scholarly journals Plasma convection in the magnetotail lobes: statistical results from Cluster EDI measurements

2008 ◽  
Vol 26 (8) ◽  
pp. 2371-2382 ◽  
Author(s):  
S. Haaland ◽  
G. Paschmann ◽  
M. Förster ◽  
J. Quinn ◽  
R. Torbert ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Geomagnetic Disturbance ◽  
Plasma Convection ◽  
Data Set ◽  
Central Plasma ◽  
Strong Convection ◽  
Central Plasma Sheet ◽  
Field Lines ◽  
Convection Patterns

Abstract. A major part of the plasma in the Earth's magnetotail is populated through transport of plasma from the solar wind via the magnetotail lobes. In this paper, we present a statistical study of plasma convection in the lobes for different directions of the interplanetary magnetic field and for different geomagnetic disturbance levels. The data set used in this study consists of roughly 340 000 one-minute vector measurements of the plasma convection from the Cluster Electron Drift Instrument (EDI) obtained during the period February 2001 to June 2007. The results show that both convection magnitude and direction are largely controlled by the interplanetary magnetic field (IMF). For a southward IMF, there is a strong convection towards the central plasma sheet with convection velocities around 10 km s−1. During periods of northward IMF, the lobe convection is almost stagnant. A By dominated IMF causes a rotation of the convection patterns in the tail with an oppositely directed dawn-dusk component of the convection for the northern and southern lobe. Our results also show that there is an overall persistent duskward component, which is most likely a result of conductivity gradients in the footpoints of the magnetic field lines in the ionosphere.

scholarly journals Measuring the dayside reconnection rate during an interval of due northward interplanetary magnetic field

2004 ◽  
Vol 22 (12) ◽  
pp. 4243-4258 ◽  
Author(s):  
G. Chisham ◽  
M. P. Freeman ◽  
I. J. Coleman ◽  
M. Pinnock ◽  
M. R. Hairston ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Interplanetary Magnetic Field ◽  
Line Length ◽  
Hf Radar ◽  
Plasma Convection ◽  
Ionosphere Plasma ◽  
Reconnection Region ◽  
Field Lines ◽  
First Time

Abstract. This study presents, for the first time, detailed spatiotemporal measurements of the reconnection electric field in the Northern Hemisphere ionosphere during an extended interval of northward interplanetary magnetic field. Global convection mapping using the SuperDARN HF radar network provides global estimates of the convection electric field in the northern polar ionosphere. These are combined with measurements of the ionospheric footprint of the reconnection X-line to determine the spatiotemporal variation of the reconnection electric field along the whole X-line. The shape of the spatial variation is stable throughout the interval, although its magnitude does change with time. Consequently, the total reconnection potential along the X-line is temporally variable but its typical magnitude is consistent with the cross-polar cap potential measured by low-altitude satellite overpasses. The reconnection measurements are mapped out from the ionosphere along Tsyganenko model magnetic field lines to determine the most likely reconnection location on the lobe magnetopause. The X-line length on the lobe magnetopause is estimated to be ~6–11 RE in extent, depending on the assumptions made when determining the length of the ionospheric X-line. The reconnection electric field on the lobe magnetopause is estimated to be ~0.2mV/m in the peak reconnection region. Key words. Space plasma physics (Magnetic reconnection) – Magnetospheric physics (Magnetopause, cusp and boundary layers) – Ionosphere (Plasma convection)

scholarly journals Transpolar aurora: time evolution, associated convection patterns, and a possible cause

2005 ◽  
Vol 23 (5) ◽  
pp. 1917-1930 ◽  
Author(s):  
L. G. Blomberg ◽  
J. A. Cumnock ◽  
I. I. Alexeev ◽  
E. S. Belenkaya ◽  
S. Yu. Bobrovnikov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electric Fields ◽  
Auroral Oval ◽  
Plasma Convection ◽  
Ionosphere Plasma ◽  
Auroral Electrons ◽  
Field Lines ◽  
Convection Patterns ◽  
Auroral Emissions ◽  
Set Up

Abstract. We present two event studies illustrating the detailed relationships between plasma convection, field-aligned currents, and polar auroral emissions, as well as illustrating the influence of the Interplanetary Magnetic Field's y-component on theta aurora development. The transpolar arc of the theta aurorae moves across the entire polar region and becomes part of the opposite side of the auroral oval. Electric and magnetic field and precipitating particle data are provided by DMSP, while the POLAR UVI instrument provides measurements of auroral emissions. Ionospheric electrostatic potential patterns are calculated at different times during the evolution of the theta aurora using the KTH model. These model patterns are compared to the convection predicted by mapping the magnetopause electric field to the ionosphere using the Paraboloid Model of the magnetosphere. The model predicts that parallel electric fields are set up along the magnetic field lines projecting to the transpolar aurora. Their possible role in the acceleration of the auroral electrons is discussed. Keywords. Ionosphere (Plasma convection; Polar ionosphere) – Magnetospheric physics (Magnetosphereionosphere interactions)

scholarly journals Multi-scale observations of magnetotail flux transport during IMF-northward non-substorm intervals

2007 ◽  
Vol 25 (7) ◽  
pp. 1709-1720 ◽  
Author(s):  
A. Grocott ◽  
T. K. Yeoman ◽  
S. E. Milan ◽  
O. Amm ◽  
H. U. Frey ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Plasma Sheet ◽  
Plasma Convection ◽  
Flux Transport ◽  
Multi Scale ◽  
Central Plasma ◽  
Central Plasma Sheet ◽  
Field Lines

Abstract. Simultaneous observations by the Cluster spacecraft and SuperDARN radars are presented of magnetotail flux transport during northward, but BY-dominated IMF. Two events are discussed, which occurred on 14 August 2004 and 17 September 2005, during intervals of negative and positive IMF BY, respectively. During both intervals the Cluster spacecraft observed isolated bursts of Earthward plasma convection in the central plasma sheet. During the first event, the flows observed by Cluster also had a significant V⊥Y component in the duskward direction, consistent with westward azimuthal flows observed in the midnight sector by the Northern Hemisphere SuperDARN radars. During the second event, Cluster 4 observed a significant dawnward V⊥Y component, again consistent with the Northern Hemisphere SuperDARN observations which revealed eastward azimuthal flow. In this instance, however, Cluster 3 observed a duskward V⊥Y component which was more consistent with the duskward sense of the convection observed by the Southern Hemisphere SuperDARN radars. This implies that Cluster 3 and Cluster 4 were located on different field lines which experienced opposite net azimuthal forces and hence observed oppositely directed convection. These observations are consistent with previous SuperDARN studies of nightside flows under northward IMF and, more importantly, provide the first simultaneous in-situ evidence for a mode of tail reconnection occurring during non-substorm intervals in an asymmetric tail.

scholarly journals Central polar cap convection response to short duration southward Interplanetary Magnetic Field

2000 ◽  
Vol 18 (8) ◽  
pp. 887-896 ◽  
Author(s):  
P. T. Jayachandran ◽  
J. W. MacDougall
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Short Duration ◽  
Initial Response ◽  
Plasma Convection ◽  
Polar Cap ◽  
Ionosphere Plasma ◽  
Rapid Transition ◽  
Convection Speed ◽  
A Chain

Abstract. Central polar cap convection changes associated with southward turnings of the Interplanetary Magnetic Field (IMF) are studied using a chain of Canadian Advanced Digital Ionosondes (CADI) in the northern polar cap. A study of 32 short duration (~1 h) southward IMF transition events found a three stage response: (1) initial response to a southward transition is near simultaneous for the entire polar cap; (2) the peak of the convection speed (attributed to the maximum merging electric field) propagates poleward from the ionospheric footprint of the merging region; and (3) if the change in IMF is rapid enough, then a step in convection appears to start at the cusp and then propagates antisunward over the polar cap with the velocity of the maximum convection. On the nightside, a substorm onset is observed at about the time when the step increase in convection (associated with the rapid transition of IMF) arrives at the polar cap boundary.Key words: Ionosphere (plasma convection; polar ionosphere) - Magnetospheric physics (solar wind - magnetosphere interaction)

scholarly journals Magnetopause energy transfer dependence on the interplanetary magnetic field and the Earth's magnetic dipole axis orientation

2012 ◽  
Vol 30 (3) ◽  
pp. 515-526 ◽  
Author(s):  
M. Palmroth ◽  
R. C. Fear ◽  
I. Honkonen
Keyword(s):  
Magnetic Field ◽  
Energy Transfer ◽  
Interplanetary Magnetic Field ◽  
Large Data ◽  
Seasonal Effect ◽  
Dipole Orientation ◽  
Data Set ◽  
Axis Orientation ◽  
Simulation Results ◽  
The Imf

Abstract. We examine the spatial variation of magnetospheric energy transfer using a global magnetohydrodynamic (MHD) simulation (GUMICS-4) and a large data set of flux transfer events (FTEs) observed by the Cluster spacecraft. Our main purpose is to investigate whether it is possible to validate previous results on the spatial energy transfer variation from the GUMICS-4 simulation using the statistical occurrence of FTEs, which are manifestations of magnetospheric energy transfer. Previous simulation results have suggested that the energy transfer pattern at the magnetopause rotates according to the interplanetary magnetic field (IMF) orientation, and here we investigate whether a similar rotation is seen in the locations at which FTE signatures are observed. We find that there is qualitative agreement between the simulation and observed statistics, as the peaks in both distributions rotate as a function of the IMF clock angle. However, it is necessary to take into account the modulation of the statistical distribution that is caused by a bias towards in situ FTE signatures being observed in the winter hemisphere (an effect that has previously been predicted and observed in this data set). Taking this seasonal effect into account, the FTE locations support the previous simulation results and confirm the earlier prediction that the energy transfers in the plane of the IMF. In addition, we investigate the effect of the dipole orientation (both the dipole tilt angle and its orientation in the plane perpendicular to the solar wind flow) on the energy transfer spatial distribution. We find that the energy transfer occurs mainly in the summer hemisphere, and that the dayside reconnection region is located asymmetrically about the subsolar position. Finally, we find that the energy transfer is 10% larger at equinox conditions than at solstice, contributing to the discussion concerning the semiannual variation of magnetospheric dynamics (known as "the Russell-McPherron effect").

scholarly journals Cusp-like plasma in high altitudes: a statistical study of the width and location of the cusp from Magion-4

2002 ◽  
Vol 20 (3) ◽  
pp. 311-320 ◽  
Author(s):  
J. Mĕrka ◽  
J. Šafránková ◽  
Z. Nĕmeček
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
High Altitudes ◽  
Data Set ◽  
Latitudinal Dependence ◽  
Merging Process ◽  
Low Altitude ◽  
Field Lines ◽  
The Magnetic Field ◽  
Dipole Tilt

Abstract. The width of the cusp region is an indicator of the strength of the merging process and the degree of opening of the magnetosphere. During three years, the Magion-4 satellite, as part of the Interball project, has collected a unique data set of cusp-like plasma observations in middle and high altitudes. For a comparison of high- and low-altitude cusp determination, we map our observations of cusp-like plasma along the magnetic field lines down to the Earth’s surface. We use the Tsyganenko and Stern 1996 model of the magnetospheric magnetic field for the mapping, taking actual solar wind and IMF parameters from the Wind observations. The footprint positions show substantial latitudinal dependence on the dipole tilt angle. We fit this dependence with a linear function and subtract this function from observed cusp position. This process allows us to study both statistical width and location of the inspected region as a function of the solar wind and IMF parameters. Our processing of the Magion-4 measurements shows that high-altitude regions occupied by the cusp-like plasma (cusp and cleft) are projected onto a much broader area (in magnetic local time as well as in a latitude) than that determined in low altitudes. The trends of the shift of the cusp position with changes in the IMF direction established by low-altitude observations have been confirmed.Key words. Magnetospheric physics (magnetopause, cusp and boundary layer; solar wind – magnetosphere interactions)

scholarly journals Excitation of transient lobe cell convection and auroral arc at the cusp poleward boundary during a transition of the interplanetary magnetic field from south to north

2001 ◽  
Vol 19 (5) ◽  
pp. 487-493 ◽  
Author(s):  
P. E. Sandholt ◽  
C. J. Farrugia ◽  
S. W. H. Cowley ◽  
M. Lester ◽  
J.-C. Cerisier
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Large Scale ◽  
Intermediate Phase ◽  
Bright Spot ◽  
Convection Cell ◽  
Plasma Convection ◽  
Cell Pattern ◽  
Auroral Phenomena ◽  
Lobe Reconnection

Abstract. We document the activation of transient polar arcs emanating from the cusp within a 15 min long intermediate phase during the transition from a standard two-cell convection pattern, representative of a strongly southward interplanetary magnetic field (IMF), to a "reverse" two-cell pattern, representative of strongly northward IMF conditions. During the 2–3 min lifetime of the arc, its base in the cusp, appearing as a bright spot, moved eastward toward noon by ~ 300 km. As the arc moved, it left in its "wake" enhanced cusp precipitation. The polar arc is a tracer of the activation of a lobe convection cell with clockwise vorticity, intruding into the previously established large-scale distorted two-cell pattern, due to an episode of localized lobe reconnection. The lobe cell gives rise to strong flow shear (converging electric field) and an associated sheet of outflowing field-aligned current, which is manifested by the polar arc. The enhanced cusp precipitation represents, in our view, the ionospheric footprint of the lobe reconnection process.Key words. Magnetospheric physics (auroral phenomena; magnetopause, cusp, and boundary layers; plasma convection)

scholarly journals O<sup>+</sup> transport in the dayside magnetosheath and its dependence on the IMF direction

2015 ◽  
Vol 33 (3) ◽  
pp. 301-307 ◽  
Author(s):  
R. Slapak ◽  
H. Nilsson ◽  
L. G. Westerberg ◽  
R. Larsson
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Ion Flux ◽  
Opposite Hemisphere ◽  
Oxygen Ions ◽  
Upper Limit ◽  
Field Lines ◽  
Lobe Reconnection ◽  
Open Magnetic Field ◽  
The Imf

Abstract. Recent studies have shown that the escape of oxygen ions (O+) into the magnetosheath along open magnetic field lines from the terrestrial cusp and mantle is significant. We present a study of how O+ transport in the dayside magnetosheath depends on the interplanetary magnetic field (IMF) direction. There are clear asymmetries in the O+ flows for southward and northward IMF. The asymmetries can be understood in terms of the different magnetic topologies that arise due to differences in the location of the reconnection site, which depends on the IMF direction. During southward IMF, most of the observed magnetosheath O+ is transported downstream. In contrast, for northward IMF we observe O+ flowing both downstream and equatorward towards the opposite hemisphere. We observe evidence of dual-lobe reconnection occasionally taking place during strong northward IMF conditions, a mechanism that may trap O+ and bring it back into the magnetosphere. Its effect on the overall escape is however small: we estimate the upper limit of trapped O+ to be 5%, a small number considering that ion flux calculations are rough estimates. The total O+ escape flux is higher by about a factor of 2 during times of southward IMF, in agreement with earlier studies of O+ cusp outflow.

How does the magnetosphere go to sleep?

2020 ◽  
Author(s):  
Therese Moretto Jorgensen ◽  
Michael Hesse ◽  
Lutz Rastaetter ◽  
Susanne Vennerstrom ◽  
Paul Tenfjord
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Exponential Decay ◽  
Rate Of Change ◽  
Total Field ◽  
Summer Hemisphere ◽  
Field Aligned Current ◽  
Field Lines ◽  
Line Tying

&lt;p&gt;Energy and circulation in the Earth&amp;#8217;s magnetosphere and ionosphere are largely determined by conditions in the solar wind and interplanetary magnetic field. When the driving from the solar wind is turned off (to a minimum), we expect the activity to die down but exactly how this happens is not known. &amp;#160;Utilizing global MHD modelling, we have addressed the questions of what constitutes the quietest state for the magnetosphere and how it is approached following a northward turning in the IMF that minimizes the driving. We observed an exponential decay with a decay time of about 1 hr in several integrated parameters related to different aspects of magnetospheric activity, including the total field-aligned current into and out of the ionosphere.&amp;#160; The time rate of change for the cessation of activity was also measured in total field aligned current estimates from the AMPERE project, adding observational support to this finding.&amp;#160; Events of distinct northward turnings of the interplanetary magnetic field were identified, with prolonged periods of stable southward driving conditions followed by northward interplanetary magnetic field conditions. A well-defined exponential decay could be identified in the total hemispheric field-aligned current following the northward turning with a generic decay constant of 0.9, corresponding to an e-folding time of 1.1 hr. A possible physical explanation for the exponential decay follows from considering what needs to happen for the convection in the magnetosphere to slow down, or stop, namely the unwinding of the field-aligned current carrying flux tubes in the coupled magnetosphere-ionosphere system. A statistical analysis of the ensemble of events also reveals both a seasonal and a day/night variation in the decay parameter, with faster decay observed in the winter than in the summer hemisphere and on the nightside than on the dayside. These results can be understood in terms of stronger/weaker line tying of the ionospheric foot points of magnetospheric field lines for higher/lower conductivity.&amp;#160; Additional global modeling results with varying conductance scenarios for the ionosphere confirm this interpretation. &amp;#160;&amp;#160;&lt;/p&gt;

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