scholarly journals Global characteristics of auroral Hall currents derived from the Swarm constellation: dependences on season and IMF orientation

2017 ◽  
Vol 35 (6) ◽  
pp. 1249-1268 ◽  
Author(s):  
Tao Huang ◽  
Hermann Lühr ◽  
Hui Wang
Keyword(s):  
Magnetic Field ◽  
Hall Current ◽  
Flow Direction ◽  
Magnetic Activity ◽  
The Novel ◽  
Polar Cap ◽  
Magnetic Field Data ◽  
Electrojet Current ◽  
Wind Input ◽  
The Imf

Abstract. On the basis of field-aligned currents (FACs) and Hall currents derived from high-resolution magnetic field data of the Swarm constellation, the average characteristics of these two current systems in the auroral regions are comprehensively investigated by statistical methods. This is the first study considering both current types determined simultaneously by the same spacecraft in both hemispheres. The FAC distribution, derived from the novel Swarm dual-spacecraft approach, reveals the well-known features of Region 1 (R1) and Region 2 (R2) FACs. At high latitudes, Region 0 (R0) FACs appear on the dayside. Their flow direction, up or down, depends on the orientation of the interplanetary magnetic field (IMF) By component. Of particular interest is the distribution of auroral Hall currents. The prominent auroral electrojets are found to be closely controlled by the solar wind input, but we find no dependence of their intensity on the IMF By orientation. The eastward electrojet is about 1.5 times stronger in local summer than in winter. Conversely, the westward electrojet shows less dependence on season. As to higher latitudes, part of the electrojet current is closed over the polar cap. Here the seasonal variation of conductivity mainly controls the current density. During local summer of the Northern Hemisphere, there is a clear channeling of return currents over the polar cap. For positive (negative) IMF By a dominant eastward (westward) Hall current circuit is formed from the afternoon (morning) electrojet towards the dawn side (dusk side) polar cap return current. The direction of polar cap Hall currents in the noon sector depends directly on the orientation of the IMF By. This is true for both signs of the IMF Bz component. Comparable Hall current distributions can be observed in the Southern Hemisphere but for opposite IMF By signs. Around the midnight sector the westward substorm electrojet is dominating. As expected, it is highly dependent on magnetic activity, but it shows only little response to season and IMF By polarity. An important finding is that all the IMF By dependences of FACs and Hall currents practically disappear in the dark winter hemisphere.

scholarly journals Characteristics of the electrojet during intense magnetic disturbances

2018 ◽  
Vol 36 (5) ◽  
pp. 1361-1391
Author(s):  
Liudmila I. Gromova ◽  
Matthias Förster ◽  
Yakov I. Feldstein ◽  
Patricia Ritter
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Ring Current ◽  
Flow Direction ◽  
Field Measurements ◽  
Main Phase ◽  
Champ Satellite ◽  
Electrojet Current ◽  
Magnetic Disturbances ◽  
The Imf

Abstract. Hall current variations in different time sectors during six magnetic storms from the summer seasons in 2003 and 2005 (Ritter, 2018) are examined, namely three storms in the day–night meridional sector and three storms in the dawn–dusk sector. The sequence of the phenomena, their structure and positions, and the strength of the polar (PE) and the auroral (AE) Hall electrojets were investigated using scalar magnetic field measurements obtained from the CHAllenging Minisatellite Payload (CHAMP) satellite in accordance with the study of Ritter et al. (2004a). We analyzed the correlations of the PE and AE as well as the obtained regression relations of the magnetic latitude MLat and the electrojet current intensity I with auroral and ring current activity, the interplanetary magnetic field, and the Newell et al. (2007) coupling function for the state of the solar wind. The following typical characteristics of the electrojets were revealed: The PE appears in the daytime sector at MLat ∼80∘–73∘, with a westward or an eastward direction depending on the interplanetary magnetic field (IMF) By component (By < 0 nT or By > 0 nT). Changes in the current flow direction in the PE can occur repeatedly during the storm, but only due to changes in the IMF By orientation. The PE increases with the intensity of the IMF By component from I∼0.4 A m−1 for By∼0 nT up to I∼1.0 A m−1 for By∼23 nT. The MLat position of the PE does not depend on the direction and intensity of the By component. There is no connection between MLat and I in the PE and the symmetric part of the magnetospheric ring current (index SymH). There is a correlation between I in the PE and the AsyH index, but only a very weak interconnection of this index with the MLat of the PE. Substorms occurring before the storm's main phase are accompanied by the appearance of an eastward electrojet (EE) at MLat ∼64∘ as well as that of a westward electrojet (WE). In the nighttime sector, a WE appears at MLat ∼64∘. During the main phase both electrojets persist. The daytime EE and the nighttime WE shift toward sub-auroral latitudes of MLat ∼56∘ and grow in intensity up to I∼1.5 A m−1. The WE is then located about 6∘ closer to the pole than the EE during evening hours and about 2∘–3∘ closer during daytime hours.

scholarly journals Predictions of local ground geomagnetic field fluctuations during the 7-10 November 2004 events studied with solar wind driven models

2005 ◽  
Vol 23 (9) ◽  
pp. 3095-3101 ◽  
Author(s):  
P. Wintoft ◽  
M. Wik ◽  
H. Lundstedt ◽  
L. Eliasson
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Flow Direction ◽  
Strong Dependence ◽  
Solar Wind Plasma ◽  
Magnetic Field Data ◽  
Solar Wind Magnetic Field ◽  
Solar Wind Flow ◽  
Field Fluctuations ◽  
Ground Magnetic

Abstract. The 7-10 November 2004 period contains two events for which the local ground magnetic field was severely disturbed and simultaneously, the solar wind displayed several shocks and negative Bz periods. Using empirical models the 10-min RMS and at Brorfelde (BFE, 11.67° E, 55.63° N), Denmark, are predicted. The models are recurrent neural networks with 10-min solar wind plasma and magnetic field data as inputs. The predictions show a good agreement during 7 November, up until around noon on 8 November, after which the predictions become significantly poorer. The correlations between observed and predicted log RMS is 0.77 during 7-8 November but drops to 0.38 during 9-10 November. For RMS the correlations for the two periods are 0.71 and 0.41, respectively. Studying the solar wind data for other L1-spacecraft (WIND and SOHO) it seems that the ACE data have a better agreement to the near-Earth solar wind during the first two days as compared to the last two days. Thus, the accuracy of the predictions depends on the location of the spacecraft and the solar wind flow direction. Another finding, for the events studied here, is that the and models showed a very different dependence on Bz. The model is almost independent of the solar wind magnetic field Bz, except at times when Bz is exceptionally large or when the overall activity is low. On the contrary, the model shows a strong dependence on Bz at all times.

scholarly journals Corrigendum to "Substorm activity in Venus's magnetotail" published in Ann. Geophys., 27, 2321–2330, doi:10.5194/angeo-27-2321-2009, 2009

2010 ◽  
Vol 28 (10) ◽  
pp. 1877-1878 ◽  
Author(s):  
M. Volwerk ◽  
M. Delva ◽  
Y. Futaana ◽  
A. Retinò ◽  
Z. Vörös ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Field Data ◽  
Hall Current ◽  
Magnetic Field Data ◽  
Guide Field ◽  
Substorm Activity ◽  
Original Interpretation ◽  
Current Signatures ◽  
The Magnetic Field

Abstract. A re-evaluation of the reconnection event reported by Volwerk et al. (2009) shows that the original interpretation of the magnetic field data as quadrupolar Hall-current signatures around a reconnection site was mistaken. It could be interpreted as the signature of reconnection in the presence of a guide field. The path of VEX through the active region in Venus's magnetotail is re-evaluated and the strongly energized ions associated to this event are now in agreement with the magnetic field data.

scholarly journals Comment on Invariability of relationship between the polar cap magnetic activity and geoeffective interplanetary electric field by Troshichev et al. (2011)

2020 ◽  
Author(s):  
Peter Stauning
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Interplanetary Magnetic Field ◽  
Magnetic Activity ◽  
The Arctic ◽  
Polar Cap ◽  
Antarctic Research Institute ◽  
Scaling Parameters ◽  
Antarctic Research ◽  
Research Institute

Abstract. In the publication Troshichev et al. (2006) on the Polar Cap (PC) indices, PCN (North) and PCS (South), an error was made by using components of the Interplanetary Magnetic Field (IMF) in their Geocentric Solar Ecliptic (GSE) representation instead of the prescribed Geocentric Solar Magnetosphere (GSM) representation for calculations of index scaling parameters in the version AARI_1998-2001 (named AARI#3) issued from the Arctic and Antarctic Research Institute (AARI) in St Petersburg, Russia. The mistake has caused a trail of incorrect relations and wrong conclusions extending since 2006 up to now (2020). The authors of the publication commented here, Troshichev, Podorozhkina, Janzhura (2011): Invariability of relationship between the polar cap magnetic activity and geoeffective interplanetary electric field, Ann. Geophys., 29, 1479-1489, state that they have used scaling parameters of the (invalid) AARI#3 PC index version in their work but have substituted parameters from the more recent AARI_1995-2005 (AARI#4) version instead. The mingling of PC index versions have resulted in erroneous illustrations in their Figs. 1, 2, 3, 6, 7, and 8 and the issuing of non-substantiated statements.

scholarly journals Dynamics of the electrojet during intense magnetic disturbances

2018 ◽  
Author(s):  
Liudmila I. Gromova ◽  
Matthias Förster ◽  
Iakov I. Feldstein ◽  
Patricia Ritter
Keyword(s):  
Magnetic Field ◽  
Magnetic Storm ◽  
Current Density ◽  
Ring Current ◽  
Geomagnetic Storms ◽  
Flow Direction ◽  
Main Phase ◽  
Local Times ◽  
Temporal Behaviour ◽  
The Imf

Abstract. Hall current variations in different time sectors during six magnetic storms of the summer seasons in 2003 and 2005 are examined in detail: three storms in the day-night meridional sector and three storms in the dawn-dusk sector. We investigate the sequence of the phenomena, their structure, positions and the density of the polar (PE) and the auroral (AE) Hall electrojets using scalar magnetic field measurements obtained from the CHAMP satellite in accordance with the study of Ritter et al. (2004a). Particular attention is devoted to the spatial-temporal behaviour of the PE at ionospheric altitudes during daytime hours both under geomagnetically quiet and under magnetic storm conditions. We analyze the correlations of the PE and AE with various activity indices like SYM/H and ASYM/H, that stand for large-scale current systems in the magnetosphere, AL for ionospheric currents, and the IndN coupling function for the state of the solar wind. We obtain regression relations of the magnetic latitude MLat and the electrojet current density I with those indices and with the interplanetary By and Bz magnetic field components. For the geomagnetic storms during summer seasons investigated here, we obtain the following typical characteristics for the electrojets' dynamics: 1. The PE appears at magnetic latitudes (MLat) and local times (MLT) of the cusp position. 2. This occurs in the day-time sector at MLat ∼ 73°–80° with a westward or an eastward direction, depending on the orientation of the IMF By component. Changes of current flow direction in the PE can occur repeatedly during the storm, but only due to changes of the IMF By orientation. 3. The current density in the PE increases with the intensity of the IMF By component from I ∼ 0.4 A/m for By ∼ 0 nT up to I ∼ 1.0 A/m for By ∼ 23 nT. 4. The MLat position of the PE does not depend on the orientation and the strength of the IMF By component. It depends, however, on the strength of the IMF Bz component. 5. The PE is situated at MLat ∼ 73° on the dayside during geomagnetically quiet periods and the recovery phase of a magnetic storm, and it shifts equatorward during intense substorms and the main phase of a storm. 6. There is no connection between MLat and the current density I in the PE with the magnetospheric ring current DR (index SYM/H). 7. There is a correlation between the current density I in the PE and the partial ring current in the magnetosphere (PRC, index ASYM/H), but practically no correlation of this index with MLat of the PE. 8. Substorms that occur before and during the beginning of a storm main phase are accompanied in the daytime by the appearance of an eastward electrojet (EE) at MLat ∼ 64° and then also by a westward electrojet (WE). In the nighttime sector the WE appears at MLat ∼ 64°. 9. During the development of the main storm phase, the daytime EE and the nighttime WE shift toward subauroral latitudes of MLat ∼ 56° and intensify up to I ∼ 1.5 A/m. Both electrojets persist during the main phase of the storm. The WE is then located about 6° closer to the pole than the EE during evening hours and about 2°–3° during daytime hours.

MAVEN observations of factors influencing the magnetotail twist at Mars

2020 ◽  
Author(s):  
Gina A. DiBraccio ◽  
Norberto Romanelli ◽  
Jacob R. Gruesbeck ◽  
Jasper Halekas ◽  
Suranga Ruhunusiri ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Twist Angle ◽  
Direct Interaction ◽  
Field Measurements ◽  
Ecliptic Plane ◽  
Initial Study ◽  
Field Orientation ◽  
Magnetic Field Data ◽  
Crustal Field ◽  
The Imf

&lt;p&gt;At Mars, recent studies based on a combination of MAVEN data and modeling have determined the Martian magnetotail exhibits a ~45&amp;#176; twist, either clockwise or counterclockwise from the ecliptic plane, away from the nominal interplanetary magnetic field (IMF) draping morphology. An initial study by DiBraccio et al. [2018] employed MAVEN magnetic field measurements, coupled with MHD simulations, to indicate that the twist is likely a result of the sun-planetary interaction. Now with several more years of MAVEN data available, we augment this work using a statistical analysis of MAVEN magnetic field data from November 2014 through November 2019. We utilized ~6000 orbits, requiring that MAVEN observed both the magnetotail and the upstream IMF over a given orbit. For periods when the upstream IMF measurements were not available due to MAVEN&amp;#8217;s orbit precession, we utilize an IMF proxy to determine characteristics of the upstream orientation. The location of the magnetotail lobes, identified in the data as the regions of magnetic field behind the planet directed towards and away from Mars, are analyzed as a function of the upstream IMF dawn-dusk component. In the previous DiBraccio et al. [2018] study, this dawn-dusk component was found to be the separating factor in the direction of magnetotail twisting. To quantify the degree of tail twisting for a given scenario, we determine the vector between the center of the towards/away tail lobes and calculate the angle between this vector and the expected direction for nominal IMF draping. This calculated tail twist angle is then assessed as a function of a variety of factors including strong crustal field location, Mars season, and downtail distance. In all cases, we determine that the degree of tail twisting is larger when the IMF is oriented in the duskward direction, suggesting enhanced coupling between the IMF and planetary crustal fields. Furthermore, we demonstrate that the degree of tail twisting exhibits different trends for crustal field orientation under dawnward versus duskward IMF configurations. Seasonal variations indicate that tail twisting may vary over the course of the Martian year, but additional data are needed during the northern fall and winter periods for confirmation. Finally, when assessing the tail twist with downtail distance we find that the degree of twisting increases with distance from the planet. This result is similar to Earth where observations of the magnetotail twist increases away from the planet as the torque exerted by the IMF on the planetary field increases. From these findings we confirm that the tail twist at Mars is likely a result of the direct interaction between the IMF and the planetary crustal fields; however, we find evidence suggesting that the degree of twisting is larger for duskward IMF orientations. This implies that magnetic reconnection on the dayside of Mars, between the IMF and crustal fields, may be favorable under specific IMF configurations.&lt;/p&gt;

scholarly journals VHF scintillations, orientation of the anisotropy of F-region irregularities and direction of plasma convection in the polar cap

2008 ◽  
Vol 26 (7) ◽  
pp. 1725-1730 ◽  
Author(s):  
E. D. Tereshchenko ◽  
N. Yu. Romanova ◽  
A. V. Koustov
Keyword(s):  
Magnetic Field ◽  
Plasma Flow ◽  
Flow Direction ◽  
Ionospheric Irregularities ◽  
Plasma Convection ◽  
Polar Cap ◽  
Data Set ◽  
Multiple Peaks ◽  
F Region ◽  
The Magnetic Field

Abstract. Scintillation data recorded at the polar cap station Barentsburg are shown to occasionally exhibit two or more peaks in the latitudinal profiles of the amplitude dispersion. Comparison with concurrent SuperDARN radar convection maps indicates that multiple peaks occur when Barentsburg is located within the area of strong changes in the plasma flow direction. When parameters of the ionospheric irregularities are inferred from the scintillation data, the orientation of the irregularity anisotropy in a plane perpendicular to the magnetic field is found to coincide well with the E×B flow direction, individually for each peak of the scintillation data. The differences were found to be mostly less than 20° for a data set comprised of 104 events. The conclusion is made that analysis of scintillation data allows one to infer the direction of plasma flow with a certain degree of detail.

scholarly journals Polar cap influx

2005 ◽  
Vol 23 (5) ◽  
pp. 1755-1761
Author(s):  
J. MacDougall ◽  
P. T. Jayachandran
Keyword(s):  
Magnetic Field ◽  
Magnetospheric Physics ◽  
Plasma Convection ◽  
Polar Cap ◽  
Cusp Region ◽  
Ionosphere Plasma ◽  
Latitude Station ◽  
The Imf

Abstract. This study uses digital ionosonde data from a cusp latitude station (Cambridge Bay, 77° CGM lat.) to study the convection into the polar cap. Days when the IMF magnetic field was relatively steady were used. On many days it was possible to distinguish an interval near noon MLT when the ionosonde data had a different character from that at earlier and later times. Based on our data, and other published measurements, we used the interval 10:00-13:00 MLT as the cusp interval and calculated the convection into the polar cap in this interval. The integrated convection accounted for only ~1/3 of the open polar cap flux. If the convection through the prenoon/postnoon regions on either side of the cusp was calculated the remaining 2/3 of the flux could be accounted for. The characteristics of the prenoon/postnoon regions were different from the cusp region, and we attribute this to transient flank merging versus more steady frontside merging for the cusp. Keywords. Ionosphere (Plasma convection) Magnetospheric physics (Polar cap phenomenon)

An Augmented Iteratively Re-weighted and Refined Least Squares Method for lp Minimization Problem in Inverse Modeling of Potential Field Magnetic Data

2020 ◽  
Vol 1 (3) ◽  
Author(s):  
Maysam Abedi
Keyword(s):  
Magnetic Field ◽  
Magnetic Susceptibility ◽  
Least Squares ◽  
Minimization Problem ◽  
Potential Field ◽  
Field Data ◽  
Least Squares Method ◽  
Porphyry Copper ◽  
Magnetic Data ◽  
Magnetic Field Data

The presented work examines application of an Augmented Iteratively Re-weighted and Refined Least Squares method (AIRRLS) to construct a 3D magnetic susceptibility property from potential field magnetic anomalies. This algorithm replaces an lp minimization problem by a sequence of weighted linear systems in which the retrieved magnetic susceptibility model is successively converged to an optimum solution, while the regularization parameter is the stopping iteration numbers. To avoid the natural tendency of causative magnetic sources to concentrate at shallow depth, a prior depth weighting function is incorporated in the original formulation of the objective function. The speed of lp minimization problem is increased by inserting a pre-conditioner conjugate gradient method (PCCG) to solve the central system of equation in cases of large scale magnetic field data. It is assumed that there is no remanent magnetization since this study focuses on inversion of a geological structure with low magnetic susceptibility property. The method is applied on a multi-source noise-corrupted synthetic magnetic field data to demonstrate its suitability for 3D inversion, and then is applied to a real data pertaining to a geologically plausible porphyry copper unit.  The real case study located in  Semnan province of  Iran  consists  of  an arc-shaped  porphyry  andesite  covered  by  sedimentary  units  which  may  have  potential  of  mineral  occurrences, especially  porphyry copper. It is demonstrated that such structure extends down at depth, and consequently exploratory drilling is highly recommended for acquiring more pieces of information about its potential for ore-bearing mineralization.

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