Investigation of ∼ 20–40 mHz ULF waves and their driving mechanisms in Mercury's dayside magnetosphere

Elisabet Liljeblad,Tomas Karlsson

doi:10.5194/angeo-35-879-2017

Elisabet Liljeblad, Tomas Karlsson

Open Access

https://doi.org/10.5194/angeo-35-879-2017

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Journal: Annales Geophysicae	Publication Date: Jul 28, 2017
Citations: 7	License type: CC BY 3.0

Affiliation: KTH Royal Institute of Technology

Abstract

Abstract. Ultra-low-frequency (ULF) waves in the ∼ 20–40 mHz range are frequently observed in the Mercury magnetosphere using Mercury Surface Space Environment Geochemistry, and Ranging (MESSENGER) magnetic field data. The majority of these waves have very similar characteristics to the waves likely driven by Kelvin–Helmholtz (KH) ULF waves (which are retained as a subset of the wave events studied in this paper) identified in a previous study. Significant ULF wave activity is observed in the dawn sector of the magnetosphere. This indicates that Mercury KH waves may be more common between 6 and 12 magnetic local time than previously predicted and that magnetospheric ULF waves in the frequency band ∼ 20–40 mHz can be used as a detection tool for Hermean KH waves.

Highlights

Ultra-low-frequency (ULF) waves were first observed in the magnetic environment of Mercury with Mariner 10 (Russell, 1989)
A study by James et al (2016) covering MESSENGER magnetosphere crossings over the time period 2011–2015 suggests that ULF waves, with similar characteristics as those Kelvin–Helmholtz instability (KHI)-ULF waves reported in Liljeblad et al (2016), could be KHI driven
Observing a large part of the general ULF waves at the dawnside magnetosphere is surprising, assuming they are likely driven by the KHI. This either means that the dawnside general ULF waves are not generated by the KHI or that dawnside Kelvin–Helmholtz waves (KHWs) are more common on Mercury than previously thought

Summary

Introduction

Ultra-low-frequency (ULF) waves were first observed in the magnetic environment of Mercury with Mariner 10 (Russell, 1989). The ULF waves followed the KHW occurrence asymmetry and appear mainly at the duskside magnetopause between 14 and 17 magnetic local time These waves were observed most often in the narrow frequency range of 20–40 mHz and in the same range as the KHWs. The overall results, including similar characteristics and the close temporal connection between the ULF waves and the KHWs, argue for the KHI as a driver. This study will analyze the magnetic field of all dayside magnetospheric crossings of MESSENGER during the year 2011 to identify clear ULF wave activity Such ULF waves will be investigated by evaluation of their characteristics and by comparing them to the dayside likely KHI-generated ULF waves reported in Liljeblad et al (2016) to discern possible driving mechanisms

Observations and results

Findings

Discussion

Conclusions