Cluster-C1 observations on the geometrical structure of linear magnetic holes in the solar wind at 1 AU

Abstract. Interplanetary linear magnetic holes (LMHs) are structures in which the magnetic field magnitude decreases with little change in the field direction. They are a 10–30% subset of all interplanetary magnetic holes (MHs). Using magnetic field and plasma measurements obtained by Cluster-C1, we surveyed the LMHs in the solar wind at 1 AU. In total 567 interplanetary LMHs are identified from the magnetic field data when Cluster-C1 was in the solar wind from 2001 to 2004. We studied the relationship between the durations and the magnetic field orientations, as well as that of the scales and the field orientations of LMHs in the solar wind. It is found that the geometrical structure of the LMHs in the solar wind at 1 AU is consistent with rotational ellipsoid and the ratio of scales along and across the magnetic field is about 1.93:1. In other words, the structure is elongated along the magnetic field at 1 AU. The occurrence rate of LMHs in the solar wind at 1 AU is about 3.7 per day. It is shown that not only the occurrence rate but also the geometrical shape of interplanetary LMHs has no significant change from 0.72 AU to 1 AU in comparison with previous studies. It is thus inferred that most of interplanetary LMHs observed at 1 AU are formed and fully developed before 0.72 AU. The present results help us to study the formation mechanism of the LMHs in the solar wind.

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The evolution of inverted magnetic fields through the inner heliosphere

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa951 ◽

2020 ◽

Vol 494 (3) ◽

pp. 3642-3655 ◽

Cited By ~ 2

Author(s):

Allan R Macneil ◽

Mathew J Owens ◽

Robert T Wicks ◽

Mike Lockwood ◽

Sarah N Bentley ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Radial Distance ◽

Occurrence Rate ◽

Slow Solar Wind ◽

The Sun ◽

Radial Evolution ◽

In Transit ◽

The Magnetic Field ◽

Inner Heliosphere

ABSTRACT Local inversions are often observed in the heliospheric magnetic field (HMF), but their origins and evolution are not yet fully understood. Parker Solar Probe has recently observed rapid, Alfvénic, HMF inversions in the inner heliosphere, known as ‘switchbacks’, which have been interpreted as the possible remnants of coronal jets. It has also been suggested that inverted HMF may be produced by near-Sun interchange reconnection; a key process in mechanisms proposed for slow solar wind release. These cases suggest that the source of inverted HMF is near the Sun, and it follows that these inversions would gradually decay and straighten as they propagate out through the heliosphere. Alternatively, HMF inversions could form during solar wind transit, through phenomena such velocity shears, draping over ejecta, or waves and turbulence. Such processes are expected to lead to a qualitatively radial evolution of inverted HMF structures. Using Helios measurements spanning 0.3–1 au, we examine the occurrence rate of inverted HMF, as well as other magnetic field morphologies, as a function of radial distance r, and find that it continually increases. This trend may be explained by inverted HMF observed between 0.3 and 1 au being primarily driven by one or more of the above in-transit processes, rather than created at the Sun. We make suggestions as to the relative importance of these different processes based on the evolution of the magnetic field properties associated with inverted HMF. We also explore alternative explanations outside of our suggested driving processes which may lead to the observed trend.

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On the magnetic characteristics of magnetic holes in the solar wind between Mercury and Earth

10.5194/angeo-2019-127 ◽

2019 ◽

Cited By ~ 1

Author(s):

Martin Volwerk ◽

Charlotte Goetz ◽

Ferdinand Plaschke ◽

Tomas Karlsson ◽

Daniel Heyner

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Occurrence Rate ◽

Magnetic Characteristics ◽

The Earth ◽

The Magnetic Field

Abstract. The occurrence rate of linear and pseudo magnetic holes has been determined during MESSENGER's cruise phase starting from Earth (2005) and arriving at Mercury (2011). It is shown that the occurrence rate of linear magnetic holes, defined as a maximum of 10° rotation of the magnetic field over the hole, slowly decreases from Mercury to Earth. The pseudo magnetic holes, defined as a rotation between 10° and 45° over the hole, have mostly a constant occurrence rate, with a slight increase in front of the Earth and a decrease around the Earth. The width and depth of these structures seem to strongly differ depending on whether they are inside or outside of Venus's orbit.

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Unusually high magnetic fields in the coma of 67P/Churyumov-Gerasimenko during its high-activity phase

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833544 ◽

2019 ◽

Vol 630 ◽

pp. A38 ◽

Cited By ~ 2

Author(s):

C. Goetz ◽

B. T. Tsurutani ◽

P. Henri ◽

M. Volwerk ◽

E. Behar ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Unusual Behavior ◽

Cometary Plasma ◽

Unusual Event ◽

Interplanetary Coronal Mass Ejection ◽

Magnetic Field Magnitude ◽

Solar Wind Origin ◽

The Impact ◽

The Magnetic Field

Aims. On July 3, 2015, an unprecedented increase in the magnetic field magnitude was measured by the Rosetta spacecraft orbiting comet 67P/Churyumov-Gerasimenko (67P). This increase was accompanied by large variations in magnetic field and ion and electron density and energy. To our knowledge, this unusual event marks the highest magnetic field ever measured in the plasma environment of a comet. Our goal here is to examine possible physical causes for this event, and to explain this reaction of the cometary plasma and magnetic field and its trigger. Methods. We used observations from the entire Rosetta Plasma Consortium as well as energetic particle measurements from the Standard Radiation Monitor on board Rosetta to characterize the event. To provide context for the solar wind at the comet, observations at Earth were compared with simulations of the solar wind. Results. We find that the unusual behavior of the plasma around 67P is of solar wind origin and is caused by the impact of an interplanetary coronal mass ejection, combined with a corotating interaction region. This causes the magnetic field to pile up and increase by a factor of six to about 300 nT compared to normal values of the enhanced magnetic field at a comet. This increase is only partially accompanied by an increase in plasma density and energy, indicating that the magnetic field is connected to different regions of the coma.

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Multi-point observations of a reconnection outflow associated with interacting flux ropes in the solar wind

10.5194/egusphere-egu2020-8621 ◽

2020 ◽

Author(s):

Zoltan Vörös ◽

Emiliya Yordanova ◽

Owen Roberts ◽

Yasuhito Narita

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Flow Shear ◽

Magnetic Flux Ropes ◽

Interplanetary Coronal Mass Ejection ◽

Flux Ropes ◽

Magnetic Field Magnitude ◽

Field Fluctuations ◽

Mass Ejection ◽

The Magnetic Field

Twisted magnetic flux ropes embedded in an interplanetary coronal mass ejection (ICME) often contain oppositely oriented magnetic fields and potentially reconnecting current sheets. Reconnection outflows in the solar wind can be identified through magnetic field and plasma signatures, for example, through decreasing magnetic field magnitude, enhanced bulk velocity, temperature and (anti)correlated rotations of the magnetic field and plasma velocity. We investigate a reconnection outflow observed by ACE, WIND and Geotail spacecraft within the interaction region of two flux ropes embedded into an ICME. The SOHO spacecraft, located 15 RE upstream, 120 RE in GSE Y and 5 RE in GSE Z direction from the ACE spacecraft, does not see any plasma signatures of the reconnection outflow. At the same time the other spacecraft, also separated by more than 200 RE in X and Y GSE directions, observe strong plasma and magnetic field fluctuations at the border of the exhaust. &#160;The fluctuations could be associated with Kelvin-Helmholtz (KH) instability at the border of the reconnection outflow with strong flow shear.&#160; It is speculated that the KH instability driven fluctuations and dissipation is responsible for stopping the reconnection outflow which is therefore not seen by SOHO.

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Interinstrument calibration using magnetic field data from the flux-gate magnetometer (FGM) and electron drift instrument (EDI) onboard Cluster

Geoscientific Instrumentation Methods and Data Systems ◽

10.5194/gi-3-1-2014 ◽

2014 ◽

Vol 3 (1) ◽

pp. 1-11 ◽

Cited By ~ 13

Author(s):

R. Nakamura ◽

F. Plaschke ◽

R. Teubenbacher ◽

L. Giner ◽

W. Baumjohann ◽

...

Keyword(s):

Magnetic Field ◽

Field Data ◽

Spin Axis ◽

Electron Drift ◽

Magnetic Field Data ◽

Field Magnitude ◽

Magnetic Field Magnitude ◽

Flux Gate ◽

Axis Offset ◽

The Magnetic Field

Abstract. We compare the magnetic field data obtained from the flux-gate magnetometer (FGM) and the magnetic field data deduced from the gyration time of electrons measured by the electron drift instrument (EDI) onboard Cluster to determine the spin-axis offset of the FGM measurements. Data are used from orbits with their apogees in the magnetotail, when the magnetic field magnitude was between about 20 and 500 nT. Offset determination with the EDI–FGM comparison method is of particular interest for these orbits, because no data from solar wind are available in such orbits to apply the usual calibration methods using the Alfvén waves. In this paper, we examine the effects of the different measurement conditions, such as direction of the magnetic field relative to the spin plane and field magnitude in determining the FGM spin-axis offset, and also take into account the time-of-flight offset of the EDI measurements. It is shown that the method works best when the magnetic field magnitude is less than about 128 nT and when the magnetic field is aligned near the spin-axis direction. A remaining spin-axis offset of about 0.4 ∼ 0.6 nT was observed for Cluster 1 between July and October 2003. Using multipoint multi-instrument measurements by Cluster we further demonstrate the importance of the accurate determination of the spin-axis offset when estimating the magnetic field gradient.

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The relationship between the magnetic field in the Martian magnetotail and upstream solar wind parameters

Journal of Geophysical Research Atmospheres ◽

10.1029/94ja00946 ◽

1994 ◽

Vol 99 (A9) ◽

pp. 17199 ◽

Cited By ~ 5

Author(s):

H. Rosenbauer ◽

M. I. Verigin ◽

G. A. Kotova ◽

S. Livi ◽

A. P. Remizov ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Solar Wind Parameters ◽

Upstream Solar Wind ◽

The Relationship ◽

The Magnetic Field

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Statistical study of foreshock cavitons

Annales Geophysicae ◽

10.5194/angeo-31-2163-2013 ◽

2013 ◽

Vol 31 (12) ◽

pp. 2163-2178 ◽

Cited By ~ 14

Author(s):

P. Kajdič ◽

X. Blanco-Cano ◽

N. Omidi ◽

K. Meziane ◽

C. T. Russell ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Statistical Study ◽

Low Frequency ◽

Bow Shock ◽

Occurrence Rate ◽

Time Intervals ◽

Distinct Structure ◽

Wide Range ◽

The Magnetic Field

Abstract. In this work we perform a statistical analysis of 92 foreshock cavitons observed with the Cluster spacecraft 1 during the period 2001–2006. We analyze time intervals during which the spacecraft was located in the Earth's foreshock with durations longer than 10 min. Together these amount to ~ 50 days. The cavitons are transient structures in the Earth's foreshock. Their main signatures in the data include simultaneous depletions of the magnetic field intensity and plasma density, which are surrounded by a rim of enhanced values of these two quantities. Cavitons form due to nonlinear interaction of transverse and compressive ultra-low frequency (ULF) waves and are therefore always surrounded by intense compressive ULF fluctuations. They are carried by the solar wind towards the bow shock. This work represents the first systematic study of a large sample of foreshock cavitons. We find that cavitons appear for a wide range of solar wind and interplanetary magnetic field conditions and are therefore a common feature upstream of Earth's quasi-parallel bow shock with an average occurrence rate of ~ 2 events per day. We also discuss their observational properties in the context of other known upstream phenomena and show that the cavitons are a distinct structure in the foreshock.

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Steepening of magnetosonic waves in the inner coma of comet 67P/Churyumov–Gerasimenko

Annales Geophysicae ◽

10.5194/angeo-39-721-2021 ◽

2021 ◽

Vol 39 (4) ◽

pp. 721-742

Author(s):

Katharina Ostaszewski ◽

Karl-Heinz Glassmeier ◽

Charlotte Goetz ◽

Philip Heinisch ◽

Pierre Henri ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Interaction Region ◽

Occurrence Rate ◽

Solar Wind Interaction ◽

Background Magnetic Field ◽

The Waves ◽

Comet 67P ◽

The Magnetic Field ◽

Field Enhancements

Abstract. We present a statistical survey of large-amplitude, asymmetric plasma and magnetic field enhancements detected outside the diamagnetic cavity at comet 67P/Churyumov–Gerasimenko from December 2014 to June 2016. Based on the concurrent observations of plasma and magnetic field enhancements, we interpret them to be magnetosonic waves. The aim is to provide a general overview of these waves' properties over the mission duration. As the first mission of its kind, the ESA Rosetta mission was able to study the plasma properties of the inner coma for a prolonged time and during different stages of activity. This enables us to study the temporal evolution of these waves and their characteristics. In total, we identified ∼ 70 000 steepened waves in the magnetic field data by means of machine learning. We observe that the occurrence of these steepened waves is linked to the activity of the comet, where steepened waves are primarily observed at high outgassing rates. No clear indications of a relationship between the occurrence rate and solar wind conditions were found. The waves are found to propagate predominantly perpendicular to the background magnetic field, which indicates their compressional nature. Characteristics like amplitude, skewness, and width of the waves were extracted by fitting a skew normal distribution to the magnetic field magnitude of individual steepened waves. With increasing mass loading, the average amplitude of the waves decreases, while the skewness increases. Using a modified 1D magnetohydrodynamic (MHD) model, we investigated if the waves can be described by the combination of nonlinear and dissipative effects. By combining the model with observations of amplitude, width and skewness, we obtain an estimate of the effective plasma diffusivity in the comet–solar wind interaction region and compare it with suitable reference values as a consistency check. At 67P/Churyumov–Gerasimenko, these steepened waves are of particular importance as they dominate the innermost interaction region for intermediate to high activity.

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Inter-instrument calibration using magnetic field data from Flux Gate Magnetometer (FGM) and Electron Drift Instrument (EDI) onboard Cluster

Geoscientific Instrumentation Methods and Data Systems Discussions ◽

10.5194/gid-3-459-2013 ◽

2013 ◽

Vol 3 (2) ◽

pp. 459-487

Author(s):

R. Nakamura ◽

F. Plaschke ◽

R. Teubenbacher ◽

L. Giner ◽

W. Baumjohann ◽

...

Keyword(s):

Magnetic Field ◽

Field Data ◽

Spin Axis ◽

Electron Drift ◽

Magnetic Field Data ◽

Field Magnitude ◽

Magnetic Field Magnitude ◽

Flux Gate ◽

Axis Offset ◽

The Magnetic Field

Abstract. We compare the magnetic field data obtained from the Flux-Gate Magnetometer (FGM) and the magnetic field data deduced from the gyration time of electrons measured by the Electron Drift Instrument (EDI) onboard Cluster to determine the spin axis offset of the FGM measurements. Data are used from orbits with their apogees in the magnetotail, when the magnetic field magnitude was between about 20 nT and 500 nT. Offset determination with the EDI-FGM comparison method is of particular interest for these orbits, because no data from solar wind are available in such orbits to apply the usual calibration methods using the Alfvén waves. In this paper, we examine the effects of the different measurement conditions, such as direction of the magnetic field relative to the spin plane and field magnitude in determining the FGM spin-axis offset, and also take into account the time-of-flight offset of the EDI measurements. It is shown that the method works best when the magnetic field magnitude is less than about 128 nT and when the magnetic field is aligned near the spin-axis direction. A remaining spin-axis offset of about 0.4 ~ 0.6 nT was observed between July and October 2003. Using multi-point multi-instrument measurements by Cluster we further demonstrate the importance of the accurate determination of the spin-axis offset when estimating the magnetic field gradient.

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On the magnetic characteristics of magnetic holes in the solar wind between Mercury and Earth

10.5194/egusphere-egu2020-22 ◽

2020 ◽

Author(s):

Martin Volwerk ◽

Charlotte Goetz ◽

Ferdinand Plaschke ◽

Tomas Karlsson ◽

Daniel Heyner

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Occurrence Rate ◽

Magnetic Characteristics ◽

The Earth ◽

The Magnetic Field

The occurrence rate of linear and pseudo magnetic holes has been determined during MESSENGER&#8217;s cruise phase starting from Earth (2005) and arriving at Mercury (2011). It is shown that the occurrence rate of linear magnetic holes, defined as a maximum of 10&#226;&#151;&#166; rotation of the magnetic field over the hole, slowly decreases from Mercury to Earth. The pseudo magnetic holes, defined as a rotation between 10&#226;&#151;&#166; and 45&#226;&#151;&#166; over the hole, have mostly a constant occurrence rate, with a slight increas in front of the Earth and a decrease around the Earth. The width and depth of these structures seem to strongly differ depending on whether they are inside or outside of Venus&#8217;s orbit.

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