scholarly journals Dynamics of a geomagnetic storm on 7–10 September 2015 as observed by TWINS and simulated by CIMI

2018 ◽  
Vol 36 (5) ◽  
pp. 1439-1456 ◽  
Author(s):  
Joseph D. Perez ◽  
James Edmond ◽  
Shannon Hill ◽  
Hanyun Xu ◽  
Natalia Buzulukova ◽  
...  
Keyword(s):  
Partial Pressure ◽  
Ring Current ◽  
Inner Magnetosphere ◽  
Pressure Distributions ◽  
Global View ◽  
Ae Index ◽  
Night Side ◽  
Electric Potentials ◽  
First Time ◽  
Electric Shielding

Abstract. For the first time, direct comparisons of the equatorial ion partial pressure and pitch angle anisotropy observed by TWINS and simulated by CIMI are presented. The TWINS ENA images are from a 4-day period, 7–10 September 2015. The simulations use both the empirical Weimer 2K and the self-consistent RCM electric potentials. There are two moderate storms in succession during this period. In most cases, we find that the general features of the ring current in the inner magnetosphere obtained from the observations and the simulations are similar. Nevertheless, we do also see consistent contrasts between the simulations and observations. The simulated partial pressure peaks are often inside the observed peaks and more toward dusk than the measured values. There are also cases in which the measured equatorial ion partial pressure shows multiple peaks that are not seen in the simulations. This occurs during a period of intense AE index. The CIMI simulations consistently show regions of parallel anisotropy spanning the night side between approximately 6 and 8 RE, whereas the parallel anisotropy is seen in the observations only during the main phase of the first storm. The evidence from the unique global view provided by the TWINS observations strongly suggests that there are features in the ring current partial pressure distributions that can be best explained by enhanced electric shielding and/or spatially localized, short-duration injections.

scholarly journals Dynamics Geomagnetic Storm on 7–10 September 2015 as Observed by TWINS and Simulated by CIMI

2018 ◽  
Author(s):  
Joseph D. Perez ◽  
James Edmond ◽  
Shannon Hill ◽  
Hanyun Xu ◽  
Natalia Buzulukova ◽  
...  
Keyword(s):  
Ring Current ◽  
Magnetic Shielding ◽  
Inner Magnetosphere ◽  
Pressure Distributions ◽  
Global View ◽  
Ae Index ◽  
Self Consistent ◽  
Night Side ◽  
Electric Potentials ◽  
First Time

Abstract. For the first time, direct comparisons of the equatorial ion pressure and pitch angle anisotropy observed by TWINS and simulated by CIMI are presented. The TWINS ENA images are from a 4-day period, 7–10 September 2015. The simulations use both the empirical Weimer 2K and the self-consistent RCM electric potentials. There are two moderate storms in succession during this period. In most cases, we find that the general features of the ring current in the inner magnetosphere obtained from the observations and the simulations are similar. Nevertheless, we do see consistent indications of enhanced electric and magnetic shielding in the TWINS observations. The simulated pressure peaks are often inside the observed peaks and more toward dusk than the measured values. There are also cases in which the measured equatorial ion pressure shows multiple peaks that are not seen in the simulations. This occurs during a period of intense AE index, suggesting time and spatially dependent injections from the plasma sheet that are not included in these simulations. The simulations consistently show regions of parallel anisotropy spanning the night side between approximately 6 and 8 RE whereas the parallel anisotropy is seen in the observations only during the main phase of the first storm. This may indicate stronger electric and magnetic shielding than is present in the simulations. The evidence form the unique global view provided by the TWIN observations strongly suggests that there are features in the ring current pressure distributions that can be best explained by enhanced electric and magnetic shielding and/or spatially-localized, short-duration injections..

scholarly journals On the Relationship between Low Latitude Scintillation Onset and Sunset Terminator over Africa

2021 ◽  
Vol 13 (11) ◽  
pp. 2087
Author(s):  
Mogese Wassaie Mersha ◽  
Elias Lewi ◽  
Norbert Jakowski ◽  
Volker Wilken ◽  
Jens Berdermann ◽  
...  
Keyword(s):  
Moving Boundary ◽  
Occurrence Rate ◽  
Scintillation Index ◽  
Small Scale ◽  
Bahir Dar ◽  
Remarkable Change ◽  
Equatorial Africa ◽  
Night Side ◽  
Solar Terminator ◽  
First Time

The solar terminator is a moving boundary between day-side and night-side regions on the Earth, which is a substantial source of perturbations in the ionosphere. In the vicinity of the solar terminator, essential parameters like S4 index measurements are widely analyzed in order to monitor and predict perturbations in the ionosphere. The utilization of the scintillation index S4 is a well-accepted approach to describe the amplitude/intensity fluctuation of a received signal, predominantly caused by small-scale irregularities of the ionospheric plasma. We report on the longitudinal daily and seasonal occurrence of GNSS signal scintillations, using the data derived from the GNSS stations in Bahir Dar, Ethiopia, Lomé, Togo and Dakar, Senegal. The observed seasonal climatology of GNSS signal scintillations in equatorial Africa is adequately explained by the alignment of the solar terminator and local geomagnetic declination line. It should be pointed out that the strongest scintillations are most frequently observed during the time when the solar terminator is best aligned with the geomagnetic declination line. At all three stations, the comparison of computational and observational results indicated that the scintillation activity culminated around equinoxes in the years 2014, 2015 and 2016. Comparatively, the western equatorial Africa sector has the most intense, longest-lasting, and highest scintillation occurrence rate in equinoctial seasons in all three years. For the first time, we show that the seasonal variation of the scintillation peaks changes systematically from west to east at equatorial GNSS stations over Africa. A detailed analysis of the solar day–night terminator azimuth at ionospheric heights including the time equation shows that the scintillation intensity has a maximum if the azimuth of the terminator coincides with the declination line of the geomagnetic field. Due to the remarkable change of the declination by about 10° at the considered GNSS stations, the distance between scintillation peaks increases by 46 days when moving westward from the Bahir Dar to the Dakar GNSS station. The observations agree quite well with the computational results, thus confirming Tsunoda’s theory.

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 Another way of deriving the ring current decay time during disturbed periods

1995 ◽  
Vol 38 (2) ◽  
Author(s):  
M. M. Zossi de Artigas ◽  
J. R. Manzano
Keyword(s):  
Ring Current ◽  
Coupling Parameter ◽  
Life Time ◽  
Recovery Phase ◽  
Main Phase ◽  
Physical Analysis ◽  
Inner Magnetosphere ◽  
Current Decay ◽  
The Many ◽  
Energy Dissipated

Coupling parameter, E, and the total energy dissipated by the magnetosphere, UT, are determined for six disturbed periods, following three known criteria for UT computation. It is observed that UT exceeds E for Dst < -90 nT, for alI models. Differences between models reside on the estimated valnes for the particles' life time il1 the equatorial ring current. The values of TR, used in the models, are small during the main phase of the di."turbance, in disagreement with the charge exchange life time of the majority species, H+ and O'-. Based on this conclusion, a different criterion to calculate TR is proposed, differentiating the different stages of the perturbation. TR is calculated, for the main phase of the storm, from the rate of energy deposition estimation, Q, in the ring current. For Dst recovery phase, the vallles are obtained from a ring current decay law computation. The UTvu calculated, physically more coherent with the processes occurring during the event, is now smaller than expected. In this sense, it is understood that the power generated by the solar wind-magnetosphere dy- namo, should also be distributed in the inner magnetosphere, auroral zones and equatorial ring current, as in the outer magnetosphere, plasmoids in the tail shot in antisolar direction. A further adjustment of E, with the Chapman-Ferraro distance, 10' variable, has been made. Although the reslllts, improve the estimation of E, they are sti!l smaller than UT, except UTNU, for some disturbed periods. This result indicates the uncertainty in the computation of the input energy, by using the many expressions proposed in the literature, which are always presented as laws proportional to a given group of parameters, with an unknown factor of proportionality, which deserves more detailed physical analysis.

scholarly journals Storm time dynamics of ring current protons: Implications for the long‐term energy budget in the inner magnetosphere

2016 ◽  
Vol 43 (10) ◽  
pp. 4736-4744 ◽  
Author(s):  
Matina Gkioulidou ◽  
A. Y. Ukhorskiy ◽  
D. G. Mitchell ◽  
L. J. Lanzerotti
Keyword(s):  
Energy Budget ◽  
Ring Current ◽  
Inner Magnetosphere ◽  
Time Dynamics ◽  
Term Energy

scholarly journals The distribution of the ring current: Cluster observations

2011 ◽  
Vol 29 (9) ◽  
pp. 1655-1662 ◽  
Author(s):  
Q.-H. Zhang ◽  
M. W. Dunlop ◽  
M. Lockwood ◽  
R. Holme ◽  
Y. Kamide ◽  
...  
Keyword(s):  
Current Density ◽  
Ring Current ◽  
Local Times ◽  
Distribution Profile ◽  
Full Circle ◽  
Equatorial Current ◽  
The Mean ◽  
Current Flows ◽  
First Time

Abstract. Extending previous studies, a full-circle investigation of the ring current has been made using Cluster 4-spacecraft observations near perigee, at times when the Cluster array had relatively small separations and nearly regular tetrahedral configurations, and when the Dst index was greater than −30 nT (non-storm conditions). These observations result in direct estimations of the near equatorial current density at all magnetic local times (MLT) for the first time and with sufficient accuracy, for the following observations. The results confirm that the ring current flows westward and show that the in situ average measured current density (sampled in the radial range accessed by Cluster ~4–4.5 RE) is asymmetric in MLT, ranging from 9 to 27 nA m−2. The direction of current is shown to be very well ordered for the whole range of MLT. Both of these results are in line with previous studies on partial ring extent. The magnitude of the current density, however, reveals a distinct asymmetry: growing from 10 to 27 nA m−2 as azimuth reduces from about 12:00 MLT to 03:00 and falling from 20 to 10 nA m−2 less steadily as azimuth reduces from 24:00 to 12:00 MLT. This result has not been reported before and we suggest it could reflect a number of effects. Firstly, we argue it is consistent with the operation of region-2 field aligned-currents (FACs), which are expected to flow upward into the ring current around 09:00 MLT and downward out of the ring current around 14:00 MLT. Secondly, we note that it is also consistent with a possible asymmetry in the radial distribution profile of current density (resulting in higher peak at ~4–4.5 RE). We note that part of the enhanced current could reflect an increase in the mean AE activity (during the periods in which Cluster samples those MLT).

scholarly journals First current density measurements in the ring current region using simultaneous multi-spacecraft CLUSTER-FGM data

2005 ◽  
Vol 23 (5) ◽  
pp. 1849-1865 ◽  
Author(s):  
C. Vallat ◽  
I. Dandouras ◽  
M. Dunlop ◽  
A. Balogh ◽  
E. Lucek ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Current Density ◽  
Ring Current ◽  
Magnetic Activity ◽  
Activity Level ◽  
Local Current Density ◽  
Magnetospheric Configuration And Dynamics ◽  
Local Current ◽  
Current Region ◽  
First Time

Abstract. The inner magnetosphere's current mapping is one of the key elements for current loop closure inside the entire magnetosphere. A method for directly computing the current is the multi-spacecraft curlometer technique, which is based on the application of Maxwell-Ampère's law. This requires the use of four-point magnetic field high resolution measurements. The FGM experiment on board the four Cluster spacecraft allows, for the first time, an instantaneous calculation of the magnetic field gradients and thus a measurement of the local current density. This technique requires, however, a careful study concerning all the factors that can affect the accuracy of the J estimate, such as the tetrahedral geometry of the four spacecraft, or the size and orientation of the current structure sampled. The first part of this paper is thus providing a detailed analysis of the method accuracy, and points out the limitations of this technique in the region of interest. The second part is an analysis of the ring current region, which reveals, for the first time, the large latitudinal extent of the ring current, for all magnetic activity levels, as well as the latitudinal evolution of the perpendicular (and parallel) components of the current along the diffuse auroral zone. Our analysis also points out the sharp transition between two distinct plasma regions, with the existence of high diamagnetic currents at the interface, as well as the filamentation of the current inside the inner plasma sheet. A statistical study over multiple perigee passes of Cluster (at about 4 RE from the Earth) reveals the azimuthal extent of the partial ring current. It also reveals that, at these distances and all along the evening sector, there isn't necessarily a strong dependence of the local current density value on the magnetic activity level. This is a direct consequence of the ring current morphology evolution, as well as the relative positioning of the spacecraft with respect to the bulk of the ring current. It also proves the existence of a substantial ring current at these distances, all over the evening and the post-midnight sector. Keywords. Magnetospheric physics (Current systems; Energetic particles, trapped; Magnetospheric configuration and dynamics)

scholarly journals Strong Southward and Northward Currents Observed in the Inner Plasma Sheet

2019 ◽  
Author(s):  
Yanyan Yang ◽  
Chao Shen ◽  
Yong Ji
Keyword(s):  
Magnetic Field ◽  
Plasma Sheet ◽  
Ring Current ◽  
Generation Mechanism ◽  
Storm Events ◽  
Current Generation ◽  
Inner Magnetosphere ◽  
Latitude Region ◽  
Field Lines ◽  
The Magnetic Field

Abstract. It is generally believed that field aligned currents (FACs) and the ring current (RC) are two dominant parts of the inner magnetosphere. However, using the Cluster spacecraft crossing of the pre-midnight inner plasma sheet in the latitude region between 10° N and 30° N, it is found that, during large storm events, in addition to FACs and the RC, there also exist strong southward and northward currents, which cannot be FACs, because the magnetic field in these regions is mainly along the XY plane. Detailed investigation shows that both magnetic field lines (MFLs) and currents in these regions highly fluctuate. When the curvature of MFLs changes direction in the XY plane, the current also alternatively switches between southward and northward. Further analysis of the current generation mechanism indicates that the most reasonable candidate for the origin of these southward and northward currents is the curvature drift of energetic particles.

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.

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