arXiv subjects

Karin Dissauer

Publications and source records attributed to Karin Dissauer.

52 records · Page 3Linked to original sources

arXiv2020

Differential Emission Measure Plasma Diagnostics of a Long-Lived Coronal Hole

We use Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) data to reconstruct the plasma properties from differential emission measure (DEM) analysis for a previously studied long-lived, low-latitude coronal hole (CH) over its lifetime of ten solar rotations. We initially obtain a non-isothermal DEM distribution with a dominant component centered around 0.9 MK and a secondary smaller component at 1.5 - 2.0 MK. We find that deconvolving the data with the instrument point spread function (PSF) to account for long-range scattered light reduces the secondary hot component. Using the 2012 Venus transit and a 2013 lunar eclipse to test the efficiency of this deconvolution, significant amounts of residual stray light are found for the occulted areas. Accounting for this stray light in the error budget of the different AIA filters further reduces the secondary hot emission, yielding CH DEM distributions that are close to isothermal with the main contribution centered around 0.9 MK. Based on these DEMs, we analyze the evolution of the emission measure (EM), density, and averaged temperature during the CH's lifetime. We find that once the CH is clearly observed in EUV images, the bulk of the CH plasma reveals a quite constant state, i.e. temperature and density reveal no major changes, whereas the total CH area and the photospheric magnetic fine structure inside the CH show a distinct evolutionary pattern. These findings suggest that CH plasma properties are mostly "set" at the CH formation or/and that all CHs have similar plasma properties.

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arXiv2019

CME-CME Interactions as Sources of CME Geo-effectiveness: The Formation of the Complex Ejecta and Intense Geomagnetic Storm in Early September 2017

Coronal mass ejections (CMEs) are the primary sources of intense disturbances at Earth, where their geo-effectiveness is largely determined by their dynamic pressure and internal magnetic field, which can be significantly altered during interactions with other CMEs in interplanetary space. We analyse three successive CMEs that erupted from the Sun during September 4-6, 2017, investigating the role of CME-CME interactions as source of the associated intense geomagnetic storm (Dst_min=-142 nT on September 7). To quantify the impact of interactions on the (geo-)effectiveness of individual CMEs, we perform global heliospheric simulations with the EUHFORIA model, using observation-based initial parameters with the additional purpose of validating the predictive capabilities of the model for complex CME events. The simulations show that around 0.45 AU, the shock driven by the September 6 CME started compressing a preceding magnetic ejecta formed by the merging of two CMEs launched on September 4, significantly amplifying its Bz until a maximum factor of 2.8 around 0.9 AU. The following gradual conversion of magnetic energy into kinetic and thermal components reduced the Bz amplification until its almost complete disappearance around 1.8 AU. We conclude that a key factor at the origin of the intense storm triggered by the September 4-6, 2017 CMEs was their arrival at Earth during the phase of maximum Bz amplification. Our analysis highlights how the amplification of the magnetic field of individual CMEs in space-time due to interaction processes can be characterised by a growth, a maximum, and a decay phase, suggesting that the time interval between the CME eruptions and their relative speeds are critical factors in determining the resulting impact of complex CMEs at various heliocentric distances (helio-effectiveness).

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arXiv2019

A Hot Cusp-Shaped Confined Solar Flare

We analyze a confined flare that developed a hot cusp-like structure high in the corona (H ~ 66 Mm). A growing cusp-shaped flare arcade is a typical feature in the standard model of eruptive flares, caused by magnetic reconnection at progressively larger coronal heights. In contrast, we observe a static hot cusp during a confined flare. Despite an initial vertical temperature distribution similar to that in eruptive flares, we observe a distinctly different evolution during the late (decay) phase, in the form of prolonged hot emission. The distinct cusp shape, rooted at locations of non-thermal precursor activity, was likely caused by a magnetic field arcade that kinked near the top. Our observations indicate that the prolonged heating was a result of slow local reconnection and an increased thermal pressure near the kinked apexes due to continuous plasma upflows.

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arXiv2019

Statistical Analysis and Catalog of Non-polar Coronal Holes Covering the SDO-era using CATCH

Coronal holes are usually defined as dark structures as seen in the extreme ultraviolet and X-ray spectrum which are generally associated with open magnetic field. Deriving reliably the coronal hole boundary is of high interest, as its area, underlying magnetic field, and other properties give important hints towards high speed solar wind acceleration processes and on compression regions arriving at Earth. In this study we present a new threshold based extraction method that incorporates the intensity gradient along the coronal hole boundary, which is implemented as a user-friendly SSWIDL GUI. The Collection of Analysis Tools for Coronal Holes (CATCH) enables the user to download data, perform guided coronal hole extraction and analyze the underlying photospheric magnetic field. We use CATCH to analyze non-polar coronal holes during the SDO-era, based on 193 Å filtergrams taken by the Atmospheric Imaging Assembly (AIA) and magnetograms taken by the Heliospheric and Magnetic Imager (HMI), both on board the Solar Dynamics Observatory (SDO). Between 2010 and 2019 we investigate 707 coronal holes that are located close to the central meridian. We find coronal holes distributed across latitudes of about +/- 60 degree for which we derive sizes between 1.6 x 10 9 and 1.8 x 10 11 km^2 . The absolute value of the mean signed magnetic field strength tends towards an average of 2.9 +/- 1.9 G. As far as the abundance and size of coronal holes is concerned, we find no distinct trend towards the northern or southern hemisphere. We find that variations in local and global conditions may significantly change the threshold needed for reliable coronal hole extraction and thus, we can highlight the importance of individually assessing and extracting coronal holes.

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arXiv2019

CME -- HSS interaction and characteristics tracked from Sun to Earth

In a thorough study, we investigate the origin of a remarkable plasma and magnetic field configuration observed in situ on June 22, 2011 near L1, which appears to be a magnetic ejecta (ME) and a shock signature engulfed by a solar wind high-speed stream (HSS). We identify the signatures as an Earth-directed coronal mass ejection (CME), associated with a C7.7 flare on June 21, 2011, and its interaction with a HSS, which emanates from a coronal hole (CH) close to the launch site of the CME. The results indicate that the major interaction between the CME and the HSS starts at a height of 1.3 Rsun up to 3 Rsun. Over that distance range, the CME undergoes a strong north-eastward deflection of at least 30 degrees due to the open magnetic field configuration of the CH. We perform a comprehensive analysis for the CME-HSS event using multi-viewpoint data (from the Solar TErrestrial RElations Observatories, the Solar and Heliospheric Observatory and the Solar Dynamics Observatory), and combined modeling efforts (nonlinear force-free field modeling, Graduated Cylindrical Shell CME modeling, and the Forecasting a CMEs Altered Trajectory ForeCAT model). We aim at better understanding its early evolution and interaction process as well as its interplanetary propagation and related in situ signatures, and finally the resulting impact on the Earth's magnetosphere.

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arXiv2019

Unusual plasma and particle signatures at Mars and STEREO-A related to CME-CME interaction

On July 25 2017 a multi-step Forbush decrease (FD) with the remarkable total amplitude of more than 15\% was observed by MSL/RAD at Mars. We find that these particle signatures are related to very pronounced plasma and magnetic field signatures detected in situ by STEREO-A on July 24 2017, with a higher than average total magnetic field strength reaching more than 60 nT. In the observed time period STEREO-A was at a relatively small longitudinal separation (46 degrees) to Mars and both were located at the back side of the Sun as viewed from Earth. We analyse a number of multi-spacecraft and multi-instrument (both in situ and remote-sensing) observations, and employ modelling to understand these signatures. We find that the solar sources are two CMEs which erupted on July 23 2017 from the same source region on the back side of the Sun as viewed from Earth. Moreover, we find that the two CMEs interact non-uniformly, inhibiting the expansion of one of the CMEs in STEREO-A direction, whereas allowing it to expand more freely in the Mars direction. The interaction of the two CMEs with the ambient solar wind adds up to the complexity of the event, resulting in a long, sub-structured interplanetary disturbance at Mars, where different sub-structures correspond to different steps of the FD, adding-up to a globally large-amplitude FD.

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arXiv2019

Spectroscopy and Differential Emission Measure diagnostics of a coronal dimming associated with a fast halo CME

We study the coronal dimming caused by the fast halo CME (deprojected speed v =1250 km s $^{-1})$ associated with the C3.7 two-ribbon flare on 2012 September 27, using Hinode/EIS spectroscopy and SDO/AIA Differential Emission Measure (DEM) analysis. The event reveals bipolar core dimmings encompassed by hook-shaped flare ribbons located at the ends of the flare-related polarity inversion line, and marking the footpoints of the erupting filament. In coronal emission lines of $\log T \, [{\rm K}] = 5.8-6.3$, distinct double component spectra indicative of the superposition of a stationary and a fast up-flowing plasma component with velocities up to 130 km s$^{-1}$ are observed at regions, which were mapped by the scanning EIS slit close in time of their impulsive dimming onset. The outflowing plasma component is found to be of the same order and even dominant over the stationary one, with electron densities in the upflowing component of $2\times 10^{9}$cm$^{-3}$ at $\log T \, [{\rm K}] = 6.2$. The density evolution in core dimming regions derived from SDO/AIA DEM analysis reveals impulsive reductions by $40 - 50\%$ within $\lesssim$10 min, and remains at these reduced levels for hours. The mass loss rate derived from the EIS spectroscopy in the dimming regions is of the same order than the mass increase rate observed in the associated white light CME ($1 \times 10^{12} {\rm \; g \; s}^{-1}$), indicative that the CME mass increase in the coronagraphic field-of-view results from plasma flows from below and not from material piled-up ahead of the outward moving and expanding CME front.

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arXiv2019

3D reconstructions of EUV wave front heights and their influence on wave kinematics

EUV waves are large-scale disturbances in the solar corona initiated by coronal mass ejections. However, solar EUV images show only the wave fronts projections along the line-of-sight of the spacecraft. We perform 3D reconstructions of EUV wave front heights using multi-point observations from STEREO-A and STEREO-B, and study their evolution to properly estimate the EUV wave kinematics. We develop two different methods to solve the matching problem of the EUV wave crest on pairs of STEREO-A/-B images by combining epipolar geometry with the investigation of perturbation profiles. The proposed approaches are applicable at the early and maximum stage of the event when STEREO-A/-B see different facets of the EUV wave, but also at the later stage when the wave front becomes diffusive and faint. The techniques developed are demonstrated on two events observed at different separation of the STEREO spacecraft (42$^\circ$ and 91$^\circ$). For the 7 December 2007 event, we find that the emission of the EUV wave front mainly comes from a height range up to 90-104 Mm, decreasing later to 7-35 Mm. Including the varying height of the EUV wave front allows us to correct the wave kinematics for the projection effects, resulting in velocities in the range 217-266 km/s. For the 13 February 2009 event, the wave front height doubled from 54 to 93 Mm over 10 min, and the velocity derived is 205-208 km/s. In the two events under study, the corrected speeds differ by up to 25% from the uncorrected ones, depending on the wave front height evolution.

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arXiv2018

Genesis and impulsive evolution of the 2017 September 10 coronal mass ejection

The X8.2 event of 10 September 2017 provides unique observations to study the genesis, magnetic morphology and impulsive dynamics of a very fast CME. Combining GOES-16/SUVI and SDO/AIA EUV imagery, we identify a hot ($T\approx 10-15$ MK) bright rim around a quickly expanding cavity, embedded inside a much larger CME shell ($T\approx 1-2$ MK). The CME shell develops from a dense set of large AR loops ($\gtrsim$0.5 $R_s$), and seamlessly evolves into the CME front observed in LASCO C2. The strong lateral overexpansion of the CME shell acts as a piston initiating the fast EUV wave. The hot cavity rim is demonstrated to be a manifestation of the dominantly poloidal flux and frozen-in plasma added to the rising flux rope by magnetic reconnection in the current sheet beneath. The same structure is later observed as the core of the white light CME, challenging the traditional interpretation of the CME three-part morphology. The large amount of added magnetic flux suggested by these observations explains the extreme accelerations of the radial and lateral expansion of the CME shell and cavity, all reaching values of $5 - 10$ km s$^{-2}$. The acceleration peaks occur simultaneously with the first RHESSI $100-300$ keV hard X-ray burst of the associated flare, further underlining the importance of the reconnection process for the impulsive CME evolution. Finally, the much higher radial propagation speed of the flux rope in relation to the CME shell causes a distinct deformation of the white light CME front and shock.

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arXiv2018

Statistics of coronal dimmings associated with coronal mass ejections. II. Relationship between coronal dimmings and their associated CMEs

We present a statistical study of 62 coronal dimming events associated with Earth-directed CMEs during the quasi-quadrature period of STEREO and SDO. This unique setting allows us to study both phenomena in great detail and compare characteristic quantities statistically. Coronal dimmings are observed on-disk by SDO/AIA and HMI, while the CME kinematics during the impulsive acceleration phase is studied close to the limb with STEREO/EUVI and COR, minimizing projection effects. The dimming area, its total unsigned magnetic flux and its total brightness, reflecting properties of the total dimming region at its final extent, show the highest correlations with the CME mass ($c\sim0.6-0.7$). Their corresponding time derivatives, describing the dynamics of the dimming evolution, show the strongest correlations with the CME peak velocity ($c\sim 0.6$). The highest correlation of $c=0.68\pm0.08$ is found with the mean intensity of dimmings, indicating that the lower the CME starts in the corona, the faster it propagates. No significant correlation between dimming parameters and the CME acceleration was found. However, for events where high-cadence STEREO observations were available, the mean unsigned magnetic field density in the dimming regions tends to be positively correlated with the CME peak acceleration ($c=0.42\pm0.20$). This suggests that stronger magnetic fields result in higher Lorentz forces providing stronger driving force for the CME acceleration. Specific coronal dimming parameters correlate with both, CME and flare quantities providing further evidence for the flare-CME feedback relationship. For events in which the CME occurs together with a flare, coronal dimmings statistically reflect the properties of both phenomena.

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arXiv2018

Statistics of coronal dimmings associated with coronal mass ejections. I. Characteristic dimming properties and flare association

Coronal dimmings, localized regions of reduced emission in the EUV and soft X-rays, are interpreted as density depletions due to mass loss during the CME expansion. They contain crucial information on the early evolution of CMEs low in the corona. For 62 dimming events, characteristic parameters are derived, statistically analyzed and compared with basic flare quantities. On average, coronal dimmings have a size of $2.15\times10^{10}$ km$^{2}$, contain a total unsigned magnetic flux of $1.75\times10^{21}$ Mx, and show a total brightness decrease of $-1.91\times10^{6}$ DN, which results in a relative decrease of $\sim$60% compared to the pre-eruption intensity level. Their main evacuation phase lasts for $\sim$50 minutes. The dimming area, the total dimming brightness, and the total unsigned magnetic flux show the highest correlation with the flare SXR fluence ($c\gtrsim0.7$). Their corresponding time derivatives, describing the dimming dynamics, strongly correlate with the GOES flare class ($c\gtrsim 0.6$). For 60% of the events we identified core dimmings, i.e. signatures of an erupting flux rope. They contain 20% of the magnetic flux covering only 5% of the total dimming area. Secondary dimmings map overlying fields that are stretched during the eruption and closed down by magnetic reconnection, thus adding flux to the erupting flux rope via magnetic reconnection. This interpretation is supported by the strong correlation between the magnetic fluxes of secondary dimmings and flare reconnection fluxes ($c=0.63\pm0.08$), the balance between positive and negative magnetic fluxes ($c=0.83\pm0.04$) within the total dimmings and the fact that for strong flares ($>$M1.0) the reconnection and secondary dimming fluxes are roughly equal.

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arXiv2018

A comparative study between a failed and a successful eruption initiated from the same polarity inversion line in AR 11387

In this paper, we analyzed a failed and a successful eruption that initiated from the same polarity inversion line within NOAA AR 11387 on December 25, 2011. They both started from a reconnection between sheared arcades, having distinct pre-eruption conditions and eruption details: before the failed one, the magnetic fields of the core region had a weaker non-potentiality; the external fields had a similar critical height for torus instability, a similar local torus-stable region, but a larger magnetic flux ratio (of low corona and near-surface region) as compared to the successful one. During the failed eruption, a smaller Lorentz force impulse was exerted on the outward ejecta; the ejecta had a much slower rising speed. Factors that might lead to the initiation of the failed eruption are identified: 1) a weaker non-potentiality of the core region, and a smaller Lorentz force impulse gave the ejecta a small momentum; 2) the large flux ratio, and the local torus-stable region in the corona provided strong confinements that made the erupting structure regain an equilibrium state.

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arXiv2018

Plasma diagnostics of coronal dimming events

Coronal mass ejections (CMEs) are often associated with coronal dimmings, i.e. transient dark regions that are most distinctly observed in Extreme Ultra-violet (EUV) wavelengths. Using Atmospheric Imaging Assembly (AIA) data, we apply Differential Emission Measure (DEM) diagnostics to study the plasma characteristics of six coronal dimming events. In the core dimming region, we find a steep and impulsive decrease of density with values up to 50-70%. Five of the events also reveal an associated drop in temperature of 5-25%. The secondary dimming regions also show a distinct decrease in density, but less strong, decreasing by 10-45%. In both the core and the secondary dimming the density changes are much larger than the temperature changes, confirming that the dimming regions are mainly caused by plasma evacuation. In the core dimming, the plasma density reduces rapidly within the first 20-30 min after the flare start, and does not recover for at least 10 hrs later, whereas the secondary dimming tends to be more gradual and starts to replenish after 1-2 hrs. The pre-event temperatures are higher in the core dimming (1.7-2.6 MK) than in the secondary dimming regions (1.6-2.0 MK). Both core and secondary dimmings are best observed in the AIA 211 Å and 193 Å filters. These findings suggest that the core dimming corresponds to the footpoints of the erupting flux rope rooted in the AR, while the secondary dimming represents plasma from overlying coronal structures that expand during the CME eruption.

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arXiv2018

On the detection of coronal dimmings and the extraction of their characteristic properties

Coronal dimmings are distinct phenomena associated to coronal mass ejections (CMEs). The study of coronal dimmings and the extraction of their characteristic parameters helps us to obtain additional information of CMEs, especially on the initiation and early evolution of Earth-directed CMEs. We present a new approach to detect coronal dimming regions based on a thresholding technique applied on logarithmic base-ratio images. Characteristic dimming parameters describing the dynamics, morphology, magnetic properties and the brightness of coronal dimming regions are extracted by cumulatively summing newly dimmed pixels over time. It is also demonstrated how core dimming regions are identified as a subset of the overall identified dimming region. We successfully apply our method to two well-observed coronal dimming events. For both events the core dimming regions are identified and the spatial evolution of the dimming area reveals the expansion of the dimming region around these footpoints. We also show that in the early impulsive phase of the dimming expansion the total unsigned magnetic flux involved in the dimming regions is balanced and that up to 30% of this flux results from the localized core dimming regions. Furthermore, the onset in the profile of the area growth rate is co-temporal with the start of the associated flares and in one case also with the fast rise of the CME, indicating a strong relationship of coronal dimmings with both flare and CMEs.

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arXiv2016

Projection effects in coronal dimmings and associated EUV wave event

We investigate the high-speed ($v >$ 1000 km s$^{-1}$) extreme-ultraviolet (EUV) wave associated with an X1.2 flare and coronal mass ejection (CME) from NOAA active region 11283 on 2011 September 6 (SOL2011-09-06T22:12). This EUV wave features peculiar on-disk signatures, in particular we observe an intermittent "disappearance" of the front for 120 s in SDO/AIA 171, 193, 211 Å data, whereas the 335 Å filter, sensitive to hotter plasmas (T$\sim$2.5 MK), shows a continuous evolution of the wave front. The eruption was also accompanied by localized coronal dimming regions. We exploit the multi-point quadrature position of SDO and STEREO-A, to make a thorough analysis of the EUV wave evolution, with respect to its kinematics and amplitude evolution and reconstruct the SDO line-of-sight (LOS) direction of the identified coronal dimming regions in STEREO-A. We show that the observed intensities of the dimming regions in SDO/AIA depend on the structures that are lying along their LOS and are the combination of their individual intensities, e.g. the expanding CME body, the enhanced EUV wave and CME front. In this context, we conclude that the intermittent disappearance of the EUV wave in the AIA 171, 193, 211 Å filters, which are channels sensitive to plasma with temperatures below $\sim$2 MK is also caused by such LOS integration effects. These observations clearly demonstrate that single-view image data provide us with limited insight to correctly interpret coronal features.

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arXiv2013

Perturbative extension of the standard model with a 125 GeV Higgs and Magnetic Dark Matter

We introduce a perturbative extension of the standard model featuring a new dark matter sector together with a 125 GeV Higgs. The new sector consists of a vector-like heavy electron E, a complex scalar electron S and a standard model singlet Dirac fermion χ. The interactions among the dark matter candidate χand the standard model particles occur via loop-induced processes involving the operator SEχy, with y being the Yukawa-like coupling. The model is an explicit underlying realization of the light magnetic dark matter effective model introduced earlier to alleviate the tension among several direct dark matter search experiments. We further constrain the parameters of the underlying theory using results from the Large Hadron Collider. The extension can accommodate the recently observed properties of the Higgs-like state and leads to interesting predictions. Finally we show that the model's collider phenomenology and constraints nicely complement the ones coming from dark matter searches.

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