Superposed Epoch Analysis of Nighttime Magnetic Perturbation Events Observed in Arctic Canada

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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Classification of fast flows in central plasma sheet: Superposed epoch analysis based on THEMIS observations

Journal of Geophysical Research Space Physics ◽

10.1002/2014ja020105 ◽

2014 ◽

Vol 119 (9) ◽

pp. 7199-7213 ◽

Cited By ~ 1

Author(s):

H. Li ◽

C. Wang ◽

S. Y. Fu

Keyword(s):

Plasma Sheet ◽

Superposed Epoch Analysis ◽

Central Plasma ◽

Central Plasma Sheet ◽

Epoch Analysis

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Specific interplanetary conditions for CIR-, Sheath-, and ICME-induced geomagnetic storms obtained by double superposed epoch analysis

Annales Geophysicae ◽

10.5194/angeo-28-2177-2010 ◽

2010 ◽

Vol 28 (12) ◽

pp. 2177-2186 ◽

Cited By ~ 57

Author(s):

Yu. I. Yermolaev ◽

N. S. Nikolaeva ◽

I. G. Lodkina ◽

M. Yu. Yermolaev

Keyword(s):

Large Scale ◽

Geomagnetic Storms ◽

Magnetic Cloud ◽

Magnetic Storms ◽

Main Phase ◽

Corotating Interaction Region ◽

Superposed Epoch Analysis ◽

Epoch Analysis ◽

Archive Data ◽

Scale Types

Abstract. A comparison of specific interplanetary conditions for 798 magnetic storms with Dst <−50 nT during 1976–2000 was made on the basis of the OMNI archive data. We categorized various large-scale types of solar wind as interplanetary drivers of storms: corotating interaction region (CIR), Sheath, interplanetary CME (ICME) including both magnetic cloud (MC) and Ejecta, separately MC and Ejecta, and "Indeterminate" type. The data processing was carried out by the method of double superposed epoch analysis which uses two reference times (onset of storm and minimum of Dst index) and makes a re-scaling of the main phase of the storm in a such way that all storms have equal durations of the main phase in the new time reference frame. This method reproduced some well-known results and allowed us to obtain some new results. Specifically, obtained results demonstrate that (1) in accordance with "output/input" criteria the highest efficiency in generation of magnetic storms is observed for Sheath and the lowest one for MC, and (2) there are significant differences in the properties of MC and Ejecta and in their efficiencies.

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Trends in volcanic degassing through eruption cycles: insights from satellite measurements

10.5194/egusphere-egu21-14092 ◽

2021 ◽

Author(s):

Simon Carn ◽

Vitali Fioletov ◽

Chris McLinden ◽

Nickolay Krotkov ◽

Can Li

Keyword(s):

Volcanic Emissions ◽

Ozone Monitoring Instrument ◽

Satellite Measurements ◽

Volcanic Gas ◽

Volcanic Degassing ◽

Superposed Epoch Analysis ◽

Decadal Scale ◽

Gas Measurements ◽

Epoch Analysis ◽

Lower Magnitude

Effective use of volcanic gas measurements for eruption forecasting and hazard mitigation at active volcanoes requires an understanding of long-term degassing behavior as context. Much recent progress has been made in quantifying global volcanic emissions of sulfur dioxide (SO2) and other gas species by expanding the coverage of ground-based sensor networks and through analysis of decadal-scale satellite datasets. Combined, these advances have provided valuable constraints on the magnitude and variability of SO2 emissions at over 120 actively degassing volcanoes worldwide. Being less constrained by the style or location of volcanic activity, satellite measurements can provide greater insight into trends in volcanic degassing during eruption cycles. Here, we present an analysis of ~15 years of volcanic SO2 measurements by the ultraviolet (UV) Ozone Monitoring Instrument (OMI) aboard NASA&#8217;s Aura satellite, focused on observed trends in SO2 emissions spanning eruptions of varying magnitude. The Aura/OMI measurements have been used to estimate annual mean SO2 emissions at ~100 volcanoes active between 2005 and 2020, around 80 of which erupted during the 15-year period. Superposed epoch analysis (SEA) of SO2 emission trends for the erupting volcanoes (with eruption magnitudes ranging from Volcanic Explosivity Index [VEI] 2 to 4) provides evidence that volcanoes exhibiting higher levels of SO2 emission in the years prior to eruption typically produce eruptions of lower magnitude, and vice versa. Post-eruptive SO2 degassing exceeds pre-eruptive emissions for several years after eruptions with VEI 3-4 and may scale with eruption size; perhaps consistent with larger eruptions being supplied by larger magma intrusions which continue to degas in subsequent years. The SEA is most robust for eruptions of intermediate magnitude (VEI 3) which are the most common events in the recent global eruption record covered by the OMI measurements. Limited observations of larger eruptions (VEI 5+) suggest significant differences in degassing trends during these larger events. Future work will extend the satellite-based estimates of volcanic SO2 emissions both forward and backward in time using other UV satellite instruments, generating longer records of SO2 degassing (extending back to 1978 for the strongest volcanic sources of SO2) that will be used to further explore and constrain these relationships. &#160;

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The Variation of Ionospheric O+ and H+ Outflow during Sawtooth Oscillations

10.5194/egusphere-egu21-13991 ◽

2021 ◽

Author(s):

Niloufar Nowrouzi ◽

Lynn Kistler ◽

Eric Lund ◽

Kai Zhao

Keyword(s):

Plasma Sheet ◽

Statistical Study ◽

Onset Time ◽

Direct Access ◽

Data Set ◽

Superposed Epoch Analysis ◽

3D Data ◽

Before And After ◽

Epoch Analysis ◽

Sawtooth Oscillations

Sawtooth events are repeated injections of energetic particles at geosynchronous orbit. Although studies have shown that 94% of sawtooth events occur during &#160;magnetic storm times, the main factor that causes a sawtooth event is unknown. Simulations have suggested that heavy ions like O+&#160;may play a role in driving the sawtooth mode by increasing the magnetotail pressure and causing the magnetic tail to stretch. O+&#160;ions located in the nightside auroral region have a direct access to the near-earth plasma-sheet. O+ in the dayside cusp can reach to the midtail plasma-sheet when the convection velocity is sufficiently strong. Whether the dayside or nightside source is more important is not known.We show results of a statistical study of the variation of the O+ and H+ outflow flux during sawtooth events for SIR and ICME sawtooth events. We perform a superposed epoch analysis of the ion outflow using the TEAMS (Time-of-Flight Energy Angle Mass Spectrograph) instrument on the FAST spacecraft. TEAMS measures the ion composition over the energy range of 1 eV e-1&#160;to 12 keV e-1.&#160;&#160;We have done major corrections and calibrations (producing 3D data set, anode calibration, mass classification, removing ram effect and incorporating dead time corrections) on&#160;TEAMS data and produced a data set for four data species (H+, O+, and He+).&#160;From 1996 to 2007, we have data for 133 orbits of CME-driven and for 103 orbits of SIR-driven sawtooth events with an altitude above 1500 km. We found that:<ul><li>the averaged O+ outflow flux is more intense in the cusp dayside than in the nightside, before and after onset time.</li> <li>Before onset, an intense averaged outflow flux in the dawnside of CME events is seen. This outflow decreases after onset time.</li> <li>In both CME-driven and SIR-driven, the averaged O+ outflow increases after onset time, in the nightside, cusp dayside. This increase is greater on the nightside than in the cusp.</li> </ul>We will develop this study by performing a similar statistical study for H+ outflow and finally will compare the H+ result with the O+ result.

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Superposed epoch analysis of coupling mechanisms captured by meteor radars during sudden stratospheric warmings

10.5194/dach2022-84 ◽

2021 ◽

Author(s):

Benedikt Gast ◽

Ales Kuchar ◽

Gunter Stober ◽

Christoph Jacobi ◽

Dimitry Pokhotelov ◽

...

Keyword(s):

Zonal Wind ◽

Lower Thermosphere ◽

Rio Grande ◽

Meridional Wind ◽

Meteorological Conditions ◽

Special Focus ◽

Wind Component ◽

Superposed Epoch Analysis ◽

Epoch Analysis ◽

Coupling Mechanisms

Previous studies that analysed the mesosphere and lower thermosphere (MLT) dynamics during sudden stratospheric warmings (SSWs) were limited only to particular SSWs or focused on a particular station representative only for some regions. Here we describe a comprehensive study of the average meteorological conditions during SSWs with a special focus on the general contribution of planetary (PW) and gravity (GW) waves as primary coupling mechanisms between lower and upper atmosphere. The average meteorological conditions in the MLT during SSWs were analyzed using a superposed epoch analysis (Denton et al., 2019) of meteor radar measurements for stations in the northern (NH: Collm, Kiruna, Sodankyla, CMOR) and the southern hemisphere (SH: Rio Grande, Davis, Rothera) for the altitude range of 80&#8211;100 km Using the adaptive spectral filtering method (Stober et al., 2021), we study in detail PW and GW characteristics in addition to measured zonal and meridional wind components in a time period from 2000 to 2020. In the NH the zonal wind is typically decreasing from around two weeks before the SSW onset, corresponding to an increased PW activity. Around the SSW onset, latitudinal differences in the zonal wind component as well as the PW activity can be seen. In the weeks before the SSW onset, the stations in the NH also show an increased level of GW kinetic energy. The meridional wind at the NH stations fluctuates with a periodicity of about 10 days before and around the onset. In contrast to previous studies (e.g. Yasui et al., 2016), the measurements in the SH are consistent with the inter-hemispheric coupling hypothesis. The expected downward shift of GW drag (K&#246;rnich and Becker, 2010) was reproduced by a downward travelling layer of enhanced GW activity at Davis and Rio Grande. Finally, the role of the terdiurnal tide in the GW energy composite is considered.

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The ionospheric heating beneath the magnetospheric cleft revisited

Annales Geophysicae ◽

10.5194/angeo-23-827-2005 ◽

2005 ◽

Vol 23 (3) ◽

pp. 827-830 ◽

Cited By ~ 4

Author(s):

G. W. Prölss

Keyword(s):

Magnetic Activity ◽

Topside Ionosphere ◽

Ionospheric Heating ◽

Superposed Epoch Analysis ◽

Theoretical Predictions ◽

Northern Winter ◽

The Mean ◽

Epoch Analysis ◽

Winter Hemisphere ◽

Prominent Peak

Abstract. A prominent peak in the electron temperature of the topside ionosphere is observed beneath the magnetospheric cleft. The present study uses DE-2 data obtained in the Northern Winter Hemisphere to investigate this phenomenon. First, the dependence of the location and magnitude of the temperature peak on the magnetic activity is determined. Next, using a superposed epoch analysis, the mean latitudinal profile of the temperature enhancement is derived. The results of the present study are compared primarily with those obtained by Titheridge (1976), but also with more recent observations and theoretical predictions.

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On the alignment of velocity and magnetic fields within magnetosheath jets

Annales Geophysicae ◽

10.5194/angeo-38-287-2020 ◽

2020 ◽

Vol 38 (2) ◽

pp. 287-296

Author(s):

Ferdinand Plaschke ◽

Maria Jernej ◽

Heli Hietala ◽

Laura Vuorinen

Keyword(s):

Magnetic Fields ◽

Entire Range ◽

Dynamic Pressure ◽

Bow Shock ◽

Superposed Epoch Analysis ◽

Magnetospheric Multiscale ◽

Study Results ◽

Epoch Analysis ◽

The Magnetic Field

Abstract. Jets in the subsolar magnetosheath are localized enhancements in dynamic pressure that are able to propagate all the way from the bow shock to the magnetopause. Due to their excess velocity with respect to their environment, they push slower ambient plasma out of their way, creating a vortical plasma motion in and around them. Simulations and case study results suggest that jets also modify the magnetic field in the magnetosheath on their passage, aligning it more with their velocity. Based on Magnetospheric Multiscale (MMS) jet observations and corresponding superposed epoch analyses of the angles ϕ between the velocity and magnetic fields, we can confirm that this suggestion is correct. However, while the alignment is more significant for faster than for slower jets, and for jets observed close to the bow shock, the overall effect is small: typically, reductions in ϕ of around 10∘ are observed at jet core regions, where the jets' velocities are largest. Furthermore, time series of ϕ pertaining to individual jets significantly deviate from the superposed epoch analysis results. They usually exhibit large variations over the entire range of ϕ: 0 to 90∘. This variability is commonly somewhat larger within jets than outside them, masking the systematic decrease in ϕ at core regions of individual jets.

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Solar 27-day signatures in standard phase height measurements above central Europe

10.5194/acp-2018-799 ◽

2018 ◽

Author(s):

Christian von Savigny ◽

Dieter H. W. Peters ◽

Günter Entzian

Keyword(s):

Central Europe ◽

Time Scale ◽

Solar Minimum ◽

Solar Maximum ◽

Solar Forcing ◽

Superposed Epoch Analysis ◽

Height Change ◽

Underlying Mechanisms ◽

Epoch Analysis ◽

Good Agreement

Abstract. We report on the effect of solar variability at the 27-day and the 11-year time scale on standard phase height measurements carried out in central Europe. Using the superposed epoch analysis (SEA) method, we extract statistically highly significant solar 27-day signatures in standard phase heights. The 27-day signatures are roughly anti-correlated to solar proxies, such as the F10.7 cm radio flux or the Lyman-α flux. The sensitivity of standard phase height change to solar forcing at the 27-day time scale is found to be in good agreement with the sensitivity for the 11-year solar cycle, suggesting similar underlying mechanisms. The amplitude of the 27-day signature in standard phase height is larger during solar minimum than during solar maximum, indicating that the signature is not only driven by photo-ionisation of NO. We identified statistical evidence for an influence of ultra-long planetary waves on the quasi 27-day signature of standard phase height in winters of solar minimum periods.

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