospheric and exospheric processes than the WSA-ENLIL model alone.