scholarly journals Comment on Lockwood and Davis, "On the longitudinal extent of magnetopause reconnection pulses"

1999 ◽  
Vol 17 (2) ◽  
pp. 173-177 ◽  
Author(s):  
W. J. Heikkila
Keyword(s):  
Electric Field ◽  
Solar Wind Plasma ◽  
Closed Field ◽  
Transient Phenomena ◽  
Superposed Epoch Analysis ◽  
Dayside Magnetopause ◽  
Field Lines ◽  
Epoch Analysis ◽  
Definition Of ◽  
Magnetopause Reconnection

Abstract. Lockwood and Davis (1996) present a concise description of magnetopause reconnection pulses, with the claimed support of three types of observations: (1) flux transfer events (FTE), (2) poleward-moving auroral forms on the dayside, and (3) steps in cusp ion dispersion characteristics. However, there are a number of errors and misconceptions in the paper that make their conclusions untenable. They do not properly take account of the fact that the relevant processes operate in the presence of a plasma. They fail to notice that the source of energy (a dynamo with E · J<0) must be close to the region of dissipation (the electrical load with E · J>0) in transient phenomena, since energy (or information) cannot travel faster than the group velocity of waves in the medium (here the Alfvén velocity VA). In short, Lockwood and Davis use the wrong contour in their attempt to evaluate the electromotive force (emf). This criticism goes beyond their article: a dynamo is not included in the usual definition of reconnection, only the reconnection load. Without an explicit source of energy in the assumed model, the idea of magnetic reconnection is improperly posed. Recent research has carried out a superposed epoch analysis of conditions near the dayside magnetopause and has found the dynamo and the load, both within the magnetopause current sheet. Since the magnetopause current is from dawn to dusk, the sign of E · J reflects the sign of the electric field. The electric field reverses, within the magnetopause; this can be discovered by an application of Lenz's law using the concept of erosion of the magnetopause. The net result is plasma transfer across the magnetopause to feed the low latitude boundary layer, at least partly on closed field lines, and viscous interaction as the mechanism by which solar wind plasma couples to the magnetosphere.

scholarly journals A numerical model of the ionospheric signatures of time-varying magnetic reconnection: III. Quasi-instantaneous convection responses in the Cowley-Lockwood paradigm

2006 ◽  
Vol 24 (3) ◽  
pp. 961-972 ◽  
Author(s):  
S. K. Morley ◽  
M. Lockwood
Keyword(s):  
The Other ◽  
Closed Field ◽  
Time Varying ◽  
Residual Flow ◽  
Numerical Implementation ◽  
Ionospheric Convection ◽  
Dayside Magnetopause ◽  
History Of ◽  
Closed Field Line ◽  
Magnetopause Reconnection

Abstract. Using a numerical implementation of the cowlock92 model of flow excitation in the magnetosphere-ionosphere (MI) system, we show that both an expanding (on a ~12-min timescale) and a quasi-instantaneous response in ionospheric convection to the onset of magnetopause reconnection can be accommodated by the Cowley-Lockwood conceptual framework. This model has a key feature of time dependence, necessarily considering the history of the coupled MI system. We show that a residual flow, driven by prior magnetopause reconnection, can produce a quasi-instantaneous global ionospheric convection response; perturbations from an equilibrium state may also be present from tail reconnection, which will superpose constructively to give a similar effect. On the other hand, when the MI system is relatively free of pre-existing flow, we can most clearly see the expanding nature of the response. As the open-closed field line boundary will frequently be in motion from such prior reconnection (both at the dayside magnetopause and in the cross-tail current sheet), it is expected that there will usually be some level of combined response to dayside reconnection.

scholarly journals Statistical analysis of storm-time near-Earth current systems

2015 ◽  
Vol 33 (8) ◽  
pp. 965-982 ◽  
Author(s):  
M. W. Liemohn ◽  
R. M. Katus ◽  
R. Ilie
Keyword(s):  
Electric Field ◽  
Ring Current ◽  
Recovery Phase ◽  
Hot Electron ◽  
Early Recovery ◽  
Superposed Epoch Analysis ◽  
Tail Current ◽  
Near Earth Space ◽  
Epoch Analysis ◽  
Current Systems

Abstract. Currents from the Hot Electron and Ion Drift Integrator (HEIDI) inner magnetospheric model results for all of the 90 intense storms (disturbance storm-time (Dst) minimum < −100 nT) from solar cycle 23 (1996–2005) are calculated, presented, and analyzed. We have categorized these currents into the various systems that exist in near-Earth space, specifically the eastward and westward symmetric ring current, the partial ring current, the banana current, and the tail current. The current results from each run set are combined by a normalized superposed epoch analysis technique that scales the timeline of each phase of each storm before summing the results. It is found that there is a systematic ordering to the current systems, with the asymmetric current systems peaking during storm main phase (tail current rising first, then the banana current, followed by the partial ring current) and the symmetric current systems peaking during the early recovery phase (westward and eastward symmetric ring current having simultaneous maxima). The median and mean peak amplitudes for the current systems ranged from 1 to 3 MA, depending on the setup configuration used in HEIDI, except for the eastward symmetric ring current, for which the mean never exceeded 0.3 MA for any HEIDI setup. The self-consistent electric field description in HEIDI yielded larger tail and banana currents than the Volland–Stern electric field, while the partial and symmetric ring currents had similar peak values between the two applied electric field models.

Convection For Northward Interplanetary Field

1996 ◽  
Author(s):  
Charles F. Kennel
Keyword(s):  
Field Line ◽  
Dynamic Pressure ◽  
Field Conditions ◽  
Closed Field ◽  
Flow State ◽  
Dayside Magnetopause ◽  
Statistical Studies ◽  
Closed Field Line ◽  
Field Lines ◽  
Lobe Reconnection

Besides common sense, a number of results suggest that we can learn more about the slow “viscous” flow state by studying the magnetosphere during northward interplanetary field conditions. In particular, statistical studies have consistently identified a “residual” state of magnetospheric and ionospheric convection in northward field conditions. The integrated potential across the high latitudeionosphere does not drop below a certain resting value of about 20 kV even when the interplanetary field has been due north for several hours. There appears to be a similar residual component of geomagnetic activity that is independent of the direction of the interplanetary field (Scurry and Russell, 1991). Its correlation with the dynamic pressure of the solar wind strengthens our suspicion that it is related to viscosity. Will we be able to prove the convection in this residual state is driven by viscosity? Does the flow in northward field conditions resemble the underlying irregular flow state of the plasma sheet found at other times? Does the magnetosphere approach the teardrop configuration during prolonged intervals of northward interplanetary field? These are but a few of the questions that whet our interest in convection during northward field conditions. One does not arrive at the state of pure viscous convection immediately after the interplanetary field swings northward. Dungey (1963) was the first of many to argue that a northward magnetosheath field line will reconnect with an open tail lobe field line to create one that is connected to the ionosphere at one end and draped over the dayside magnetopause at the other. The sudden reconfiguration of stress will lead to sunward convection on the newly reconnected field lines. In the ionosphere, this superposes a “reverse” two-cell convection pattern in the central polar cap upon the two “direct” convection cells. If and when the draped reconnected field line finds a partner in the opposite tail lobe with which to reconnect, a newly closed field line will form. Dungey had imagined that the same magnetosheath field line would reconnect simultaneously with both tail lobes, in which case the rate at which open magnetic flux is closed depends upon the rate of tail-lobe reconnection.

Dependence of magnetopause reconnection events on interplanetary parameters

2020 ◽  
Author(s):  
Walter Gonzalez ◽  
Daiki Koga
Keyword(s):  
Solar Wind ◽  
Mach Number ◽  
Electric Field ◽  
Magnetic Reconnection ◽  
Flow Direction ◽  
Time History ◽  
Normal Vector ◽  
Dayside Magnetopause ◽  
Energy And Momentum ◽  
Magnetopause Reconnection

&lt;p&gt;Magnetic reconnection permits topological rearrangements of the interplanetary and magnetospheric magnetic fields and the entry of solar wind mass, energy, and momentum into the magnetosphere. Thus, magnetic reconnection is a key issue to understand space weather. However, it hasnot been fully understood yet under which interplanetary/magnetosheath conditions magnetic reconnection takes place more effectively at the dayside magnetopause. For this purpose,&amp;#160; in the present study 25 dayside magnetopause reconnection events are investigated using the Time History of Events and Macroscale Interactions during Substorms ( THEMIS ) spacecraft &amp;#160;observations. It was found, (1) that the reconnection electric field is proportional to the interplanetary electric field, (2) that the reconnection electric field is inversely proportional to the solar wind-Alfv&amp;#233;n Mach number, &amp;#160;(3) that thereconnection outflow speed is proportional to the solar wind Alfv&amp;#233;n speed, and (4) that the reconnection outflow speed is&amp;#160; inversely proportional to the magnetosheath plasma beta. Finally, it is shown that the range of magnetic shear angles for which magnetic reconnection should occur is restricted to large shears as the magnetosheath flow direction becomes more perpendicular to the direction of the local magnetopause normal vector. Since these results refer to fairly typical solar wind-Alfv&amp;#233;n Mach number condition, they may not apply to more extreme cases.&lt;/p&gt;

scholarly journals Predicted signatures of pulsed reconnection in ESR data

1996 ◽  
Vol 14 (12) ◽  
pp. 1246-1256 ◽  
Author(s):  
C. J. Davis ◽  
M. Lockwood
Keyword(s):  
Magnetic Field ◽  
Closed Field ◽  
Background Rate ◽  
Incoherent Scatter ◽  
Dayside Magnetopause ◽  
Cusp Conditions ◽  
Closed Field Line ◽  
Field Lines ◽  
The Magnetic Field ◽  
Open Magnetic Field

Abstract. Early in 1996, the latest of the European incoherent-scatter (EISCAT) radars came into operation on the Svalbard islands. The EISCAT Svalbard Radar (ESR) has been built in order to study the ionosphere in the northern polar cap and in particular, the dayside cusp. Conditions in the upper atmosphere in the cusp region are complex, with magnetosheath plasma cascading freely into the atmosphere along open magnetic field lines as a result of magnetic reconnection at the dayside magnetopause. A model has been developed to predict the effects of pulsed reconnection and the subsequent cusp precipitation in the ionosphere. Using this model we have successfully recreated some of the major features seen in photometer and satellite data within the cusp. In this paper, the work is extended to predict the signatures of pulsed reconnection in ESR data when the radar is pointed along the magnetic field. It is expected that enhancements in both electron concentration and electron temperature will be observed. Whether these enhancements are continuous in time or occur as a series of separate events is shown to depend critically on where the open/closed field-line boundary is with respect to the radar. This is shown to be particularly true when reconnection pulses are superposed on a steady background rate.

scholarly journals Investigation of the outer and inner low-latitude boundary layers

2001 ◽  
Vol 19 (9) ◽  
pp. 1065-1088 ◽  
Author(s):  
T. M. Bauer ◽  
R. A. Treumann ◽  
W. Baumjohann
Keyword(s):  
Boundary Layer ◽  
Solar Wind ◽  
Tangential Stress ◽  
Solar Wind Plasma ◽  
Alfven Wave ◽  
Bulk Velocity ◽  
Closed Field ◽  
Low Latitude ◽  
Field Lines ◽  
Low Latitude Boundary Layer

Abstract. We analyze 22 AMPTE/IRM crossings of the day-side low-latitude boundary layer for which a dense outer part can be distinguished from a dilute inner part. Whereas the plasma in the outer boundary layer (OBL) is dominated by solar wind particles, the partial densities of solar wind and magnetospheric particles are comparable in the inner boundary layer (IBL). For 11 events we find a reasonable agreement between observed plasma flows and those predicted by the tangential stress balance of an open magnetopause. Thus, we conclude that, at least in these cases, the OBL is formed by a local magnetic reconnection. The disagreement with the tangential stress balance in the other 11 cases might be due to reconnection being time-dependent and patchy. The north-south component of the proton bulk velocity in the boundary layer is, on average, directed toward high latitudes for both low and high magnetic shear across the magnetopause. This argues clearly against the possibility that the dayside low-latitude boundary layer is populated with solar wind plasma primarily from the cusps. "Warm", counterstreaming electrons that originate primarily from the magnetosheath and have a field-aligned temperature that is higher than the electron temperature in the magnetosheath by a factor of 1–5, are a characteristic feature of the IBL. Profiles of the proton bulk velocity and the density of hot ring current electrons provide evidence that the IBL is on closed field lines. Part of the IBL may be on newly opened field lines. Using the average spectra of electric and magnetic fluctuations in the boundary layer, we estimate the diffusion caused by lower hybrid drift instability, gyroresonant pitch angle scattering, or kinetic Alfvén wave turbulence. We find that cross-field diffusion cannot transport solar wind plasma into the OBL or IBL at a rate that would account for the thickness ( ~ 1000 km) of these sublayers. On the duskside, the dawn-dusk component of the proton bulk velocity in the IBL and magnetosphere is, on average, directed from the nightside toward local noon. Formation of the IBL may also be due to mechanisms operating in the magnetotail.Key words. Magnetospheric physics (magnetopause, cusp and boundary layer; magnetospheath)

scholarly journals Cusp observations during a sequence of fast IMF <I>B<sub>Z</sub></I> reversals

2009 ◽  
Vol 27 (7) ◽  
pp. 2721-2737 ◽  
Author(s):  
H. T. Cai ◽  
I. W. McCrea ◽  
M. W. Dunlop ◽  
J. A. Davies ◽  
Y. V. Bogdanova ◽  
...  
Keyword(s):  
Hf Radar ◽  
Closed Field ◽  
Radar Observations ◽  
Dayside Magnetopause ◽  
Low Latitudes ◽  
Closed Field Line ◽  
Polarity Reversals ◽  
Field Lines ◽  
Magnetospheric Cusp ◽  
The Imf

Abstract. In recent years, a large number of papers have reported the response of the cusp to solar wind variations under conditions of northward or southward Interplanetary Magnetic Field (IMF) Z-component (BZ). These studies have shown the importance of both temporal and spatial factors in determining the extent and morphology of the cusp and the changes in its location, connected to variations in the reconnection geometry. Here we present a comparative study of the cusp, focusing on an interval characterised by a series of rapid reversals in the BZ-dominated IMF, based on observations from space-borne and ground-based instrumentation. During this interval, from 08:00 to 12:00 UT on 12 February 2003, the IMF BZ component underwent four reversals, remaining for around 30 min in each orientation. The Cluster spacecraft were, at the time, on an outbound trajectory through the Northern Hemisphere magnetosphere, whilst the mainland VHF and Svalbard (ESR) radars of the EISCAT facility were operating in support of the Cluster mission. Both Cluster and the EISCAT were, on occasion during the interval, observing the cusp region. The series of IMF reversals resulted in a sequence of poleward and equatorward motions of the cusp; consequently Cluster crossed the high-altitude cusp twice before finally exiting the dayside magnetopause, both times under conditions of northward IMF BZ. The first magnetospheric cusp encounter, by all four Cluster spacecraft, showed reverse ion dispersion typical of lobe reconnection; subsequently, Cluster spacecraft 1 and 3 (only) crossed the cusp for a second time. We suggest that, during this second cusp crossing, these two spacecraft were likely to have been on newly closed field lines, which were first reconnected (opened) at low latitudes and later reconnected again (re-closed) poleward of the northern cusp. At ionospheric altitudes, the latitudinal excursions of the cusp/cleft region in response to the series of the IMF polarity changes were clearly captured by both the ESR and the Pykkvibaer radar of the SuperDARN HF network. The Open-Closed field-line Boundary (OCB) inferred from the HF radar observations underwent latitudinal variations in response to the IMF polarity changes that are in accordance with those predicted by Newell et al. (1989). Furthermore, variations in the ionospheric parameters yielded by the EISCAT VHF and ESR radars are basically consistent with inferences drawn from the HF radar observations. We conclude that Cluster spacecraft 1 and 3 crossed the cusp for a second time as a result of the latitudinal migration of the cusp in response to the IMF polarity reversals; at that time, however, the cusp lay poleward of spacecraft 4. Snapshots of the cusp from two DMSP satellite passes provide further support for this interpretation.

scholarly journals Saturn's polar ionospheric flows and their relation to the main auroral oval

2004 ◽  
Vol 22 (4) ◽  
pp. 1379-1394 ◽  
Author(s):  
S. W. H. Cowley ◽  
E. J. Bunce ◽  
R. Prangé
Keyword(s):  
Solar Wind ◽  
Open Field ◽  
Auroral Oval ◽  
Closed Field ◽  
Polar Cap ◽  
Space Telescope ◽  
Planetary Rotation ◽  
Dayside Magnetopause ◽  
Field Lines ◽  
Upward Current

Abstract. We consider the flows and currents in Saturn's polar ionosphere which are implied by a three-component picture of large-scale magnetospheric flow driven both by planetary rotation and the solar wind interaction. With increasing radial distance in the equatorial plane, these components consist of a region dominated by planetary rotation where planetary plasma sub-corotates on closed field lines, a surrounding region where planetary plasma is lost down the dusk tail by the stretching out of closed field lines followed by plasmoid formation and pinch-off, as first described for Jupiter by Vasyliunas, and an outer region driven by the interaction with the solar wind, specifically by reconnection at the dayside magnetopause and in the dawn tail, first discussed for Earth by Dungey. The sub-corotating flow on closed field lines in the dayside magnetosphere is constrained by Voyager plasma observations, showing that the plasma angular velocity falls to around half of rigid corotation in the outer magnetosphere, possibly increasing somewhat near the dayside magnetopause, while here we provide theoretical arguments which indicate that the flow should drop to considerably smaller values on open field lines in the polar cap. The implied ionospheric current system requires a four-ring pattern of field-aligned currents, with distributed downward currents on open field lines in the polar cap, a narrow ring of upward current near the boundary of open and closed field lines, and regions of distributed downward and upward current on closed field lines at lower latitudes associated with the transfer of angular momentum from the planetary atmosphere to the sub-corotating planetary magnetospheric plasma. Recent work has shown that the upward current associated with sub-corotation is not sufficiently intense to produce significant auroral acceleration and emission. Here we suggest that the observed auroral oval at Saturn instead corresponds to the ring of upward current bounding the region of open and closed field lines. Estimates indicate that auroras of brightness from a few kR to a few tens of kR can be produced by precipitating accelerated magnetospheric electrons of a few keV to a few tens of keV energy, if the current flows in a region which is sufficiently narrow, of the order of or less than ~1000 km (~1° latitude) wide. Arguments are also given which indicate that the auroras should typically be significantly brighter on the dawn side of the oval than at dusk, by roughly an order of magnitude, and should be displaced somewhat towards dawn by the down-tail outflow at dusk associated with the Vasyliunas cycle. Model estimates are found to be in good agreement with data derived from high quality images newly obtained using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, both in regard to physical parameters, as well as local time effects. The implication of this picture is that the form, position, and brightness of Saturn's main auroral oval provide remote diagnostics of the magnetospheric interaction with the solar wind, including dynamics associated with magnetopause and tail plasma interaction processes. Key words. Magnetospheric physics (auroral phenomena, magnetosphere-ionosphere interactions, solar windmagnetosphere interactions)

The Reconnecting Magnetosphere

1996 ◽  
Author(s):  
Charles F. Kennel
Keyword(s):  
Solar Wind ◽  
Neutral Line ◽  
Flow Region ◽  
Solar Wind Plasma ◽  
Closed Field ◽  
Solar Origin ◽  
Polar Caps ◽  
Slow Expansion ◽  
Convection Model ◽  
Field Lines

Dungey’s (1961a) pattern of internal magnetospheric convection was similar to that of Axford and Hines (1961). However, his model made testable statements about the structure of the magnetosphere that were not contained in the viscous convection model. It predicted that solar wind plasma enters the magnetosphere over the polar caps, that open field lines connect the polar caps directly to the interplanetary magnetic field, and that these field lines are stretched into a long, low-density magnetic tail. There would be a current layer separating the two lobes of the tail, and surrounding it, a sheet of relatively dense, hot, earthward-convecting plasma confined by closed field lines. A second magnetic neutral line would terminate the earthward flow region (Levy et al., 1964; Axford et al., 1965; Petschek, 1966; Axford, 1969). To preserve the steady state, reconnection at the tail neutral line had to have the same rate as at the dayside magnetopause. Clearly, the two reconnection regions ought to be major drivers of magnetospheric activity. Yet unambiguous proof of the existence of magnetopause reconnection was not found until 1979, 18 years after the reconnection model was proposed, and no one knew where to look for tail reconnection, because Dungey’s model did not say how far away the tail neutral line was. However, the closure of the slow expansion fans carrying solar wind plasma into the tail lobes was a natural way to force tail reconnection (Coroniti and Kennel, 1979). This closure point is fifty to one hundred earth radii downstream of earth. Twenty-four years were to pass before the average location of the tail neutral line could be established, because no spacecraft until ISEE-3 spent enough time that far downtail. In retrospect, it is a testament to the power of the paradigm that so many would search for so long for direct evidence of dayside and nightside reconnection without jettisoning Dungey’s model altogether. Faith in Dungey’s model was sustained by its collateral predictions. The access of energetic particles of solar origin to the polar cap ionosphere confirmed that reconnection occurs.

scholarly journals Evidence for impulsive solar wind plasma penetration through the dayside magnetopause

2003 ◽  
Vol 21 (2) ◽  
pp. 457-472 ◽  
Author(s):  
R. Lundin ◽  
J.-A. Sauvaud ◽  
H. Rème ◽  
A. Balogh ◽  
I. Dandouras ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Electric Fields ◽  
Solar Wind Plasma ◽  
Weak Current ◽  
Cluster Data ◽  
Dayside Magnetopause ◽  
Field Lines ◽  
Electric Fields And Currents ◽  
Transient Plasma

Abstract. This paper presents in situ observational evidence from the Cluster Ion Spectrometer (CIS) on Cluster of injected solar wind "plasma clouds" protruding into the day-side high-latitude magnetopause. The plasma clouds, presumably injected by a transient process through the day-side magnetopause, show characteristics implying a generation mechanism denoted impulsive penetration (Lemaire and Roth, 1978). The injected plasma clouds, hereafter termed "plasma transfer events", (PTEs), (Woch and Lundin, 1991), are temporal in nature and relatively limited in size. They are initially moving inward with a high velocity and a magnetic signature that makes them essentially indistinguishable from regular magnetosheath encounters. Once inside the magnetosphere, however, PTEs are more easily distinguished from magnetopause encounters. The PTEs may still be moving while embedded in an isotropic background of energetic trapped particles but, once inside the magnetosphere, they expand along magnetic field lines. However, they frequently have a significant transverse drift component as well. The drift is localised, thus constituting an excess momentum/motional emf generating electric fields and currents. The induced emf also acts locally, accelerating a pre-existing cold plasma (e.g. Sauvaud et al., 2001). Observations of PTE-signatures range from "active" (strong transverse flow, magnetic turbulence, electric current, local plasma acceleration) to "evanescent" (weak flow, weak current signature). PTEs appear to occur independently of Interplanetary Magnetic Field (IMF) Bz in the vicinity of the polar cusp region, which is consistent with observations of transient plasma injections observed with mid- and high-altitude satellites (e.g. Woch and Lundin, 1992; Stenuit et al., 2001). However the characteristics of PTEs in the magnetosphere boundary layer differ for southward and northward IMF. The Cluster data available up to now indicate that PTEs penetrate deeper into the magnetosphere for northward IMF than for southward IMF. This may or may not mark a difference in nature between PTEs observed for southward and northward IMF. Considering that flux transfer events (FTEs), (Russell and Elphic, 1979), are observed for southward IMF or when the IMF is oriented such that antiparallel merging may occur, it seems likely that PTEs observed for southward IMF are related to FTEs.Key words. Magnetospheric physics (magnetopause, cusp, and boundary layers; magnetosphere-ionosphere interactions; solar-wind magnetosphere interactions)

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