scholarly journals Magnetic holes in the solar wind between 0.3 AU and 17 AU

2000 ◽  
Vol 7 (3/4) ◽  
pp. 191-200 ◽  
Author(s):  
K. Sperveslage ◽  
F. M. Neubauer ◽  
K. Baumgärtel ◽  
N. F. Ness
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Heliocentric Distance ◽  
Occurrence Rate ◽  
Automatic Identification ◽  
Soliton Theory ◽  
Theoretical Approaches ◽  
Maximum Angle ◽  
Using Data ◽  
Initial Magnetic Field

Abstract. Magnetic holes (MHs) are depressions of the magnetic field magnitude. Turner et al. (1977) identified the first MHs in the solar wind and determined an occurrence rate of 1.5 MHs/d. Winterhalter et al. (1994) developed an automatic identification criterion to search for MHs in Ulysses data in the solar wind between 1 AU and 5.4 AU. We adopt their criterion to expand the search to the heliocentric distances down to 0.3 AU using data from Helios 1 and 2 and up to 17 AU using data from Voyager 2. We relate our observations to two theoretical approaches which describe the so-called linear MHs in which the magnetic vector varies in magnitude rather than direction. Therefore we focus on such linear MHs with a directional change less than 10º. With our observations of about 850 MHs we present the following results: Approximately 30% of all the identified MHs are linear. The maximum angle between the initial magnetic field vector and any vector inside the MH is 20º in average and shows a weak relation to the depth of the MHs. The angle between the initial magnetic field and the minimum variance direction of those structures is large and very probably close to 90º. The MHs are placed in a high β environment even though the average solar wind shows a smaller β. The widths decrease from about 50 proton inertial length in a region between 0.3 AU and 0.4 AU heliocentric distance to about 15 proton inertial length at distances larger than 10 AU. This quantity is correlated with the β of the MH environments with respect to the heliocentric distance. There is a clear preference for the occurrence of depressions instead of compressions. We discuss these results with regard to the main theories of MHs, the mirror instability and the alternative soliton approach. Although our observational results are more consistent with the soliton theory we favour a combination of both. MHs might be the remnants of initial mirror mode structures which can be described as solitons during the main part of their lifetime.

scholarly journals Automatic identification of magnetic clouds and cloud-like regions at 1 AU: occurrence rate and other properties

2005 ◽  
Vol 23 (7) ◽  
pp. 2687-2704 ◽  
Author(s):  
R. P. Lepping ◽  
C.-C. Wu ◽  
D. B. Berdichevsky
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Real Time ◽  
False Positives ◽  
Large Percentage ◽  
Occurrence Rate ◽  
Small Scale ◽  
Automatic Identification ◽  
Interplanetary Magnetic Fields ◽  
Interplanetary Physics

Abstract. A scheme is presented whose purpose is twofold: (1) to enable the automatic identification of an interplanetary magnetic cloud (MC) passing Earth from real-time measurements of solar wind magnetic field and plasma quantities or (2) for on-ground post-data collection MC identification ("detection" mode). In the real-time ("prediction") mode the scheme should be applicable to data from a spacecraft upstream of Earth, such as ACE, or to that of any near real-time field and plasma monitoring platform in the solar wind at/near 1AU. The initial identification of a candidate MC-complex is carried out by examining proton plasma beta, degree of small-scale smoothness of the magnetic field's directional change, duration of a candidate structure, thermal speed, and field strength. In a final stage, there is a test for large-scale B-field smoothness within the candidate regions that were identified in the first stage. The scheme was applied to WIND data over the period 1995 through mid-August of 2003 (i.e. over 8.6 years), in order to determine its effectiveness in identifying MC passages of any type (i.e. NS, SN, all S, all N, etc. types). (NS refers to the B component of the magnetic field going from north (+) to south (-) in GSE coordinates.) The distribution of these MC types for WIND is provided. The results of the scheme are compared to WIND MCs previously identified by visual inspection (called MFI MCs) with relatively good agreement, in the sense of capturing a large percentage of MFI MCs, but at the expense of finding a large percentage of "false positives". The scheme is shown to be able to find some previously ignored MCs among the false positives. It should be effective in helping to identify in real time most NS MCs for magnetic storm forecasting. The NS type of MC is expected to be most prevalent in solar cycle 24, which should start around 2007. The scheme is likely to be applicable to solar wind measurements taken well within 1 AU to well beyond it. Keywords. Interplanetary physics (Interplanetary magnetic fields; Solar wind plasma) – Magnetospheric physics (Solar wind-magnetosphere interactions)

scholarly journals The evolution of inverted magnetic fields through the inner heliosphere

2020 ◽  
Vol 494 (3) ◽  
pp. 3642-3655 ◽  
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.

scholarly journals Model for vortex turbulence with discontinuities in the solar wind

2003 ◽  
Vol 10 (4/5) ◽  
pp. 335-343 ◽  
Author(s):  
O. P. Verkhoglyadova ◽  
B. Dasgupta ◽  
B. T. Tsurutani
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
High Speed ◽  
Vector Fields ◽  
Field Vector ◽  
Theoretical Modelling ◽  
Occurrence Rate ◽  
Embedded Discontinuities ◽  
Magnetometer Data ◽  
Speed Solar Wind

Abstract. A model of vortex with embedded discontinuities in plasma flow is developed in the framework of ideal MHD in a low b plasma. Vortex structures are considered as a result of 2-D evolution of nonlinear shear Alfvén waves in the heliosphere. Physical properties of the solutions and vector fields are analyzed and the observational aspects of the model are discussed. The ratio of normal components to the discontinuity Br /Vr can be close to -2. The alignment between velocity and magnetic field vectors takes place. Spacecraft crossing such vortices will typically observe a pair of discontinuities, but with dissimilar properties. Occurrence rate for different discontinuity types is estimated and agrees with observations in high-speed solar wind stream. Discontinuity crossing provides a backward rotation of magnetic field vector and can be observed as part of a backward arc. The Ulysses magnetometer data obtained in the fast solar wind are compared with the results of theoretical modelling.

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

2010 ◽  
Vol 28 (9) ◽  
pp. 1695-1702 ◽  
Author(s):  
T. Xiao ◽  
Q. Q. Shi ◽  
T. L. Zhang ◽  
S. Y. Fu ◽  
L. Li ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Geometrical Structure ◽  
Occurrence Rate ◽  
Geometrical Shape ◽  
Magnetic Field Data ◽  
Magnetic Field Magnitude ◽  
The Relationship ◽  
Plasma Measurements ◽  
The Magnetic Field

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.

A Survey of Interplanetary Small Flux Ropes at Mercury

2020 ◽  
Author(s):  
Réka Winslow ◽  
Amy Murphy ◽  
Nathan Schwadron ◽  
Noé Lugaz ◽  
Wenyuan Yu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Current Sheet ◽  
Heliocentric Distance ◽  
Free Field ◽  
Flux Rope ◽  
Solar Wind Plasma ◽  
The Sun ◽  
Superposed Epoch Analysis ◽  
Flux Ropes

<p>Small flux ropes (SFRs) are interplanetary magnetic flux ropes with durations from a few minutes to a few hours. We have built a comprehensive catalog of SFRs at Mercury using magnetometer data from the orbital phase of the MESSENGER mission (2011-2015). In the absence of solar wind plasma measurements, we developed strict identification criteria for SFRs in the magnetometer observations, including conducting force-free field fits for each flux rope. We identified a total of 48 events that met our strict criteria, with events ranging in duration from 2.5 minutes to 4 hours. Using superposed epoch analysis, we obtained the generic SFR magnetic field profile at Mercury. Due to the large variation in Mercury's heliocentric distance (0.31-0.47 AU), we split the data into two distance bins. We found that the average SFR profile is more symmetric "farther from the Sun", in line with the idea that SFRs form closer to the Sun and undergo a relaxation process in the solar wind. Based on this result, as well as the SFR durations and the magnetic field strength fall-off with heliocentric distance, we infer that the SFRs observed at Mercury are expanding as they propagate with the solar wind. We also determined that the SFR occurrence frequency is nearly four times as high at Mercury as for similarly detected events at 1 AU. Most interestingly, we found two SFR populations in our dataset, one likely generated in a quasi-periodic formation process near the heliospheric current sheet, and the other formed away from the current sheet in isolated events.</p>

scholarly journals Whistler waves observed by Solar Orbiter during its first orbit

2021 ◽  
Author(s):  
Matthieu Kretschmar ◽  
Thomas Chust ◽  
Daniel Graham ◽  
Volodya Krasnosekskikh ◽  
Lucas Colomban ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Electromagnetic Waves ◽  
Heliocentric Distance ◽  
Plasma Waves ◽  
Distribution Functions ◽  
The Sun ◽  
Whistler Waves ◽  
Velocity Distribution Functions ◽  
The Waves

<p>Plasma waves can play an important role in the evolution of the solar wind and the particle velocity distribution functions in particular. We analyzed the electromagnetic waves observed above a few Hz by the Radio Plasma Waves (RPW) instrument suite onboard Solar Orbiter, during its first orbit, which covered a distance from the Sun between 1 AU and 0.5 AU.  We identified the majority of the detected waves as whistler waves with frequency around  0.1 f_ce and right handed circular polarisation. We found these waves to be mostly aligned or anti aligned with the ambient magnetic field, and rarely oblique. We also present and discuss their direction of propagation and the variation of the waves' properties with heliocentric distance.</p>

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

2019 ◽  
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.

scholarly journals Statistical study of foreshock cavitons

2013 ◽  
Vol 31 (12) ◽  
pp. 2163-2178 ◽  
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.

scholarly journals Galactic Cosmic Ray Variability at Two Neutron Monitors: Relation to Kp Index

2015 ◽  
Vol 2015 ◽  
pp. 1-5 ◽  
Author(s):  
Kingsley Chukwudi Okpala
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar Activity ◽  
Cosmic Ray ◽  
Neutron Monitors ◽  
Flow Pressure ◽  
The Difference ◽  
Using Data ◽  
Galactic Cosmic Ray ◽  
Present Understanding

The average characteristics of year-to-year variability of Galactic cosmic ray (GCR) flux measured in one mid-latitude neutron monitor stations (Newark) and high latitude station (Apatity) have been studied under different planetary disturbance (Kp) conditions. The year-to-year variability which oscillates in response to solar cycle was analyzed using Fourier technique and the amplitude of variation was obtained using data for 1980–2005. There is a noticeable trend in the difference between the amplitudes of the year-to-year variation of the two stations. The difference is highest during low Kp conditions and lowest during high Kp condition. There is generally lesser association of GCR with solar wind (SW) flow pressure and density as the Kp index increases. Similar feature is observed with the interplanetary magnetic field IMF (total). These observations have important implications for our present understanding of the effect of solar activity to variability in GCR flux.

scholarly journals Occurrence rate of ultra-low frequency waves in the foreshock of Mercury increases with heliocentric distance

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
N. Romanelli ◽  
G. A. DiBraccio
Keyword(s):  
Solar Wind ◽  
Heliocentric Distance ◽  
Low Frequency ◽  
Occurrence Rate ◽  
Eccentric Orbit ◽  
Low Intensity ◽  
Magnetometer Data ◽  
Favorable Conditions ◽  
Open Question ◽  
Low Frequency Waves

AbstractStudies of Mercury’s foreshock have analyzed in detail the properties of ultra-low frequency waves. However, an open question remains in regards to understanding favorable conditions for these planetary foreshocks waves. Here, we report that 0.05–0.41 Hz quasi-monochromatic waves are mostly present under quasi-radial and relatively low intensity Interplanetary Magnetic Field, based on 17 Mercury years of MESSENGER Magnetometer data. These conditions are consistent with larger foreshock size and reflection of solar wind protons, their most likely source. Consequently, we find that the wave occurrence rate increases with Mercury’s heliocentric distance. Detection of these waves throughout Mercury’s highly eccentric orbit suggests the conditions for backstreaming protons are potentially present for all of Mercury’s heliocentric distances, despite the relatively low solar wind Alfvén Mach number regime. These results are relevant for planetary magnetospheres throughout the solar system, and the magnetospheres of exoplanets, and provide knowledge of particle acceleration mechanisms occurring inside foreshocks.

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