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

<p>Energy and circulation in the Earth’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.  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.  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.  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.  Additional global modeling results with varying conductance scenarios for the ionosphere confirm this interpretation.   </p>

scholarly journals Cluster survey of the mid-altitude cusp: 1. size, location, and dynamics

2006 ◽  
Vol 24 (11) ◽  
pp. 3011-3026 ◽  
Author(s):  
F. Pitout ◽  
C. P. Escoubet ◽  
B. Klecker ◽  
H. Rème
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Time Delay ◽  
Interplanetary Magnetic Field ◽  
Statistical Study ◽  
Proper Time ◽  
Dynamic Pressure ◽  
Solar Wind Dynamic Pressure ◽  
Summer Hemisphere ◽  
External Conditions

Abstract. We present a statistical study of four years of Cluster crossings of the mid-altitude cusp. In this first part of the study, we start by introducing the method we have used a) to define the cusp properties, b) to sort the interplanetary magnetic field (IMF) conditions or behaviors into classes, c) to determine the proper time delay between the solar wind monitors and Cluster. Out of the 920 passes that we have analyzed, only 261 fulfill our criteria and are considered as cusp crossings. We look at the size, location and dynamics of the mid-altitude cusp under various IMF orientations and solar wind conditions. For southward IMF, Bz rules the latitudinal dynamics, whereas By governs the zonal dynamics, confirming previous works. We show that when |By| is larger than |Bz|, the cusp widens and its location decorrelates from By. We interpret this feature in terms of component reconnection occurring under By-dominated IMF. For northward IMF, we demonstrate that the location of the cusp depends primarily upon the solar wind dynamic pressure and upon the Y-component of the IMF. Also, the multipoint capability of Cluster allows us to conclude that the cusp needs typically more than ~20 min to fully adjust its location and size in response to changes in external conditions, and its speed is correlated to variations in the amplitude of IMF-Bz. Indeed, the velocity in °ILAT/min of the cusp appears to be proportional to the variation in Bz in nT: Vcusp=0.024 ΔBz. Finally, we observe differences in the behavior of the cusp in the two hemispheres. Those differences suggest that the cusp moves and widens more freely in the summer hemisphere.

scholarly journals Venus's induced magnetosphere during active solar wind conditions at BepiColombo's Venus 1 flyby

2021 ◽  
Author(s):  
Martin Volwerk ◽  
Beatriz Sánchez-Cano ◽  
Daniel Heyner ◽  
Sae Aizawa ◽  
Nicolas André ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Coronal Mass Ejection ◽  
Interplanetary Magnetic Field ◽  
Bow Shock ◽  
Gravity Assist ◽  
Highly Active ◽  
Field Lines ◽  
Mass Ejection ◽  
The Magnetic Field

Abstract. Out of the two Venus flybys that BepiColombo uses as a gravity assist manoeuvre to finally arrive at Mercury, the first took place on 15 October 2020. After passing the bow shock, the spacecraft travelled along the induced magnetotail, crossing it mainly in the YVSO-direction. In this paper, the BepiColombo Mercury Planetary Orbiter Magnetometer (MPO-MAG) data are discussed, with support from three other plasma instruments: the Planetary Ion Camera (PICAM), the Mercury Electron Analyser (MEA) and the radiation monitor (BERM). Behind the bow shock crossing, the magnetic field showed a draping pattern consistent with field lines connected to the interplanetary magnetic field wrapping around the planet. This flyby showed a highly active magnetotail, with, e.g., strong flapping motions at a period of ~7 min. This activity was driven by solar wind conditions. Just before this flyby, Venus's induced magnetosphere was impacted by a stealth coronal mass ejection, of which the trailing side was still interacting with it during the flyby. This flyby is a unique opportunity to study the full length and structure of the induced magnetotail of Venus, indicating that the tail was most likely still present at about 48 Venus radii.

scholarly journals Venus's induced magnetosphere during active solar wind conditions at BepiColombo's Venus 1 flyby

2021 ◽  
Vol 39 (5) ◽  
pp. 811-831
Author(s):  
Martin Volwerk ◽  
Beatriz Sánchez-Cano ◽  
Daniel Heyner ◽  
Sae Aizawa ◽  
Nicolas André ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Coronal Mass Ejection ◽  
Interplanetary Magnetic Field ◽  
Bow Shock ◽  
Gravity Assist ◽  
Highly Active ◽  
Field Lines ◽  
Mass Ejection ◽  
The Magnetic Field

Abstract. Out of the two Venus flybys that BepiColombo uses as a gravity assist manoeuvre to finally arrive at Mercury, the first took place on 15 October 2020. After passing the bow shock, the spacecraft travelled along the induced magnetotail, crossing it mainly in the YVSO direction. In this paper, the BepiColombo Mercury Planetary Orbiter Magnetometer (MPO-MAG) data are discussed, with support from three other plasma instruments: the Planetary Ion Camera (SERENA-PICAM) of the SERENA suite, the Mercury Electron Analyser (MEA), and the BepiColombo Radiation Monitor (BERM). Behind the bow shock crossing, the magnetic field showed a draping pattern consistent with field lines connected to the interplanetary magnetic field wrapping around the planet. This flyby showed a highly active magnetotail, with e.g. strong flapping motions at a period of ∼7 min. This activity was driven by solar wind conditions. Just before this flyby, Venus's induced magnetosphere was impacted by a stealth coronal mass ejection, of which the trailing side was still interacting with it during the flyby. This flyby is a unique opportunity to study the full length and structure of the induced magnetotail of Venus, indicating that the tail was most likely still present at about 48 Venus radii.

scholarly journals Statistical dependence of auroral ionospheric currents on solar wind and geomagnetic parameters from 5 years of CHAMP satellite data

2009 ◽  
Vol 27 (3) ◽  
pp. 1005-1017 ◽  
Author(s):  
L. Juusola ◽  
K. Kauristie ◽  
O. Amm ◽  
P. Ritter
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Data ◽  
Dynamic Pressure ◽  
Auroral Oval ◽  
Solar Wind Dynamic Pressure ◽  
Total Field ◽  
Magnetic Field Data ◽  
Champ Satellite ◽  
Field Aligned Current

Abstract. The effects of the solar wind dynamic pressure (P), the z component of the solar wind magnetic field (Bz), the merging electric field (Em), season and the Kp index on R1 and R2 field-aligned currents are studied statistically using magnetic field data from the CHAMP satellite during 2001–2005. The ionospheric and field-aligned currents are determined from the magnetic field data by the recently developed 1-D Spherical Elementary Current System (SECS) method. During southward IMF, increasing |Bz| is observed to clearly increase the total field-aligned current, while during northward IMF, the amount of field-aligned current remains fairly constant regardless of |Bz|. The dependence of the field-aligned current on Bz is given by |Ir[MA]|=0.054·Bz[nT]2−0.34·Bz[nT]+2.4. With increasing P, the intensity of the field-aligned current is also found to increase according to |Ir[MA]|=0.62·P[nPa]+1.6, and the auroral oval is observed to move equatorward. Increasing Em produces similar behaviour, described by |Ir[MA]|=1.41·Em[mV/m]+1.4. While the absolute intensity of the ionospheric current is stronger during negative than during positive Bz, the relative change in the intensity of the currents produced by a more intense solar wind dynamic pressure is observed to be approximately the same regardless of the Bz direction. Increasing Kp from 0 to ≥5 widens the auroral oval and moves it equatorward from between 66°–74° AACGM latitude to 59°–71° latitude. The total field aligned current as a function of Kp is given by |Ir[MA]|=1.1·Kp+0.6. In agreement with previous studies, total field-aligned current in the summer is found to be 1.4 times stronger than in the winter.

Venus’s induced magnetosphere during active solar wind conditionsat BepiColombo’s Venus 1 flyby

2021 ◽  
Author(s):  
Martin Volwerk ◽  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Coronal Mass Ejection ◽  
Interplanetary Magnetic Field ◽  
Bow Shock ◽  
Gravity Assist ◽  
Highly Active ◽  
Field Lines ◽  
Mass Ejection ◽  
The Magnetic Field

<p>Out of the two Venus flybys that BepiColombo uses as a gravity assist manoeuvre to finally arrive at Mercury, the first took place on 15 October 2020. After passing the bow shock, the spacecraft travelled along the induced magnetotail, crossing it mainly in the Y<sub>VSO</sub>-direction. We discuss the BepiColombo Mercury Planetary Orbiter Magnetometer (MPOMAG)<br />data, with support from three other plasma instruments: the Planetary Ion Camera (PICAM), the Mercury<br />Electron Analyser (MEA) and the radiation monitor (BERM). Behind the bow shock crossing, the magnetic field showed a<br />draping pattern consistent with field lines connected to the interplanetary magnetic field wrapping around the planet. This flyby showed a highly active magnetotail, with, e.g., strong flapping motions at a period of ~7 min. This activity was driven by solar wind conditions. Just before this flyby, Venus’s induced magnetosphere was impacted by a stealth coronal mass ejection, of which the trailing side was still interacting with it during the flyby. This flyby is a unique opportunity to study the full length and structure of the induced magnetotail of Venus, indicating that the tail was most likely still present at about 48 Venus radii. This presentation will take place after the second Venus flyby by Solar Orbiter and BepiColombo and Solar Orbiter on 9 and 10 August, respectively.</p>

H-Cmes and Ii-Type Radio Bursts Related Intense Geomagnetic Storms in Relation With Interplanetary Magnetic Field and Solar Wind Disturbances

2012 ◽  
Vol 2 (10) ◽  
pp. 1-3 ◽  
Author(s):  
Praveen Kumar Gupta ◽  
◽  
Puspraj Singh Puspraj Singh ◽  
Puspraj Singh Puspraj Singh ◽  
P. K. Chamadia P. K. Chamadia
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Geomagnetic Storms ◽  
Radio Bursts ◽  
Solar Wind Disturbances

scholarly journals Interplanetary magnetic field control of Saturn's polar cusp aurora

2005 ◽  
Vol 23 (4) ◽  
pp. 1405-1431 ◽  
Author(s):  
E. J. Bunce ◽  
S. W. H. Cowley ◽  
S. E. Milan
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Interplanetary Magnetic Field ◽  
Field Line ◽  
High Latitude ◽  
Closed Field ◽  
Vortical Flows ◽  
Dayside Magnetopause ◽  
Closed Field Line ◽  
Lobe Reconnection

Abstract. Dayside UV emissions in Saturn's polar ionosphere have been suggested to be the first observational evidence of the kronian "cusp" (Gérard et al., 2004). The emission has two distinct states. The first is a bright arc-like feature located in the pre-noon sector, and the second is a more diffuse "spot" of aurora which lies poleward of the general location of the main auroral oval, which may be related to different upstream interplanetary magnetic field (IMF) orientations. Here we take up the suggestion that these emissions correspond to the cusp. However, direct precipitation of electrons in the cusp regions is not capable of producing significant UV aurora. We have therefore investigated the possibility that the observed UV emissions are associated with reconnection occurring at the dayside magnetopause, possibly pulsed, akin to flux transfer events seen at the Earth. We devise a conceptual model of pulsed reconnection at the low-latitude dayside magnetopause for the case of northwards IMF which will give rise to pulsed twin-vortical flows in the magnetosphere and ionosphere in the vicinity of the open-closed field-line boundary, and hence to bi-polar field-aligned currents centred in the vortical flows. During intervals of high-latitude lobe reconnection for southward IMF, we also expect to have pulsed twin-vortical flows and corresponding bi-polar field-aligned currents. The vortical flows in this case, however, are displaced poleward of the open-closed field line boundary, and are reversed in sense, such that the field-aligned currents are also reversed. For both cases of northward and southward IMF we have also for the first time included the effects associated with the IMF By effect. We also include the modulation introduced by the structured nature of the solar wind and IMF at Saturn's orbit by developing "slow" and "fast" flow models corresponding to intermediate and high strength IMF respectively. We then consider the conditions under which the plasma populations appropriate to either sub-solar reconnection or high-latitude lobe reconnection can carry the currents indicated. We have estimated the field-aligned voltages required, the resulting precipitating particle energy fluxes, and the consequent auroral output. Overall our model of pulsed reconnection under conditions of northwards and southwards IMF, and for varying orientations of IMF By, is found to produce a range of UV emission intensities and geometries which is in good agreement with the data presented by Gérard et al. (2004). The recent HST-Cassini solar wind campaign provides a unique opportunity to test the theoretical ideas presented here.

scholarly journals Magnetic reconnection at the heliospheric current sheet and the formation of closed magnetic field lines in the solar wind

2006 ◽  
Vol 33 (17) ◽  
Author(s):  
J.T. Gosling ◽  
D.J. McComas ◽  
R.M. Skoug ◽  
C.W. Smith
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Heliospheric Current Sheet ◽  
Field Lines
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