Saturn’s ring current observed during Cassini’s Grand Finale

2020 ◽  
Author(s):  
Gabrielle Provan ◽  
Tom Bradley ◽  
Emma Bunce ◽  
Stan Cowley ◽  
Michele Dougherty ◽  
...  
Keyword(s):  
Solar Wind ◽  
Current Density ◽  
Ring Current ◽  
Current System ◽  
Current Model ◽  
Internal Field ◽  
Total Current ◽  
Magnetometer Data ◽  
Proton Data ◽  
Azimuthal Current

<p>The presence of a substantial azimuthal current sheet in Saturn’s magnetosphere was identified in Voyager and Pioneer magnetometer data.  Data from these spacecraft showed depressions in the strength of the field below that expected for the internal field of the planet alone.  This ring current was  modelled  as a simple axisymmetric current system by Connerney et al. [1980, 1983].  In this study we utilise the Connerney ring current model to look at the size, shape, current density and total current of Saturn’s ring current as observed during the Cassini proximal orbits.  We compare the variations in these parameters with the phases of the planetary period oscillations and with the occurrence of magnetospheric storms as determined from propagated solar wind data and LEMMS electron and proton data. Overall, we find that Saturn’s ring current is a dynamical environment which varies in size and magnitude due to  both  planetary period oscillations and solar-driven storms.  </p>

scholarly journals A note on the ring current in Saturn’s magnetosphere: Comparison of magnetic data obtained during the Pioneer-11 and Voyager-1 and -2 fly-bys

2003 ◽  
Vol 21 (3) ◽  
pp. 661-669 ◽  
Author(s):  
E. J. Bunce ◽  
S. W. H. Cowley
Keyword(s):  
Magnetic Field ◽  
Ring Current ◽  
Current System ◽  
Magnetic Data ◽  
Total Current ◽  
Planetary Magnetospheres ◽  
Magnetospheric Configuration And Dynamics ◽  
Magnetospheric Configuration ◽  
First Time ◽  
Current Systems

Abstract. We examine the residual (measured minus internal) magnetic field vectors observed in Saturn’s magnetosphere during the Pioneer-11 fly-by in 1979, and compare them with those observed during the Voyager-1 and -2 fly-bys in 1980 and 1981. We show for the first time that a ring current system was present within the magnetosphere during the Pioneer-11 encounter, which was qualitatively similar to those present during the Voyager fly-bys. The analysis also shows, however, that the ring current was located closer to the planet during the Pioneer-11 encounter than during the comparable Voyager-1 fly-by, reflecting the more com-pressed nature of the magnetosphere at the time. The residual field vectors have been fit using an adaptation of the current system proposed for Jupiter by Connerney et al. (1981a). A model that provides a reasonably good fit to the Pioneer-11 Saturn data extends radially between 6.5 and 12.5 RS (compared with a noon-sector magnetopause distance of 17 RS), has a north-south extent of 4 RS, and carries a total current of 9.6 MA. A corresponding model that provides a qualitatively similar fit to the Voyager data, determined previously by Connerney et al. (1983), extends radially between 8 and 15.5 RS (compared with a noon-sector magnetopause distance for Voyager-1 of 23–24 RS), has a north-south extent of 6 RS, and carries a total current of 11.5 MA.Key words. Magnetospheric physics (current systems, magnetospheric configuration and dynamics, planetary magnetospheres)

scholarly journals Study of the applicability of the curlometer technique with the four Cluster spacecraft in regions close to Earth

2012 ◽  
Vol 30 (3) ◽  
pp. 597-611 ◽  
Author(s):  
S. Grimald ◽  
I. Dandouras ◽  
P. Robert ◽  
E. Lucek
Keyword(s):  
Magnetic Field ◽  
Current Density ◽  
Ring Current ◽  
Current System ◽  
Sufficient Conditions ◽  
Magnetic Activity ◽  
Inner Magnetosphere ◽  
Good Proxy ◽  
The Magnetic Field ◽  
Magnetospheric Current System

Abstract. Knowledge of the inner magnetospheric current system (intensity, boundaries, evolution) is one of the key elements for the understanding of the whole magnetospheric current system. In particular, the calculation of the current density and the study of the changes in the ring current is an active field of research as it is a good proxy for the magnetic activity. The curlometer technique allows the current density to be calculated from the magnetic field measured at four different positions inside a given current sheet using the Maxwell-Ampere's law. In 2009, the CLUSTER perigee pass was located at about 2 RE allowing a study of the ring current deep inside the inner magnetosphere, where the pressure gradient is expected to invert direction. In this paper, we use the curlometer in such an orbit. As the method has never been used so deep inside the inner magnetosphere, this study is a test of the curlometer in a part of the magnetosphere where the magnetic field is very high (about 4000 nT) and changes over small distances (ΔB = 1nT in 1000 km). To do so, the curlometer has been applied to calculate the current density from measured and modelled magnetic fields and for different sizes of the tetrahedron. The results show that the current density cannot be calculated using the curlometer technique at low altitude perigee passes, but that the method may be accurate in a [3 RE; 5 RE] or a [6 RE; 8.3 RE] L-shell range. It also demonstrates that the parameters used to estimate the accuracy of the method are necessary, but not sufficient conditions.

The MLT distribution and detailed structure of ring current:  MMS observations

2021 ◽  
Author(s):  
Xin Tan ◽  
Malcolm Dunlop ◽  
Xiangcheng Dong ◽  
Yanyan Yang ◽  
Christopher Russell
Keyword(s):  
Current Density ◽  
Large Scale ◽  
Ring Current ◽  
Current System ◽  
Radial Profile ◽  
Three Dimensional ◽  
Current Density Distribution ◽  
Magnetic Storms ◽  
In Situ Data

<p>The ring current is an important part of the large-scale magnetosphere-ionosphere current system; mainly concentrated in the equatorial plane, between 2-7 R<sub>E</sub>, and strongly ordered between ± 30 ° latitude. The morphology of ring current directly affects the geomagnetic field at low to middle latitudes. Rapid changes in ring current densities can occur during magnetic storms/sub-storms. Traditionally, the Dst index is used to characterize the intensity of magnetic storms and to reflect the variation of ring current intensity, but this index does not reflect the MLT distribution of ring current. In fact, the ring current has significant variations with MLT, depending on geomagnetic activity, due to the influence of multiple factors; such as, the partial ring current, region 1/region 2 field-aligned currents, the magnetopause current and sub-storm cycle (magnetotail current). The form of the ring current has been inferred from the three-dimensional distribution of ion differential fluxes from neutral atom imaging; however, this technique can not directly obtain the current density distribution (as can be obtained using multi-spacecraft in situ data). Previous in situ estimates of current density have used: Cluster, THEMIS and other spacecraft groups to study the distribution of the ring current for limited ranges of either radial profile, or MLT and MLAT variations. Here, we report on an extension to these studies using FGM data from MMS obtained during the period September 1, 2015 to December 31, 2016, when the MMS orbit and configuration provided good coverage. We employ the curlometer method to calculate the current density, statistically, to analysis the MLT distribution according to different geomagnetic conditions. Our results show the clear asymmetry of the ring current and its different characteristics under different geomagnetic conditions.</p>

scholarly journals Metrics analysis of the coupled Block Adaptive-Tree Solar Wind Roe-Type Upwind Scheme and Fok ring current model performance

Space Weather ◽  
2007 ◽  
Vol 5 (11) ◽  
pp. n/a-n/a ◽  
Author(s):  
A. Taktakishvili ◽  
M. Kuznetsova ◽  
M. Hesse ◽  
L. Rastätter ◽  
A. Chulaki ◽  
...  
Keyword(s):  
Solar Wind ◽  
Ring Current ◽  
Current Model ◽  
Model Performance ◽  
Upwind Scheme

scholarly journals Mercury’s Ring Current: MESSENGER Observations and Test-Particle Simulations

2021 ◽  
Author(s):  
Jiutong Zhao ◽  
Qiugang Zong ◽  
Chao Yue ◽  
Weijie Sun ◽  
Hui Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Test Particle ◽  
Ring Current ◽  
Current System ◽  
Wind Forcing ◽  
Particle Simulation ◽  
Space Environment ◽  
Magnetic Field Model ◽  
Particle Simulations

Abstract Energetic protons can carry a longitudinal electric current via their gradient and curvature drift around a planet and form a current system known as the ring current. The ring current has been observed in the intrinsic magnetosphere of Earth, Jupiter, and Saturn. However, there is still lacking evidence of ring current in Mercury’s magnetosphere, which contains significantly weaker and oppressive “dipolar” magnetic field and the charged particles are thought able to efficiently escape the magnetosphere through magnetopause shadowing and/or directly hitting the surface. Here we present the first observational evidence of Mercury ring current with the measurement of MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER). The ring current is bifurcated under moderate solar wind forcing, which is caused by the off-equatorial magnetic minima on the noon side and tends to vanish during weak solar wind forcing. This morphology is validated by a test-particle simulation with a Mercury’s dynamic magnetic field model. The total energy stored in the ring current exceeds 5x1010 J during active times, indicating that magnetic storms may also occur in Mercury’s magnetosphere.

The fine structure of the subsolar MPB current layer from MAVEN observations: Implications for the Lorentz force

2020 ◽  
Author(s):  
Gabriela Boscoboinik ◽  
Cesar Bertucci ◽  
Daniel Gomez ◽  
Laura Morales ◽  
Christian Mazelle ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Fine Structure ◽  
Lorentz Force ◽  
Current Density ◽  
Current System ◽  
Minimum Variance ◽  
Current Layer ◽  
The Earth ◽  
Steady Current

<p>We report on the local structure of the Martian subsolar Magnetic Pileup Boundary (MPB) from minimum variance analysis of the magnetic field measured by the MAVEN spacecraft for six orbits. In particular, we detect a well defined current layer within the MPB’s fine structure and<br>provide a local estimate of its current density and compare these results with the current density obtained by multi-fluid simulations.<br>This current is of the order of hundreds of nAm<sup>-2</sup> which results in a sunward Lorentz force of the order of 10<sup>-14</sup> Nm<sup>-3</sup>. We compare these results with multifluid numerical simulations.<br>This force is associated with the gradient of the magnetic pressure, it accounts for the deflection of the solar wind ions near the MPB and for the acceleration of solar wind electrons which carry the interplanetary magnetic field through the MPB into the MPR. We also find that the<br>thickness of the MPB current layer is of the order of both the upstream (magnetosheath) solar wind proton inertial length and convective gyroradius. The former is consistent with the demagnetization of the ions due to the Hall electric field, an effect observed recently at the Earth magnetopause, while the latter would imply kinetic processes are important at the MPB.<br>This study supports recent results that report the presence of a steady current system around Mars in a similar way to the Earth.</p>

Ring current model of the naphthalene molecule

1997 ◽  
Vol 92 (3) ◽  
pp. 609-617 ◽  
Author(s):  
RICCARDO ZANASI ◽  
PAOLO LAZZERETTI
Keyword(s):  
Ring Current ◽  
Current Model ◽  
Naphthalene Molecule

scholarly journals Prediction of SYM-H index during large storms by NARX neural network from IMF and solar wind data

2010 ◽  
Vol 28 (2) ◽  
pp. 381-393 ◽  
Author(s):  
L. Cai ◽  
S. Y. Ma ◽  
Y. L. Zhou
Keyword(s):  
Neural Network ◽  
Solar Wind ◽  
Correlation Coefficient ◽  
Characteristic Time ◽  
Ring Current ◽  
Wind Data ◽  
Distinct Advantage ◽  
Elman Network ◽  
H Index ◽  
Narx Neural Network

Abstract. Similar to the Dst index, the SYM-H index may also serve as an indicator of magnetic storm intensity, but having distinct advantage of higher time-resolution. In this study the NARX neural network has been used for the first time to predict SYM-H index from solar wind (SW) and IMF parameters. In total 73 time intervals of great storm events with IMF/SW data available from ACE satellite during 1998 to 2006 are used to establish the ANN model. Out of them, 67 are used to train the network and the other 6 samples for test. Additionally, the NARX prediction model is also validated using IMF/SW data from WIND satellite for 7 great storms during 1995–1997 and 2005, as well as for the July 2000 Bastille day storm and November 2001 superstorm using Geotail and OMNI data at 1 AU, respectively. Five interplanetary parameters of IMF Bz, By and total B components along with proton density and velocity of solar wind are used as the original external inputs of the neural network to predict the SYM-H index about one hour ahead. For the 6 test storms registered by ACE including two super-storms of min. SYM-H<−200 nT, the correlation coefficient between observed and NARX network predicted SYM-H is 0.95 as a whole, even as high as 0.95 and 0.98 with average relative variance of 13.2% and 7.4%, respectively, for the two super-storms. The prediction for the 7 storms with WIND data is also satisfactory, showing averaged correlation coefficient about 0.91 and RMSE of 14.2 nT. The newly developed NARX model shows much better capability than Elman network for SYM-H prediction, which can partly be attributed to a key feedback to the input layer from the output neuron with a suitable length (about 120 min). This feedback means that nearly real information of the ring current status is effectively directed to take part in the prediction of SYM-H index by ANN. The proper history length of the output-feedback may mainly reflect on average the characteristic time of ring current decay which involves various decay mechanisms with ion lifetimes from tens of minutes to tens of hours. The Elman network makes feedback from hidden layer to input only one step, which is of 5 min for SYM-H index in this work and thus insufficient to catch the characteristic time length.

scholarly journals A Digital Signature Model Using XAdES Standard as a Rest Service

Information ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 289
Author(s):  
Renato Carauta Ribeiro ◽  
Murilo Góes de Almeida ◽  
Edna Dias Canedo
Keyword(s):  
Public Administration ◽  
Digital Signature ◽  
Current System ◽  
Current Model ◽  
Ministry Of Education ◽  
Java Language ◽  
Digital Format ◽  
Rest Service ◽  
Proposed Model ◽  
Guidelines And Standards

The digital signature of documents and degrees is a topic widely discussed in the Federal Public Administration. Several laws and ordinances were created to standardize the issuance, validation and legal validity of digitally signed documents in national territory, such as the ordinances created by the Ministry of Education (MEC) to regulate the issuance of degrees in digital format. These ordinances created guidelines and standards that must be adopted by Federal Universities for the signing of in digital format. The main objective of this work is to study these ordinances, the main technologies and digital signature standards used in the literature to create a digital signature system model for University of Brasília-UnB, which complies with the MEC and ICP-Brazil standards. Moreover, the model must be developed with the main standards and technologies in the market, cohesive to the current UnB architecture, easy to maintain and update to new standards that may emerge, and also be a fully open source project. An architectural model and a prototype in Java language were developed using XAdES4j library as a microservice intermediated by the bus used in UnB. The prototype developed was compared with the current digital signature system named C3Web. The comparative tests and results between the two solutions showed that the current system used in UnB does not perform the signature in accordance with the standard proposed by the MEC, in addition to being a private system using proprietary technologies for the execution of digital signatures. The tests performed with the proposed model demonstrated that it performs the digital signature in accordance with the XAdES-T standard, regulations of the MEC and ICP-Brazil. In addition, the solution presented a performance comparable to the current system used by UnB with a little more effective security than the current system used. The current model developed in this work can be a basis for the creation of future subscription systems for Brazilian Universities.

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