title: Modular model for Mercury's magnetospheric magnetic field confined within the average observed magnetopause.
abstract: Accurate knowledge of Mercury's magnetospheric magnetic field is required to understand the sources of the planet's internal field. We present the first model of Mercury's magnetospheric magnetic field confined within a magnetopause shape derived from Magnetometer observations by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft. The field of internal origin is approximated by a dipole of magnitude 190 nTRM3, whereRMis Mercury's radius, offset northward by 479 km along the spin axis. External field sources include currents flowing on the magnetopause boundary and in the cross-tail current sheet. The cross-tail current is described by a disk-shaped current near the planet and a sheet current at larger (≳ 5RM) antisunward distances. The tail currents are constrained by minimizing the root-mean-square (RMS) residual between the model and the magnetic field observed within the magnetosphere. The magnetopause current contributions are derived by shielding the field of each module external to the magnetopause by minimizing the RMS normal component of the magnetic field at the magnetopause. The new model yields improvements over the previously developed paraboloid model in regions that are close to the magnetopause and the nightside magnetic equatorial plane. Magnetic field residuals remain that are distributed systematically over large areas and vary monotonically with magnetic activity. Further advances in empirical descriptions of Mercury's magnetospheric external field will need to account for the dependence of the tail and magnetopause currents on magnetic activity and additional sources within the magnetosphere associated with Birkeland currents and plasma distributions near the dayside magnetopause.
authors.affiliation: The Johns Hopkins University Applied Physics Laboratory Laurel Maryland USA.
authors.forename: Haje
authors.initials: H
authors.lastname: Korth
authors.affiliation: Institute and Faculty of Physics Saint Petersburg State University Saint Petersburg Russia.
authors.forename: Nikolai A
authors.initials: NA
authors.lastname: Tsyganenko
authors.affiliation: Department of Earth, Ocean and Atmospheric Sciences University of British Columbia Vancouver British Columbia Canada; Planetary Science Institute Tucson Arizona USA.
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Johnson
authors.affiliation: Department of Earth, Ocean and Atmospheric Sciences University of British Columbia Vancouver British Columbia Canada.
authors.forename: Lydia C
authors.initials: LC
authors.lastname: Philpott
authors.affiliation: The Johns Hopkins University Applied Physics Laboratory Laurel Maryland USA.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Anderson
authors.affiliation: Department of Earth, Ocean and Atmospheric Sciences University of British Columbia Vancouver British Columbia Canada; Saudi Aramco Dharan Saudi Arabia.
authors.forename: Manar M
authors.initials: MM
authors.lastname: Al Asad
authors.affiliation: Department of Terrestrial Magnetism Carnegie Institution of Washington Washington District of Columbia USA; Lamont-Doherty Earth Observatory Columbia University Palisades New York USA.
authors.forename: Sean C
authors.initials: SC
authors.lastname: Solomon
authors.affiliation: The Johns Hopkins University Applied Physics Laboratory Laurel Maryland USA.
authors.forename: Ralph L
authors.initials: RL
authors.lastname: McNutt
keywords: MESSENGER; Mercury; magnetic field model