66 research outputs found
Solar wind interaction with a comet: evolution, variability, and implication
Once a cometary plasma cloud has been created through ionisation of the
cometary neutrals, it presents an obstacle to the solar wind and the magnetic
field within it. The acceleration and incorporation of the cometary plasma by
the solar wind is a complex process that shapes the cometary plasma environment
and is responsible for the creation of boundaries such as a bow shock and
diamagnetic cavity boundary. It also gives rise to waves and electric fields
which in turn contribute to the acceleration of the plasma. This chapter aims
to provide an overview of how the solar wind is modified by the presence of the
cometary plasma, and how the cometary plasma is incorporated into the solar
wind. We will also discuss models and techniques widely used in the
investigation of the plasma environment in the context of recent findings by
Rosetta. In particular, this chapter highlights the richness of the processes
and regions within this environment and how processes on small scales can shape
boundaries on large scales. It has been fifteen years since the last book on
Comets was published and since then we have made great advances in the field of
cometary research. But many open questions remain which are listed and
discussed with particular emphasis on how to advance the field of cometary
plasma science through future space missions.Comment: Chapter 17 as part of book: Comets II
Editorial : Sources and propagation of ultra-low frequency waves in planetary magnetospheres
Non peer reviewe
Current Sheet Flapping Motions in the Tailwind Flow of Magnetic Reconnection
The feature and origin of current sheet flapping motions are one of most interesting issues of magnetospheric dynamics. In this paper we report the flapping motion of the current sheet detected in the tailward flow of a magnetic reconnection event on 7 February 2009. This flapping motion with frequency about 12âmHz was accompanied by magnetic turbulence. The observations by the tailâelongated fleet of five Time History of Events and Macroscale Interactions during Substorms probes indicate that these flapping oscillations were rather confined within the tailward flow than were due to a global process. This flapping motion could be due to the instability driven by the free energy associated with the ion temperature anisotropy in the tailward flow. Our observations indicate that the flapping motion in the tailward flow could have a different generation mechanism with that in the earthward flow
On the magnetic characteristics of magnetic holes in the solar wind between Mercury and Venus
The occurrence rate of linear and pseudo magnetic holes has been determined during MESSENGER's cruise phase starting from Venus (2007) and arriving at Mercury (2011). It is shown that the occurrence rate of linear magnetic holes, defined as a maximum of 10â rotation of the magnetic field over the hole, slowly decreases from Mercury to Venus. The pseudo magnetic holes, defined as a rotation between 10 and 45â over the hole, have mostly a constant occurrence rate
Making waves: Mirror Mode structures around Mars observed by the MAVEN spacecraft
We present an in-depth analysis of a time interval when quasi-linear mirror
mode structures were detected by magnetic field and plasma measurements as
observed by the NASA/Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft.
We employ ion and electron spectrometers in tandem to support the magnetic
field measurements and confirm that the signatures are indeed mirror modes.
Wedged against the magnetic pile-up boundary, the low-frequency signatures last
on average 10 s with corresponding sizes of the order of 15-30 upstream
solar wind proton thermal gyroradii, or 10-20 proton gyroradii in the immediate
wake of the quasi-perpendicular bow shock. Their peak-to-peak amplitudes are of
the order of 30-35 nT with respect to the background field, and appear as a
mixture of dips and peaks, suggesting that they may have been at different
stages in their evolution. Situated in a marginally stable plasma with
1, we hypothesise that these so-called magnetic bottles,
containing a relatively higher energy and denser ion population with respect to
the background plasma, are formed upstream of the spacecraft behind the
quasi-perpendicular shock. These signatures are very reminiscent of magnetic
bottles found at other unmagnetised objects such as Venus and comets, also
interpreted as mirror modes. Our case study constitutes the first unmistakable
identification and characterisation of mirror modes at Mars from the joint
points of view of magnetic field, electron and ion measurements. Up until now,
the lack of high-temporal resolution plasma measurements has prevented such an
in-depth study.Comment: 37 pages, 11 figures, 1 tabl
Statistical study of linear magnetic hole structures near Earth
The Magnetospheric Multiscale mission (MMS1) data for 8 months in the winter periods of 2017-2018 and 2018-2019, when MMS had its apogee in the upstream solar wind of the Earth's bow shock, are used to study linear magnetic holes (LMHs). These LMHs are characterized by a magnetic depression of more than 50 % and a rotation of the background magnetic field of less then 10g . A total of 406 LMHs are found and, based on their magnetoplasma characteristics, are split into three categories: cold (increase in density, little change in ion temperature), hot (increase in ion temperature, decrease in density) and sign change (at least one magnetic field component changes sign). The occurrence rate of LMHs is 2.3 per day. All LMHs are basically in pressure balance with the ambient plasma. Most of the linear magnetic holes are found in ambient plasmas that are stable against the mirror-mode generation, but only half of the holes are mirror-mode-stable inside
What are the fundamental modes of energy transfer and partitioning in the coupled Magnetosphere-Ionosphere system?
The fundamental processes responsible for energy exchange between large-scale electromagnetic fields and plasma are well understood theoretically, but in practice these theories have not been tested. These processes are ubiquitous in all plasmas, especially at the interface between high and low beta plasmas in planetary magnetospheres and other magnetic environments. Although such boundaries pervade the plasma Universe, the processes responsible for the release of the stored magnetic and thermal plasma energy have not been fully identified and the importance of the relative impact of each process is unknown. Despite advances in understanding energy release through the conversion of magnetic to kinetic energy in magnetic reconnection, how the extreme pressures in the regions between stretched and more relaxed field lines in the transition region are balanced and released through adiabatic convection of plasma and fields is still a mystery. Recent theoretical advances and the predictions of large-scale instabilities must be tested. In essence, the processes responsible remain poorly understood and the problem unresolved. The aim of the White Paper submitted to ESA's Voyage 2050 call, and the contents of this paper, is to highlight three outstanding open science questions that are of clear international interest: (i) the interplay of local and global plasma physics processes: (ii) the partitioning during energy conversion between electromagnetic and plasma energy: and (iii) what processes drive the coupling between low and high beta plasmas. We present a discussion of the new measurements and technological advances required from current state-of-the-art, and several candidate mission profiles with which these international high-priority science goals could be significantly advanced.Peer reviewe
Two-point observations of low-frequency waves at 67P/Churyumov-Gerasimenko during the descent of PHILAE: comparison of RPCMAG and ROMAP
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