Mirror mode structures near Venus and Comet P/Halley

Abstract

Abstract.In this paper, we study where mirror mode structures are generated near unmagnetized solar system bodies (Venus and comet P/Halley measured in situ by Venus Express and Giotto). To estimate the location of the mirror mode source region at Venus, we apply a turbulent diffusion model of mirror mode structures, which has already been successfully tested in planetary magnetosheaths (Earth, Jupiter, Saturn). It enables us to estimate the distance between the measured location of the mirror mode and the origin of the mirror mode structure through the mirror mode size. We find that the scenario of mirror mode excitation at the bow shock with subsequent convection and diffusion downstream to the magnetopause is valid for Venus. In the cometary case, however, we find that the size of the mirror mode structure is comparable to the gyroradius of water group ions. This suggests local production of mirror mode structures in the cometary magnetosheath, most likely through fresh ion pickup, as opposed to the convection and diffusion mechanism at Venus.

Mass-loading, pile-up, and mirror-mode waves at comet 67P/Churyumov-Gerasimenko

“…For water ions at a magnetic field strength of B m ≈ 20 nT this leads to T mm ≈ 9 α s. With the measured T mm mentioned above this leads to 11 ≤ α ≤ 16, which is similar to what was found by Tsurutani et al (1999) at comet 21P/Giacobini-Zinner, α GZ ≈ 12, but much larger than what was found by Schmid et al (2014) at comet 1P/Halley, α H ≈ 1-2. Taking the ion velocity as measured by IES, the Larmor radius for water ions becomes ρ H 2 O, i ≈ 280 km.…”

“…at comet 1P/Halley (see e.g. Schmid et al, 2014;Volwerk et al, 2014). The instability criterion for MM waves is given by:…”

“…This could imply that the freshly mass-loaded magnetospheric magnetic field is mirror-mode unstable (see e.g. Hasegawa, 1969;Tsurutani et al, 1999;Schmid et al, 2014;Volwerk et al, 2014). As the resolution of the plasma data is too low to check the pressure balance over the MM structures, the magnetic-field-only method by Lucek et al (1999) is used to investigate the data for MM waves.…”

Statistical analysis of mirror mode waves in sheath regions driven by interplanetary coronal mass ejection

“…The shock compression has been argued to be a source of free energy that generates peak-like MMs and likely both sources need to be available in order to generate the largest amplitude MMs (Tsurutani et al, 2011b). In the heliosheath and cometosheaths, the ion pickup process is also identified as a free energy source (e.g., Tsurutani et al, 1999Tsurutani et al, , 2011aSchmid et al, 2014).…”

“…They are frequently observed in heliospheric plasma, in particular in different sheath structures. They are the most widely studied in the planetary magnetosheaths (e.g., Tsurutani et al, 1982;Hellinger et al, 2003;Soucek et al, 2008Soucek et al, , 2015Volwerk et al, 2008;Génot et al, 2009b;Herčík et al, 2013;Schmid et al, 2014;Volwerk et al, 2016), but also found in cometosheaths (e.g., Russell et al, 1991;Glassmeier et al, 1993;Tsurutani et al, 1999;Schmid et al, 2014), in the heliosheath (e.g., Liu et al, 2007;Génot, 2008;Tsurutani et al, 2011a) and ahead of the dipolarization front (Wang et al, 2016). MMs are also studied in the solar wind (e.g., Hellinger et al, 2006Hellinger et al, , 2017Bale et al, 2009;Russell et al, 2009), behind interplanetary shocks ) and in addition in interplanetary coronal mass ejections (ICMEs; Siu-Tapia et al, 2015).…”