scholarly journals Multipoint spacecraft observations of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere on 1–2 May 2014

2016 ◽  
Vol 34 (11) ◽  
pp. 985-998 ◽  
Author(s):  
Galina Korotova ◽  
David Sibeck ◽  
Mark Engebretson ◽  
John Wygant ◽  
Scott Thaller ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Time History ◽  
Satellite System ◽  
Local Times ◽  
Spectral Structure ◽  
Nodal Structure ◽  
Van Allen Probes ◽  
History Of ◽  
Solar Wind Parameters ◽  
The Magnetic Field

Abstract. We use magnetic field and plasma observations from the Van Allen Probes, Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Geostationary Operational Environmental Satellite system (GOES) spacecraft to study the spatial and temporal characteristics of long-lasting poloidal Pc4 pulsations in the dayside magnetosphere. The pulsations were observed after the main phase of a moderate storm during low geomagnetic activity. The pulsations occurred during various interplanetary conditions and the solar wind parameters do not seem to control the occurrence of the pulsations. The most striking feature of the Pc4 magnetic field pulsations was their occurrence at similar locations during three of four successive orbits. We used this information to study the latitudinal nodal structure of the pulsations and demonstrated that the latitudinal extent of the magnetic field pulsations did not exceed 2 Earth radii (RE). A phase shift between the azimuthal and radial components of the electric and magnetic fields was observed from ZSM  =  0.30 RE to ZSM  =  −0.16 RE. We used magnetic and electric field data from Van Allen Probes to determine the structure of ULF waves. We showed that the Pc4 magnetic field pulsations were radially polarized and are the second-mode harmonic waves. We suggest that the spacecraft were near a magnetic field null during the second orbit when they failed to observe the magnetic field pulsations at the local times where pulsations were observed on previous and successive orbits. We investigated the spectral structure of the Pc4 pulsations. Each spacecraft observed a decrease of the dominant period as it moved to a smaller L shell (stronger magnetic field strength). We demonstrated that higher frequencies occurred at times and locations where Alfvén velocities were greater, i.e., on Orbit 1. There is some evidence that the periods of the pulsations increased during the plasmasphere refilling following the storm.

Magnetic field within magnetosheath jets during northward and southward interplanetary magnetic field conditions

2020 ◽  
Author(s):  
Laura Vuorinen ◽  
Heli Hietala ◽  
Ferdinand Plaschke
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Dynamic Pressure ◽  
Time History ◽  
Magnetic Shear ◽  
History Of ◽  
High Dynamic ◽  
The Magnetic Field ◽  
Magnetopause Reconnection

<p>Downstream of the Earth's quasi-parallel shock, transients with higher earthward velocities than the surrounding magnetosheath plasma are often observed. These transients have been named magnetosheath jets. Due to their high dynamic pressure, jets can cause multiple types of effects when colliding into the magnetopause. Recently, jets have been linked to triggering magnetopause reconnection in case studies by Hietala et al. (2018) and Nykyri et al. (2019). Jets have been proposed to affect magnetopause reconnection in multiple ways. Jets can compress the magnetopause and make it thin enough for reconnection to occur. Jets could also affect the magnetic shear either by indenting the magnetopause or via the magnetic field of the jets themselves. Here we want to study whether the magnetic field of jets can statistically affect magnetopause reconnection. In particular, we are interested in whether jets could enhance reconnection during more quiet northward IMF conditions.</p><p>We statistically study the magnetic field within jets in the subsolar magnetosheath using measurements from the five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and OMNI solar wind data from 2008–2011. We investigate jets next to the magnetopause and find that the magnetic field within jets is statistically different compared to the non-jet magnetosheath. Our results suggest that during southward IMF, the non-jet magnetosheath magnetic field itself has more variation than the jets. This suggests that jets should have no statistical, neither enhancing nor suppressing, effect on reconnection during southward IMF. However, during northward IMF, the magnetic field within jets is statistically favorable for enhancing magnetic reconnection at the subsolar magnetopause as around 70 % of these jets exhibit southward fields close to the magnetopause.</p>

scholarly journals Plasma transport into the duskside magnetopause caused by Kelvin–Helmholtz vortices in response to the northward turning of the interplanetary magnetic field observed by THEMIS

2019 ◽  
Author(s):  
Guang Qing Yan ◽  
George K. Parks ◽  
Chun Lin Cai ◽  
Tao Chen ◽  
James P. McFadden ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Boundary Layer ◽  
Interplanetary Magnetic Field ◽  
Time History ◽  
Plasma Transport ◽  
Low Latitude ◽  
Unique Event ◽  
History Of ◽  
The Magnetic Field ◽  
Low Latitude Boundary Layer

Abstract. A train of Kelvin–Helmholtz (K–H) vortices with plasma transport across the magnetopause has been observed by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) when the interplanetary magnetic field (IMF) abruptly turns northward. This unique event occurred without pre-existing denser boundary layer to facilitate the instability. Two THEMIS spacecraft, TH-A and TH-E, separated by 3 Re, periodically encountered the duskside magnetopause and the low-latitude boundary layer (LLBL) with a period of 2 minutes and tailward propagation of 194 km/s. There was no high-velocity low-density feature, but the rotations in the bulk velocity observation, distorted magnetopause with plasma parameter fluctuations and the magnetic field line stretching, indicate the formation of rolled-up K–H vortices at the duskside magnetopause. A mixture of magnetosheath ions with magnetospheric ions and enhanced energy flux of hot electrons is identified in the K–H vortices. This mixture region appears more periodic at the upstream spacecraft and more dispersive at the downstream location, indicating a significant transport can occur and evolve during the tailward propagation of the K–H waves. There is still much work to fully understand the Kelvin–Helmholtz mechanism. The observations of direct response to the northward turning of the IMF, the unambiguous plasma transport within the vortices, involving both ion and electron fluxes can provide additional clues to the K–H mechanism.

scholarly journals Plasma transport into the duskside magnetopause caused by Kelvin–Helmholtz vortices in response to the northward turning of the interplanetary magnetic field observed by THEMIS

2020 ◽  
Vol 38 (1) ◽  
pp. 263-273
Author(s):  
Guang Qing Yan ◽  
George K. Parks ◽  
Chun Lin Cai ◽  
Tao Chen ◽  
James P. McFadden ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Time History ◽  
Plasma Transport ◽  
Downstream Location ◽  
Low Latitude ◽  
Unique Event ◽  
History Of ◽  
The Magnetic Field ◽  
Low Latitude Boundary Layer

Abstract. A train of likely Kelvin–Helmholtz (K–H) vortices with plasma transport across the magnetopause has been observed by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) at the duskside of the magnetopause. This unique event occurs when the interplanetary magnetic field (IMF) abruptly turns northward, which is the immediate change to facilitate the K–H instability. Two THEMIS spacecraft, TH-A and TH-E, separated by 3 RE, periodically encountered the duskside magnetopause and the low-latitude boundary layer (LLBL) with a period of 2 min and tailward propagation of 212 km s−1. Despite surface waves also explaining some of the observations, the rotations in the bulk velocity observation, a distorted magnetopause with plasma parameter fluctuations and the magnetic field perturbations, as well as a high-velocity low-density feature indicate the possible formation of rolled-up K–H vortices at the duskside of the magnetopause. The coexistence of magnetosheath ions with magnetospheric ions and enhanced energy flux of hot electrons is identified in the K–H vortices. These transport regions appear more periodic at the upstream spacecraft and more dispersive at the downstream location, indicating significant transport can occur and evolve during the tailward propagation of the K–H waves. There is still much work to do to fully understand the Kelvin–Helmholtz mechanism. The observations of the direct response to the northward turning of the IMF, the possible evidence of plasma transport within the vortices, involving both ion and electron fluxes, can provide additional clues as to the K–H mechanism.

Time-dependent motions of the cavity formed when a uniform corpuscular flux is incident on the magnetic field of a line current

1968 ◽  
Vol 2 (1) ◽  
pp. 51-57 ◽  
Author(s):  
R. C. Hewson-Browne ◽  
D. N. Burghes
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Time History ◽  
Time Dependent ◽  
Two Dimensional ◽  
Dimensional Problem ◽  
Line Current ◽  
History Of ◽  
Steady State Solutions ◽  
The Magnetic Field

This paper concerns the time-dependent motions of the cavity formed when a uniform corpuscular flux is incident on the magnetic field of a line current. The two-dimensional problem is formulated and solved with two particular classes of solutions being given; namely, the steady-state solutions and the time-history of the interaction with a cloud of flux.

scholarly journals Jets in the Magnetosheath: IMF Control of Where They Occur

2019 ◽  
Author(s):  
Laura Vuorinen ◽  
Heli Hietala ◽  
Ferdinand Plaschke
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Spatial Distribution ◽  
Interplanetary Magnetic Field ◽  
Cone Angle ◽  
Time History ◽  
Bow Shock ◽  
The Earth ◽  
Parallel Side ◽  
History Of

Abstract. Magnetosheath jets are localized regions of plasma that move faster towards the Earth than the surrounding magnetosheath plasma. Due to their high velocities, they can cause indentations when colliding into the magnetopause and trigger processes such as magnetic reconnection and magnetopause surface waves. We statistically study the occurrence of these jets in the subsolar magnetosheath using measurements from the five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and OMNI solar wind data from 2008–2011. We present the observations in the BIMF-vSW plane and study the spatial distribution of jets during different interplanetary magnetic field (IMF) orientations. Jets occur downstream of the quasi-parallel bow shock approximately 9 times as often as downstream of the quasi-perpendicular shock, suggesting that foreshock processes are responsible for most jets. For oblique IMF, with 30°–60° cone angle, the occurrence increases monotonically from the quasi-perpendicular side to the quasi-parallel side. This study offers predictability for the numbers and locations of jets observed during different IMF orientations allowing us to better forecast the formation of these jets and their impact on the magnetosphere.

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

1994 ◽  
Vol 99 (A9) ◽  
pp. 17199 ◽  
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

scholarly journals The Evolution of the Magnetic Fields of Neutron Stars

1992 ◽  
Vol 128 ◽  
pp. 26-34
Author(s):  
Dipankar Bhattacharya
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Theoretical Models ◽  
Radio Pulsars ◽  
Secular Evolution ◽  
History Of ◽  
Field Decay ◽  
The Magnetic Field

AbstractThe evolution of the magnetic field strength plays a major role in the life history of a neutron star. In this article the observational evidence of field evolution, in particular that of field decay and magnetic alignment, are critically examined. It is concluded that the observed decay of the spindown torque on radio pulsars cannot be caused by a secular evolution of the “obliqueness” of the neutron star, as suggested by some authors. Recent observations provide a strong indication that the decay of the magnetic field strength of a neutron star may be closely related to its evolution in a binary system. Theoretical models for such an evolution are discussed.

scholarly journals Revisiting the magnetization of comet 67P/Churyumov-Gerasimenko

2019 ◽  
Vol 630 ◽  
pp. A46 ◽  
Author(s):  
P. Heinisch ◽  
H.-U. Auster ◽  
I. Richter ◽  
K. H. Glassmeier
Keyword(s):  
Magnetic Field ◽  
Magnetic Measurements ◽  
Field Observations ◽  
Upper Limit ◽  
Background Magnetic Field ◽  
Surface Magnetization ◽  
Cometary Material ◽  
History Of ◽  
Comet 67P ◽  
The Magnetic Field

Context. The landing of the Philae probe as part of the ESA Rosetta mission made it possible to study the magnetization of comet 67P/Churyumov-Gerasimenko (67P) by combining observations from the lander and orbiter. In this work, we revisit the magnetic properties with information gained during the progression of the mission for a comprehensive understanding of the circumstances of Philae’s descent and landing. Aims. The aim is to derive a limit for any possible magnetization of the cometary material on the surface of 67P. To achieve this, the surface contacts of Philae were analyzed. Combined with a more detailed understanding of the background magnetic field, this allows us to interpret the underlying magnetic measurements in detail. Methods. We combined magnetic field observations from the ROMAP magnetometer on board Philae with observations from the RPC-MAG instrument on board the Rosetta orbiter. To facilitate this, a correlation analysis was used to correct phase shifts between the observed signals. Additionally, in-flight calibration of the ROMAP offsets was performed using information about the dynamics of Philae during flight. These corrections made it possible to use the orbiter measurements as reference for the comet-based Philae observations. We assumed a simple dipole model and used the magnetic field observations to derive an upper limit for the magnetization of the cometary material. Results. An upper limit of 0.9 nT for the observed magnetic field on the surface of 67P was derived for any contribution from surface magnetization. For homogeneously magnetized pebbles with a size of typical aggregates in the range of ~5 cm, this translates into an upper limit of ~5 × 10−5 Am2 kg−1 for the specific magnetic moment. Depending on the exact history of formation, this results in an upper limit of 4 μT for the magnitude of the magnetic field in the solar nebula during the formation of comet 67P.

scholarly journals A comparison between FUV remote sensing of magnetotail stretching and the T01 model during quiet conditions and growth phases

2007 ◽  
Vol 25 (1) ◽  
pp. 161-170 ◽  
Author(s):  
C. Blockx ◽  
J.-C. Gérard ◽  
V. Coumans ◽  
B. Hubert ◽  
M. Meurant
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Line ◽  
Time History ◽  
Field Configuration ◽  
Growth Phases ◽  
Theoretical Position ◽  
Proton Precipitation ◽  
Field Lines ◽  
The Magnetic Field

Abstract. In a previous study, Blockx et al. (2005) showed that the SI12 camera on board the IMAGE spacecraft is an excellent tool to remotely determine the position of the isotropy boundary (IB) in the ionosphere, and thus is able to provide a reasonable estimate of the amount of stretching of the magnetic field lines in the magetotail. By combining an empirical model of the magnetospheric configuration with Sergeev's criterion for non-adiabatic motion, it is also possible to obtain a theoretical position of IB in the ionosphere, for known conditions in the solar wind. Earlier studies have demonstrated the inadequacy of the Tsyganenko-1989 (T89) model to quantitatively reproduce the field line stretching, particularly during growth phases. In this study, we reexamine this question using the T01 model which considers the time history of the solar wind parameters. We compare the latitude of IB derived from SI12 global images near local midnight with that calculated from the T01 model and the Sergeev's criterion. Observational and theoretical results are found to frequently disagree. We use in situ measurements of the magnetic field with the GOES-8 satellite to discriminate which of the two components in the calculation of the theoretical position of the IB (the T01 model or Sergeev's criterion) induces the discrepancy. For very quiet magnetic conditions, we find that statistically the T01 model approximately predicts the correct location of the maximum proton precipitation. However, large discrepancies are observed in individual cases, as demonstrated by the large scatter of predicted latitudes. For larger values of the AE index, the model fails to predict the observed latitude of the maximum proton intensity, as a consequence of the lack of consideration of the cross-tail current component which produces a more elongated field configuration at the location of the proton injection along the field lines. We show that it is possible to match the observed location of the maximum proton precipitation by decreasing the current sheet half-thickness D parameter. We thus conclude that underestimation of the field line stretching leads to inadequately prediction of the boundary latitude of the non-adiabatic proton precipitation region.

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