A satellite study of dayside auroral conjugacy

Abstract. A study of dayside auroral conjugacy has been done using the cleft/boundary layer auroral particle boundaries observed by the DMSP-F7 satellite in the southern hemisphere and the global UV auroral images taken by the Viking spacecraft in the northern hemisphere. The 22 events have been studied on the basis of an internal IGRF 1985 magnetic field; it is shown that there is a displacement of up to 4° in latitude from the conjugate points with the northern aurora appearing to be located poleward of the conjugate point. No local time dependence of the north-south auroral location difference was seen. The use of a more realistic magnetic field model for tracing field lines which incorporates the dipole tilt angle and Kp index, the Tsyganenko 1987 long model plus the IGRF 1985 internal magnetic field model, appears to organize the data better. Although with this external plus internal model some tracings did not close in the opposite hemisphere, 70% of those that did indicated satisfactory conjugacy. The study shows that the degree of auroral conjugacy is dependent upon the accuracy of the magnetic field model used to trace to the conjugate point, especially in the dayside region where the field lines can either go to the dayside magnetopause near the subsolar point or sweep all the way back to the flanks of the magnetotail. Also the discrepancy in the latitude of northern and southern aurora can be partially explained by the displacement of the neutral sheet (source region of the aurora) by the dipole tilt effect.

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Relevance of the magnetic field model for studying the beaming cone of the Jovian decameter emission

10.5194/egusphere-egu2020-10781 ◽

2020 ◽

Author(s):

Patrick Galopeau ◽

Mohammed Boudjada

Keyword(s):

Magnetic Field ◽

Field Model ◽

Source Region ◽

Local Magnetic Field ◽

Hollow Cone ◽

The North ◽

Cyclotron Maser ◽

Specific Direction ◽

Magnetic Field Model ◽

The Magnetic Field

We use five different Jupiter&#8217;s magnetic field models (O6, VIP4, VIT4, VIPAL and JRM09) to investigate the angular distribution of the Jovian decameter radiation occurrence probability, relatively to the local magnetic field B and its gradient &#8711;B in the source region. The most recent model JRM09, proposed by Connerney et al. [Geophys. Res. Lett., 45, 2590-2596, 2018], was derived from Juno&#8217;s first nine orbits observations. The JRM09 model confirms the results obtained several years ago using older models (O6, VIP4, VIT4 and VIPAL): the radio emission is beamed in a hollow cone presenting a flattening in a specific direction. The same assumptions were made as in the previous studies: the Jovian decameter radiation is supposed to be produced by the cyclotron maser instability (CMI) in a plasma where B and&#160;&#8711;B are not parallel. As a consequence, the emission cone does not have any axial symmetry and then presents a flattening in a privileged direction. This flattening appears to be more important for the northern emission (34.8%) than for the southern emission (12.5%) probably due to the fact that the angle between the directions of B and&#160;&#8711;B is greater in the North (~10&#176;) than in the South (~4&#176;).

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The ionospheric footprint of antiparallel merging regions on the dayside magnetopause

Annales Geophysicae ◽

10.1007/s00585-000-0511-2 ◽

2000 ◽

Vol 18 (5) ◽

pp. 511-516 ◽

Cited By ~ 8

Author(s):

I. J. Coleman ◽

M. Pinnock ◽

A. S. Rodger

Keyword(s):

Magnetic Field ◽

Seasonal Variation ◽

Boundary Layers ◽

Electric Fields ◽

Field Model ◽

Magnetospheric Physics ◽

Dayside Magnetopause ◽

Magnetic Field Model ◽

Geomagnetic Fields ◽

Dipole Tilt

Abstract. The antiparallel merging hypothesis states that reconnection takes place on the dayside magnetopause where the solar and geomagnetic fields are oppositely directed. With this criterion, we have mapped the predicted merging regions to the ionosphere using the Tsyganenko 96 magnetic field model, distinguishing between regions of sub-Alfvénic and super-Alfvénic magnetosheath flow, and identifying the day-night terminator. We present the resulting shape, width and latitude of the ionospheric dayside merging regions in both hemispheres, showing their dependence on the Earth's dipole tilt. The resulting seasonal variation of the longitudinal width is consistent with the conjugate electric fields in the northern and southern cusps, as measured by the SuperDARN HF radars, for example. We also find a seasonal shift in latitude similar to that observed in satellite cusp data.Key words: Ionosphere (ionosphere-magnetosphere interactions) · Magnetospheric physics (magnetopause · cusp and boundary layers; magnetosphere-ionosphere interactions)

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Coronal Loop Mapping to Infer the Best Magnetic Field Models for Active Region Prominences

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313011344 ◽

2013 ◽

Vol 8 (S300) ◽

pp. 416-417

Author(s):

G. Allen Gary ◽

Qiang Hu ◽

Jong Kwan Lee

Keyword(s):

Magnetic Field ◽

Coronal Loop ◽

Field Model ◽

Three Dimensional ◽

Coronal Loops ◽

Magnetic Field Model ◽

Free Parameters ◽

Field Lines ◽

Fitness Parameter ◽

The Magnetic Field

AbstractThis article comments on the results of a new, rapid, and flexible manual method to map on-disk individual coronal loops of a two-dimensional EUV image into the three-dimensional coronal loops. The method by Gary, Hu, and Lee (2013) employs cubic Bézier splines to map coronal loops using only four free parameters per loop. A set of 2D splines for coronal loops is transformed to the best 3D pseudo-magnetic field lines for a particular coronal model. The results restrict the magnetic field models derived from extrapolations of magnetograms to those admissible and inadmissible via a fitness parameter. This method uses the minimization of the misalignment angles between the magnetic field model and the best set of 3D field lines that match a set of closed coronal loops. We comment on the implication of the fitness parameter in connection with the magnetic free energy and comment on extensions of our earlier work by considering the issues of employing open coronal loops or employing partial coronal loop.

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The asymmetric geospace as displayed during the geomagnetic storm on 17 August 2001

Annales Geophysicae ◽

10.5194/angeo-36-1577-2018 ◽

2018 ◽

Vol 36 (6) ◽

pp. 1577-1596 ◽

Cited By ~ 4

Author(s):

Nikolai Østgaard ◽

Jone P. Reistad ◽

Paul Tenfjord ◽

Karl M. Laundal ◽

Theresa Rexer ◽

...

Keyword(s):

Magnetic Field ◽

Tilt Angle ◽

Convection Cell ◽

Expansion Phase ◽

The North ◽

Parker Spiral ◽

Field Lines ◽

Convection Patterns ◽

Auroral Imaging ◽

Dipole Tilt

Abstract. Previous studies have shown that conjugate auroral features are displaced in the two hemispheres when the interplanetary magnetic field (IMF) has a transverse (Y) component. It has also been shown that a BY component is induced in the closed magnetosphere due to the asymmetric loading of magnetic flux in the lobes following asymmetric dayside reconnection when the IMF has a Y component. The magnetic field lines with azimuthally displaced footpoints map into a “banana”-shaped convection cell in one hemisphere and an “orange”-shaped cell in the other. Due to the Parker spiral our system is most often exposed to a BY-dominated IMF. The dipole tilt angle, varying between ±34∘, leads to warping of the plasma sheet and oppositely directed BY components in dawn and dusk in the closed magnetosphere. As a result of the Parker spiral and dipole tilt, geospace is asymmetric most of the time. The magnetic storm on 17 August 2001 offers a unique opportunity to study the dynamics of the asymmetric geospace. IMF BY was 20–30 nT and tilt angle was 23∘. Auroral imaging revealed conjugate features displaced by 3–4 h magnetic local time. The latitudinal width of the dawnside aurora was quite different (up to 6∘) in the two hemispheres. The auroral observations together with convection patterns derived entirely from measurements indicate dayside, lobe and tail reconnection in the north, but most likely only dayside and tail reconnection in the Southern Hemisphere. Increased tail reconnection during the substorm expansion phase reduces the asymmetry.

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The asymmetric geospace as displayed during the geomagnetic storm on August 17, 2001

10.5194/angeo-2018-65 ◽

2018 ◽

Cited By ~ 2

Author(s):

Nikolai Østgaard ◽

Jone P. Reistad ◽

Paul Tenfjord ◽

Karl M. Laundal ◽

Theresa Rexer ◽

...

Keyword(s):

Magnetic Field ◽

Tilt Angle ◽

Convection Cell ◽

Expansion Phase ◽

The North ◽

Parker Spiral ◽

Field Lines ◽

Convection Patterns ◽

Auroral Imaging ◽

Dipole Tilt

Abstract. Previous studies have shown that conjugate auroral features are displaced in the two hemispheres when the interplanetary magnetic field (IMF) has a transverse (Y) component. It has also been shown that a BY component is induced in the closed magnetosphere due to the asymmetric loading of magnetic flux in the lobes following asymmetric dayside reconnection when the IMF has a Y component. The magnetic field lines with azimuthally displaced footpoints map into a banana shaped convection cell in one hemisphere and an orange shaped cell in the other. Due to the Parker spiral our system is most often exposed to a BY dominated IMF. The dipole tilt angle, varying between ±34 deg, leads to warping of the plasma sheet and oppositely directed BY components in dawn and dusk in the closed magnetosphere. As a result of the Parker spiral and dipole tilt, geospace is most of the time asymmetric. The magnetic storm on August 17, 2001 offers a unique opportunity to study the dynamics of the asymmetric geospace. IMF BY was 20–30 nT and tilt angle was 23 deg. Auroral imaging revealed conjugate features displaced by 3–4 hours magnetic local time. The latitudinal width of the dawnside aurora was quite different (up to 6 deg) in the two hemispheres. The auroral observations together with convection patterns derived entirely from data indicate both dayside, lobe and tail reconnection in the north, but most likely only dayside and tail reconnection in the southern hemisphere. Increased tail reconnection during substorm expansion phase reduces the asymmetry.

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

Annales Geophysicae ◽

10.5194/angeo-20-311-2002 ◽

2002 ◽

Vol 20 (3) ◽

pp. 311-320 ◽

Cited By ~ 32

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)

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A case study of the plasma in the magneto-sheath using the numerical magnetosheath-magnetosphere model and THEMIS measure-ments

MATEC Web of Conferences ◽

10.1051/matecconf/201814503004 ◽

2018 ◽

Vol 145 ◽

pp. 03004

Author(s):

Polya Dobreva ◽

Olga Nitcheva ◽

Monio Kartalev

Keyword(s):

Magnetic Field ◽

Field Model ◽

Specific Aspect ◽

Plasma Parameters ◽

Ion Density ◽

Magnetic Field Model ◽

Wind Spacecraft ◽

The Mean ◽

The Magnetic Field

This paper presents a case study of the plasma parameters in the magnetosheath, based on THEMIS measurements. As a theoretical tool we apply the self-consistent magnetosheath-magnetosphere model. A specific aspect of the model is that the positions of the bow shock and the magnetopause are self-consistently determined. In the magnetosheath the distribution of the velocity, density and temperature is calculated, based on the gas-dynamic theory. The magnetosphere module allows for the calculation of the magnetopause currents, confining the magnetic field into an arbitrary non-axisymmetric magnetopause. The variant of the Tsyganenko magnetic field model is applied as an internal magnetic field model. As solar wind monitor we use measurements from the WIND spacecraft. The results show that the model quite well reproduces the values of the ion density and velocity in the magnetosheath. The simlicity of the model allows calulations to be perforemed on a personal computer, which is one of the mean advantages of our model.

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Random Walk and Trapping of Interplanetary Magnetic Field Lines: Global Simulation, Magnetic Connectivity, and Implications for Solar Energetic Particles

10.5194/egusphere-egu21-3719 ◽

2021 ◽

Author(s):

David Ruffolo ◽

Rohit Chhiber ◽

William H. Matthaeus ◽

Arcadi V. Usmanov ◽

Paisan Tooprakai ◽

...

Keyword(s):

Magnetic Field ◽

Random Walk ◽

Field Line ◽

Large Scale ◽

Transport Model ◽

Source Region ◽

Science Research ◽

Energetic Particles ◽

Solar Energetic Particles ◽

Field Lines

The random walk of magnetic field lines is an important ingredient in understanding how the connectivity of the magnetic field affects the spatial transport and diffusion of charged particles. As solar energetic particles (SEPs) propagate away from near-solar sources, they interact with the fluctuating magnetic field, which modifies their distributions. We develop a formalism in which the differential equation describing the field line random walk contains both effects due to localized magnetic displacements and a non-stochastic contribution from the large-scale expansion. We use this formalism together with a global magnetohydrodynamic simulation of the inner-heliospheric solar wind, which includes a turbulence transport model, to estimate the diffusive spreading of magnetic field lines that originate in different regions of the solar atmosphere. We first use this model to quantify field line spreading at 1 au, starting from a localized solar source region, and find rms angular spreads of about 20 &#8211; 60 degrees. In the second instance, we use the model to estimate the size of the source regions from which field lines observed at 1 au may have originated, thus quantifying the uncertainty in calculations of magnetic connectivity; the angular uncertainty is estimated to be about 20 degrees. Finally, we estimate the filamentation distance, i.e., the heliocentric distance up to which field lines originating in magnetic islands can remain strongly trapped in filamentary structures. We emphasize the key role of slab-like fluctuations in the transition from filamentary to more diffusive transport at greater heliocentric distances. This research has been supported in part by grant RTA6280002 from Thailand Science Research and Innovation and the Parker Solar Probe mission under the ISOIS project (contract NNN06AA01C) and a subcontract to University of Delaware from Princeton University (SUB0000165). &#160;MLG acknowledges support from the Parker Solar Probe FIELDS MAG team. &#160;Additional support is acknowledged from the&#160; NASA LWS program&#160; (NNX17AB79G) and the HSR program (80NSSC18K1210 & 80NSSC18K1648).

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