A statistical survey of ultralow‐frequency wave power and polarization in the Hermean magnetosphere. Issue 9 (28th September 2016)

• Record Type: Journal Article
• Authors: James, Matthew K.; Bunce, Emma J.; Yeoman, Timothy K.; Imber, Suzanne M.; Korth, Haje
• Is Part Of: Journal of geophysical research. Volume 121:Issue 9(2016:Sep.)
• Page Start: 8755
• Page End: 8772
• Publication Date: 2016-09-28
• Subjects: ULF -- waves -- Mercury -- MESSENGER; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2016JA023103
• Languages: English
• ISSNs: 2169-9380

Abstract

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 . Key Points: Evidence that the Kelvin‐Helmholtz instability is driving Hermean ULF wave activity Observations suggest that Earth‐like field line resonance is possible at Mercury Wave power mapped to Mercury's surface reveals the likely average polar cap boundary location