arXiv subjects

Manuela Temmer

Publications and source records attributed to Manuela Temmer.

At least 55 records · Page 3Linked to original sources

arXiv2020

Earth-affecting Solar Transients: A Review of Progresses in Solar Cycle 24

This review article summarizes the advancement in the studies of Earth-affecting solar transients in the last decade that encompasses most of solar cycle 24. The Sun Earth is an integrated physical system in which the space environment of the Earth sustains continuous influence from mass, magnetic field and radiation energy output of the Sun in varying time scales from minutes to millennium. This article addresses short time scale events, from minutes to days that directly cause transient disturbances in the Earth space environment and generate intense adverse effects on advanced technological systems of human society. Such transient events largely fall into the following four types: (1) solar flares, (2) coronal mass ejections (CMEs) including their interplanetary counterparts ICMEs, (3) solar energetic particle (SEP) events, and (4) stream interaction regions (SIRs) including corotating interaction regions (CIRs). In the last decade, the unprecedented multi viewpoint observations of the Sun from space, enabled by STEREO Ahead/Behind spacecraft in combination with a suite of observatories along the Sun-Earth lines, have provided much more accurate and global measurements of the size, speed, propagation direction and morphology of CMEs in both 3-D and over a large volume in the heliosphere. Several advanced MHD models have been developed to simulate realistic CME events from the initiation on the Sun until their arrival at 1 AU. Much progress has been made on detailed kinematic and dynamic behaviors of CMEs, including non-radial motion, rotation and deformation of CMEs, CME-CME interaction, and stealth CMEs and problematic ICMEs. The knowledge about SEPs has also been significantly improved.

astro-ph.SR↗

arXiv2020

Search for flares and associated CMEs on late-type main-sequence stars in optical SDSS spectra

This work aims to detect and classify stellar flares and potential stellar coronal mass ejection (CME) signatures in optical spectra provided by the Sloan Digital Sky Survey (SDSS) data release 14. The sample is constrained to all F, G, K, and M main-sequence type stars, resulting in more than 630,000 stars. This work makes use of the individual spectral exposures provided by the SDSS. An automatic flare search was performed by detecting significant amplitude changes in the $Hα$ and $Hβ$ spectral lines after a Gaussian profile was fit to the line core. CMEs were searched for by identifying asymmetries in the Balmer lines caused by the Doppler effect of plasma motions in the line of sight. We identified 281 flares on late-type stars (spectral types K3 to M9). We identified six possible CME candidates showing excess flux in Balmer line wings. Flare energies in $Hα$ were calculated and masses of the CME candidates were estimated. The derived $Hα$ flare energies range from $3 \times 10^{28} - 2 \times 10^{33}$ erg. The $Hα$ flare energy increases with earlier types, while the fraction of flaring times increases with later types. Mass estimates for the CME candidates are in the range of $6 \times 10^{16} - 6 \times 10^{18}$ g, and the highest projected velocities are $\sim300 - 700\:$ km/s. The low detection rate of CMEs we obtained agrees with previous studies, suggesting that for late-type main-sequence stars the CME occurrence rate that can be detected with optical spectroscopy is low.

astro-ph.SR↗

arXiv2020

Solar Flare-CME Coupling Throughout Two Acceleration Phases of a Fast CME

Solar flares and coronal mass ejections (CMEs) are closely coupled through magnetic reconnection. CMEs are usually accelerated impulsively within the low solar corona, synchronized with the impulsive flare energy release. We investigate the dynamic evolution of a fast CME and its associated X2.8 flare occurring on 2013 May 13. The CME experiences two distinct phases of enhanced acceleration, an impulsive one with a peak value of ~5 km s$^{-2}$ followed by an extended phase with accelerations up to 0.7 km s$^{-2}$. The two-phase CME dynamics is associated with a two-episode flare energy release. While the first episode is consistent with the "standard" eruption of a magnetic flux rope, the second episode of flare energy release is initiated by the reconnection of a large-scale loop in the aftermath of the eruption and produces stronger nonthermal emission up to $γ$-rays. In addition, this long-duration flare reveals clear signs of ongoing magnetic reconnection during the decay phase, evidenced by extended HXR bursts with energies up to 100--300 keV and intermittent downflows of reconnected loops for >4 hours. The observations reveal that the two-step flare reconnection substantially contributes to the two-phase CME acceleration, and the impulsive CME acceleration precedes the most intense flare energy release. The implications of this non-standard flare/CME observation are discussed.

astro-ph.SR↗

arXiv2020

Evolution of coronal mass ejections and the corresponding Forbush decreases: modelling vs multi-spacecraft observations

One of the very common in situ signatures of interplanetary coronal mass ejections (ICMEs), as well as other interplanetary transients, are Forbush decreases (FDs), i.e. short-term reductions in the galactic cosmic ray (GCR) flux. A two-step FD is often regarded as a textbook example, which presumably owes its specific morphology to the fact that the measuring instrument passed through the ICME head-on, encountering first the shock front (if developed), then the sheath and finally the CME magnetic structure. The interaction of GCRs and the shock/sheath region, as well as the CME magnetic structure, occurs all the way from Sun to Earth, therefore, FDs are expected to reflect the evolutionary properties of CMEs and their sheaths. We apply modelling to different ICME regions in order to obtain a generic two-step FD profile, which qualitatively agrees with our current observation-based understanding of FDs. We next adapt the models for energy dependence to enable comparison with different GCR measurement instruments (as they measure in different particle energy ranges). We test these modelling efforts against a set of multi-spacecraft observations of the same event, using the Forbush decrease model for the expanding flux rope (ForbMod). We find a reasonable agreement of the ForbMod model for the GCR depression in the CME magnetic structure with multi-spacecraft measurements, indicating that modelled FDs reflect well the CME evolution.

astro-ph.SR↗

arXiv2020

A statistical study of long-term evolution of coronal hole properties as observed by SDO

The study of the evolution of coronal holes (CHs) is especially important in the context of high-speed solar wind streams (HSS) emanating from them. Stream interaction regions may deliver large amount of energy into the Earths system, cause geomagnetic storms, and shape interplanetary space. By statistically analysing 16 long-living CHs observed by the SDO, we focus on coronal, morphological and underlying photospheric magnetic field characteristics as well as investigate the evolution of the associated HSSs. We use CATCH to extract and analyse CHs using observations taken by AIA and HMI. We derive changes in the CH properties and correlate them to the CH evolution. Further we analyse the properties of the HSS signatures near 1au from OMNI data by manually extracting the peak bulk velocity of the solar wind plasma. We find that the area evolution of CHs mostly shows a rough trend of growing to a maximum followed by a decay. No correlation of the area evolution to the evolution of the signed magnetic flux and signed magnetic flux density enclosed in the projected CH area was found. From this we conclude that the magnetic flux within the extracted CH boundaries is not the main cause for its area evolution. We derive CH area change rates (growth and decay) of 14.2 +/- 15.0 * 10^8 km^2/day showing a reasonable anti-correlation (cc =-0.48) to the solar activity, approximated by the sunspot number. The change rates of the signed mean magnetic flux density (27.3 +/- 32.2 mG/day) and the signed magnetic flux (30.3 +/- 31.5 * 10^18 Mx/day) were also found to be dependent on solar activity (cc =0.50 and cc =0.69 respectively) rather than on the individual CH evolutions. Further we find that the CH area-to-HSS peak velocity relation is valid for each CH over its evolution but revealing significant variations in the slopes of the regression lines.

astro-ph.SR↗

arXiv2020

Comparing the Properties of ICME-Induced Forbush Decreases at Earth and Mars

Forbush decreases (FDs), which are short-term drops in the flux of galactic cosmic rays, are caused by the shielding from strong and/or turbulent magnetic structures in the solar wind, especially interplanetary coronal mass ejections (ICMEs) and their associated shocks, as well as corotating interaction regions. Such events can be observed at Earth, for example, using neutron monitors, and also at many other locations in the solar system, such as on the surface of Mars with the Radiation Assessment Detector instrument onboard Mars Science Laboratory. They are often used as a proxy for detecting the arrival of ICMEs or corotating interaction regions, especially when sufficient in situ solar wind measurements are not available. We compare the properties of FDs observed at Earth and Mars, focusing on events produced by ICMEs. We find that FDs at both locations show a correlation between their total amplitude and the maximum hourly decrease, but with different proportionality factors. We explain this difference using theoretical modeling approaches and suggest that it is related to the size increase of ICMEs, and in particular their sheath regions, en route from Earth to Mars. From the FD data, we can derive the sheath broadening factor to be between about 1.5 and 1.9, agreeing with our theoretical considerations. This factor is also in line with previous measurements of the sheath evolution closer to the Sun.

physics.space-ph↗

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.

astro-ph.SR↗

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).

astro-ph.SR↗

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.

astro-ph.SR↗

arXiv2019

Photospheric magnetic structure of coronal holes

In this study, we investigate in detail the photospheric magnetic structure of 98 coronal holes using line-of-sight magnetograms of SDO/HMI, and for a subset of 42 coronal holes using HINODE/SOT G-band filtergrams. We divided the magnetic field maps into magnetic elements and quiet coronal hole regions by applying a threshold at $\pm 25$ G. We find that the number of magnetic bright points in magnetic elements is well correlated with the area of the magnetic elements (cc=$0.83\pm 0.01$). Further, the magnetic flux of the individual magnetic elements inside coronal holes is related to their area by a power law with an exponent of $1.261\pm 0.004$ (cc=$0.984\pm 0.001$). Relating the magnetic elements to the overall structure of coronal holes, we find that on average ($69\pm 8$) % of the overall unbalanced magnetic flux of the coronal holes arises from long-lived magnetic elements with lifetimes > 40 hours. About ($22\pm 4$) % of the unbalanced magnetic flux arises from a very weak background magnetic field in the quiet coronal hole regions with a mean magnetic field density of about 0.2 to 1.2 G. This background magnetic field is correlated to the flux of the magnetic elements with lifetimes of > 40 h (cc=$0.88\pm 0.02$). The remaining flux arises from magnetic elements with lifetimes < 40 hours. By relating the properties of the magnetic elements to the overall properties of the coronal holes, we find that the unbalanced magnetic flux of the coronal holes is completely determined by the total area that the long-lived magnetic elements cover (cc=$0.994\pm 0.001$).

astro-ph.SR↗

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.

astro-ph.SR↗

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.

astro-ph.SR↗

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.

astro-ph.SR↗

arXiv2019

Tracking and Validating ICMEs Propagating Toward Mars Using STEREO Heliospheric Imagers Combined With Forbush Decreases Detected by MSL/RAD

The Radiation Assessment Detector (RAD) instrument onboard the Mars Science Laboratory (MSL) mission's Curiosity rover has been measuring galactic cosmic rays (GCR) as well as solar energetic particles (SEP) on the surface of Mars for more than 6 years since its landing in August 2012. The observations include a large number of Forbush decreases (FD) caused by interplanetary coronal mass ejections (ICMEs) and/or their associated shocks shielding away part of the GCR particles with their turbulent and enhanced magnetic fields while passing Mars. This study combines MSL/RAD FD measurements and remote tracking of ICMEs using the Solar TErrestrial RElations Observatory (STEREO) Heliospheric Imager (HI) telescopes in a statistical study for the first time. The large data set collected by HI makes it possible to analyze 149 ICMEs propagating toward MSL both during its 8-month cruise phase and after its landing on Mars. We link 45 of the events observed at STEREO-HI to their corresponding FDs at MSL/RAD and study the accuracy of the ICME arrival time at Mars predicted from HI data using different methods. The mean differences between the predicted arrival times and those observed using FDs range from -11 to 5 hr for the different methods, with standard deviations between 17 and 20 hr. These values for predictions at Mars are very similar compared to other locations closer to the Sun and also comparable to the precision of some other modeling approaches.

physics.space-ph↗

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.

astro-ph.SR↗

arXiv2019

Heliospheric Evolution of Magnetic Clouds

Interplanetary evolution of eleven magnetic clouds (MCs) recorded by at least two radially aligned spacecraft is studied. The in situ magnetic field measurements are fitted to a cylindrically symmetric Gold-Hoyle force-free uniform-twist flux-rope configuration. The analysis reveals that in a statistical sense the expansion of studied MCs is compatible with self-similar behavior. However, individual events expose a large scatter of expansion rates, ranging from very weak to very strong expansion. Individually, only four events show an expansion rate compatible with the isotropic self-similar expansion. The results indicate that the expansion has to be much stronger when MCs are still close to the Sun than in the studied 0.47 - 4.8 AU distance range. The evolution of the magnetic field strength shows a large deviation from the behavior expected for the case of an isotropic self-similar expansion. In the statistical sense, as well as in most of the individual events, the inferred magnetic field decreases much slower than expected. Only three events show a behavior compatible with a self-similar expansion. There is also a discrepancy between the magnetic field decrease and the increase of the MC size, indicating that magnetic reconnection and geometrical deformations play a significant role in the MC evolution. About half of the events show a decay of the electric current as expected for the self-similar expansion. Statistically, the inferred axial magnetic flux is broadly consistent with it remaining constant. However, events characterized by large magnetic flux show a clear tendency of decreasing flux.

astro-ph.SR↗

arXiv2019

3D Reconstruction and Interplanetary Expansion of the 2010 April 3rd CME

We analyse the 2010 April 3rd CME using spacecraft coronagraphic images at different vantage points (SOHO, STEREO-A and STEREO-B). We perform a 3D reconstruction of both the flux rope and shock using the Graduated Cylindrical Shell (GCS) model to calculate CME kinematic and morphologic parameters (e.g. velocity, acceleration, radius). The obtained results are fitted with empirical models describing the expansion of the CME radius in the heliosphere and compared with in situ measurements from Wind spacecraft: the CME is found to expand linearly towards Earth. Finally, we relate the event with decreases in the Galactic Cosmic Ray (GCR) Flux, known as Forbush decreases (FD), detected by EPHIN instrument onboard SOHO spacecraft. We use the analytical diffusion-expansion model (ForbMod) to calculate the magnetic field power law index, obtaining a value of approximately 1.6, thus estimating a starting magnetic field of around 0.01 G and an axial magnetic flux of around 5x1E20 Mx at 15.6 Rsun.

astro-ph.SR↗

arXiv2018

CME-driven Shock and Type II Solar Radio Burst Band Splitting

Coronal Mass Ejections (CMEs) are believed to be effective in producing shocks in the solar corona and the interplanetary space. One of the important signatures of shocks and shock acceleration are Type II solar radio bursts that drift with the shock speed and produce bands of fundamental and higher harmonic plasma radio emission. An intriguing aspect of Type II radio bursts is the occasional split of a harmonic band into thinner lanes, known as band-splitting. Here, we report a detailed imaging and spectroscopic observation of a CME-driven shock producing band-splitting in a Type II burst. Using the Low Frequency Array (LOFAR), we examine the spatial and temporal relation of the Type II burst to the associated CME event, use source imaging to calculate the apparent coronal density, and demonstrate how source imaging can be used to estimate projection effects. We consider two widely accepted band-splitting models that make opposing predictions regarding the locations of the true emission sources with respect to the shock front. Our observations suggest that the locations of the upper and lower sub-band sources are spatially separated by $\sim 0.2 \pm 0.05 \, \mathrm{R_\odot}$. However, we quantitatively show, for the first time, that such separation is consistent with radio-wave scattering of plasma radio emission from a single region, implying that the split-band Type II sources could originate from nearly co-spatial locations. Considering the effects of scattering, the observations provide supporting evidence for the model that interprets the band-splitting as emission originating in the upstream and downstream regions of the shock front, two virtually co-spatial areas.

astro-ph.SR↗