ST1.1

EDI
Open Session on the Sun and Heliosphere

This session traditionally provides a forum for the discussion of all aspects of solar and heliospheric physics. Popular topics have included solar cycle dependencies of the Sun, solar wind and heliosphere, Coronal Mass Ejection research, studies of energetic particles throughout the heliosphere, and the outer boundaries of the heliosphere. We encourage contributions related to all ongoing and planned space missions, to ground-based experiments and to theoretical research. Papers presenting ideas for future space missions and experiments are very welcome in this session. The session will consist of both oral and poster presentations.

Convener: Manuela Temmer | Co-conveners: André Galli, Olga Malandraki
vPICO presentations
| Mon, 26 Apr, 11:00–12:30 (CEST), 13:30–15:00 (CEST)

vPICO presentations: Mon, 26 Apr

Chairperson: Manuela Temmer
11:00–11:05
11:05–11:07
|
EGU21-15499
José M. Vaquero

Solar activity is an essential factor for the study of many aspects of the geophysical and astronomical sciences. A very simple measure of solar activity is counting sunspots using telescopes. This task can be done even with small telescopes since the Sun is apparently a very large and luminous star. For this reason, it is possible to rescue the ancient observations of sunspots made in the past centuries to obtain an image of the evolution of solar activity during the last four centuries.

The first attempt to reconstruct solar activity from these records was made by Rudolf Wolf, who defined the Sunspot Number index in the 19th century. The Zurich Observatory (and later the Brussels Observatory) was in charge of continuing Wolf's work to the present day. In 1998, Hoyt and Schatten presented a new reconstruction of solar activity that was very different from Wolf's reconstruction (Vaquero and Vázquez, 2009). Many of these differences were solved by Clette et al. (2014).

Currently, research to improve the Sunspot Number is focused on (i) improving the database by reviewing old observations, and (ii) improving the methodologies to convert raw data into the Sunspot Number index. In this work, we try to present the latest advances in this task (Muñoz-Jaramillo and Vaquero, 2019; Arlt and Vaquero, 2020).

 

References

Arlt, R., Vaquero, J.M. (2020) Living Reviews in Solar Physics 17, 1.

Clette, F. et al. (2014) Space Science Reviews 186, 35.

Muñoz-Jaramillo, A., Vaquero, J.M. (2019) Nature Astronomy 3, 205.

Vaquero, J.M. and Vázquez, M. (2009) The Sun recorded through history (Springer).

How to cite: Vaquero, J. M.: A long-term geophysical and astronomical dataset: sunspot counting from 1610 to 2021, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15499, https://doi.org/10.5194/egusphere-egu21-15499, 2021.

11:07–11:09
|
EGU21-2555
Sandra Chapman, Scott McIntosh, Robert Leamon, and Nicholas Watkins

We construct a new solar cycle phase clock which maps each of the last 18 solar cycles onto a single normalized epoch for the approximately 22 year Hale (magnetic polarity) cycle, using the Hilbert transform of daily sunspot numbers (SSN) since 1818. We use the clock to study solar and geomagnetic climatology as seen in datasets available over multiple solar cycles. The occurrence of solar maxima on the clock shows almost no Hale cycle dependence, confirming that the clock is synchronized with polarity reversals.  The odd cycle minima lead the even cycle minima by ~ 1.1 normalized years, whereas the odd cycle terminators (when sunspot bands from opposite hemispheres have moved to the equator and coincide, thus terminating the cycle, McIntosh(2019)) lag the even cycle terminators  by ~ 2.3 normalized years.  The average interval between each minimum and terminator  is thus relatively extended for odd cycles and shortened for even ones. We re-engineer the R27 index that was orignally proposed by Sargent(1985) to parameterize 27 day recurrences in the aa index. We perform an epoch analysis of autocovariance in the aa index using the Hale cycle clock to obtain a high time resolution parameter for 27 day recurrence, <acv(27)>. This reveals that the transition to recurrence, that is, to an ordered solar wind dominated by high speed streams, is fast, occurring within 2-3 solar rotations or less. It resolves an extended late declining phase which is approximately twice as long on even Schwabe cycles as odd ones. We find that Galactic Cosmic Ray flux rises in step with <acv(27)> but then stays high. Our analysis also identifies a slow timescale trend in SSN that simply tracks the Gleissberg cycle. We find that this trend is in phase with the slow timescale trend in the modulus of sunspot latitudes, and in antiphase with that of the R27 index.

How to cite: Chapman, S., McIntosh, S., Leamon, R., and Watkins, N.: A clock for the Sun's magnetic Hale cycle and 27 day recurrences in the aa geomagnetic index, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2555, https://doi.org/10.5194/egusphere-egu21-2555, 2021.

11:09–11:11
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EGU21-14168
|
ECS
Surajit Mondal, Divya Oberoi, Ayan Biswas, Shabbir Bawaji, Ujjaini Alam, Arpit Behera, Devojyoti Kansabanik, Nick Swainston, Ramesh Bhat, and John Morgan

It has been a long standing problem as to how the solar corona can maintain its million K temperature, while the photosphere, which is the lowest layer of the solar atmosphere, is only at a temperature of 5800 K. A very promising theory to explain this is the “nanoflare” hypothesis, which suggests that numerous flares of energies ~1024 ergs are always happening in the solar corona, and maintain its million K temperature. However, detecting these nanoflares directly is challenging with the current instrumentation as they are hypothesised to occur at very small spatial, temporal and energy scales. These nanoflares are expected to produce nonthermal electrons, which are expected to emit in the radio band. These nonthermal emissions are often brighter than their thermal counterparts and might be detectable with current radio instruments. Due to their importance multiple searches for these nonthermal emissions have been done, but thus far they have been  limited to active regions. The quiet corona is also hot, and often comprises the bulk of the coronal region, so it is equally important to understand the physical processes which maintain this medium at MK temperatures. We describe the results from our effort to use the data from the Murchison Widefield Array (MWA) to search for impulsive radio emissions in the quiet solar corona. By pushing the detection threshold of nonthermal emission by about two orders of magnitude lower than previous studies, we have uncovered ubiquitous very impulsive nonthermal emissions from the quiet sun. We refer to these emissions as Weak Impulsive Narrowband Quiet Sun Emissions (WINQSEs). Using independent observations spanning very different solar conditions we show that WINQSEs are present throughout the quiet corona at all times. Their occurrence rate lies in the range of many hundreds to about a thousand per minute, implying that on average order 10 or so WINQSEs are present in every 0.5 s MWA image. Preliminary estimates suggest that WINQSEs have a bandwidth of ~2 MHz. Buoyed by  their possible connection to the hypothesised “nanoflares”, we are pursuing several projects to characterise and understand them. These include developing machine learning algorithms to identify WINQSEs in radio images and characterise their morphologies; exploring the ability of the present generation EUV and X-ray instruments to estimate the energy corresponding to the brightest of WINQSEs; and attempting very high time resolution imaging to explore their temporal structure. In this talk, I will present the results from the past and ongoing projects about WINQSEs and argue that these might be a key step towards detecting “nanoflares” and the resolution of the coronal heating problem.

 

 

How to cite: Mondal, S., Oberoi, D., Biswas, A., Bawaji, S., Alam, U., Behera, A., Kansabanik, D., Swainston, N., Bhat, R., and Morgan, J.:  First radio evidence for ubiquitous magnetic reconnections and impulsive heating in the quiet solar corona , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14168, https://doi.org/10.5194/egusphere-egu21-14168, 2021.

11:11–11:13
|
EGU21-14293
|
ECS
Rohit Sharma, Marina Battaglia, Yingjie Luo, Bin Chen, and Sijie Yu

Solar flares release enormous magnetic energy into the corona, producing the heating of ambient plasma and acceleration of particles. The flaring process is complex and often shows multiple spatially separated temporal individual episodes of energy releases, which can be hard to resolve based on the instrument capability. We analysed the multi-wavelength imaging and spectroscopy observations of multiple electron acceleration episodes during a GOES B1.7-class two-ribbon flare observed simultaneously with the Karl G. Jansky Very Large Array (VLA) at 1--2 GHz, the Reuven Ramatay High Energy Solar Spectroscopic Imager (RHESSI) in X-rays, and the Solar Dynamics Observatory in extreme ultraviolet (EUV).
We observed a total of six radio bursts. First three bursts were co-temporal, but not co-spatial nonthermal X-ray source and represent multiple electron acceleration episodes. We model the radio spectra by optically thick gyrosynchrotron emission and estimate the magnetic field strength and nonthermal electron spectral parameters in each acceleration episode. We note that the nonthermal parameters derived from X-rays differ considerably from the nonthermal parameters inferred from the radio and originates in the lower corona. Although co-temporal, our multi-wavelength analysis shows that different electron populations produce multiple acceleration episodes in radio and X-rays wavelengths. 

How to cite: Sharma, R., Battaglia, M., Luo, Y., Chen, B., and Yu, S.: Radio and X-ray Observations of Short-lived Episodes of Electron Acceleration in a Solar Microflare   , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14293, https://doi.org/10.5194/egusphere-egu21-14293, 2021.

11:13–11:15
|
EGU21-4954
Dmitrii Baranov, Elena Vernova, and Marta Tyasto

The properties of the magnetic fields of the solar photosphere are investigated, in particular, the distribution of fields of different polarity over the solar surface. As primary data, synoptic maps of the photospheric magnetic field of the Kitt Peak National Solar Observatory for 1978-2016 were used. Using the vector summation method, the non-axisymmetric component of the magnetic field is determined. It was found that the nonaxisymmetric component of weak magnetic fields B < 5 G changes in antiphase with the flux of these fields. Magnetic fields of B < 5 G constitute a significant part of the total magnetic field of the Sun, since they occupy more than 60% of the area of the photosphere. The fine structure of the distribution of weak fields can  be observed by setting the upper limit to the strength of the  fields  included in the time–latitude diagram. This allows to eliminate the contribution of the strong fields of sunspots.

On the time-latitude diagram for weak magnetic fields (B < 5 G), bands of differing colors correspond to the streams of the magnetic fields moving in the direction to the Sun’s poles.. These streams or surges show the alternation of the dominant polarity - positive or negative - which is clearly seen in all four cycles. The slopes of the bands indicate the velocity of the fields movement towards the poles. The surges can be divided into two groups. The surges of the first group belong to the so-called Rush-to-the-Poles. These are bands with the width of about three years, which begin at approximately 40° of latitude and have the same polarity as the trailing sunspots. They reach high latitudes and cause the polarity reversal of the polar field. However, in addition to these surges, for most of the solar  cycle (the descending phase, the minimum and the ascending phase), there are narrower surges of both polarities (with the width less than one year), which extend from the equator almost to the poles. These surges are most clearly visible in the southern hemisphere when the southern pole is positive. Consideration of the latitude-time diagrams separately for positive and negative polarities showed that the alternating dominance of one of the polarities is associated with the antiphase development  of the positive and negative fields of the surges. The widths of surges and the periodicity of their appearance vary significantly for the two hemispheres and from one solar cycle to the other. The mean period of the polarity alternation is about 1.5 years.

How to cite: Baranov, D., Vernova, E., and Tyasto, M.: Surges of the weak magnetic field in the photosphere of the Sun, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4954, https://doi.org/10.5194/egusphere-egu21-4954, 2021.

11:15–11:17
|
EGU21-2445
|
ECS
Jack Jenkins and Rony Keppens

We revisit the so-called levitation-condensation mechanism for the ab-inito formation of solar prominences: cool and dense clouds in the million-degree solar atmosphere. Levitation-condensation occurs following the formation of a flux rope in response to the deformation of a force-free coronal arcade by controlled magnetic footpoint motions and subsequent reconnection. Existing coronal plasma gets lifted within the forming rope, therein isolating a collection of matter now more dense than its immediate surroundings. This denser region ultimately suffers a thermal instability driven by radiative losses, and a prominence forms. We improve on various aspects that were left unanswered in the early work, by revisiting this model with our modern open-source grid- adaptive simulation code [amrvac.org]. Most notably, this tool enables a resolution of 5.6 km within a 24 Mm x 25 Mm domain size; the full global flux rope dynamics and local plasma dynamics are captured in unprecedented detail. Our 2.5D simulation (where the flux rope has realistic helical magnetic field lines) demonstrates that the thermal runaway condensation can happen at any location, not solely in the bottom part of the flux rope where the majority of prominence material is assumed to reside. Intricate thermodynamic evolution and shearing flows develop spontaneously, themselves inducing further fine-scale (magneto)hydrodynamic instabilities. Our analysis touches base with advanced linear magnetohydrodynamic stability theory, e.g. with the Convective Continuum Instability or CCI process as well as with in-situ thermal instability studies. We find that condensing prominence plasma evolves according to the internal pressure and density gradients as found previously for coronal rain condensations, but also misalignments therein suggesting the relevance of the Rayleigh-Taylor instability or RTI process in 3D. We also find evidence for resistively-driven dynamics in the prominence body, in close analogy with analytical predictions. These findings are relevant for modern studies of full 3D prominence formation and structuring. Most notably, we anticipate obtaining similar resolutions within a fully 3D setup. Such an achievement will afford us the exciting opportunity to offer crucial explanations as to the persistent discrepancy in prominence appearance when projected off- or on-disk.

How to cite: Jenkins, J. and Keppens, R.: Prominence Formation by Levitation-Condensation at Extreme Resolutions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2445, https://doi.org/10.5194/egusphere-egu21-2445, 2021.

11:17–11:19
|
EGU21-3616
|
ECS
Hechao Chen, Jiayan Yang, Junchao Hong, Haidong Li, and Yadan Duan

Increasing observations show that coronal jets may result in bubble-shaped coronal mass ejections (CMEs), but the genesis of jet-driven CMEs and their nature are not fully understood. Here, we report a direct stereoscopic observation on the magnetic coupling from a coronal blowout jet to a stellar-sized CME.  Observations in the EUV passbands of SDO/AIA show that this whole event starts with a small-scale active-region filament whose eruption occurs at a coronal geyser site due to flux emergence and cancellation. By interacting with an overlying null-point configuration, this erupting filament first breaks one of its legs and triggers an unwinding blowout jet. The release of magnetic twist in its jet spire is estimated at around 1.5−2.0 turns. This prominent twist transport in jet spire rapidly creates a newborn large-scale flux rope from the jet base to a remote site. As a result, the newborn large-scale flux rope erupts into the outer coronae causing an Earth-directed bubble-shaped CME. In particular, two sets of distinct flare post-flare loops form in its source region in sequence, indicating this eruptive event couples with twice flare reconnection. This observation highlights a real pathway for jet-CME magnetic coupling and provides a new hint for the buildup of large-scale CME flux ropes. 

How to cite: Chen, H., Yang, J., Hong, J., Li, H., and Duan, Y.: Direct Observation of A Large-scale CME Flux Rope Event Arising from an Unwinding Coronal Jet , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3616, https://doi.org/10.5194/egusphere-egu21-3616, 2021.

11:19–11:21
|
EGU21-1461
Alexander Kosovichev and Ivan Sharykin

Helioseismic response to solar flares ("sunquakes") occurs due to localized force or/and momentum impacts observed during the flare impulsive phase in the lower atmosphere. Such impacts may be caused by precipitation of high-energy particles, downward shocks, or magnetic Lorentz force. Understanding the mechanism of sunquakes is a key problem of the flare energy release and transport. Our statistical analysis of M-X class flares observed by the Solar Dynamics Observatory during Solar Cycle 24 has shown that contrary to expectations, many relatively weak M-class flares produced strong sunquakes, while for some powerful X-class flares, helioseismic waves were not observed or were weak. The analysis also revealed that there were active regions characterized by the most efficient generation of sunquakes during the solar cycle. We found that the sunquake power correlates with maximal values of the X-ray flux derivative better than with the X-ray class. The sunquake data challenge the current theories of solar flares.

How to cite: Kosovichev, A. and Sharykin, I.: Characteristics of Sunquake Events Observed in Solar Cycle 24, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1461, https://doi.org/10.5194/egusphere-egu21-1461, 2021.

11:21–11:23
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EGU21-13091
|
ECS
Cosima Breu, Hardi Peter, Robert Cameron, Sami Solanki, Pradeep Chitta, and Damien Przybylski

The corona of the Sun, and probably also of other stars, is built up by loops defined through the magnetic field. They vividly appear in solar observations in the extreme UV and X-rays. High-resolution observations show individual strands with diameters down to a few 100 km, and so far it remains open what defines these strands, in particular their width, and where the energy to heat them is generated.

The aim of our study is to understand how the magnetic field couples the different layers of the solar atmosphere, how the energy generated by magnetoconvection is transported into the upper atmosphere and dissipated, and how this process determines the scales of observed bright strands in the loop.

To this end, we conduct 3D resistive MHD simulations with the MURaM code. We include the effects of heat conduction, radiative transfer and optically thin radiative losses.
We study an isolated coronal loop that is rooted with both footpoints in a shallow convection zone layer. To properly resolve the internal structure of the loop while limiting the size of the computational box, the coronal loop is modelled as a straightened magnetic flux tube. By including part of the convection zone, we drive the evolution of the corona self-consistently by magnetoconvection.

We find that the energy injected into the loop is generated by internal coherent motions within strong magnetic elements. 
The resulting Poynting flux is channelled into the loop in vortex tubes forming a magnetic connection between the photosphere and corona, where it is dissipated and heats the upper atmosphere.

The coronal emission as it would be observed in solar extreme UV or X-ray observations, e.g. with AIA or XRT, shows transient bright strands.
The widths of these strands are consistent with observations. From our model we find that the width of the strands is governed by the size of the individual photospheric magnetic field concentrations where the field lines through these strands are rooted. Essentially, each coronal strand is mainly rooted in a single magnetic patch in the photosphere, and the energy to heat the strand is generated by internal motions within this magnetic concentration.

With this model we can build a coherent picture of how energy and matter are transported into the upper solar atmosphere and how these processes structure the interior of coronal loops.

How to cite: Breu, C., Peter, H., Cameron, R., Solanki, S., Chitta, P., and Przybylski, D.: Coronal loops in a box: 3D models of their internal structure, dynamics and heating, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13091, https://doi.org/10.5194/egusphere-egu21-13091, 2021.

11:23–11:25
|
EGU21-1013
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ECS
Zhenyong Hou, Hui Tian, Hechao Chen, Xiaoshuai Zhu, Jiansen He, Xianyong Bai, Zhenghua Huang, and Lidong Xia

Coronal loops are building blocks of solar active regions (ARs). However, their formation is not well understood. Here we present direct observational evidence for the formation of coronal loops through magnetic reconnection as new magnetic fluxes emerge to the solar atmosphere. Observations in the EUV passbands of SDO/AIA clearly show the newly formed loops following magnetic reconnection within a vertical current sheet. Formation of the loops is also seen in the Hα images taken by NVST. The SDO/HMI observations show that a positive-polarity flux concentration moves toward a negative-polarity one with a speed of ~0.5 km s-1 before the apparent formation of coronal loops. During the formation of coronal loops, we found signatures of flux cancellation and subsequent enhancement of the transverse field between the two polarities. We have reconstructed the three-dimensional magnetic field structure through a magnetohydrostatic model, which shows field lines consistent with the loops in AIA images. Numerous bright blobs with a width of ~1.5 Mm appear intermittently in the current sheet and move upward with apparent velocities of ~80 km s-1. We have also identified plasma blobs moving to the footpoints of the newly formed large loops, with apparent velocities ranging from 30 to 50 km s-1. A differential emission measure analysis shows that the temperature, emission measure and density of the bright blobs are 2.5-3.5 MK, 1.1-2.3×1028 cm-5 and 8.9-12.9×109 cm-3, respectively. Power spectral analysis of these blobs indicates that the magnetic reconnection is inconsistent with the turbulent reconnection scenario.

How to cite: Hou, Z., Tian, H., Chen, H., Zhu, X., He, J., Bai, X., Huang, Z., and Xia, L.: Formation of solar coronal loops through magnetic reconnection in an emerging active region, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1013, https://doi.org/10.5194/egusphere-egu21-1013, 2021.

11:25–11:27
|
EGU21-3134
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ECS
Galina Chikunova, Karin Dissauer, Tatiana Podladchikova, and Astrid Veronig

We studied 43 coronal dimming events associated with Earth-directed coronal mass ejections (CMEs) that were observed in quasi-quadrature by the SDO and STEREO satellites. We derived the properties of the dimmings as observed above the limb by STEREO EUVI, and compared them with the mass and speed of the associated CMEs. The unique satellite constellation allowed us to compare our findings with the results from Dissauer et al. (2018, 2019), who studied these events observed against the solar disk by SDO AIA. Such statistics is done for the first time and confirms the close relation between characteristic dimming and CME parameters for the off-limb viewpoint. We find that the dimming areas are typically larger for off-limb observations (mean value of 1.24±1.23×1011 km2 against 3.51±0.71×1010 km2 for on-disk), while the decrease in the total extreme ultraviolet intensity is similar (c=0.60±0.14). The off-limb dimming areas and brightnesses are strongly correlated with the CME mass (c=0.82±0.06 and 0.75±0.08), whereas the dimming area and brightness change rate correlate with the CME speed (c∼0.6). Our findings suggest that coronal dimmings have the potential to provide early estimates of the Earth-directed CMEs parameters, relevant for space weather forecasts, for satellite locations at both L1 and L5.

How to cite: Chikunova, G., Dissauer, K., Podladchikova, T., and Veronig, A.: Coronal dimmings associated with coronal mass ejections on the solar limb, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3134, https://doi.org/10.5194/egusphere-egu21-3134, 2021.

11:27–11:29
|
EGU21-31
Lijuan Liu, Yuming Wang, Zhenjuan Zhou, and Jun Cui

Major flares and coronal mass ejections (CMEs) tend to originate from the compact polarity inversion lines (PILs) in the solar active regions (ARs). Recently, a scenario named as “collisional shearing” is proposed by Chintzoglou et al. (2019) to explain the phenomenon, which suggests that the collision between different emerging bipoles is able to form the compact PIL, driving the shearing and flux cancellation that are responsible to the subsequent large activities. In this work, through tracking the evolution of 19 emerging ARs from their birth until they produce the first major flares or CMEs, we investigated the source PILs of the activities, i.e., the active PILs, to explore the generality of “collisional shearing”. We find that none of the active PILs is the self PIL (sPIL) of a single bipole. We further find that 11 eruptions originate from the collisional PILs (cPILs) formed due to the collision between different bipoles, 6 from the conjoined systems of sPIL and cPIL, and 2 from the conjoined systems of sPIL and ePIL (external  PIL between the AR and the nearby preexisting polarities). Collision accompanied by shearing and flux cancellation is found developing at all PILs prior to the eruptions, with 84% (16/19) cases having collisional length longer than 18 Mm. Moreover, we find that the magnitude of the flares is positively correlated with the collisional length of the active PILs, indicating that the intenser activities tend to originate from the PILs with severer collision. The results suggest that the “collisional shearing”, i.e., bipole-bipole interaction during the flux emergence is a common process in driving the major activities in emerging ARs.

How to cite: Liu, L., Wang, Y., Zhou, Z., and Cui, J.: The Source Locations of Major Flares and CMEs in the Emerging Active Regions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-31, https://doi.org/10.5194/egusphere-egu21-31, 2020.

11:29–11:31
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EGU21-10578
Ryun Young Kwon

We present a novel method to derive the shock density compression ratio of coronal shock waves that are occasionally observed as halo coronal mass ejections (CMEs). Our method uses the three-dimensional (3-D) geometry and enables us to access the reliable shock density compression ratio. We show the 3-D properties of coronal shock waves seen from multiple vantage point observations, i.e., geometry, kinematics, and compression ratio (Mach number). The significant findings are as follows: (1) Halo CMEs are the manifestation of spherically shaped fast-mode waves/shocks, rather than a matter of the projection of expanding flux ropes. The footprints of halo CMEs on the coronal base are the so-called EIT/EUV waves. (2) These spherical fronts arise from a driven shock (bow- or piston-type) close to the CME nose, and it is gradually becoming a freely propagating (decaying) fast-mode shock wave at the flank. (3) The shock density compressions peak around the CME nose and decrease at larger position angles (flank). (4) Finally, the supercritical region extends over a large area of the shock and lasts longer than past reports.  These results offer a simple unified picture of the different manifestations for CME-associated (shock) waves, such as EUV waves and SEP events observed in various regimes and heliocentric distances. We conclude that CME shocks can accelerate energetic particles in the corona over extended spatial and temporal scales and are likely responsible for the wide longitudinal distribution of these particles in the inner heliosphere.

How to cite: Kwon, R. Y.: The three-dimensional density compression ratio of shock fronts observed as halo coronal mass ejections , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10578, https://doi.org/10.5194/egusphere-egu21-10578, 2021.

11:31–11:33
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EGU21-642
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ECS
Zihao Yang, Christian Bethge, Hui Tian, Steven Tomczyk, Richard Morton, Giulio Del Zanna, Scott McIntosh, Bidya Binay Karak, Sarah Gibson, Tanmoy Samanta, Jiansen He, Yajie Chen, Linghua Wang, and Xianyong Bai

Magnetoseismology, a technique of magnetic field diagnostics based on observations of magnetohydrodynamic (MHD) waves, has been widely used to estimate the field strengths of oscillating structures in the solar corona. However, previously magnetoseismology was mostly applied to occasionally occurring oscillation events, providing an estimate of only the average field strength or one-dimensional distribution of field strength along an oscillating structure. This restriction could be eliminated if we apply magnetoseismology to the pervasive propagating transverse MHD waves discovered with the Coronal Multi-channel Polarimeter (CoMP). Using several CoMP observations of the Fe XIII 1074.7 nm and 1079.8 nm spectral lines, we obtained maps of the plasma density and wave phase speed in the corona, which allow us to map both the strength and direction of the coronal magnetic field in the plane of sky. We also examined distributions of the electron density and magnetic field strength, and compared their variations with height in the quiet Sun and active regions. Such measurements could provide critical information to advance our understanding of the Sun's magnetism and the magnetic coupling of the whole solar atmosphere.

How to cite: Yang, Z., Bethge, C., Tian, H., Tomczyk, S., Morton, R., Del Zanna, G., McIntosh, S., Binay Karak, B., Gibson, S., Samanta, T., He, J., Chen, Y., Wang, L., and Bai, X.: Mapping the global magnetic field in the solar corona through magnetoseismology, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-642, https://doi.org/10.5194/egusphere-egu21-642, 2021.

11:33–11:35
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EGU21-3990
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ECS
Jenny Marcela Rodriguez Gomez, Tatiana Podlachikova, Astrid Veronig, Alexander Ruzmaikin, Joan Feynman, and Anatoly Petrukovich

Coronal Mass Ejections (CMEs) and their interplanetary counterparts (ICMEs) are the major sources for strong space weather disturbances. We present a study of statistical properties of fast CMEs (v≥1000 km/s) that occurred during solar cycles 23 and 24. We apply the Max Spectrum and the declustering threshold time methods. The Max Spectrum can detect the predominant clusters, and the declustering threshold time method provides details on the typical clustering properties and timescales. Our analysis shows that during the different phases of solar cycles 23 and 24, fast CMEs preferentially occur as isolated events and in clusters with, on average, two members. However, clusters with more members appear, particularly during the maximum phases of the solar cycles. During different solar cycle phases, the typical declustering timescales of fast CMEs are τc =28-32 hrs, irrespective of the very different occurrence frequencies of CMEs during a solar minimum and maximum. These findings suggest that  τc   for extreme events may reflect the characteristic energy build-up time for large flare and CME-prolific active regions. Statistically associating the clustering properties of fast CMEs with the disturbance storm time index at Earth suggests that fast CMEs occurring in clusters tend to produce larger geomagnetic storms than isolated fast CMEs. Our results highlight the importance of CME-CME interaction and their impact on Space Weather.

How to cite: Rodriguez Gomez, J. M., Podlachikova, T., Veronig, A., Ruzmaikin, A., Feynman, J., and Petrukovich, A.: Clustering of Fast Coronal Mass Ejections during Solar Cycles 23 and 24 and Implications for CME–CME Interactions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3990, https://doi.org/10.5194/egusphere-egu21-3990, 2021.

11:35–11:37
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EGU21-7602
Ciara Maguire, Eoin Carley, Pietro Zucca, Nicole Vilmer, and Peter Gallagher

The Sun produces highly dynamic and eruptive events that can drive shocks through the corona. These shocks can accelerate electrons, which result in plasma emission in the form of a type II radio burst. Despite a large number of type II radio bursts observations, the precise origin of coronal shocks is still subject to investigation. Here we present a well-observed solar eruptive event that occurred on 16 October 2015, focusing on a jet observed in the extreme ultraviolet by the SDO Atmospheric Imaging Assembly, a streamer observed in white-light by the Large Angle and  Spectrometric Coronagraph, and a metric type II radio burst observed by the LOw-Frequency Array (LOFAR) radio telescope. For the first time, LOFAR has interferometrically imaged the fundamental and harmonic sources of a type II radio burst and revealed that the sources did not appear to be co-spatial, as would be expected from the plasma emission mechanism. We correct for the separation between the fundamental and harmonic using a model which accounts for the scattering of radio waves by electron density fluctuations in a turbulent plasma. This allows us to show the type II radio sources were located ∼0.5 Rsun above the jet and propagated at a speed of ∼1000 km s−1, which was significantly faster than the jet speed of ∼200 km s−1. This suggests that the type II burst was generated by a piston shock driven by the jet in the low corona.

How to cite: Maguire, C., Carley, E., Zucca, P., Vilmer, N., and Gallagher, P.: LOFAR observations of a jet-driven piston shock in the low solar corona, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7602, https://doi.org/10.5194/egusphere-egu21-7602, 2021.

11:37–11:39
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EGU21-11089
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ECS
Devojyoti Kansabanik, Surajit Mondal, Divya Oberoi, and Angelos Vourlidas

Coronal Mass Ejections (CMEs) are large-scale explosive eruptions of magnetised plasma from the Sun into the Heliosphere. Measuring the physical parameters of CMEs is crucial for understanding their physics and for assessing their geo-effectiveness. Radio observations offer the most direct means for estimating these plasma parameters when gyrosynchrotron (GS) emission is detected from the CME plasma. However, since the first detection by Bastian et al.2001, only a handful of studies have successfully detected GS emission from CME plasma. This is usually attributed to the challenges involved in obtaining the high dynamic range imaging required for observing this faint gyrosynchrotron emission in the vicinity of active solar emissions.

The newly developed imaging pipeline (Mondal et al., 2019) designed for the data from Murchison Widefield Array (MWA) marks a significant improvement in metrewave solar radio imaging. Our work suggests that we should now be able to routinely detect GS emission from CME plasma. We present an example where we have successfully detected radio emission from CME plasma and modelled it as GS emission, leading to reliable estimates of CME magnetic field as well as the distribution of energetic electrons (Mondal et al. 2020). In a different example we are able to detect the radio emission from the CME plasma out to as far as 8.3 solar radii. We find that the observed spectra are not always consistent with simple GS models. This highlights that more complicated physics might be at play and points to the need for building more detailed models for interpreting these emissions. We hope that with the availability of polarimetric imaging capability, which we are in the process of developing, this technique will provide a robust way to routinely measure CME magnetic fields along with its other physical parameters. We note that these are the weakest detections of GS emissions from CME plasma reported yet.

How to cite: Kansabanik, D., Mondal, S., Oberoi, D., and Vourlidas, A.: High fidelity spectroscopic imaging at low radio frequencies to estimate plasma parameters of solar coronal mass ejections at higher coronal heights, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11089, https://doi.org/10.5194/egusphere-egu21-11089, 2021.

11:39–11:41
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EGU21-13004
Junho Shin, Ryouhei Kano, Takashi Sakurai, Yeon-Han Kim, and Yong-Jae Moon

The X-Ray Telescope (XRT) onboard the Hinode satellite has a specially designed Wolter type grazing-incidence (GI) optics with a paraboloid-hyperboloid mirror assembly to measure the solar coronal plasma of temperatures up to 10 MK with a resolution of about one arc sec. One of the main purposes of this scientific mission is to investigate the detailed mechanism of energy transfer processes from the photosphere to the upper coronal region leading to its heating and the solar wind acceleration. An astronomical telescope is in general designed such that the best-focused image of an object is achieved at or very close to the optical axis, and inevitably the optical performance deteriorates away from the on-axis position. The Sun is, however, a large astronomical object and thus targets near the limb of full-disk images are placed at the outskirt of the field of view. The design of a solar telescope should thus consider the uniformity of imaging quality over a wide FOV, and it is particularly so for X-ray telescopes whose targets can be in the corona high above the limb.

 

We will explain in this presentation the importance of detailed calibration of the off-axis optical characteristics for Hinode/XRT. It have been revealed that the scattered light caused by the GI mirror surface has a power-law distribution and shows an energy dependence. We will also introduce the basic scheme of how the level of scattering wing is determined and connected to the core from the analysis of highly saturated in-flight data. Vignetting is another important optical characteristics for describing the telescope's performance, which reflects the ability to collect incoming light at different locations and photon energies. We have evaluated the vignetting effect in Hinode/XRT by analyzing the ground experimental data and found that the degree of vignetting varies linearly from the optical center and its pattern shows an energy dependence. Many interesting results on the calibration of Hinode/XRT optical characteristics will be introduced and discussed thoroughly. 

How to cite: Shin, J., Kano, R., Sakurai, T., Kim, Y.-H., and Moon, Y.-J.: Detailed Calibration of the Off-Axis Optical Characteristics for the X-Ray Telescope onboard Hinode, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13004, https://doi.org/10.5194/egusphere-egu21-13004, 2021.

11:41–11:43
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EGU21-6760
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ECS
Prantika Bhowmik and Anthony Yeates

During Solar Minimum, the Sun is perceived to be quite inactive with barely any spots emerging on the solar surface. Consequently, we observe a drop in the number of highly energetic events such as solar flares and coronal mass ejections (CMEs), which are often associated with active regions on the photosphere. However, our magnetofrictional simulations during the minimum period suggest that the solar corona could still be significantly dynamic while evolving in response to the large-scale shearing velocities on the solar surface. The non-potential evolution of the corona leads to the accumulation of magnetic free energy and helicity, which is periodically lost through eruptive events. Our study shows that these events can be categorised into two distinct classes. One set of events are caused due to full-scale eruption of low-lying coronal flux ropes and could be associated with occasional filament erupting CMEs observed during Solar Minimum. The other set of events are not driven by destabilisation of low-lying structures but rather by eruption from overlying sheared arcades. These could be linked with streamer blowouts or stealth CMEs. The two classes differ considerably in the amount of magnetic flux and helicity shed through the outer coronal boundary. We additionally investigate how other measurables such as current, open magnetic flux, free energy, coronal holes area, and the horizontal component of the magnetic field on the outer model boundary vary during the two classes of event. This study demonstrates and emphasises the importance and necessity of understanding the dynamics of the coronal magnetic field during Solar Minimum.

How to cite: Bhowmik, P. and Yeates, A.: Two classes of eruptive events during Solar Minimum, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6760, https://doi.org/10.5194/egusphere-egu21-6760, 2021.

11:43–12:30
Lunch break
Chairperson: André Galli
13:30–13:32
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EGU21-2076
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ECS
Carlos Larrodera, Lidia Nikitina, and Consuelo Cid

Society’s dependence on technology has increased during the past years. Therefore, understanding the hazardous events including space weather events that lead to technological problems is now critical. As solar wind is the driver of space weather, identifying extreme solar wind is important. In this work extreme value theory is used to characterize the solar wind parameters most relevant to space weather: interplanetary magnetic field strength and proton speed. This is done using an extreme value distribution for all data above a certain threshold for each parameter. Analysis demonstrates that these thresholds are around 900 km/s for the proton speed and around 95 nT for the interplanetary magnetic field. Based on 20 years of solar wind data, we made an estimation for the interplanetary magnetic field and solar wind proton speed with return periods corresponding to 4 and 6 solar cycles with a 99% confidence interval.

How to cite: Larrodera, C., Nikitina, L., and Cid, C.: Extreme event theory applied to the solar wind, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2076, https://doi.org/10.5194/egusphere-egu21-2076, 2021.

13:32–13:34
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EGU21-14653
Giuseppe Nisticò, Valery M. Nakariakov, Timothy Duckenfield, Miloslav Druckmüller, and Gaetano Zimbardo

Space telescopes of the SoHO, STEREO and SDO missions have occasionally acquired observations of comets, providing an interesting opportunity to investigate the structure and dynamics of the heliospheric plasma.  Cometary plasma tails exhibit a wave-like motion, which is believed to be a response to the physical conditions of the local interplanetary medium. Furthermore, sungrazing comets diving in the solar atmosphere provide us with an unprecedented way to diagnose the coronal plasma at distances which are unaccessible from the current spacecraft. Here, we present observations of Comet Lovejoy C/2011 W3 from SDO/AIA, which was seen to cross the EUV solar corona in December 2011. The cometary ions produced by the sublimation of the comet nucleus were channelled along the magnetic field lines forming some filamented structures. Such structures appear to show small amplitude kink oscillations, which are used to determine the magnitude of the coronal magnetic field by coronal seismology.

How to cite: Nisticò, G., Nakariakov, V. M., Duckenfield, T., Druckmüller, M., and Zimbardo, G.: Probing the solar corona magnetic field with sungrazing comets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14653, https://doi.org/10.5194/egusphere-egu21-14653, 2021.

13:34–13:36
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EGU21-11094
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ECS
Aoife Maria Ryan, Peter T. Gallagher, Eoin P. Carley, Michiel A. Brentjens, Pearse C. Murphy, Christian Vocks, Diana E. Morosan, Hamish Reid, Jasmina Magdalenic, Frank Breitling, Pietro Zucca, Richard Fallows, Gottfried Mann, Alain Kerdraon, and Ronald Halfwerk

The solar corona is a highly-structured plasma which can reach temperatures of more than 2 MK. At low frequencies (decimetric and metric wavelengths), scattering and refraction of electromagnetic waves are thought to considerably increase the imaged radio source sizes (up to a few arcminutes). However, exactly how source size relates to scattering due to turbulence is still subject to investigation. The theoretical predictions relating source broadening to propagation effects have not been fully confirmed by observations, due to the rarity of high spatial resolution observations of the solar corona at low frequencies. Here, the LOw Frequency ARray (LOFAR) was used to observe the solar corona at 120–180 MHz using baselines of up to 3.5 km (corresponding to a resolution of 1–2’) during the partial solar eclipse of 2015 March 20. A lunar de-occultation technique was used to achieve higher spatial resolution (0.6’) than that attainable via standard interferometric imaging (2.4’). This provides a means of studying the contribution of scattering to apparent source size broadening. This study shows that the de-occultation technique can reveal a more structured quiet corona that is not resolved from standard imaging, implying scattering may be overestimated in this region when using standard imaging techniques. However, an active region source was measured to be 4’ using both de-occultation and standard imaging. This may be explained by increased scattering of radio waves by turbulent density fluctuations in active regions, which is more severe than in the quiet Sun.



How to cite: Ryan, A. M., Gallagher, P. T., Carley, E. P., Brentjens, M. A., Murphy, P. C., Vocks, C., Morosan, D. E., Reid, H., Magdalenic, J., Breitling, F., Zucca, P., Fallows, R., Mann, G., Kerdraon, A., and Halfwerk, R.: LOFAR Imaging of the Solar Corona during the 2015 March 20 Solar Eclipse, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11094, https://doi.org/10.5194/egusphere-egu21-11094, 2021.

13:36–13:38
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EGU21-4795
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ECS
Andreas Wagner, Manuela Temmer, and Eleanna Asvestari

With the increasing amount of space weather forecasting simulation codes being developed, assessing their performance becomes crucial. Especially the errors resulting from coronal magnetic field models are a critical factor, because these will get propagated further by various solar wind models. We present a first result for a benchmarking system that allows a rather easy-to-implement  assessment of the performance quality of any coronal magnetic field model. This will allow for a standardized comparison between different models. The benchmarking system is based on stepwise visual and semi-automatized comparisons between model output and EUV on-disk and coronograph white-light data. We are using various viewpoints and instrumental data provided by STEREO, SOHO and SDO. 
In our work we exemplarily apply this scheme to the coronal model currently implemented in EUHFORIA, an adaption of the Wang-Sheeley-Arge (WSA) model, with varying input parameters. Furthermore, with this system we also show its possible usage for the derivation of an ideal parameter set. 

How to cite: Wagner, A., Temmer, M., and Asvestari, E.: Quality assessment for objective inter-comparison of coronal models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4795, https://doi.org/10.5194/egusphere-egu21-4795, 2021.

13:38–13:40
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EGU21-2864
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ECS
Tereza Durovcova, Jana Šafránková, and Zdeněk Němeček

Two large-scale interaction regions between the fast solar wind emanating from coronal holes and the slow solar wind coming from streamer belt are usually distinguished. When the fast stream pushes up against the slow solar wind ahead of it, a compressed interaction region that co-rotates with the Sun (CIR) is created. It was already shown that the relative abundance of alpha particles, which usually serve as one of solar wind source identifiers can change within this region. By symmetry, when the fast stream outruns the slow stream, a corotating rarefaction region (CRR) is formed. CRRs are characterized by a monotonic decrease of the solar wind speed, and they are associated with the regions of small longitudinal extent on the Sun. In our study, we use near-Earth measurements complemented by observations at different heliocentric distances, and focus on the behavior of alpha particles in the CRRs because we found that the large variations of the relative helium abundance (AHe) can also be observed there. Unlike in the CIRs, these variations are usually not connected with the solar wind speed and alpha-proton relative drift changes. We thus apply a superposed-epoch analysis of identified CRRs with a motivation to determine the global profile of alpha particle parameters through these regions. Next, we concentrate on the cases with largest AHe variations and investigate whether they can be associated with the changes of the solar wind source region or whether there is a relation between the AHe variations and the non-thermal features in the proton velocity distribution functions like the temperature anisotropy and/or presence of the proton beam.

How to cite: Durovcova, T., Šafránková, J., and Němeček, Z.: Study of alpha particle properties across rarefaction regions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2864, https://doi.org/10.5194/egusphere-egu21-2864, 2021.

13:40–13:42
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EGU21-12772
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ECS
Marlon Köberle, Radoslav Bucik, Nina Dresing, Bernd Heber, Andreas Klassen, and Linghua Wang

3He-rich solar energetic particle (SEP) events are characterized by a peculiar elemental composition with rare species like 3He or ultra-heavy ions tremendously enhanced over the solar system abundances.
We report on 3He rich SEP periods measured by the Suprathermal Ion Telescope (SIT) onboard STEREO-A beginning in 2007 until 2020, covering the whole solar cycle 24.
The mass resolution capabilities of SIT do not allow to easily distinguish between 3He and 4He especially in cases of a low 3He to 4He ratio.
We therefore developed a semi-automatic detection algorithm to find time periods during which a 3He enhancement can be statistically determined.
Using this method we found 112 3He rich periods.
These periods were further examined in regards of their 3He/4He and Fe/O ratio. 
Previously about ten 3He-rich SEP periods measured by SIT on STEREO-A have been reported.
An association with in-situ electron measurements by STEREO-SEPT and STEREO-STE showed that ~60% of the 112 periods are accompanied with electron events.
The here presented catalogue of 3He rich periods is intended to serve as a reference for the community.

How to cite: Köberle, M., Bucik, R., Dresing, N., Heber, B., Klassen, A., and Wang, L.: 3He rich periods measured by the Suprathermal Ion Telescope (SIT) on STEREO-A during solar cycle 24, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12772, https://doi.org/10.5194/egusphere-egu21-12772, 2021.

13:42–13:44
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EGU21-11921
Alessandro Bemporad, Olga Katushkina, Vladislav Izmodenov, Dimitra Koutroumpa, and Eric Quemerais

The Sun modulates with the solar wind flow the shape of the whole Heliosphere interacting with the surrounding interstellar medium. Recent results from IBEX and INCA experiments, as well as recent measurements from Voyager 1 and 2, demonstrated that this interaction is much more complex and subject to temporal and heliolatitudinal variations than previously thought. These variations could be also related with the evolution of solar wind during its journey through the Heliosphere. Hence, understanding how the solar wind evolves from its acceleration region in the inner corona to the Heliospheric boundaries is very important.

In this work, SWAN Lyman-α full-sky observations from SOHO are combined for the very first time with measurements acquired in the inner corona by SOHO UVCS and LASCO instruments, to trace the solar wind expansion from the Sun to 1 AU. The solar wind mass flux in the inner corona was derived over one full solar rotation period in 1997, based on LASCO polarized brightness measurements, and on the Doppler dimming technique applied to UVCS Lyman-α emission from neutral H coronal atoms due to resonant scattering of chromospheric radiation. On the other hand, the SWAN Lyman-α emission (due to back-scattering from neutral H atoms in the interstellar medium) was analyzed based on numerical models of the interstellar hydrogen distribution in the heliosphere and the radiation transfer. The SWAN full-sky Lyman-α intensity maps are used for solving of the inverse problem and deriving of the solar wind mass flux at 1 AU from the Sun as a function of heliolatitude. First results from this comparison for a chosen time period in 1997 are described here, and possible future applications for Solar Orbiter data are discussed.

How to cite: Bemporad, A., Katushkina, O., Izmodenov, V., Koutroumpa, D., and Quemerais, E.: Evolution of solar wind flows from the inner corona to 1 AU: constraints provided by SOHO UVCS and SWAN data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11921, https://doi.org/10.5194/egusphere-egu21-11921, 2021.

13:44–13:46
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EGU21-13185
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ECS
Renata Modzelewska and Agnieszka Gil

We study the 27-day variations of galactic cosmic rays (GCRs) based on neutron monitor (NM), ACE/CRIS, STEREO and SOHO/EPHIN measurements, in solar minima 23/24 and 24/25 characterized by the opposite polarities of solar magnetic cycle. Now there is an opportunity to re-analyze the polarity dependence of the amplitudes of the recurrent GCR variations in 2007-2009 for negative A < 0 solar magnetic polarity and to compare it with the clear periodic variations related to solar rotation in 2017-2019 for positive A > 0. We use the Fourier analysis method to study the periodicity in the GCR fluxes. Since the GCR recurrence is a consequence of solar rotation, we analyze not only GCR fluxes, but also solar and heliospheric parameters examining the relationships between the 27-day GCR variations and heliospheric, as well as, solar wind parameters. We find that the polarity dependence of the amplitudes of the 27-day variations of the GCR intensity and anisotropy for NMs data is kept for the last two solar minima: 23/24 (2007-2009) and 24/25 (2017-2019) with greater amplitudes in positive A > 0 solar magnetic polarity. ACE/CRIS, SOHO/EPHIN and STEREO measurements are not governed by this principle of greater amplitudes in positive A > 0 polarity. GCR recurrence caused by the solar rotation for low energy (< 1GeV) cosmic rays is more sensitive to the enhanced diffusion effects, resulting in the same level of the 27-day amplitudes for positive and negative polarities. While high energy (> 1GeV) cosmic rays registered by NMs, are more sensitive to the large-scale drift effect leading to the 22-year Hale cycle in the 27-day GCR variation, with the larger amplitudes in the A > 0 polarity than in the A < 0.

How to cite: Modzelewska, R. and Gil, A.: 27-day variations of the galactic cosmic rays intensity and anisotropy in solar minima 23/24 and 24/25 by ACE/CRIS, STEREO, SOHO/EPHIN and neutron monitors, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13185, https://doi.org/10.5194/egusphere-egu21-13185, 2021.

13:46–13:48
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EGU21-13829
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ECS
Anastasiia Moskaleva, Maria Riazantseva, Yuri Yermolaev, and Irina Lodkina

The efficiency of the solar wind interaction with the Earth's magnetosphere is determined not only by the values of solar wind parameters, but also by the direction of its flow.  As a rule, the slow quiet and uniform solar wind extends radially, but at the same time there are different large-scale solar wind streams, that differ in the values of the plasma parameters and in the flow direction. The most significant changes of solar wind flow direction can be observed in areas of stream interaction, for example Sheath (compression regions before the fast interplanetary coronal mass ejections) and CIR (corotating interaction regions, that are predate high-speed flows from coronal holes) [1]. In the present study, using plasma measurements on the WIND spacecraft, the statistical distributions of the values and fluctuations of flow direction angles in the solar wind were analyzed.  The angles variations were considered on temporal scales from several ten seconds to an hour. The statistical distributions in the quiet solar wind and in various large-scale solar wind streams using the catalog of large-scale solar wind phenomena from the ftp://ftp.iki.rssi.ru/pub/omni/catalog were compared [2].

At the result of this work, it was shown , that maximum values of modules longitude (φ) and latitude (θ) angles, and of their variations are observed for Sheath and CIR regions, the probability of large deviations from the radial direction (>5 degrees)  also increases. Meanwhile the dependence on the solar wind type reduces with decreasing scale. The relation of the values and fluctuations of the direction angles on the values of the plasma parameters in the solar wind were also analyzed.

The work was supported by the RFBR, grant № 19-02-00177а.

1.Yermolaev Y. I., Lodkina I. G., Nikolaeva N. S., Yermolaev M. Y. 2017, Solar Physics, 292 (12),193, https://doi.org/10.1007/s11207-017-1205-1
2. Yermolaev, Yu.I., Nikolaeva, N.S., Lodkina, I.G., Yermolaev, M.Yu.: 2009, Catalog of large-scale solar wind phenomena during 1976 – 2000. Cosm. Res. 47(2),81;Eng.transl.Kosm.Issled.47(2),99, https://doi.org/10.1134/S0010952509020014

How to cite: Moskaleva, A., Riazantseva, M., Yermolaev, Y., and Lodkina, I.: Statistical analysis of flow direction and its variations in different types of solar wind streams, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13829, https://doi.org/10.5194/egusphere-egu21-13829, 2021.

13:48–13:50
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EGU21-14937
Caterina Tiburzi, Golam Shaifullah, and Pietro Zucca

Pulsars are highly-magnetized, fast-rotating neutron stars whose radiation is mainly detected at radio frequencies. Their clock-like emission and high degree of linear polarization make them ideal background sources to probe the electron density and magnetic field of the interplanetary medium.
The Soltrack project is a cutting-edge experiment that combines high-quality pulsar observations carried out with LOFAR with the study of the heliosphere and its phenomena. It recently confirmed the first evidence of the Solar cycle's impact on pulsar data, developed a new software to detect pulsar occultations by coronal mass ejections, identified the influence of Solar streamers on pulsar observations and applied pulsar-derived measurements to the validation efforts of the EUHFORIA magneto-hydrodynamic software, that simulate the Solar wind properties for Space weather purposes.
Here I will describe the fundamental concepts at the basis of the Soltrack experiments, and describe the results reached while paving the road for the application of pulsar data to heliospheric analyses.

How to cite: Tiburzi, C., Shaifullah, G., and Zucca, P.: Sampling the heliosphere through low-frequency observations of pulsars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14937, https://doi.org/10.5194/egusphere-egu21-14937, 2021.

13:50–13:52
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EGU21-7107
Karl-Ludwig Klein and the NRH team

The Nancay Radioheliograph is dedicated to imaging the solar corona at decimetre-to-metre wavelengths. The imaged structures are the quiet corona, through thermal bremsstrahlung, and bright collective emissions due to electrons accelerated in quiescent, flaring and eruptive active regions. The instrument produced nearly daily maps of the Sun between 1996 and 2015, at several frequencies in the 150-450 MHz range with sub-second cadence. The observations were stopped in 2015 for a major technical upgrade through the replacement of the correlator and the data acquisition system. They were resumed in November 2020, and at the time of writing the commissioning of the instrument is well underway. This contribution will give a brief overview of the technical changes and present observations at eight frequencies of solar activity since November 2020, including the coronal mass ejection (CME) of December 14 seen in some images of the total solar eclipse, observations conducted during the present perihelion passage of the Parker Solar Probe mission, as well as during periods of interest to the Solar Orbiter mission. The data are freely available, and special products of common visualisation with the space missions will be illustrated.

How to cite: Klein, K.-L. and the NRH team: Solar observations with the Nancay Radioheliograph in support of the Solar Orbiter and Parker Solar Probe missions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7107, https://doi.org/10.5194/egusphere-egu21-7107, 2021.

13:52–13:54
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EGU21-10868
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ECS
Su Wei

TianQin is a proposed space-borne gravitational wave (GW) observatory composed of three identical satellites orbiting around the geocenter with a distance of 105 km. It aims at detecting GWs in 0.1 mHz – 1 Hz. The detection of GW relies on the high precision measurement of optical path length at 10−12 m level. The dispersion of space plasma can lead to the optical path difference (OPD, ∆l) along the propagation of laser beams between a pair of satellites. Here, we study the OPD noises for TianQin. The Space Weather Modeling Framework is used to simulate the interaction between the Earth magnetosphere and solar wind. From the simulations, we extract the magnetic field and plasma parameters on the orbits of TianQin at four relative positions of the satellite constellation in the Earth magnetosphere. We calculate the OPD noise for single link, Michelson, and Time-Delay Interferometry (TDI) data combinations (α and X). For single link and Michelson interferometer, the maxima of ∆l are on the order of 1 pm. For the TDI combinations, these can be suppressed to about 0.05 pm. The OPD noise of Michelson combination is colored in the concerned frequency range; while the ones for the TDI combinations are roughly white. Furthermore, we calculate the ratio of the equivalent strain of the OPD noise to that of TQ, and find that the OPD noises for the TDI combinations can be neglected in the most sensitive frequency range of f < 0.1 Hz.

How to cite: Wei, S.: Analyses of Laser Propagation Noise for TianQin Gravitational Wave Observatory Based on the Global Magnetosphere MHD Simulation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10868, https://doi.org/10.5194/egusphere-egu21-10868, 2021.

13:54–13:56
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EGU21-15048
Pietro Zucca

Understanding and modelling the complex state of the Sun-solar wind-heliosphere system, requires a comprehensive set of multiwavelength observations. LOFAR has unique capabilities in the radio domain. Some examples of these include: a) the ability to take high-resolution solar dynamic spectra and radio images of the Sun; b) observing the scintillation (interplanetary scintillation - IPS) of distant, compact, astronomical radio sources to determine the density, velocity and turbulence structure of the solar wind; and c) the use of Faraday rotation as a tool to probe the interplanetary magnetic-field strength and direction. However, to better understand and predict how the Sun, its atmosphere, and more in general the Heliosphere works and impacts Earth, the combination of in-situ spacecraft measurements and ground-based remote-sensing observations of coronal and heliospheric plasma parameters is extremely useful. Ground-based observations can be used to infer a global picture of the inner heliosphere, providing the essential context into which in-situ measurements from spacecraft can be placed. Conversely, remote-sensing observations usually contain information from extended lines of sight, with some deconvolution and modelling necessary to build up a three-dimensional (3-D) picture. Precise spacecraft measurements, when calibrated, can provide ground truth to constrain these models. The PSP mission is observing the solar corona and near-Sun interplanetary space. It has a highly-elliptical orbit taking the spacecraft as close as nearly 36 sola radii from the Sun centre on its first perihelion passage, and subsequent passages ultimately reaching as close as 9.8 solar radii. Four instruments are on the spacecraft’s payload: FIELDS measuring the radio emission, electric and magnetic fields, Poynting flux, and plasma waves as well as the electron density and temperature; ISOIS measuring energetic electrons, protons, and heavy ions in the energy range 10 keV-100 MeV; SWEAP measuring the density, temperature, and flow speed of electrons, protons, and alphas in the solar wind; and finally, WISPR imaging coronal streamers, coronal mass ejections (CMEs), their associated shocks, and other solar wind structures in the corona and near-Sun interplanetary space, and provide context for the other three in-situ instruments. In this talk, the different observing modes of LOFAR and several results of the joint LOFAR/PSP campaign will be presented, including fine structures of radio bursts, localization and kinematics of propagating radio sources in the heliosphere, and the challenges and plans for future observing campaigns including PSP and Solar Orbiter.

 

How to cite: Zucca, P.: Observing the Sun with LOFAR: an overview of the telescope capabilities and the recent results from the PSP groud base support campaign., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15048, https://doi.org/10.5194/egusphere-egu21-15048, 2021.

13:56–13:58
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EGU21-9506
Dimitra Koutroumpa, Eric Quémerais, Lucile Conan, Philippe Lamy, Stéphane Ferron, and Hugo Gilardy

For more than two decades the SOHO/SWAN instrument has been monitoring the full-sky hydrogen backscattered Lyman-α emission, and the derived three-dimensional solar wind proton flux. We present a comparison of the time series of the latitude-integrated hydrogen ionization rates (β) derived from the inversion of the SWAN full-sky maps with the integrated coronal electron density derived from the inversion of SOHO/LASCO-C2 white light images. The analysis shows a variable time lag of the SWAN β of a few Carrington rotations, correlated with the solar cycle phase (larger delay during solar maxima compared to minima). This is a direct consequence of the variation of the size of the hydrogen ionization cavity and the time it takes for hydrogen atoms to propagate in the inner heliosphere. This effect should be taken into account in studies of the interstellar neutral populations in interplanetary space.

How to cite: Koutroumpa, D., Quémerais, E., Conan, L., Lamy, P., Ferron, S., and Gilardy, H.: Response of the interplanetary hydrogen population to global changes of solar activity: a quantitative analysis based on SOHO/SWAN and SOHO/LASCO-C2 data comparison., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9506, https://doi.org/10.5194/egusphere-egu21-9506, 2021.

13:58–14:00
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EGU21-14279
Zixuan Liu, Linghua Wang, Liu Yang, Wimmer-Schweingruber Robert, Quanqi Shi, and Bale Stuart

We present a statistical study of in-situ shock acceleration of ~1-100 keV solar wind suprathermal electrons at Earth’s bow shock, by using Wind 3D plasma and energetic particle measurements in ambient solar wind and MMS measurements in shock downstream. We pick out 74 shock cases (1 quasi-parallel shock, 73 quasi-perpendicular shocks) during 2015 October - 2017 January, and classify them into 4 types according to their energy spectra in downstream: type 0 (23 cases) without significant electron acceleration after shock passage, type 1 (24 cases) with power-law spectrum, J ∝εβ1_dn, at ~0.8-10 keV, type 2 (16 cases) with power-law-spectrum at ~0.8-10 keV and significant flux enhancement above 30 keV, and type 3 (11 cases) with a clear double-power-law spectrum, J ∝ εβ1_dn (J ∝ εβ2_dn) when ε « εdntr  (ε » εdntr), bending down at εdntr ~20-90 keV. The spectral indexes at lower energies for type 1, type 2 and type 3, β1dn, range from 2.5 to 5, while the spectral indexes at higher energies for type 3, β2dn, range from 4 to 9, and all the spectral indexes have no significant correlation with those in ambient solar wind. Among the 4 types, type 3 is the strongest acceleration with the largest flux enhancement and the lowest β1dn. Besides, we find that the flux ratio between downstream and ambient solar wind Jdn/Jab is field-perpendicular for most cases in both low and high energies, and Jdn/Jab1dn) has positive (negative) correlations with θBn and magnetic field compression ratio, rB, which favor the shock drift acceleration (SDA) mechanism. However, Jdn/Jab has no correlation with the drift electric field Ed, while the normalized drift time, Td/Ttr, has a positive correlation with θBn, it suggests that θBn can influence electron drift time and thus influence the acceleration efficiency.

How to cite: Liu, Z., Wang, L., Yang, L., Robert, W.-S., Shi, Q., and Stuart, B.: Shock Acceleration of ~1-100 Kev Electrons at Earth's Bow Shock, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14279, https://doi.org/10.5194/egusphere-egu21-14279, 2021.

14:00–14:02
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EGU21-10504
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ECS
Elena Provornikova, Pontus C. Brandt, Ralph L. McNutt, Jr., Robert DeMajistre, Edmond C. Roelof, Parisa Mostafavi, Drew Turner, Matthew E. Hill, Jeffrey L. Linsky, Seth Redfield, Andre Galli, Carey Lisse, Kathleen Mandt, Abigail Rymer, and Kirby Runyon

The Interstellar Probe is a space mission to discover physical interactions shaping globally the boundary of our Sun`s heliosphere and its dynamics and for the first time directly sample the properties of the local interstellar medium (LISM). Interstellar Probe will go through the boundary of the heliosphere to the LISM enabling for the first time to explore the boundary with a dedicated instrumentation, to take the image of the global heliosphere by looking back and explore in-situ the unknown LISM. The pragmatic concept study of such mission with a lifetime 50 years that can be implemented by 2030 was funded by NASA and has been led by the Johns Hopkins University Applied Physics Laboratory (APL). The study brought together a diverse community of more than 400 scientists and engineers spanning a wide range of science disciplines across the world.

Compelling science questions for the Interstellar Probe mission have been with us for many decades. Recent discoveries from a number of space missions exploring the heliosphere raised new questions strengthening the science case. The very shape of the heliosphere, a manifestation of complex global interactions between the solar wind and the LISM, remains the biggest mystery. Interpretations of imaging the heliosphere in energetic neutral atoms (ENAs) in different energy ranges on IBEX and Cassini/INCA from inside show contradictory pictures. Global physics-based models also do not agree on the global shape. Interstellar Probe on outbound trajectory will image the heliosphere from outside for the first time and will provide a unique determination of the global shape.

The LISM is a completely new area for exploration and discovery. We have a crude understanding of the LISM inferred from in-situ measurements inside the heliosphere of interstellar helium, pick-up-ions, ENAs, remote observations of solar backscattered Lyman-alpha emission and absorption line spectroscopy in the lines of sight of stars. We have no in-situ measurements of most LISM properties, e.g. ionization, plasma and neutral gas, magnetic field, composition, dust, and scales of possible inhomogeneities. Voyagers with limited capabilities have explored 30 AU beyond the heliosphere which appeared to be a region of significant heliospheric influence. The LISM properties are among the key unknowns to understand the Sun`s galactic neighborhood and how it shapes our heliosphere. Interstellar Probe will be the first NASA mission to discover the very nature of the LISM and shed light on whether the Sun enters a new region in the LISM in the near future.

In this presentation we give an overview of heliophysics science for the Interstellar Probe mission focusing on the critical science questions of the three objectives for the mission. We will discuss in more details a need for direct measurements in the LISM uniquely enabled by the Interstellar Probe.

How to cite: Provornikova, E., Brandt, P. C., McNutt, Jr., R. L., DeMajistre, R., Roelof, E. C., Mostafavi, P., Turner, D., Hill, M. E., Linsky, J. L., Redfield, S., Galli, A., Lisse, C., Mandt, K., Rymer, A., and Runyon, K.: Unique heliophysics science opportunities along the Interstellar Probe journey up to 1000 AU from the Sun, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10504, https://doi.org/10.5194/egusphere-egu21-10504, 2021.

14:02–14:04
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EGU21-3308
Pontus Brandt, Ralph McNutt, Elena Provornikova, Carey Lisse, Kathleen Mandt, Kirby Runyon, Abigail Rymer, Parisa Mostafavi, Robert DeMajistre, Edmond Roelof, Drew Turner, Matthew Hill, James Kinnison, Gabe Rogers, Clayton Smith, Glen Fountain, David Copeland, Peter Kollmann, Reza Ashtari, and Robert Stough and the The Interstellar Probe Study Team

An Interstellar Probe mission to the Very Local Interstellar Medium (VLISM) would bring new scientific discoveries of the mechanisms upholding our vast heliosphere and directly sample the unexplored Local Interstellar Clouds that our Sun is moving through in relatively short galactic timescales. As such, it would represent Humanity's first explicit step in to the galaxy and become perhaps NASA's boldest step in space exploration. Such a mission has been discussed and studied since 1960, but the stumbling block has often been propulsion. Now this hurdle has been overcome by the availability of new and larger launch vehicles. An international team of scientists and experts are now progressing towards the final year of a NASA-funded study led by The Johns Hopkins University Applied Physics Laboratory (APL) to develop pragmatic example mission concepts for an Interstellar Probe with a nominal design lifetime of 50 years. Together with the Space Launch System (SLS) Office at the NASA Marshall Space Flight Center, the team has analyzed dozens of launch configurations and demonstrate that asymptotic speeds in excess of 7.5 Astronomical Units (AU) per year can be achieved using existing or near-term propulsion stages with a powered or passive Jupiter Gravity Assist (JGA). These speeds are more than twice that of the fastest escaping man-made spacecraft to date, which is Voyager 1 currently at 3.59 AU/year. An Interstellar Probe would therefore reach the Termination Shock (TS) in less than 12 years and cross the Heliopause into the VLISM after about 16 years from launch.

In this presentation we provide an overview and update of the study, the science mission concept, discuss the compelling discoveries that await, and the associated example science payload, measurements and operations ensuring a historic data return that would push the boundaries of space exploration by going where no one has gone before.

How to cite: Brandt, P., McNutt, R., Provornikova, E., Lisse, C., Mandt, K., Runyon, K., Rymer, A., Mostafavi, P., DeMajistre, R., Roelof, E., Turner, D., Hill, M., Kinnison, J., Rogers, G., Smith, C., Fountain, G., Copeland, D., Kollmann, P., Ashtari, R., and Stough, R. and the The Interstellar Probe Study Team: Interstellar Probe: A Mission to the Heliospheric Boundary and Interstellar Medium for the Next Decade, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3308, https://doi.org/10.5194/egusphere-egu21-3308, 2021.

14:04–15:00