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

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 & 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.

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Statistical analysis of storm-time near-Earth current systems

Annales Geophysicae ◽

10.5194/angeo-33-965-2015 ◽

2015 ◽

Vol 33 (8) ◽

pp. 965-982 ◽

Cited By ~ 8

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.

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

Annales Geophysicae ◽

10.5194/angeo-27-659-2009 ◽

2009 ◽

Vol 27 (2) ◽

pp. 659-668 ◽

Cited By ~ 55

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.

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Сomparison of ion pressure variations derived from Cluster/CODIF and the combined Cluster/CODIF&RAPID data during prolonged dipolarizations in the near Earth magnetotail

10.5194/egusphere-egu2020-1488 ◽

2020 ◽

Author(s):

Andrey Malykhin ◽

Elena Grigorenko ◽

Elena Kronberg ◽

Patrick Daly

Keyword(s):

Energy Range ◽

Energy Flux ◽

Total Pressure ◽

High Energy ◽

Plasma Pressure ◽

Energy Threshold ◽

Superposed Epoch Analysis ◽

Flux Increase ◽

Epoch Analysis ◽

Thermal Part

Usually, for the plasma pressure estimation in the plasma sheet&#160; ion observations in the energy range up to ~40 keV are used. However, the thermal part of the distribution function can pass beyond the high energy threshold of an instrument during active events like dipolarizations. In such cases the entire ion population is not measured and the ion pressure can be underestimated. We study this problem by using Cluster mission observations provided&#160; by two instruments: thermal plasma instrument - CODIF (up to 38 keV) and suprathermal instrument - RAPID (from 40 up to 1500 keV). We analyzed 11 dipolarization events and showed that in all events the maximum of ion energy flux was shifted to high energy threshold of CODIF instrument. Simultaneously, the energy flux increase in suprathermal energy range was observed by RAPID. For H+ and O+ ion components we calculate the pressure of suprathermal population and showed that the total pressure estimated by using both CODIF and RAPID instruments at some intervals exceeds the pressure estimated only from CODIF data up to 5 times. The superposed epoch analysis applied to 11 dipolarization events from our data base showed that the total pressure of H+ and O+ ion components can be in 2-5 times underestimated in the course of dipolarization.

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Superposed epoch analysis applied to large-amplitude travelling convection vortices

Annales Geophysicae ◽

10.1007/s00585-998-0743-0 ◽

1998 ◽

Vol 16 (7) ◽

pp. 743-753 ◽

Cited By ~ 9

Author(s):

H. Lühr ◽

M. Rother ◽

T. Iyemori ◽

T. L. Hansen ◽

R. P. Lepping

Keyword(s):

Solar Wind ◽

Large Amplitude ◽

Selection Criteria ◽

Solar Rotation ◽

Current System ◽

Azimuthal Direction ◽

Superposed Epoch Analysis ◽

Northern Half ◽

Epoch Analysis ◽

Image Network

Abstract. For the six months from 1 October 1993 to 1 April 1994 the recordings of the IMAGE magnetometer network have been surveyed in a search for large-amplitude travelling convection vortices (TCVs). The restriction to large amplitudes (>100 nT) was chosen to ensure a proper detection of evens also during times of high activity. Readings of all stations of the northern half of the IMAGE network were employed to check the consistency of the ground signature with the notation of a dual-vortex structure moving in an azimuthal direction. Applying these stringent selection criteria we detected a total of 19 clear TCV events. The statistical properties of our selection resemble the expected characteristics of large-amplitude TCVs. New and unexpected results emerged from the superposed epoch analysis. TCVs tend to form during quiet intervals embedded in moderately active periods. The occurrence of events is not randomly distributed but rather shows a clustering around a few days. These clusters recur once or twice every 27 days. Within a storm cycle they show up five to seven days after the commencement. With regard to solar wind conditions, we see the events occurring in the middle of the IMF sector structure. Large-amplitude TCVs seem to require certain conditions to make solar wind transients 'geoeffective', which have the tendency to recur with the solar rotation period.Key words. Ionosphere (Aural ionosphere; Ionosphere- magnetosphere interactions) · Magnetospheric Physics (current system)

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Superposed epoch analysis of dense plasma access to geosynchronous orbit

Annales Geophysicae ◽

10.5194/angeo-23-2519-2005 ◽

2005 ◽

Vol 23 (7) ◽

pp. 2519-2529 ◽

Cited By ~ 32

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)

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Superposed Epoch Analysis of the Energetic Electron Flux Variations During CIRs Measured by BD‐IES

Space Weather ◽

10.1029/2019sw002296 ◽

2019 ◽

Vol 17 (12) ◽

pp. 1765-1782

Author(s):

Zefan Yin ◽

Hong Zou ◽

Yuguang Ye ◽

Qiugang Zong ◽

Yongfu Wang

Keyword(s):

Electron Flux ◽

Energetic Electron ◽

Superposed Epoch Analysis ◽

Epoch Analysis

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Superposed Epoch Analyses of electron-driven and proton-driven magnetic dips

10.5194/egusphere-egu21-9315 ◽

2021 ◽

Author(s):

Hui Zhu ◽

Lunjin Chen

Keyword(s):

Statistical Characteristics ◽

Relativistic Electrons ◽

Magnetic Fluctuations ◽

Inner Magnetosphere ◽

Superposed Epoch Analysis ◽

Van Allen Probes ◽

Epoch Analysis ◽

The Relationship ◽

Statistical Results

In this study, we use the Van Allen Probes data statistically to investigate the features of magnetic dips by the means of superposed epoch analysis. Based on the different max values of electron and proton plasma betas, we categorize the dips into two types: electron-driven dips and proton-driven dips. Superposed epoch analysis on two types of magnetic dips suggests the correlation between the magnetic fluctuations and plasma betas. Moreover, the occurrence of the butterfly distributions of relativistic electrons driven by the magnetic dips is confirmed by the statistical results. Our results reveal the statistical characteristics of magnetic dips and build up the relationship among the magnetic fluctuations and several parameters, indicating the potentially important role of magnetic dips in the dynamics of the inner magnetosphere.

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

Solar Physics ◽

10.1007/s11207-021-01796-3 ◽

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.

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