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, Pietro Zucca, Jasmina Magdalenic
| Attendance Fri, 08 May, 14:00–15:45 (CEST), Attendance Fri, 08 May, 16:15–18:00 (CEST)

Files for download

Download all presentations (148MB)

Chat time: Friday, 8 May 2020, 14:00–15:45

Chairperson: Manuela Temmer
D2570 |
Tibor Torok, Yang Liu, James E. Leake, Xudong Sun, and Viacheslav S. Titov

The physical conditions that determine the eruptive activity of solar active regions (ARs) are still not well understood. Various proxies for predicting eruptive activity have been suggested, with relatively limited success. Moreover, it is presently unclear under which conditions an eruption will remain confined to the low corona or produce a coronal mass ejection (CME).

Using vector magnetogram data from SDO/HMI, we investigate the association between electric-current neutralization and eruptive activity for a sample of ARs. We find that the vast majority of CME-producing ARs are characterized by a strongly non-neutralized total current, while the total current in ARs that do not produce CMEs is almost perfectly neutralized, even if those ARs produce strong (X-class) confined flares. This suggests that the degree of current neutralization can serve as a good proxy for assessing the ability of ARs to produce CMEs. 


How to cite: Torok, T., Liu, Y., Leake, J. E., Sun, X., and Titov, V. S.: Electric-current Neutralization and Eruptive Activity of Solar Active Regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1654, https://doi.org/10.5194/egusphere-egu2020-1654, 2020.

D2571 |
Camilla Scolini, Jens Pomoell, Emmanuel Chané, Stefaan Poedts, Luciano Rodriguez, Emilia Kilpua, Manuela Temmer, Christine Verbeke, Karin Dissauer, Astrid Veronig, Erika Palmerio, and Mateja Dumbović

Coronal Mass Ejections (CMEs) are the primary source of strong space weather disturbances at Earth and other locations in the heliosphere. Understanding the physical processes involved in their formation at the Sun, propagation in the heliosphere, and impact on planetary bodies is therefore critical to improve current space weather predictions throughout the heliosphere. The capability of CMEs to drive strong space weather disturbances at Earth and other planetary and spacecraft locations primarily depends on their dynamic pressure, internal magnetic field strength, and magnetic field orientation at the impact location. In addition, phenomena such as the interaction with the solar wind and other solar transients along the way, or the pre-conditioning of interplanetary space due to the passage of previous CMEs, can significantly modify the properties of individual CMEs and alter their ultimate space weather impact. Investigating and modeling such phenomena via advanced physics-based heliospheric models is therefore crucial to improve the space weather prediction capabilities in relation to both single and complex CME events. 

In this talk, we present our progress in developing novel methods to model CMEs in the inner heliosphere using the EUHFORIA MHD model in combination with remote-sensing solar observations. We discuss the various observational techniques that can be used to constrain the initial CME parameters for EUHFORIA simulations. We present current efforts in developing more realistic magnetised CME models aimed at describing their internal magnetic structure in a more realistic fashion. We show how the combination of these two approaches allows the investigation of CME propagation and evolution throughout the heliosphere to a higher level of detail, and results in significantly improved predictions of CME impact at Earth and other locations in the heliosphere. Finally, we discuss current limitations and future improvements in the context of studying space weather events throughout the heliosphere.

How to cite: Scolini, C., Pomoell, J., Chané, E., Poedts, S., Rodriguez, L., Kilpua, E., Temmer, M., Verbeke, C., Dissauer, K., Veronig, A., Palmerio, E., and Dumbović, M.: Observation-based modelling of magnetised CMEs in the inner heliosphere with EUHFORIA, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1777, https://doi.org/10.5194/egusphere-egu2020-1777, 2020.

D2572 |
| solicited
David McComas

The Interstellar Boundary Explorer (IBEX) was launched in 2008 and has now returned observations over a full 11-year solar cycle (Solar Cycle 24). IBEX remotely images global ion distributions via charge exchange Energetic Neutral Atoms (ENAs) propagating inward from the heliosheath – the region between the termination shock and heliopause – and beyond. These observations have led to numerous discoveries about the outer heliosphere and its interaction with the surrounding interstellar medium. Heliospheric ENAs arise largely from two sources: the IBEX Ribbon, which is likely generated beyond the heliopause, in the very local interstellar medium, and the globally distributed flux (GDF), which is primarily produced in the heliosheath. In this talk we summarize some of the critical advances driven by IBEX observations. We also examine how the heliosphere and its interstellar interaction have evolved over the past solar cycle. For most of IBEX’s 11 years of observations, there was an overall reduction and then flattening of the ENA fluxes at all energies, consistent with a generally deflating, or shrinking, heliosphere. Over the past few years, IBEX has been observing the progressive response of the heliosphere to a large persistent increase in the solar wind output that passed 1 AU in the second half of 2014. This enhancement arrived at the outer heliosphere as indicated by an increase in the ENAs returning from the closest region of the inner heliosheath, south of the upwind direction, starting in the second half of 2016. Since then, the region of enhanced ENA emissions has expanded progressively outward from there, exposing increasingly further away regions of the heliosheath. IBEX observations over the past 11-years have led to a true scientific revolution in our understanding of the outer heliosphere and its interstellar interaction.

How to cite: McComas, D.: A Solar Cycle of Observations with the Interstellar Boundary Explorer (IBEX), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5536, https://doi.org/10.5194/egusphere-egu2020-5536, 2020.

D2573 |
| Hannes Alfvén Medal Lecture
Qiugang Zong

Sudden changes in solar wind forcing, e.g., those associated with interplanetary shocks and/or solar wind dynamic pressure pulses, can cause many fundamentally important phenomena in the Earth’s magnetosphere including electromagnetic wave generation, plasma heating and energetic particle acceleration. This presentation summarizes our present understanding of the magnetospheric response to solar wind forcing in the aspects of radiation belt electrons, ring current ions and plasmaspheric plasma based on in situ spacecraft measurements, ground-based magnetometer data, MHD and kinetic simulations. 

Magnetosphere response to sudden changes in solar wind forcing, is not a “one-kick” scenario. It is found that after the impact of solar wind structures on the Earth’s magnetosphere, plasma heating and energetic particle acceleration started nearly immediately and could last for a few hours. Even a small dynamic pressure change associated with an interplanetary shock or a solar wind pressure pulse can play a non-negligible role in magnetospheric physics. The impact leads to different kinds of waves including poloidal mode ULF waves. The fast acceleration of energetic electrons in the radiation belt and energetic ions in the ring current region usually contains two steps: (1) the initial adiabatic acceleration due to the magnetospheric compression; (2) followed by the wave-particle resonant acceleration dominated by global or localized poloidal ULF waves excited at various L-shells. 

Generalized theory of drift and drift-bounce resonance with growing or decaying ULF waves  (globally distributed or localized)  has been developed to explain in situ spacecraft observations. The new wave-related observational features like distorted energy spectrum, boomerang and fishbone pitch angle distributions of radiation belt electrons, ring current ions and plasmaspheric plasma can be explained in the frame work of this generalized theory. The results showed in this presentation can be widely used in the interaction of the solar wind with other planets such as Mercury, Jupiter, Saturn, Uranus and Neptune, and other astrophysical objects with magnetic fields.

How to cite: Zong, Q.: Magnetospheric Response to Solar Wind Forcing -ULF Wave - Particle interaction Perspective , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2069, https://doi.org/10.5194/egusphere-egu2020-2069, 2020.

D2574 |
Donald M. Hassler, Jeff Newmark, Sarah Gibson, Louise Harra, Thierry Appourchaux, Frederic Auchere, David Berghmans, Robin Colaninno, Silvano Fineschi, Laurent Gizon, Sanjay Gosain, Todd Hoeksema, Christian Kintziger, John Linker, Pierre Rochus, Jesper Schou, Nicholeen Viall, Matt West, Tom Woods, and Jean-Pierre Wuelser and the Solaris Team

The solar poles are one of the last unexplored regions of the solar system. Although Ulysses flew over the poles in the 1990s, it did not have remote sensing instruments onboard to probe the Sun’s polar magnetic field or surface/sub-surface flows.

We will discuss Solaris, a proposed Solar Polar MIDEX mission to revolutionize our understanding of the Sun by addressing fundamental questions that can only be answered from a polar vantage point. Solaris uses a Jupiter gravity assist to escape the ecliptic plane and fly over both poles of the Sun to >75 deg. inclination, obtaining the first high-latitude, multi-month-long, continuous remote-sensing solar observations. Solaris will address key outstanding, breakthrough problems in solar physics and fill holes in our scientific understanding that will not be addressed by current missions.

With focused science and a simple, elegant mission design, Solaris will also provide enabling observations for space weather research (e.g. polar view of CMEs), and stimulate future research through new unanticipated discoveries.

How to cite: Hassler, D. M., Newmark, J., Gibson, S., Harra, L., Appourchaux, T., Auchere, F., Berghmans, D., Colaninno, R., Fineschi, S., Gizon, L., Gosain, S., Hoeksema, T., Kintziger, C., Linker, J., Rochus, P., Schou, J., Viall, N., West, M., Woods, T., and Wuelser, J.-P. and the Solaris Team: The Solaris Solar Polar Mission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17703, https://doi.org/10.5194/egusphere-egu2020-17703, 2020.

D2575 |
Martin Volwerk, Charlotte Goetz, Ferdinand Plaschke, Tomas Karlsson, and Daniel Heyner

The occurrence rate of linear and pseudo magnetic holes has been determined during MESSENGER’s cruise phase starting from Earth (2005) and arriving at Mercury (2011). It is shown that the occurrence rate of linear magnetic holes, defined as a maximum of 10â—¦ rotation of the magnetic field over the hole, slowly decreases from Mercury to Earth. The pseudo magnetic holes, defined as a rotation between 10â—¦ and 45â—¦ over the hole, have mostly a constant occurrence rate, with a slight increas in front of the Earth and a decrease around the Earth. The width and depth of these structures seem to strongly differ depending on whether they are inside
or outside of Venus’s orbit.

How to cite: Volwerk, M., Goetz, C., Plaschke, F., Karlsson, T., and Heyner, D.: On the magnetic characteristics of magnetic holes in the solar wind between Mercury and Earth, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22, https://doi.org/10.5194/egusphere-egu2020-22, 2020.

D2576 |
Diana Morosan, Emilia Kilpua, Erika Palmerio, Benjamin Lynch, Jens Pomoell, Rami Vainio, Minna Palmroth, and Juska Räsänen

Flares and coronal mass ejections (CMEs) from the Sun are the most powerful and spectacular explosions in the solar system, capable of releasing vast amounts of magnetic energy over relatively short periods of time. These phenomena are often associated with particle acceleration processes that are often observed directly by spacecraft here at Earth. At the Sun, there are no direct methods of measuring these particles, which is necessary to predict their origin and propagation direction through the heliosphere. However, accelerated particles, in particular fast electrons, can generate emission at radio wavelengths through various mechanisms. Here, we exploit radio observations of Type II and Type IV radio bursts that accompany CME eruptions, in particular those radio bursts that show movement with the CME expansion in the low solar corona. Using multi-wavelength analysis, reconstruction of the radio emission and CME in three dimensions, we aim to determine the sources and locations of electron acceleration responsible for the Type II and Type IV emission in relation to the CME location and propagation. Such studies are important to understand CMEs and the sources of electron acceleration to ultimately improve the lead time to these impacts here at Earth.

How to cite: Morosan, D., Kilpua, E., Palmerio, E., Lynch, B., Pomoell, J., Vainio, R., Palmroth, M., and Räsänen, J.: The nature and origin of moving solar radio bursts associated with coronal mass ejections, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5379, https://doi.org/10.5194/egusphere-egu2020-5379, 2020.

D2577 |
Nariaki Nitta, Meng Jin, and Christina Cohen

One of the mysteries of solar energetic particle (SEP) events is the compositional variability in those events that are clearly shock-related and may be called gradual events.  In particular, the reason for the enhancement of Fe with respect to O or C at high energies has been debated over the past two decades, and yet it is still unsettled.  One hypothesis relates the compositional variability with whether the CME-driven shock is quasi-parallel or quad-perpendicular near the Sun, but this may not be easily tested using remote-sensing data alone. In recent years, however, CME-driven shock waves have been modelled by fitting shock-like features in EUV and white-light images with relatively simple shapes, and in combination with magnetic field models, ir is possible to compute shock parameters at the shock surface. In this presentation, we simulate a few CMEs whose associated SEP events show widely different Fe/O, using the Alfven wave Solar Model (AWSoM) that is part of the Space Weather Modeling Framework (SWMF). We constrain the input parameters of the simulations so that the observed pre-eruption corona, eruption and CME are well-reproduced. The shock surface, across which the shock parameters are highly non-uniform, is carefully traced, and the time-dependent connectivity of the shock surface with the observer at multiple spacecraft is compared with the SEP properties including composition. We discuss how much about the compositional variability of SEP events can be learned with this technique.

How to cite: Nitta, N., Jin, M., and Cohen, C.: Understanding the Origin of Variable Compositions of Gradual Solar Energetic Particle Events by Combining Observations and Numerical Simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21333, https://doi.org/10.5194/egusphere-egu2020-21333, 2020.

D2578 |
Manuel Flores Soriano and Consuelo Cid

SMOS is an Earth observing satellite that is been adapted to provide full polarization observations of the Sun at 1.4 GHz 24 hours a day. Its solar radio observations from the last decade will be released to the community by the middle of this year. In this presentation we show the capabilities of SMOS as a solar radio observatory and compare some of the most relevant radio bursts with data from GOES, LASCO, SDO and RSTN. We show how SMOS responds to different kinds of solar flares depending on their x-ray flux, and the kind of mass ejection or solar dimming that they have produced, if any. In addition to this we also show the potential of SMOS as a space weather tool to monitor GNSS satellites signal fades and to provide an early warning of Earth-directed coronal mass ejections.

How to cite: Flores Soriano, M. and Cid, C.: Comparing different types of solar flares with radio bursts detected by SMOS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18133, https://doi.org/10.5194/egusphere-egu2020-18133, 2020.

D2579 |
Aoife Maria Ryan, Peter T. Gallagher, Eoin P. Carley, Diana E. Morosan, Michiel A. Brentjens, Pietro Zucca, Richard Fallows, Christian Vocks, Gottfried Mann, Frank Breitling, Jasmina Magdalenic, Alain Kerdraon, and Hamish Reid

The solar corona is a highly-structured plasma which reaches temperatures of more than ~2MK. At low radio frequencies (≤ 400 MHz), scattering and refraction of electromagnetic waves are thought to broaden sources to several arcminutes. However, exactly how source size relates to scattering due to turbulence is still subject to investigation. This is mainly due to the lack of high spatial resolution observations of the solar corona at low frequencies. Here, we use the LOw Frequency ARray (LOFAR) to observe the solar corona at 120-180 MHz using baselines of up to ~3.5 km (~1--2’) during a partial solar eclipse of 2015 March 20. We use a lunar de-occultation technique to achieve higher spatial resolution than that attainable via traditional interferometric imaging. This provides a means of studying source sizes in the corona that are smaller than the angular width of the interferometric point spread function. 

How to cite: Ryan, A. M., Gallagher, P. T., Carley, E. P., Morosan, D. E., Brentjens, M. A., Zucca, P., Fallows, R., Vocks, C., Mann, G., Breitling, F., Magdalenic, J., Kerdraon, A., and Reid, H.: Imaging the Solar Corona during the 2015 March 20 Eclipse using LOFAR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18173, https://doi.org/10.5194/egusphere-egu2020-18173, 2020.

D2580 |
Nat Gopalswamy and Pertti Mäkelä

It has recently been shown that the sustained gamma-ray emission (SGRE) from the Sun that lasts for hours beyond the impulsive phase of the associated flare is closely related to radio emission from interplanetary shocks (Gopalswamy et al. 2019, JPhCS, 1332, 012004, 2019). This relationship supports the idea that >300 MeV protons accelerated by CME-driven shocks propagate toward the Sun, collide with chromospheric protons and produce neutral pions that promptly decay into >80 MeV gamma-rays. There have been two challenges to this idea. (i) Since the location of the shock can be halfway between the Sun and Earth at the SGRE end time, it has been suggested that magnetic mirroring will not allow the high energy protons to precipitate. (ii) Lack of correlation between the number protons involved in the production of >100 MeV gamma-rays (Ng) and the number of protons (Nsep) in the associated solar energetic particle (SEP) event has been reported. In this paper, we show that the mirror ratio problem is no different from that in flare loops where electrons and protons precipitate to produce impulsive phase emissions. We also suggest that the lack of Ng – Nsep correlation is due to two reasons: (1) Nsep is underestimated in the case of eruptions happening at large ecliptic latitudes because the high-energy protons accelerated near the nose do not reach the observer. (2) In the case of limb events, the Ng is underestimated because gamma-rays from some part of the extended gamma-ray source do not reach the observer.

How to cite: Gopalswamy, N. and Mäkelä, P.: Interplanetary shocks as a source of sustained gamma-ray emission from the Sun, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21334, https://doi.org/10.5194/egusphere-egu2020-21334, 2020.

D2581 |
Olga Khabarova, Valentina Zharkova, Qian Xia, and Olga Malandraki

Recent observational and theoretical studies have shown that there is an unaccounted population of electrons and protons accelerated locally to suprathermal energies at reconnecting current sheets (RCSs) and 3-D dynamical plasmoids or 2-D magnetic islands (MIs) in the solar wind. The findings can be summarized as following: (i) RCSs are often subject to instabilities breaking those into 3D small-scale plasmoids/blobs or 2D magnetic islands (MIs) with multiple X- and O-nullpoints; (ii) RCSs and dynamical MIs can accelerate particles up to the MeV/nuc energies; (iii) accelerated particles may form clouds expanding far from a reconnecting region; and (iv) bi-directional(or counterstreaming) strahls observed in pitch-angle distributions (PADs) of suprathermal electrons may simply represent a signature of magnetic reconnection occurring at closed IMF structures (e.g., MIs), not necessarily connected to the Sun (Zharkova & Khabarova, 2012, 2015; Zank et al. 2014, 2015; Khabarova et al. 2015, 2016, 2017; 2018; le Roux 2016, 2017, 2018, 2019; Khabarova & Zank, 2017; Adhikari et al. 2019; Xia & Zharkova, 2018, 2020; Malandraki et al. 2019; Mingalev et al. 2019). We will briefly present an overview of the effects of local ion acceleration as observed at different heliocentric distances and focus on the impact of the locally-borne population of suprathermal electrons on typical patterns of PADs. 

Suprathermal electrons with energies of ~70eV and above are observed at 1 AU as dispersionless halo and magnetic field-aligned beams of strahls. For a long time, it has been thought that both populations originate only from the solar corona. This view has consequently impacted interpretation of typical patterns of suprathermal electron PADs observed in the solar wind. We present multi-spacecraft observations of counterstreaming strahls and dropouts in PADs within a previously reported region filled with plasmoids and RCSs, comparing observed PAD features with those predicted by PIC simulations extended to heliospheric conditions. We show typical features of PADs determined by acceleration of the ambient thermal electrons up to suprathermal energies in single RCSs and dynamical plasmoids. Our study suggests that locally-accelerated suprathermal electrons co-exist with those of solar origin. Therefore, some heat flux dropout and bi-directional strahl events observed in the heliosphere can be explained by local dynamical processes involving magnetic reconnection. Possible implications of the results for the interpretation of the strahl/halo relative density change with heliocentric distance and puzzling features of suprathermal electrons observed at crossings of the heliospheric current sheet and cometary comas are also discussed.

How to cite: Khabarova, O., Zharkova, V., Xia, Q., and Malandraki, O.: Effects of local particle acceleration in the solar wind, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3711, https://doi.org/10.5194/egusphere-egu2020-3711, 2020.

D2582 |
Hanying Wei, Lan Jian, Daniel Gershman, and Christopher Russell

Although electromagnetic ion cyclotron waves (ICWs) have been observed in the solar wind by multiple missions at heliocentric distances from 0.3 to 1 AU, there are still open questions on the generation mechanisms for these waves. Detailed analysis of the plasma distribution is needed to examine whether these waves are possibly generated locally.

In the solar wind, there are mainly three types of ion-driven instabilities responsible for parallel-propagating ICWs: ion cyclotron instabilities driven by ion component with temperature anisotropies greater than 1, parallel firehose instabilities driven by ion temperature anisotropies smaller than 1, and ion/ion magnetosonic instabilities driven by the relative drift between two ion components. In the solar wind frame, the waves due to ion cyclotron instability have left-handed polarization, while the waves due to firehose and ion/ion magnetosonic instabilities have right-handed polarization. Depending on the wave propagation parallel or anti-parallel to the magnetic field, the wave frequencies in the spacecraft frame are Doppler shifted higher or lower even with reversed handness. With the plasma data from Magnetospheric Multiscale (MMS) mission, we can examine the possible unstable mode with dispersion analysis and check if the prediction agrees with the observed wave mode. If the plasma measurements of the local solar wind do not support the wave growth, the waves could be possibly generated remotely close to the Sun and propagate away from the source region and are also carried outward by the solar wind flow. If these waves are generated remotely closer to the Sun, the wave properties at different heliocentric distances would help us better understand their sources.

The MMS spacecraft spends long periods of its orbit in the “pristine” solar wind starting end of 2017. From the 2017 December data we find over a hundred events and 42 of them last longer than 10 minutes which are called ICW storm events, and the longest event captured lasted over 2 hours. Although only about 17 of them have the plasma data available, we can perform case studies on these events first to investigate the wave properties and possible plasma instabilities, which will help us investigate the wave generation mechanisms due to local or remote sources.

How to cite: Wei, H., Jian, L., Gershman, D., and Russell, C.: MMS Observations of Ion Cyclotron Waves in the Solar Wind, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11505, https://doi.org/10.5194/egusphere-egu2020-11505, 2020.

D2583 |
Shangbin Yang, Joerg Buechner, and Hongqi Zhang

Magnetic helicity is a quantity describing the twist, writhe, and torsion of magnetic field lines and magnetic configurations . The concept of magnetic helicity has successfully been applied to characterize solar coronal processes. A conjecture about one approximation relation between free magnetic free energy and relative magnetic helicity in the MHD extreme state of solar corona has been proposed by using the concept of magnetic helicity conservation and Lie-Poisson mechanical structure of MHD. We use constant α force-free filed extrapolation to check out this relation. We also apply this relation to analyze the results from the simulations and observations. Such relation may be helpful to predict the solar activity like the solar flares and CMEs

How to cite: Yang, S., Buechner, J., and Zhang, H.: Relation between the magnetic free energy and relative magnetic helicity in the MHD extreme state of solar corona, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19255, https://doi.org/10.5194/egusphere-egu2020-19255, 2020.

D2584 |
Haimin Wang

We study the Solar Active Region (AR) 12673 in September 2017, which is the most flare productive AR in the solar cycle 24.  Observations from Goode Solar Telescope (GST) show the strong photospheric magnetic fields (nearly 6000 G) in polarity  inversion line (PIL) and apparent photospheric twist on September 6,  the day of X9.3 flare. Corresponding to the strong twist,   upflows are observed to last one day  at the center part of that section of PIL;  down flows are observed in two ends.  Transverse velocity fields are derived from flow tracking.   Both Non-Linear Force-Free Field (NLFFF) and Non-Force-Free Field (NFFF) extrapolations are carried out and compared to trace 3-D magnetic fields in corona. Combining with EOVSA, coronal magnetic fields between 1000 and 2000 gauss are found above the flaring PIL at the height range between 8 and 4Mm, outlining the structure of a fluxrope with sheared arcade.  The above magnetic and velocity fields, as well as thermal structure of corona, provide initial condition for further data-driven MHD simulation.

How to cite: Wang, H.: Three-Dimensional Magnetic and Velocity Structures of Active Region 12673, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2234, https://doi.org/10.5194/egusphere-egu2020-2234, 2020.

D2585 |
lucia sanna and Giovanni lapenta

The process of magnetic reconnection when studied in nature or when modeled in 3D simulations differs in one key way from the standard 2D paradigmatic cartoon: it is accompanied by many fluctuations in the electromagnetic fields and plasma properties. We developed a diagnostics to study the spectrum of fluctuations in the various regions around a reconnection site. We define the regions in terms of the local value of the flux function that determines the distance from the reconnection site, with positive values in the outflow and negative values in the inflow. We find that fluctuations belong to two very different regimes depending on the local plasma beta (defined as the ratio of plasma and magnetic pressures). The first regime develops in the reconnection outflows where beta is high and it is characterized by a strong link between plasma and electromagnetic fluctuations, leading to momentum and energy exchanges via anomalous viscosity and resistivity. But there is a second, low-beta regime: it develops in the inflow and in the region around the separatrix surfaces, including the reconnection electron diffusion region itself. It is remarkable that this low-beta plasma, where the magnetic pressure dominates, remains laminar even though the electromagnetic fields are turbulent.

[1] G. Lapenta et al 2020 ApJ 888 104,

How to cite: sanna, L. and lapenta, G.: Analysis of Local Regimes of Turbulence generated by 3D Magnetic Reconnection, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22028, https://doi.org/10.5194/egusphere-egu2020-22028, 2020.

D2586 |
Shabnam Nikbakhsh, Eija Tanskanen, Maarit Käpylä, and Thomas Hackman

Solar active regions (ARs) emerge on the Sun’s photosphere and they frequently produce flares and coronal mass ejections which are among major space weather drivers. Therefore, studying ARs can improve space weather forecast.

The Mount Wilson Classification has been used since 1919 in order to group groups ARs according to their magnetic structures. In this study, we investigated the magnetic classification of 4797 ARs and their cyclic variation, using our daily approach for the period of January 1996 to December 2018.

We show that the monthly number of the simple ARs (SARs) attained their maximum during first peak of the solar cycle, whereas more complex ARs (CARs) reached their maximum roughly two years later, during the second peak of the cycle. We also demonstrate that the total abundance of CARs is very similar during a period of four years around their maximum number. We also studied the latitudinal distributions of SARs and CAR in northern and southern solar hemispheres and show that the independent of the complexity type, the distributions are the same in both hemispheres.

Furthermore, we investigated the earlier claim of increase in number of CARs due to the decrease in ARs latitudinal band. Here we show that, contrary to this claim, CARs attained their maximum number before the latitudinal band started to decrease in both northern and southern hemispheres.

How to cite: Nikbakhsh, S., Tanskanen, E., Käpylä, M., and Hackman, T.: Solar cycle variation of simple and complex active regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18577, https://doi.org/10.5194/egusphere-egu2020-18577, 2020.

D2587 |
Dmitry Sokoloff, Peter Frick, Rodion Stepanov, and Frank Stefani

Spectrum of solar activity oscillations contains apart from the well-known 11-year activity cycle a continuous component, which includes, in particular, quasy-biennual oscillations as well as long-term oscillations including so-called Gleisberg cycle.  We suggest to consider the mid-term solar variability in terms of statistical dynamic of fully turbulent systems, where solid arguments are required to accept an isolated dominant frequency in a continuous (smooth) spectrum. What about the timescales longer than the Schwabe cycle, we consider them as a presence of long-term memory in solar dynamo and discuss statistical test for veryication of this interpretation. Sequences for statistical long-term forecast of solar activity are discussed.

How to cite: Sokoloff, D., Frick, P., Stepanov, R., and Stefani, F.: Continuous components of solar activity oscillation spectrum and forecasting of solar activity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2360, https://doi.org/10.5194/egusphere-egu2020-2360, 2020.

D2588 |
Junho Shin, Takashi Sakurai, Ryouhei Kano, Yong-Jae Moon, and Yeon-Han Kim

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 arcsec. 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. To theoretically model the three-dimensional coronal structures is sensitive to the values of plasma properties at the base of solar corona and thus requires beforehand accurate empirical description of those properties. Though the telescope has provided unprecedented observations of solar corona for more than a decade, due to a wide field of view of 34 x 34 arcmin covering the full Sun, the optical performance of the instrument gradually deteriorates as it goes away from the optical center. For this reason, the off-axis characteristics of Hinode/XRT should be examined with care in order to precisely interpret the coronal plasma properties near the solar limb area.

This presentation will explain the importance of accurate calibration of the optical characteristics, especially for the data taken in the off-axis region. Our previous study has shown that the scattered light caused by the XRT mirror surface roughness has a power-law distribution and also shows an energy dependence, with which the PSF profile from the core to the scattering wing has been completed. We will introduce in this study how the level of scattering wing can be determined quantitatively for each focal plane filter from in-flight data analysis. We have also evaluated the vignetting effect in Hinode/XRT by analyzing the 2D distribution of effective area in the field of view taken from MSFC/XRCF pre-launch experiment. It is revealed that, unlike the case of Yohkoh/SXT, the degree of offset of an optical center is not serious and thus shows little deviation from rotational symmetry. Also important is that the vignetting pattern in XRT shows an energy dependence, which has never been considered before for the analyses of XRT data. More interesting results on the calibration of Hinode/XRT scattered light and the correction of vignetting effect will be introduced and discussed thoroughly. 

How to cite: Shin, J., Sakurai, T., Kano, R., Moon, Y.-J., and Kim, Y.-H.: Detailed Calibration of the Off-Axis Optical Characteristics for the X-Ray Telescope onboard Hinode, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10225, https://doi.org/10.5194/egusphere-egu2020-10225, 2020.

Chat time: Friday, 8 May 2020, 16:15–18:00

Chairperson: Pietro Zucca
D2589 |
Olga Malandraki, Bernd Heber, Patrick Kuehl, Marlon Núñez, Arik Posner, Michalis Karavolos, and Nikos Milas

Solar Energetic Particles (SEPs), ranging in energy from tens of keV to a few GeV, constitute an important con-tributor to the characterization of the space environment. SEP radiation storms may have durations from a period of hours to days or even weeks and have a large range of energy spectrum profiles. They pose a threat to mod-ern technology strongly relying on spacecraft and are a serious radiation hazard to humans in space, and are additionally of concern for avionics and commercial aviation in extreme cases. The High Energy Solar Particle Events forecasting and Analysis (HESPERIA) project, supported by the HORIZON 2020 programme of the Eu-ropean Union, has furthered our prediction capability of high-energy SEP events by developing new European capabilities for SEP forecasting and warning, while exploiting novel as well as already existing datasets. The HESPERIA UMASEP-500 tool makes real-time predictions of the occurrence of >500 MeV and Ground Level Enhancement (GLE) events from the analysis of soft X-ray flux and high-energy differential proton flux measured by the GOES satellite network. Regarding the prediction of GLE events for the period 2000-2016, this tool had a Probability of Detection (POD) of 53.8% and a False Alarm Ratio (FAR) of 30.0%. For this period, the tool obtained an Advanced Warning Time (AWT) of 8 min taking as reference the alert time from the first NMstation; using the time of the warning issued by the GLE Alert Plus tool for the aforementioned period as reference, the tool obtained an AWT of 15 min (Núñez et al. 2017). Based on the Relativistic Electron Alert System for Exploration (REleASE) forecasting scheme (Posner, 2007), the HESPERIA REleASE tools generate real-time predictions of the proton flux (30-50 MeV) at the Lagrangian point L1, making use of relativistic electrons (v>0.9c) and near-relativistic (v<0.8c) electron measurements provided by the SOHO/EPHIN and ACE/EPAM experiments, respectively. Analysis of historic data from 2009 to 2016 has shown the HESPERIA REleASE tools have a low FAR (∼30%) and a high POD (63%). Both HESPERIA tools are operational through the project’s website (http://www.hesperia.astro.noa.gr) at the National Observatory of Athens and presented in the recently published book on 'Solar Particle Radiation Storms Forecasting and Analysis, The HESPERIA HORIZON 2020 Project and Beyond', edited by Malandraki and Crosby, Springer, Astrophysics and Space Sciences Library, 2018, freely available at https://www.springer.com/de/book/9783319600505. The HESPERIA tools have been selected as a top priority internationally by NASA/CCMC to be included in the simulations of the manned-mission to Mars by Johnson Space Center (ISEP project). The National Observatory of Athens participates in the ISEP project with a relevant contract.

How to cite: Malandraki, O., Heber, B., Kuehl, P., Núñez, M., Posner, A., Karavolos, M., and Milas, N.: Solar Particle Radiation Storms Forecasting and Analysis - The HESPERIA tools , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8298, https://doi.org/10.5194/egusphere-egu2020-8298, 2020.

D2590 |
Stefaan Poedts

The goal of the ESA project "Virtual Space Weather Modelling Centre - Part 3" (2019-2021) is to further develop the Virtual Space Weather Modelling Centre (VSWMC), building on the Part 2 prototype system and focusing on the interaction with the ESA SSA SWE system. A first, limited version went operational in May 2019 under the H-ESC umbrella on the ESA SSA SWE Portal. The objective and scopes of this new project include: the efficient integration of new models and new model couplings, including daily automated end-to-end (Sun to Earth) simulations, the further development and wider use of the coupling toolkit  and front-end GUI, making the operational system more robust and user-friendly. The VSWMC-Part 3 project started on 1 October 2019.

EUHFORIA (‘European heliospheric forecasting information asset’) is integrated in the VSWMC and will be upgraded with alternative coronal models (Multi-VP and Wind-Predict) and flux-rope CME models, and new couplings will be made available, e.g. to more advanced magnetospheric models and radiation belt models, geo-effects models, and even SEP models. The first results will be discussed and put into perspective.

How to cite: Poedts, S.: EUHFORIA in the ESA Virtual Space Weather Modelling Centre, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5259, https://doi.org/10.5194/egusphere-egu2020-5259, 2020.

D2591 |
Hongqiang Song

So far, most studies on the structure of coronal mass ejections (CMEs) are conducted through white-light coronagraphs, which demonstrate about one third of CMEs exhibit the typical three-part structure in the high corona (e.g., beyond 2 Rs), i.e., the bright front, the dark cavity and the bright core. In this presentation, we address the CME structure in the low corona (e.g., below 1.3 Rs) through extreme-ultraviolet (EUV) passbands and find that the three-part CMEs in the white-light images can possess a similar three-part appearance in the EUV images, i.e., a leading edge, a low-density zone, and a filament or hot channel. The analyses identify that the leading edge and the filament or hot channel in the EUV passbands evolve into the front and the core later within several solar radii in the white-light passbands, respectively. What's more, we find that the CMEs without obvious cavity in the white-light images can also exhibit the clear three-part appearance in the EUV images, which means that the low-density zone in the EUV images (observed as the cavity in white-light images) can be compressed and/or transformed gradually by the expansion of the bright core and/or the reconnection of magnetic field surrounding the core during the CME propagation outward. Our study suggests that more CMEs can possess the clear three-part structure in their early eruption stage. The nature of the low-density zone between the leading edge and the filament or hot channel is discussed.

How to cite: Song, H.: The Structure of Solar Coronal Mass Ejections in the Extreme-Ultraviolet Passbands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4293, https://doi.org/10.5194/egusphere-egu2020-4293, 2020.

D2592 |
Joe Zender, Rens van der Zwaart, Rangaiah Kariyappa, Luc Damé, and Gabriel Giono

The study of solar irradiance variability is of great importance in heliophysics, the Earth’s climate, and space weather applications. These studies require careful identifying, tracking and monitoring of features in the solar magnetosphere, chromosphere, and corona.  We studied the variability of solar irradiance for a period of 10 years (May 2010–January 2020) using the Large Yield Radiometer (LYRA), the Sun Watcher using APS and image Processing (SWAP) on board PROBA2, the Atmospheric Imaging Assembly (AIA), and the Helioseismic and Magnetic Imager (HMI) of on board the Solar Dynamics Observatory (SDO), and applied a linear model between the identified features and the measured solar irradiance by LYRA.

We used the spatial possibilistic clustering algorithm (SPoCA) to identify coronal holes, and a morphological feature detection algorithm to identify active regions (AR), coronal bright points (BPS), and the quite sun (QS) and segment coronal features from the EUV observations of AIA. The AIA segmentation maps were then applied on SWAP images, images of all AIA wavelengths, HMI line-of-sight (LOS) magnetograms, and parameters such as the intensity, fractional area, and contribution of ARs/CHs/BPs/QS features were computed and compared with LYRA irradiance measurements as a proxy for ultraviolet irradiation incident to the Earth atmosphere.

We modelled the relation between the solar disk features (ARs, CHs, BPs, and QS) applied to magnetrogram and EUV images against the solar irradiance as measured by LYRA and the F10.7 radio flux. To avoid correlation between different the segmented features, a principal component analysis (PCM) was done. Using the independent component, a straightforward linear model was used and corresponding coefficients computed using the Bayesian framework. The model selected is stable and coefficients converge well.

The application of the model to data from 2010 to 2020 indicates that both at solar cycle timeframes as well as shorter timeframes, the active region influence the EUV irradiance as measured at Earth. Our model replicates the LYRA measured irradiance well.

How to cite: Zender, J., van der Zwaart, R., Kariyappa, R., Damé, L., and Giono, G.: Segmentation of coronal features to understand the solar EIV and UV irradiance variability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19496, https://doi.org/10.5194/egusphere-egu2020-19496, 2020.

D2593 |
Ciara Maguire, Eoin Carley, Joseph McCauley, and Peter Gallagher

The Sun regularly produces large-scale eruptive events, such as coronal mass ejections (CMEs) that can drive shock waves through the solar corona. Such shocks can result in electron acceleration and subsequent radio emission in the form of a type II radio burst. However, the early-phase evolution of shock properties and its relationship to type II burst evolution is still subject to investigation. Here we study the evolution of a CME-driven shock by comparing three commonly used methods of calculating the Alfvén Mach number (MA), namely: shock geometry, a comparison of CME speed to a model of the coronal Alfvén speed, and the type II band-splitting method. We applied the three methods to the 2017 September 2 event, focusing on the shock wave observed in extreme ultraviolet (EUV) by the Solar Ultraviolet Imager (SUVI) on board GOES-16, in white-light by the Large Angle and Spectrometric Coronagraph (LASCO) on board SOHO, and the type II radio burst observed by the Irish Low Frequency Array (I-LOFAR). We show that the three different methods of estimating shock MA yield consistent results and provide a means of relating shock property evolution to the type II emission duration. The type II radio emission emerged from near the nose of the CME when MA was in the range 1.4-2.4 at a heliocentric distance of 1.6 R. The emission ceased when the CME nose reached 2.4 R, despite an increasing Alfvén Mach number (up to 4). We suggest the radio emission cessation is due to the lack of quasi-perpendicular geometry at this altitude, which inhibits efficient electron acceleration and subsequent radio emission.

How to cite: Maguire, C., Carley, E., McCauley, J., and Gallagher, P.: Evolution of the Alfvén Mach number associated with a coronal mass ejection shock, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11425, https://doi.org/10.5194/egusphere-egu2020-11425, 2020.

D2594 |
Guan-Han Huang, Chia-Hsien Lin, and Lou Chuang Lee

Coronal holes can be identified as the regions with magnetic field lines extending far away from the Sun, or the darkest regions in EUV/X-ray images with predominantly unipolar magnetic fields. A comparison between the locations of our determined regions with open magnetic field lines (OMF) and regions with low EUV intensity (LIR) reveals that only 12% of the OMF regions coincide with the LIRs. The aim of this study is to investigate the conditions leading to the different brightnesses of OMF regions, and to provide a means to predict whether an OMF region would be bright or dark. Examining the statistical distribution profiles of the magnetic field expansion factor (fs) and Atmospheric Imaging Assembly 193 Å intensity (I193) reveals that both profiles are approximately log-normal. The analysis of the spatial and temporal distributions of fs and I193 indicates that the bright OMF regions often are inside or next to regions with closed field lines, including quiet-Sun regions and regions with strong magnetic fields. Examining the relationship between I193 and fs reveals a weak positive correlation between log I193 and log fs , with a correlation coefficient ≈ 0.39. As a first-order approximation, the positive relationship is determined to be log I193 = 0.62 log fs + 1.51 based on the principle of the whitening/dewhitening transformation. This linear relationship is demonstrated to increase the consistency between the OMF regions and LIRs from 12% to 23%.

How to cite: Huang, G.-H., Lin, C.-H., and Lee, L. C.: Examination of the EUV Intensity in the Open Magnetic Field Regions Associated with Coronal Holes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1501, https://doi.org/10.5194/egusphere-egu2020-1501, 2020.

D2595 |
Zhenjun Zhou, Rui Liu, Xing Cheng, Chaowei Jiang, Yuming Wang, Lijuan Liu, Guoqiang Wang, Tielong Zhang, and Jun Cui

Coronal mass ejections (CMEs) with enhanced south-component of the magnetic field are susceptible to producing geomagnetic storms. Filament chirality, rotation direction, and morphology are responsible for CMEs’ magnetic orientation and they are manifestations of magnetic helicity. However, different models predict different relations among them. In this paper, taking advantage of stereoscopic observations and a new method of determining the chirality of erupting filaments, we analyze 12 filaments that present a clear rotation during the eruption. The results based on the small sample support the argument that the filaments with for sinistral (dextral) chirality, they rotate clockwise (counterclock-wise), indicating the transformation of twist into writhe. Moreover, we also inspect soft X-ray and EUV hot temperature images and find that, the associated sigmoids are consistent with filaments prior to the eruption morphologically. However, once starting to rise up, the erupting filaments reverse their shapes from forward S-shaped to inversed S-shaped and vice versa.

How to cite: Zhou, Z., Liu, R., Cheng, X., Jiang, C., Wang, Y., Liu, L., Wang, G., Zhang, T., and Cui, J.: On the Relation between Filament Chirality, Rotation Direction, and Morphology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4011, https://doi.org/10.5194/egusphere-egu2020-4011, 2020.

D2596 |
Dmitrii Baranov, Elena Vernova, Marta Tyasto, and Olga Danilova

On the basis of the synoptic maps of the photospheric magnetic field obtained by the National Solar Observatory Kitt Peak for 1978-2016, a latitude-time diagram of the magnetic field was built. When averaging intensity values over the heliolongitude, the magnetic field sign was taken into account. In order to consider the characteristics of the distribution of weak magnetic fields an upper limit of 5 G was set.

The latitude-time diagram clearly shows inclined bands corresponding to positive and negative polarity magnetic flows drifting towards the poles of the Sun. Two groups of flows are observed: 1. Relatively narrow bands, with alternating polarity, beginning near the equator and reaching almost the poles of the Sun. Along the time axis, the flow length of one polarity is on the order of 1-2 years; 2. short powerful flows, 3-4.5 years wide, propagating from the spot zone to the poles. These flows reach the poles simultaneously with the begin of the polar field reversal, apparently representing  the so-called “Rush to the Poles” phenomenon.

The pattern of magnetic field transport is significantly different for the northern and southern hemispheres. Alternating flows of positive and negative polarities most clearly appear in the southern hemisphere during periods of positive polarity of the southern polar field. For the northern hemisphere the picture is much less clear but for individual time intervals alternating flows of opposite polarities can be traced. The slopes of magnetic flux bands allow us to estimate the rate of meridional drift of magnetic fields, which was slightly different for the two hemispheres: V = (16±2) m/s for the southern hemisphere and V = (21±4) m/s for the northern hemisphere. The results obtained indicate that the distribution of weak magnetic fields over the surface of the Sun has a complex structure that is different for the two hemispheres and varies from cycle to cycle.

How to cite: Baranov, D., Vernova, E., Tyasto, M., and Danilova, O.: Magnetic flux transport in the photosphere of the Sun, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6928, https://doi.org/10.5194/egusphere-egu2020-6928, 2020.

D2597 |
Daniel Price, Jens Pomoell, Erkka Lumme, and Emilia Kilpua

Fully understanding solar eruptions and their eventual consequences for the Earth requires a rigorous modelling approach due to the difficulty of directly measuring magnetic fields in the solar corona. Consequently, this study employs a time-dependent data-driven magnetofrictional model (TMFM) to simulate the coronal evolution of coronal mass ejections from multiple active regions. We processed HMI vector magnetograms with the Electric Field Inversion Toolkit to generate a time series of photospheric electric field maps which were used as the lower boundary to drive our TMFM simulations. Analysis was aided by computing maps of the squashing factor and twist, as well as by calculating coronal metrics such as the volume energy and helicity, and by comparison to AIA observations. Studying multiple events simultaneously permits comparative analysis and the evaluation of the model performance.

How to cite: Price, D., Pomoell, J., Lumme, E., and Kilpua, E.: Data-driven modelling of erupting solar active regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9247, https://doi.org/10.5194/egusphere-egu2020-9247, 2020.

D2598 |
Reetika Joshi, Ramesh Chandra, Brigitte Schmieder, Guillaume Aulanier, Pooja Devi, Fernando Moreno-Insertis, and Daniel Nóbrega-Siverio

Solar jets observed at the limb are important to determine the location of reconnection sites in the corona. In this study, we investigate six recurrent hot and cool jets occurring in the active region NOAA 12644 as it is crossing the west limb on April 04, 2017. These jets are observed in all the UV/EUV filters of SDO/AIA and in cooler temperature formation lines in IRIS slit jaw images. The jets are initiated at the top of a double chamber vault with cool loops on one side and hot loops on the other side. The existence of such double chamber vaults suggests the presence of emerging flux with cool loops, the hot loops being the reconnected loops similarly as in the models of Moreno-Insertiset al. 2008, 2013 and Nóbrega-Siverio et al. 2016. In the preliminary phase of the main jets, quasi periodic intensity oscillations accompanied by smaller jets are detected in the bright current sheet between the vault and the preexisting magnetic field. Individual kernels and plasmoids are ejected in open field lines along the jets. Plasmoids may launch torsional Alfven waves and the kernels would be the result of the untwist of the plasmoids in open magnetic field as proposed in the model of Wyper et al. 2016.

How to cite: Joshi, R., Chandra, R., Schmieder, B., Aulanier, G., Devi, P., Moreno-Insertis, F., and Nóbrega-Siverio, D.: Quasi Periodic Oscillations in the Pre Phases of Recurrent Jets Highlighting Plasmoids in Current Sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22351, https://doi.org/10.5194/egusphere-egu2020-22351, 2020.

D2599 |
Kalevi Mursula, Ilpo Virtanen, Jennimari Koskela, and Ismo Tähtinen

Several studies have noted on changes in the properties of sunspots, and in the mutual relations between various global parameters of solar magnetic activity (e.g. UV/EUV irradiance, radio and IR emissions, TSI/SSI), as well as between solar and ionospheric parameters since the onset of solar cycle 23. These changes have been suggested to be related to the overall reduction of solar activity at the aftermath of the decline of the Grand modern maximum of solar activity that prevailed during most of the 20th century. We have recently derived the longest record of coronal magnetic field intensities since 1968 using Mount Wilson Observatory and Wilcox Solar Observatory observations of the photospheric magnetic field and the PFSS model, and compared it with the heliospheric magnetic field observed at the Earth. We found that the time evolution of the coronal magnetic field during the last 50 years agrees with the heliospheric magnetic field only if the effective coronal size, the distance of the coronal source surface of the heliospheric magnetic field, is allowed to change in time. We calculated the optimum distance for each solar rotation and found that it experienced an abrupt decrease in the late 1990s. The effective volume of the solar corona shrunk to less than one half of its previous value during a short period of only a few years. This shrinking was related with a systematic change in the structure of the coronal magnetic field during the same time interval. We review these dramatic changes in the solar corona and discuss their possible connection to the changes in the different solar activity parameters and the reduction of the overall solar activity.

How to cite: Mursula, K., Virtanen, I., Koskela, J., and Tähtinen, I.: Abrupt shrinking of solar corona in late 1990s and related changes in solar magnetic structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20365, https://doi.org/10.5194/egusphere-egu2020-20365, 2020.

D2600 |
Hongyu Liu, Pietro Zucca, Jasmina Magdalenic, Peijin Zhang, and Kyungsuk Cho

Type IV radio burst is the long-lasting broadband continuum emission in metric wave-length. In addition to the continuum emission Type IV radio bursts may show fine structure with high brightness temperature. The physical emission responsible for both continuum and fine structures is still under debate. In this study, we present a moving type IV radio burst observed by LOFAR. We performed a detailed comparison of NRH and LOFAR imaging. Using the full stokes parameterss from the LOFAR dynamic spectra, we have also calculated the degree of circular polarisation during the propagation of the moving type IV. Finally, we combined LOFAR interferometric data with SDO-AIA and LASCO-C2 to track the evolution of this type IV and relate it with the CME.

How to cite: Liu, H., Zucca, P., Magdalenic, J., Zhang, P., and Cho, K.: Propagation of a Solar Moving Type IV Radio Burst Using LOFAR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21894, https://doi.org/10.5194/egusphere-egu2020-21894, 2020.

D2601 |
Peijin Zhang, Pietro Zucca, Sarrvesh Sridhar, and Chuanbing Wang

Solar radio bursts originate mainly from high energy electrons accelerated by solar eruptions like solar flares, jets, and coronal mass ejections (CMEs).  A sub-category of solar radio bursts with a short time duration may be used as a proxy to understand the wave generation and propagation within the corona.  Complete case studies of the source size, position, and kinematics of short-term bursts are very limited due to instrumental limitations.
LOw-Frequency-ARray (LOFAR) is an advanced radio antenna array. It is capable of a variety of processing operations including correlation for standard interferometric imaging, the tied-array beam-forming, and the real-time triggering on incoming station data-streams. With recently upgraded LOFAR, we can achieve high spatial and temporal imaging for solar radio bursts.
Here we present a detailed analysis of the fine structures in the spectrum and of the radio source motion with imaging, the radio source of a type IIIb-III pair was imaged with the interferometric mode using the remote baselines of the (LOFAR). This study shows how the fundamental and harmonic components have a significant different source motion.  The apparent source of the fundamental emission at 26 MHz is about 4 times the speed of light, while the apparent source of the harmonic emission shows a speed of < 0.02 c.  We show that the apparent speed of the fundamental source is more affected by the scattering and refraction of the coronal medium.

How to cite: Zhang, P., Zucca, P., Sridhar, S., and Wang, C.: Source size and Position of a Type IIIb-III Pair with LOFAR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-80, https://doi.org/10.5194/egusphere-egu2020-80, 2020.

D2602 |
Bartosz Dabrowski, Paweł Flisek, Christian Vocks, Diana Morosan, Peijin Zhang, Pietro Zucca, Jasmina Magdalenic, Richard Fallows, Andrzej Krankowski, Gottfried Mann, Leszek Blaszkiewicz, Pawel Rudawy, Marcin Hajduk, Adam Fron, Peter Gallagher, Aoife Maria Ryan, Kacper Kotulak, and Barbara Matyjasiak

We hereby present the interferometric LOFAR observations made before and after the total solar eclipse on 21 August 2017, during which the type III radio bursts have been detected.

The LOw-Frequency ARray (LOFAR) is a large radio interferometer operating in the frequency range of 10–240 MHz, designed and constructed by ASTRON (the Netherlands Institute for Radio Astronomy). The LOFAR telescope is an array of stations distributed throughout the Netherlands and other parts of Europe. Currently the system consist of 52 LOFAR stations located in Europe. Apart from the high time and frequency resolution of the dynamic spectra, LOFAR allows also a 2D imaging of the radio sources and tracking of their positions through the solar corona.

In this work we present a preliminary analysis of the dynamic spectra of type III radio bursts with radio images.

How to cite: Dabrowski, B., Flisek, P., Vocks, C., Morosan, D., Zhang, P., Zucca, P., Magdalenic, J., Fallows, R., Krankowski, A., Mann, G., Blaszkiewicz, L., Rudawy, P., Hajduk, M., Fron, A., Gallagher, P., Ryan, A. M., Kotulak, K., and Matyjasiak, B.: Interferometric Observations of the Active Regions in Radio Domain Before and After the Total Solar Eclipse on 21 August 2017, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7374, https://doi.org/10.5194/egusphere-egu2020-7374, 2020.

D2603 |
ShihPing Chen, Charles C. Lin, Rajesh Panthalingal Krishnanunni, Richard Eastes, and Jong-Min Choi

The near real-time global plasma bubble map is constructed by utilizing the FORMOSAT-7/COSMIC-2(F7/C2) radio occultation(RO) scintillation observations in low latitudes. Several tools investigating plasma bubbles like the rate of TEC index(ROTI), Range-Time-Intensity(RTI) diagrams of the Jicamarca Unattended Long-term Investigations of the Ionosphere and Atmosphere(JULIA), and the Global-scale Observations of the Limb and Disk(GOLD) 135.6nm airglow observations are provided validating the RO scintillations. Result shows that the F7/C2 scintillation is sensitive detecting plasma irregularities, especially for the bottom side of these bubbles, which can be used to investigating nighttime vertical plasma drifts in low latitudinal F-region. The hourly quick look of the low latitude plasma bubble occurrence and vertical ion drift around the globe is significant to the space weather monitoring.

How to cite: Chen, S., Lin, C. C., Panthalingal Krishnanunni, R., Eastes, R., and Choi, J.-M.: Near real time plasma irregularity monitoring by FORMOSAT-7/COSMIC-2, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13366, https://doi.org/10.5194/egusphere-egu2020-13366, 2020.

D2604 |
Carlos Larrodera and Consuelo Cid

The main goal of this work is to separate the behavior of the two types of quiet solar wind at 1 AU: fast and slow.
Our approach is a bi-Gaussian distribution function, formed by the addition of two Gaussian distribution functions, where each one represents one type of wind. We check our approach by fitting the bi-Gaussian to data from ACE spacecraft. We use level 2 data measured during solar cycles 23 and 24 of different solar wind parameters, including proton speed, proton temperature, density and magnetic field. Our results show that the approach is fine and only transient events departs from the proposed function. Moreover, we can show bi modal behavior of the solar wind at 1 AU, not only for the proton speed, but also for the other analyzed parameters. We also check the solar cycle dependence of the different fitting parameters.

How to cite: Larrodera, C. and Cid, C.: Bimodal distribution of the solar wind using data from ACE spacecraft., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4747, https://doi.org/10.5194/egusphere-egu2020-4747, 2020.

D2605 |
Consuelo Cid, Carlos Larrodera, and Elena Saiz

The boundaries of interplanetary coronal mass ejections (ICMEs) are commonly established based on the magnetic field smoothness and/or the low temperature, when compared to normal solar wind. Based on the analysis of the ICME on 2015 January 6-7, observed by Wind and ACE spacecraft, Cid et al. (2016) proposed compositional signatures as the most precise diagnostic tool for the boundaries of ICMEs. Having as a starting point the ICMEs catalogues from Jian et al. (2006) and Richardson and Cane (2010), and the Wind spacecraft ICME catalogue on the NASA web site, we have compared the boundaries of all ICMEs observed by the ACE spacecraft attending to different signatures. This contribution shows the results of the study.

How to cite: Cid, C., Larrodera, C., and Saiz, E.: Comparing the boundaries of interplanetary coronal mass ejections, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19262, https://doi.org/10.5194/egusphere-egu2020-19262, 2020.

D2606 |
Iiro Virtanen, Ilpo Virtanen, Alexei Pevtsov, and Kalevi Mursula

The axial dipole moments of emerging active regions control the evolution of the axial dipole moment of the whole photospheric magnetic field and the strength of polar fields. Hale's and Joy's laws of polarity and tilt orientation affect the sign of the axial dipole moment of an active region, determining the normal sign for each solar cycle. If both laws are valid (or both violated), the sign of the axial moment is normal. However, for some active regions, only one of the two laws is violated, and the signs of these axial dipole moments are the opposite of normal. The opposite-sign axial dipole moments can potentially have a significant effect on the evolution of the photospheric magnetic field, including the polar fields.

We determine the axial dipole moments of active regions identified from magnetographic observations and study how the axial dipole moments of normal and opposite signs are distributed in time and latitude in solar cycles 21-24.We use active regions identified from the synoptic maps of the photospheric magnetic field measured at the National Solar Observatory (NSO) Kitt Peak (KP) observatory, the Synoptic Optical Long term Investigations of the Sun (SOLIS) vector spectromagnetograph (VSM), and the Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO).

We find that, typically, some 30% of active regions have opposite-sign axial dipole moments in every cycle, often making more than 20% of the total axial dipole moment. Most opposite-signed moments are small, but occasional large moments, which can affect the evolution of polar fields on their own, are observed. Active regions with such a large opposite-sign moment may include only a moderate amount of total magnetic flux. We find that in cycles 21-23 the northern hemisphere activates first and shows emergence of magnetic flux over a wider latitude range, while the southern hemisphere activates later, and emergence is concentrated to lower latitudes. We also note that cycle 24 differs from cycles 21-23 in many ways. Cycle 24 is the only cycle where the northern butterfly wing includes more active regions than the southern wing, and where axial dipole moment of normal sign emerges on average later than opposite-signed axial dipole moment. The total axial dipole moment and even the average axial moment of active regions is smaller in cycle 24 than in previous cycles.

How to cite: Virtanen, I., Virtanen, I., Pevtsov, A., and Mursula, K.: Axial dipole moments of solar active regions in cycles 21-24, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21663, https://doi.org/10.5194/egusphere-egu2020-21663, 2020.

D2607 |
Carlo Albert and Simone Ulzega

Proxies of solar activity have revealed repeated Grand Minima that occur with a certain regularity associated with the well-known Gleissberg and Süss/deVries cycles. These and other prominent cycles in the spectrum of solar activity are also seen in the spectrum of the planetary torque exerted on the solar tachocline, which has revived the hypothesis of a planetary influence on solar activity. It is not clear, however, how the extremely weak planetary forcing could influence the solar magnetic activity. Here, we suggest that stochastic resonance could explain the necessary amplification of the forcing and provide numerical evidence from stochastic time-delayed dynamo models. If the intrinsic noise of the solar dynamo allows for a frequent switching between active and quiescent stable states, tiny periodic forcings can be greatly amplified, provided the dynamo is poised close to a critical point. Such a forcing could be caused by a tidal modulation of the minimal magnetic field required for flux-tube buoyancy.

How to cite: Albert, C. and Ulzega, S.: Stochastic Resonance could explain Recurrence of Grand Minima, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15185, https://doi.org/10.5194/egusphere-egu2020-15185, 2020.