scholarly journals Statistical analysis of storm-time near-Earth current systems

2015 ◽  
Vol 33 (8) ◽  
pp. 965-982 ◽  
Author(s):  
M. W. Liemohn ◽  
R. M. Katus ◽  
R. Ilie
Keyword(s):  
Electric Field ◽  
Ring Current ◽  
Recovery Phase ◽  
Hot Electron ◽  
Early Recovery ◽  
Superposed Epoch Analysis ◽  
Tail Current ◽  
Near Earth Space ◽  
Epoch Analysis ◽  
Current Systems

Abstract. Currents from the Hot Electron and Ion Drift Integrator (HEIDI) inner magnetospheric model results for all of the 90 intense storms (disturbance storm-time (Dst) minimum < −100 nT) from solar cycle 23 (1996–2005) are calculated, presented, and analyzed. We have categorized these currents into the various systems that exist in near-Earth space, specifically the eastward and westward symmetric ring current, the partial ring current, the banana current, and the tail current. The current results from each run set are combined by a normalized superposed epoch analysis technique that scales the timeline of each phase of each storm before summing the results. It is found that there is a systematic ordering to the current systems, with the asymmetric current systems peaking during storm main phase (tail current rising first, then the banana current, followed by the partial ring current) and the symmetric current systems peaking during the early recovery phase (westward and eastward symmetric ring current having simultaneous maxima). The median and mean peak amplitudes for the current systems ranged from 1 to 3 MA, depending on the setup configuration used in HEIDI, except for the eastward symmetric ring current, for which the mean never exceeded 0.3 MA for any HEIDI setup. The self-consistent electric field description in HEIDI yielded larger tail and banana currents than the Volland–Stern electric field, while the partial and symmetric ring currents had similar peak values between the two applied electric field models.

scholarly journals A superposed epoch analysis of auroral evolution during substorm growth, onset and recovery: open magnetic flux control of substorm intensity

2009 ◽  
Vol 27 (2) ◽  
pp. 659-668 ◽  
Author(s):  
S. E. Milan ◽  
A. Grocott ◽  
C. Forsyth ◽  
S. M. Imber ◽  
P. D. Boakes ◽  
...  
Keyword(s):  
Magnetic Flux ◽  
Ring Current ◽  
Low Latitude ◽  
Superposed Epoch Analysis ◽  
Before And After ◽  
Open Magnetic Flux ◽  
Open Flux ◽  
Epoch Analysis ◽  
Proton Aurora ◽  
Current Systems

Abstract. We perform two superposed epoch analyses of the auroral evolution during substorms using the FUV instrument on the Imager for Magnetopause-to-Aurora Global Explorer (IMAGE) spacecraft. The larger of the two studies includes nearly 2000 substorms. We subdivide the substorms by onset latitude, a measure of the open magnetic flux in the magnetosphere, and determine average auroral images before and after substorm onset, for both electron and proton aurora. Our results indicate that substorms are more intense in terms of auroral brightness when the open flux content of the magnetosphere is larger, and that magnetic flux closure is more significant. The increase in auroral brightness at onset is larger for electrons than protons. We also show that there is a dawn-dusk offset in the location of the electron and proton aurora that mirrors the relative locations of the region 1 and region 2 current systems. Superposed epoch analyses of the solar wind, interplanetary magnetic field, and geomagnetic indices for the substorms under study indicate that dayside reconnection is expected to occur at a faster rate prior to low latitude onsets, but also that the ring current is enhanced for these events.

scholarly journals Semiannual Variation in radiation belts particle fluxes: Van Allen probes observations

2018 ◽  
Author(s):  
Facundo L. Poblet ◽  
Francisco Azpilicueta
Keyword(s):  
Energy Range ◽  
Ring Current ◽  
Electron Flux ◽  
Current System ◽  
Energy Levels ◽  
Superposed Epoch Analysis ◽  
Van Allen Probes ◽  
Semiannual Variation ◽  
Weather Parameters ◽  
Epoch Analysis

Abstract. The Semiannual Variation (SAV) is an annual pattern characterized by maxima around the equinoxes and minima near solstices observed in many space weather parameters. Several authors have studied this variation in the electron fluxes of the magnetosphere, focusing only in a few energy levels. In this investigation, Van Allen probes data are processed to extend SAV studies in electron fluxes of a wider energy range. A superposed epoch analysis was applied to data of the REPT and MagEIS instruments obtaining a clear semiannual pattern in the superposed year for L-shell values between 2.5 and 6.5. The Day Of Year (DOY) at which the highest electron flux values are detected near the September equinox coincide with the Russel &amp; McPherron prediction. However, the DOY of the maximum expected close the March equinox occurs with a one month lag from the prediction of the accepted models. In addition, integrating over L-shell the annual DOY-L data with the semiannual pattern resulted in temporal curves that enabled to determine the energy range for which the SAV can be detected: from MeV to tens MeV energy values. Finally, an additional analysis of the fluxes of the Ring Current principal components (H+ and O+ ions) was performed, obtaining no evidence of a SAV on them. This result could indicate that the widely recognized semiannual pattern in the geomagnetic activity is related to a different current system.

scholarly journals Relation between the ring current and the tail current during magnetic storms

2005 ◽  
Vol 23 (2) ◽  
pp. 523-533 ◽  
Author(s):  
V. V. Kalegaev ◽  
N. Y. Ganushkina ◽  
T. I. Pulkkinen ◽  
M. V. Kubyshkina ◽  
H. J. Singer ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Ring Current ◽  
Storm Events ◽  
Dst Index ◽  
Tail Current ◽  
Current Contribution ◽  
Intense Storm ◽  
Current Systems ◽  
Good Agreement

Abstract. We study the dynamics of the magnetospheric large-scale current systems during storms by using three different magnetospheric magnetic field models: the paraboloid, event-oriented, and Tsyganenko T01 models. We have modelled two storm events, one moderate storm on 25-26 June 1998, when Dst reached -120nT and one intense storm on 21-23 October 1999, when Dst dropped to -250nT. We compare the observed magnetic field from GOES 8, GOES 9, and GOES 10, Polar and Geotail satellites with the magnetic field given by the three models to estimate their reliability. All models demonstrated quite good agreement with observations. Since it is difficult to measure exactly the relative contributions from different current systems to the Dst index, we compute the contributions from ring, tail and magnetopause currents given by the three magnetic field models. We discuss the dependence of the obtained contributions to the Dst index in relation to the methods used in constructing the models. All models show a significant tail current contribution to the Dst index, comparable to the ring current contribution during moderate storms. The ring current becomes the major Dst source during intense storms.

scholarly journals Superposed epoch analysis of dense plasma access to geosynchronous orbit

2005 ◽  
Vol 23 (7) ◽  
pp. 2519-2529 ◽  
Author(s):  
B. Lavraud ◽  
M. H. Denton ◽  
M. F. Thomsen ◽  
J. E. Borovsky ◽  
R. H. W. Friedel
Keyword(s):  
Plasma Sheet ◽  
Ring Current ◽  
Dense Plasma ◽  
Transport Processes ◽  
Geosynchronous Orbit ◽  
Plasma Convection ◽  
Tail Region ◽  
Superposed Epoch Analysis ◽  
Magnetospheric Convection ◽  
Epoch Analysis

Abstract. We report on the occurrence of dense plasma access to geosynchronous orbit. We performed a superposed epoch analysis of 1464 events of dense (>2 cm–3 at onset) plasma observed by the MPA instruments on board the Los Alamos satellites, for the period 1990–2002. The results allow us to study the temporal evolution of various plasma parameters as a function of local time. We show that dense plasma access to geosynchronous orbit mostly occurs near local midnight. This dense plasma population is shown to be freshly injected from the mid-tail region, colder than the typical plasma sheet and composed of a relatively small O+ component. This population is thus probably the result of a cold, dense plasma sheet (CDPS) injection from the mid-tail region. Cold and dense ion populations are also observed on the dawnside of geosynchronous orbit at a similar epoch time. However, we demonstrate that this latter population is not the result of the dawnward transport of the population detected near midnight. The properties of this ion population may arise from the contribution of both ionospheric upflows and precipitating plasma sheet material. The correlation of an enhanced Kp index with the arrival of the CDPS at geosynchronous orbit shows that the inward transport of this population is allowed by an enhanced magnetospheric convection. Surprisingly, this dense plasma does not, in general, lead to a stronger Dst (ring current strength) within the 12 h following the CDPS injection. It is noted, however, that the superposed Kp index returns to relatively low values soon after the arrival of the CDPS. This may suggest that the dense plasma is, given the average of the 1464 events of this study, only transiting through geosynchronous orbit without accessing the inner regions and, therefore, does not contribute to the ring current. Keywords. Magnetospheric physics (Plasma convection; Plasma sheet) – Space plasma physics (Transport processes)

scholarly journals Defining and resolving current systems in geospace

2015 ◽  
Vol 33 (11) ◽  
pp. 1369-1402 ◽  
Author(s):  
N. Y. Ganushkina ◽  
M. W. Liemohn ◽  
S. Dubyagin ◽  
I. A. Daglis ◽  
I. Dandouras ◽  
...  
Keyword(s):  
Ring Current ◽  
Lower Latitude ◽  
Nonlinear Feedback ◽  
Physical Processes ◽  
Specific System ◽  
Earth Space ◽  
Near Earth Space ◽  
High Latitude Region ◽  
Latitude Region ◽  
Current Systems

Abstract. Electric currents flowing through near-Earth space (R ≤ 12 RE) can support a highly distorted magnetic field topology, changing particle drift paths and therefore having a nonlinear feedback on the currents themselves. A number of current systems exist in the magnetosphere, most commonly defined as (1) the dayside magnetopause Chapman–Ferraro currents, (2) the Birkeland field-aligned currents with high-latitude "region 1" and lower-latitude "region 2" currents connected to the partial ring current, (3) the magnetotail currents, and (4) the symmetric ring current. In the near-Earth nightside region, however, several of these current systems flow in close proximity to each other. Moreover, the existence of other temporal current systems, such as the substorm current wedge or "banana" current, has been reported. It is very difficult to identify a local measurement as belonging to a specific system. Such identification is important, however, because how the current closes and how these loops change in space and time governs the magnetic topology of the magnetosphere and therefore controls the physical processes of geospace. Furthermore, many methods exist for identifying the regions of near-Earth space carrying each type of current. This study presents a robust collection of these definitions of current systems in geospace, particularly in the near-Earth nightside magnetosphere, as viewed from a variety of observational and computational analysis techniques. The influence of definitional choice on the resulting interpretation of physical processes governing geospace dynamics is presented and discussed.

scholarly journals The Two-step Forbush Decrease: A Tale of Two Substructures Modulating Galactic Cosmic Rays within Coronal Mass Ejections

2021 ◽  
Vol 922 (2) ◽  
pp. 216
Author(s):  
Miho Janvier ◽  
Pascal Démoulin ◽  
Jingnan Guo ◽  
Sergio Dasso ◽  
Florian Regnault ◽  
...  
Keyword(s):  
Cosmic Rays ◽  
Coronal Mass Ejections ◽  
Forbush Decrease ◽  
Recovery Phase ◽  
Galactic Cosmic Rays ◽  
Space Environment ◽  
Interplanetary Coronal Mass Ejections ◽  
Superposed Epoch Analysis ◽  
Epoch Analysis

Abstract Interplanetary coronal mass ejections (ICMEs) are known to modify the structure of the solar wind as well as interact with the space environment of planetary systems. Their large magnetic structures have been shown to interact with galactic cosmic rays (GCRs), leading to the Forbush decrease (FD) phenomenon. We revisit in the present article the 17 yr of Advanced Composition Explorer spacecraft ICME detection along with two neutron monitors (McMurdo and Oulu) with a superposed epoch analysis to further analyze the role of the magnetic ejecta in driving FDs. We investigate in the following the role of the sheath and the magnetic ejecta in driving FDs, and we further show that for ICMEs without a sheath, a magnetic ejecta only is able to drive significant FDs of comparable intensities. Furthermore, a comparison of samples with and without a sheath with similar speed profiles enable us to show that the magnetic field intensity, rather than its fluctuations, is the main driver for the FD. Finally, the recovery phase of the FD for isolated magnetic ejecta shows an anisotropy in the level of the GCRs. We relate this finding at 1 au to the gradient of the GCR flux found at different heliospheric distances from several interplanetary missions.

scholarly journals Testing electric field models using ring current ion energy spectra from the Equator-S ion composition (ESIC) instrument

1999 ◽  
Vol 17 (12) ◽  
pp. 1611-1621 ◽  
Author(s):  
L. M. Kistler ◽  
B. Klecker ◽  
V. K. Jordanova ◽  
E. Möbius ◽  
M. A. Popecki ◽  
...  
Keyword(s):  
Electric Field ◽  
Recovery Phase ◽  
Energy Spectra ◽  
Spectral Features ◽  
Ion Composition ◽  
Plasma Convection ◽  
Early Recovery ◽  
Ion Energy ◽  
Storms And Substorms ◽  
Drift Path

Abstract. During the main and early recovery phase of a geomagnetic storm on February 18, 1998, the Equator-S ion composition instrument (ESIC) observed spectral features which typically represent the differences in loss along the drift path in the energy range (5–15 keV/e) where the drift changes from being E × B dominated to being gradient and curvature drift dominated. We compare the expected energy spectra modeled using a Volland-Stern electric field and a Weimer electric field, assuming charge exchange along the drift path, with the observed energy spectra for H+ and O+. We find that using the Weimer electric field gives much better agreement with the spectral features, and with the observed losses. Neither model, however, accurately predicts the energies of the observed minima.Key words. Magnetospheric physics (energetic particles trapped; plasma convection; storms and substorms)

scholarly journals Comment on Lockwood and Davis, "On the longitudinal extent of magnetopause reconnection pulses"

1999 ◽  
Vol 17 (2) ◽  
pp. 173-177 ◽  
Author(s):  
W. J. Heikkila
Keyword(s):  
Electric Field ◽  
Solar Wind Plasma ◽  
Closed Field ◽  
Transient Phenomena ◽  
Superposed Epoch Analysis ◽  
Dayside Magnetopause ◽  
Field Lines ◽  
Epoch Analysis ◽  
Definition Of ◽  
Magnetopause Reconnection

Abstract. Lockwood and Davis (1996) present a concise description of magnetopause reconnection pulses, with the claimed support of three types of observations: (1) flux transfer events (FTE), (2) poleward-moving auroral forms on the dayside, and (3) steps in cusp ion dispersion characteristics. However, there are a number of errors and misconceptions in the paper that make their conclusions untenable. They do not properly take account of the fact that the relevant processes operate in the presence of a plasma. They fail to notice that the source of energy (a dynamo with E · J<0) must be close to the region of dissipation (the electrical load with E · J>0) in transient phenomena, since energy (or information) cannot travel faster than the group velocity of waves in the medium (here the Alfvén velocity VA). In short, Lockwood and Davis use the wrong contour in their attempt to evaluate the electromotive force (emf). This criticism goes beyond their article: a dynamo is not included in the usual definition of reconnection, only the reconnection load. Without an explicit source of energy in the assumed model, the idea of magnetic reconnection is improperly posed. Recent research has carried out a superposed epoch analysis of conditions near the dayside magnetopause and has found the dynamo and the load, both within the magnetopause current sheet. Since the magnetopause current is from dawn to dusk, the sign of E · J reflects the sign of the electric field. The electric field reverses, within the magnetopause; this can be discovered by an application of Lenz's law using the concept of erosion of the magnetopause. The net result is plasma transfer across the magnetopause to feed the low latitude boundary layer, at least partly on closed field lines, and viscous interaction as the mechanism by which solar wind plasma couples to the magnetosphere.

scholarly journals Solar Irradiance Variability Due to Solar Flares Observed in Lyman-Alpha Emission

Solar Physics ◽  
2021 ◽  
Vol 296 (3) ◽  
Author(s):  
Ryan O. Milligan
Keyword(s):  
Solar Flares ◽  
Solar Spectrum ◽  
Neutral Hydrogen ◽  
Solar Limb ◽  
High Background ◽  
Superposed Epoch Analysis ◽  
Lyman Alpha ◽  
Alpha Emission ◽  
Epoch Analysis ◽  
Very High

AbstractAs the Lyman-alpha (Ly$\upalpha $ α ) line of neutral hydrogen is the brightest emission line in the solar spectrum, detecting increases in irradiance due to solar flares at this wavelength can be challenging due to the very high background. Previous studies that have focused on the largest flares have shown that even these extreme cases generate enhancements in Ly$\upalpha $ α of only a few percent above the background. In this study, a superposed-epoch analysis was performed on ≈8500 flares greater than B1 class to determine the contribution that they make to changes in the solar EUV irradiance. Using the peak of the 1 – 8 Å X-ray emission as a fiducial time, the corresponding time series of 3123 B- and 4972 C-class flares observed in Ly$\upalpha $ α emission by the EUV Sensor on the Geostationary Operational Environmental Satellite 15 (GOES-15) were averaged to reduce background fluctuations and improve the flare signal. The summation of these weaker events showed that they produced a 0.1 – 0.3% enhancement to the solar Ly$\upalpha $ α irradiance on average. For comparison, the same technique was applied to 453 M- and 31 X-class flares, which resulted in a 1 – 4% increase in Ly$\upalpha $ α emission. Flares were also averaged with respect to their heliographic angle to investigate any potential center-to-limb variation. For each GOES class, the relative enhancement in Ly$\upalpha $ α at the flare peak was found to diminish for flares that occurred closer to the solar limb due to the opacity of the line and/or foreshortening of the footpoints. One modest event included in the study, a C6.6 flare, exhibited an unusually high increase in Ly$\upalpha $ α of 7% that may have been attributed to a failed filament eruption. Increases of this magnitude have hitherto only been associated with a small number of X-class flares.

Sign in / Sign up

Export Citation Format

Share Document