title: A statistical survey of ultralow-frequency wave power and polarization in the Hermean magnetosphere.
abstract: We present a statistical survey of ultralow-frequency wave activity within the Hermean magnetosphere using the entire MErcury Surface, Space ENvironment, GEochemistry, and Ranging magnetometer data set. This study is focused upon wave activity with frequencies <0.5 Hz, typically below local ion gyrofrequencies, in order to determine if field line resonances similar to those observed in the terrestrial magnetosphere may be present. Wave activity is mapped to the magnetic equatorial plane of the magnetosphere and to magnetic latitude and local times on Mercury using the KT14 magnetic field model. Wave power mapped to the planetary surface indicates the average location of the polar cap boundary. Compressional wave power is dominant throughout most of the magnetosphere, while azimuthal wave power close to the dayside magnetopause provides evidence that interactions between the magnetosheath and the magnetopause such as the Kelvin-Helmholtz instability may be driving wave activity. Further evidence of this is found in the average wave polarization: left-handed polarized waves dominate the dawnside magnetosphere, while right-handed polarized waves dominate the duskside. A possible field line resonance event is also presented, where a time-of-flight calculation is used to provide an estimated local plasma mass density of ∼240 amu cm-3.
authors.affiliation: Department of Physics and Astronomy University of Leicester Leicester UK.
authors.forename: Matthew K
authors.initials: MK
authors.lastname: James
authors.affiliation: Department of Physics and Astronomy University of Leicester Leicester UK.
authors.forename: Emma J
authors.initials: EJ
authors.lastname: Bunce
authors.affiliation: Department of Physics and Astronomy University of Leicester Leicester UK.
authors.forename: Timothy K
authors.initials: TK
authors.lastname: Yeoman
authors.affiliation: Department of Physics and Astronomy University of Leicester Leicester UK; Department of Atmospheric, Oceanic and Space Sciences University of Michigan Ann Arbor Michigan USA.
authors.forename: Suzanne M
authors.initials: SM
authors.lastname: Imber
authors.affiliation: The Johns Hopkins University Applied Physics Laboratory Laurel Maryland USA.
authors.forename: Haje
authors.initials: H
authors.lastname: Korth
keywords: MESSENGER; Mercury; ULF; waves