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.

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.

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 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.

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.

scholarly journals Characteristic study of double substorm onsets in response to IMF variations

2018 ◽  
Author(s):  
Ching-Chang Cheng ◽  
Christopher T. Russell ◽  
Ian R. Mann ◽  
Eric Donovan ◽  
Wolfgang Baumjohann
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Time History ◽  
Spectral Features ◽  
Onset Timing ◽  
Low Latitudes ◽  
History Of ◽  
Substorm Onsets ◽  
Two Stages

Abstract. A study of the characteristics of double substorm onsets in response to variations of the interplanetary magnetic field (IMF) is undertaken with magnetotail and ground observations by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission on 18 March 2009 and 3 April 2009 (Kp ~ 0), and on 16 February 2008 and 24 February 2010 (Kp ~ 2–3). During the time of interest, THEMIS probes at −8RE > XGSM > −20RE and 5RE > YGSM > −5RE observed earth-bound flow bursts accompanied by magnetic dipolarizations varying in two stages. The keograms and all sky images close to their footprints showed two consecutive auroral breakups of which the first appeared at lower latitudes than the second. The ground-based magnetometers sensed magnetic bays and perturbations resulting from the formation of substorm current wedge. Two consecutive pulsations in the Pi2-Ps6 band period occurred simultaneously from high to low and very low latitudes. They appeared in the same cycle of growth and then decline in Kyoto-AL. The onset timing of ground pulsations mapped to the solar wind observation just in front of Earth’s magnetopause shows their occurrence under an IMF variation cycle of north-to-south and then north. Their dynamic spectrums have the spectral features of double substorm onsets triggered by northward IMF turning. Hence in response to IMF variations, double substorm onsets can be characterized with two-stage magnetic dipolarizations in the magnetotail, two auroral breakups of which the first occurring at lower latitudes than the second, and two consecutive Pi2-Ps6 band pulsations.

scholarly journals Jets in the magnetosheath: IMF control of where they occur

2019 ◽  
Vol 37 (4) ◽  
pp. 689-697 ◽  
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 to 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 an 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, locations, and magnetopause impact rates of jets observed during different IMF orientations, allowing us to better forecast the formation of these jets and their impact on the magnetosphere.

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