Current sheets and magnetic islands observed in the solar wind play a significant role in local particle acceleration to keV-MeV energies, and the resulting energetic particle enhancements constitute a potentially hazardous condition in the interplanetary and near-Earth space. Current sheets of various scales are self-organized structures that are formed ubiquitously in cosmic and laboratory plasmas owing to a change in the magnetic field direction, at strong discontinuities, and as a result of turbulence. Not surprisingly, dynamic processes occurring at current sheets and in their vicinity have a striking similarity in different plasmas. Current sheets experience magnetic reconnection that in turn leads to many subsequent nonlinear effects, triggering the development of a turbulent cascade, the formation of magnetic islands or flux ropes, and local acceleration of charged particles. These processes are observed from the corona to the outer heliosphere and may often be described by the same equations. They also can be linked physically as some of the structures originating from the corona survive and evolve further in the solar wind. These processes have been studied by different scientific teams in independent ways, but currently there is a tendency to analyze them employing a unified approach.
This interdisciplinary session will bring together specialists from different plasma physics communities, bridging gaps in the understanding of the origin of coherent structures and the development of dynamical processes associated with current sheets. We invite researchers to share recent results of their theoretical studies, modelling and observations. Contributions that discuss and compare different mechanisms of local particle energization that occur in laboratory plasmas, the solar corona, magnetospheres of planets and the heliosphere are especially welcome.

Public information:
Welcome to session ST1.7!
If you are interested in solar or space physics, especially, if you want to know more about processes related to current sheets and/or plasmoids/blobs/magnetic islands/flux ropes of various sizes and origins, you are in the right place at the right time!
Here you can find how dynamics of these structures impact magnetic reconnection, turbulence and particle acceleration from the solar corona to the outer heliosphere, and why these complex phenomena represent an important piece of the space weather puzzle.
Do not hesitate to ask questions, using the online chat opportunity below. Not all questions can be answered so far, but you will certainly get an exciting discussion. :-)

Please note that we organize a related Zoom conference on Wednesday, 2020 May 6, therefore there is an opportunity to communicate with some authors directly before or after the official EGU chat time. The program of the virtual meeting and the corresponding Zoom conference link can be found here:
https://drive.google.com/open?id=1k2uHDQnWPIHES3hXfKiy8VEYYFfyhM-8 (please copy the link to your browser to open it) .
You are welcome to attend!

Best regards,
Conveners of session ST1.7

Convener: Olga Khabarova | Co-conveners: Spiro Antiochos, Jakobus le Roux, Olga Malandraki
| Attendance Wed, 06 May, 14:00–15:45 (CEST)

Files for download

Session summary Download all presentations (153MB)

Chat time: Wednesday, 6 May 2020, 14:00–15:45

Chairperson: Olga Khabarova
D2838 |
Linghua Wang, Zixuan Liu, Haobo Fu, and Sam Krucker

Solar energetic electron events (SEEs) are one of the most common particle acceleration phenomena occurring at the Sun, and their energy spectrum likely reflects the crucial information on the acceleration. Here we present a statistical survey of the energy spectrum of 160 SEEs measured by Wind/3DP with a clear velocity dispersion at energies of ~1-200 keV from January 1995 through December 2016, utilizing a general spectrum formula proposed by Liu et al. (2000). We find that among these 160 SEEs, 144 (90%) have a power-law (or power-law-like) spectrum bending down at high energies, including 108 (67.5%) double-power-law events, 24 (15%) Ellison-Ramaty-like events and 12 (7.5%) log-parabola events, while 16 (10%) have a power-law spectrum extending to high energies. The average power-law spectral index βis 2.1±0.4 for double-power-law events, 1.7±0.8 for Ellison-Ramaty-like events, and 2.8±0.11 for single-power-law events. For the 108 double-power-law events, the spectral break energy Eranges from 2 keV to 165 keV, with an average of 71±79 keV, while the average spectral index βat energies above E0is 4.4±2.3. Eshows a positive correlation with the electron peak flux at energies above ~40 keV, while βhas a negative correlation with the electron peak flux at energies above ~15 keV.  

How to cite: Wang, L., Liu, Z., Fu, H., and Krucker, S.: The Energy Spectrum of Solar Energetic Electron Events, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1944, https://doi.org/10.5194/egusphere-egu2020-1944, 2020.

D2839 |
| solicited
| Highlight
Xiaocan Li and Fan Guo

Magnetic reconnection is a primary driver of magnetic energy release and particle acceleration processes in space and astrophysical plasmas. Solar flares are a great example where observations have suggested that a large fraction of magnetic energy is converted into nonthermal particles and radiation. One of the major unsolved problems in reconnection studies is nonthermal particle acceleration. In the past decade or two, 2D kinetic simulations have been widely used and have identified several acceleration mechanisms in reconnection. Recent 3D simulations have shown that the reconnection layer naturally generates magnetic turbulence. Here we report our recent progresses in building a macroscopic model that includes these physics for explaining particle acceleration during solar flares. We show that, for sufficient large systems, high-energy particle acceleration processes can be well described as flow compression and shear. By means of 3D kinetic simulations, we found that the self-generated turbulence is essential for the formation of power-law electron energy spectrum in non-relativistic reconnection. Based on these results, we then proceed to solve an energetic particle transport equation in a compressible reconnection layer provided by high-Lundquist-number MHD simulations. Due to the compression effect, particles are accelerated to high energies and develop power-law energy distributions. The power-law index and maximum energy are both comparable to solar flare observations. This study clarifies the nature of particle acceleration in large-scale reconnection sites and initializes a framework for studying large-scale particle acceleration during solar flares.

How to cite: Li, X. and Guo, F.: Large-scale particle acceleration during magnetic reconnection in solar flares, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1959, https://doi.org/10.5194/egusphere-egu2020-1959, 2020.

D2840 |
| solicited
| Highlight
Gregory Fleishman, Dale Gary, Bin Chen, Sijie Yu, Natsuha Kuroda, and Gelu Nita

Magnetic reconnection plays a central role in highly magnetized plasma, for example, in solar corona. Release of magnetic energy due to reconnection is believed to drive such transient phenomena as solar flares, eruptions, and jets. This energy release should be associated with a decrease of the coronal magnetic field. Quantitative measurements of the evolving magnetic field strength in the corona are required to find out where exactly and with what rate this decrease takes place. The only available methodology capable of providing such measurements employs microwave imaging spectroscopy of gyrosynchrotron emission from nonthermal electrons accelerated in flares. Here, we report microwave observations of a solar flare, showing spatial and temporal changes in the coronal magnetic field at the cusp region; well below the nominal reconnection X point. The field decays at a rate of ~5 Gauss per second for 2 minutes. This fast rate of decay implies a highly enhanced, turbulent magnetic diffusivity and sufficiently strong electric field to account for the particle acceleration that produces the microwave emission. Moreover, spatially resolved maps of the nonthermal and thermal electron densities derived from the same microwave spectroscopy data set allow us to detect the very acceleration site located within the cusp region. The nonthermal number density is extremely high, while the thermal one is undetectably low in this region indicative of a bulk acceleration process exactly where the magnetic field displays the fast decay. The decrease in stored magnetic energy is sufficient to power the solar flare, including the associated eruption, particle acceleration, and plasma heating. We discuss implications of these findings for understanding particle acceleration in solar flares and in a broader space plasma context.

How to cite: Fleishman, G., Gary, D., Chen, B., Yu, S., Kuroda, N., and Nita, G.: Characterization of turbulent magnetic reconnection in solar flares with microwave imaging spectroscopy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2099, https://doi.org/10.5194/egusphere-egu2020-2099, 2020.

D2841 |
Maria Riazantseva, Liudmila Rakhmanova, Georgy Zastenker, Yuri Yermolaev, Irina Lodkina, Jana Safrankova, Zdenek Nemecek, and Lubomir Prech

Fluctuations of solar wind parameters can be strongly affected by the presence of sharp boundaries between different large-scale structures. Turbulence cannot develop freely across such boundaries, just as it could in the undisturbed solar wind. It can lead the growing of fluctuation level and changes in shape and properties of turbulent cascade too. The compression regions, for example  Sheath regions before magnetic clouds, and CIR regions (the compression areas between fast solar wind from coronal holes and slow solar wind  from coronal streamers), are  typical examples of such transitions.  Here we present the analysis of turbulence spectrum changes during crossings of  Sheath and CIR regions. We use unique high time resolution plasma measurements by BMSW instrument at Spektr-R spacecraft in order to consider both MHD and kinetic scales of turbulent cascade.  We analyze the base properties of  turbulence spectra: spectral power and slopes at corresponding scales, break frequency between scales, and also shape of spectra. We began by examining of the case study crossings of the transition regions and then compared statistically the spectral properties in such regions with the same ones in the undisturbed solar wind. We have shown that spectra fall nonlinearly at kinetic scales and become steeper with growing of fluctuation level in transition regions, at the same time the slope of spectra at MHD scale remains almost Kolmogorov. Withal some interesting features can be observed in the vicinity of the break between characteristic scales during crossing of transition regions. The given results reveal the lack of energy balance between MHD and kinetic scales, and can indicate the intensification of dissipation processes and the additional plasma heating in the  transition regions. The work is supported by Russian Science Foundation grant 16-12-10062.

How to cite: Riazantseva, M., Rakhmanova, L., Zastenker, G., Yermolaev, Y., Lodkina, I., Safrankova, J., Nemecek, Z., and Prech, L.: Characteristics of turbulence in transition regions near large-scale boundaries in the solar wind., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7605, https://doi.org/10.5194/egusphere-egu2020-7605, 2020.

D2842 |
Qian Xia and Valentina Zharkova

We explore solar wind re-acceleration during their passage through reconnecting current sheets in the interplanetary space using the particle-in-cell approach. We investigate particle acceleration in 3D Harris-type reconnecting current sheets with a single or multiple X-nullpoints taking into account the ambient plasma feedback to the presence of accelerated particles. We also consider coalescent and squashed magnetic islands formed in the current sheets with different magnetic field topologies, thickness, ambient density, and mass ratios. With the PIC approach, we detected distinct populations of two groups of particles, transit and bounced ones, which have very different energy and asymmetric pitch-angle distributions associated with the magnetic field parameters. We present a few cross-sections of the simulated pitch-angle distributions of accelerated particles and compare them with the in-situ observations of solar wind particles. This comparison indicates that locally generated superthermal electrons can account for the counter-streaming ‘strahls’ often observed in pitch-angle distribution spectrograms of the satellites crossing heliospheric current sheets.

How to cite: Xia, Q. and Zharkova, V.: Solar wind re-acceleration in local current sheets and their diagnostics from observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9446, https://doi.org/10.5194/egusphere-egu2020-9446, 2020.

D2843 |
Vladimir Obridko and Olga Badalyan

It is shown that the solar corona rotates differentially at all heliocentric distances up to the source surface. As the distance increases, the differential rotation gradient decreases, and the rotation becomes more and more rigid. At small distances, the corona at latitudes above $\approx \pm 40^{\circ}$ rotates faster than the photosphere at the same latitudes. The type of the rotation depends also on the phase of the activity cycle. The differential rotation gradient is the largest in the vicinity of the cycle minimum. It is shown that time variations in the coronal rotation characteristics are associated with the tilt of the magnetic equator of the Sun. Based on the concept that the differential rotation of the corona reflects the rotation of deep subphotospheric layers, we compared the changes in the coronal rotation characteristics with distance with the helioseismic data and showed their satisfactory agreement. The results obtained allow us to suggest that the rotation of the solar corona can be used as indicator of the differential rotation of subphotospheric layers and calculate the nature of some current sheets in heliosphere/

How to cite: Obridko, V. and Badalyan, O.: Differential rotation of the solar corona and its importance for helioseismology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3710, https://doi.org/10.5194/egusphere-egu2020-3710, 2020.

D2844 |
Abraham C.L. Chian, Luis R. Bellot Rubio, Heng Q. Feng, Tiago F. P. Gomes, Milan Gosic, Daniela Grasso, Qiang Hu, Kanya Kusano, Rodrigo A. Miranda, Pablo R. Munoz, Erico L. Rempel, David Ruffolo, Suzana S. A. Silva, and De J. Wu

The dynamics of solar and interplanetary plasmas is governed by coherent structures such as current sheets and magnetic flux ropes which are responsible for the genesis of intermittent turbulence via magnetic reconnections in solar supergranular junctions, solar coronal loops, the shock-sheath region of an interplanetary coronal mass ejection, and the interface region of two interplanetary magnetic flux ropes. Lagrangian coherent structures provide a new powerful technique to detect time- or space-dependent transport barriers, and objective (i.e., frame invariant) kinematic and magnetic vortices in space plasma turbulence. We discuss the basic concepts of Lagrangian coherent structures in plasmas based on the computation of the finite-time Lyapunov exponent, the Lagrangian averaged vorticity deviation and the integrated averaged current deviation, as well as their applications to numerical simulations of MHD turbulence and space and ground observations.

How to cite: Chian, A. C. L., Bellot Rubio, L. R., Feng, H. Q., Gomes, T. F. P., Gosic, M., Grasso, D., Hu, Q., Kusano, K., Miranda, R. A., Munoz, P. R., Rempel, E. L., Ruffolo, D., Silva, S. S. A., and Wu, D. J.: Solar and Interplanetary Turbulence: Lagrangian Coherent Structures , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4289, https://doi.org/10.5194/egusphere-egu2020-4289, 2020.

D2845 |
Roman Kislov

The solar magnetic field (SMF) has historically been considered as dipole in order to build models of the radially expanding corona, that is, the solar wind in the solar minimum. The simplified approach suggests the existence of only one quasi-stationary current sheet (QCS) of solar origin in the heliosphere, namely, the heliospheric current sheet (HCS). However, the SMF becomes more complicated over the solar cycle, comprising higher-order components. The overlapping of the dipole and multipole components of the SMF suggests a formation of more than one QCS in the corona, which may expand further to the heliosphere. We study the impact of the quadrupole and octupole harmonics of the SMF on the formation and spatial characteristics of QCSs, building a stationary axisymmetric MHD model of QCSs in the heliosphere. It is shown that if the dipole component dominates, a single QCS appears in the solar wind at low heliolatitudes as the classic HCS. In other cases, the number of QCSs varies from one to three, depending on the relative input of the quadrupole and octupole components. QCSs possess a conic form and may occur at a wide variety of heliolatitudes. The existence of QCSs opens wide opportunities for explanations of puzzling observations of cosmic rays and energetic particles in the heliosphere and, at the same time, raises a risk of misinterpretation of in situ crossings of QCSs because of mixing up the HCS and higherheliolatitude QCSs, which can be significantly disturbed in the dynamical solar wind.

How to cite: Kislov, R.: Quasi-stationary current sheets of the solar origin in the heliosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-466, https://doi.org/10.5194/egusphere-egu2020-466, 2019.

D2846 |
Mikhail Fridman

So far, the problem of a short-term forecast of geomagnetic storms can be considered as solved. Meanwhile, mid-term prognoses of geomagnetic storms with an advance time from 3 hours to 3 days are still unsuccessful (see  https://www.swpc.noaa.gov/sites/default/files/images/u30/Max%20Kp%20and%20GPRA.pdf).

 This fact suggests a necessity of looking for specific processes in the solar wind preceding geomagnetic storms. Knowing that magnetic cavities filled with magnetic islands and current sheets are formed in front of high-speed streams of any type (Khabarova et al., 2015, 2016, 2018; Adhikari et al., 2019), we have performed an analysis of the corresponding ULF variations in the solar wind density observed at the Earth's orbit from hours to days before the arrival of a geoeffective stream or flow. The fact of the occurrence of ULF-precursors of geomagnetic storms was noticed a long time ago (Khabarova 2007; Khabarova & Yermolaev, 2007) and related prognostic methods were recently developed (Kogai et al. 2019), while the problem of automatization of the prognosis remained unsolved.

 A new geomagnetic storm forecast method, which employs a Recurrent Neural Network (RNN) for an automatic pattern search, is proposed. An ability of self-teaching and extracting deeply hidden non-linear patterns is the main advantage of Deep Neural Networks (DNNs) with multiple layers over traditional Machine Learning methods. We show a success of the RNN method, using either the unprocessed solar wind density data or Wavelet analysis coefficients as the input parameter for a DNN to perform an automatic mid-term prognosis of geomagnetic storms.  

Adhikari, L., et al. 2019, The Role of Magnetic Reconnection–associated Processes in Local Particle Acceleration in the Solar Wind, ApJ, 873, 1, 72, https://doi.org/10.3847/1538-4357/ab05c6
Kogai T.G. et al., Pre-storm ULF variations in the solar wind density and interplanetary magnetic field as key parameters to build a mid-term prognosis of geomagnetic storms. “GRINGAUZ 100: PLASMA IN THE SOLAR SYSTEM”, IKI RAS, Moscow, June 13–15, 2018, 140-143, ISBN 978-5-00015-043-6. https://www.researchgate.net/publication/327781146_Pre-storm_ULF_variations_in_the_solar_wind_density_and_interplanetary_magnetic_field_as_key_parameters_to_build_a_mid-term_prognosis_of_geomagnetic_storms
 Khabarova O. V., et al. 2018,  Re-acceleration of energetic particles in large-scale heliospheric magnetic cavities, Proceedings of the IAU, 76-82, https://doi.org/10.1017/S1743921318000285 
Khabarova O.V., et al. Small-scale magnetic islands in the solar wind and their role in particle acceleration. II. Particle energization inside magnetically confined cavities. 2016, ApJ, 827, 122, http://iopscience.iop.org/article/10.3847/0004-637X/827/2/122
Khabarova O., et al. Small-scale magnetic islands in the solar wind and their role in particle acceleration. 1. Dynamics of magnetic islands near the heliospheric current sheet. 2015, ApJ, 808, 181, https://doi.org/10.1088/0004-637X/808/2/181

Khabarova O.V., Current Problems of Magnetic Storm Prediction and Possible Ways of Their Solving. Sun&Geosphere,  http://sg.shao.az/v2n1/SG_v2_No1_2007-pp-33-38.pdf , 2(1), 33-38, 2007

Khabarova O.V. & Yu.I.Yermolaev, Solar wind parameters' behavior before and after magnetic storms, JASTP, 70, 2-4, 2008, 384-390, http://dx.doi.org/10.1016/j.jastp.2007.08.024

How to cite: Fridman, M.: Neural network applications in geomagnetic storm prognosis based on the pre-storm occurrence of magnetic islands in the solar wind, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1848, https://doi.org/10.5194/egusphere-egu2020-1848, 2019.

D2847 |
Timofey Sagitov and Roman Kislov

High speed streams originating from coronal holes are long-lived plasma structures that form corotating interaction regions (CIRs) or stream interface regions (SIRs) in the solar wind. The term CIR is used for streams existing for at least one solar rotation period, and the SIR stands for streams with a shorter lifetime. Since the plasma flows from coronal holes quasi-continuously, CIRs/SIRs simultaneously expand and rotate around the Sun, approximately following the Parker spiral shape up to the Earth’s orbit.

Coronal hole streams rotate not only around the Sun but also around their own axis of simmetry, resembling a screw. This effect may occur because of the following mechanisms: (1) the existence of a difference between the solar wind speed at different sides of the stream, (2) twisting of the magnetic field frozen into the plasma, and  (3) a vortex-like motion of the edge of the mothering coronal hole at the Sun. The screw type of the rotation of a CIR/SIR can lead to centrifugal instability if CIR/SIR inner layers have a larger angular velocity than the outer. Furthermore, the rotational plasma movement and the stream distortion can twist magnetic field lines. The latter contributes to the pinch effect in accordance with a well-known criterion of Suydam instability (Newcomb, 1960, doi: 10.1016/0003-4916(60)90023-3). Owing to the presence of a cylindrical current sheet at the boundary of a coronal hole, conditions for tearing instability can also appear at the CIR/SIR boundary. Regardless of their geometry, large scale current sheets are subject to various instabilities generating plasmoids. Altogether, these effects can lead to the formation of a turbulent region within CIRs/SIRs, making them filled with current sheets and plasmoids. 

We study a substructure of CIRs/SIRs, characteristics of their rotation in the solar wind, and give qualitative estimations of possible mechanisms which lead to splitting of the leading edge a coronal hole flow and consequent formation of current sheets within CIRs/SIRs.

How to cite: Sagitov, T. and Kislov, R.: Formation of current sheets and plasmoids within corotating/stream interaction regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2102, https://doi.org/10.5194/egusphere-egu2020-2102, 2020.

D2848 |
Olеg Mingalev and Igor Mingalev

A new form of the proton force balance equation for the plasma consisting of collisionless protons and magnetized electrons is obtained. In the equation, the electric field is expressed through the magnetic field and the divergence of electron pressure tensor. The latter is reqiured for the correct determination of boundary conditions in models of current sheets to control the force balance in the models of that type. From this, a general form of the force balance equation in a one-dimensional current sheet is obtained, and effects of electron pressure anisotropy are considered. We reproduce realistic stationary configurations of current sheets using novel methods of numerical simulations and the Vlasov equation solving. 

How to cite: Mingalev, O. and Mingalev, I.: Force balance in current sheets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2210, https://doi.org/10.5194/egusphere-egu2020-2210, 2020.

D2849 |
Natsuha Kuroda, Gregory Fleishman, Dale Gary, Gelu Nita, Bin Chen, and Sijie Yu

Hard X-ray (HXR) and microwave (MW) observations are highly complementary for studying electron acceleration and transport processes in solar flares. In recent years, a new effort has been made in the MW domain using new high-resolution, multifrequency data from The Expanded Owens Valley Solar Array (EOVSA) and a breakthrough numerical modeling infrastructure that enables us to study properties of high-energy electrons in unprecedented cadence and quantitative detail. This study introduces the observation of an M1.2 flare that occurred on 2017 September 9 and analyzes the evolution of the nonthermal electrons in the corona based on EOVSA MW spectral imaging data. We find a significant spectral hardening of the MWemitting nonthermal electron population in the corona, using EOVSA lower-frequency (<7 GHz) observations over a selected 4-minute window of the flare's impulsive phase. We compare this spectral evolution with the evolution of the spectral index of nonthermal electrons emitting in the chromosphere, derived from HXR observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager. We discuss the general picture of the evolution of the nonthermal electron population in this flare by incorporating observations at the two complementary wavelengths. We also make an estimate of the total energy of the nonthermal electrons contained in the observed coronal low-frequency MW source and discuss its temporal evolution.

How to cite: Kuroda, N., Fleishman, G., Gary, D., Nita, G., Chen, B., and Yu, S.: Evolution of Flare-accelerated Electrons in the Solar Corona and Chromosphere Revealed by Spatially Resolved Microwave and Hard X-Ray Analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3145, https://doi.org/10.5194/egusphere-egu2020-3145, 2020.

D2850 |
Olga Malandraki, Olga Khabarova, Roberto Bruno, Gary Zank, and Gang Li and the ISSI-405 team

Recent studies of particle acceleration in the heliosphere have revealed a new mechanism that can locally energize particles up to several MeV/nuc. Stream-stream interactions as well as the heliospheric current sheet – stream interactions lead to formation of large magnetic cavities, bordered by strong current sheets (CSs), which in turn produce secondary CSs and dynamical small-scale magnetic islands (SMIs) of ~0.01AU or less owing to magnetic reconnection. It has been shown that particle acceleration or re-acceleration occurs via stochastic magnetic reconnection in dynamical SMIs confined inside magnetic cavities observed at 1 AU. The study links the occurrence of CSs and SMIs with characteristics of intermittent turbulence and observations of energetic particles of keV-MeV/nuc energies at ~5.3 AU. We analyze selected samples of different plasmas observed by Ulysses during a widely discussed event, which was characterized by a series of high-speed streams of various origins that interacted beyond the Earth’s orbit in January 2005. The interactions formed complex conglomerates of merged interplanetary coronal mass ejections, stream/corotating interaction regions and magnetic cavities. We study properties of turbulence and associated structures of various scales. We confirm the importance of intermittent turbulence and magnetic reconnection in modulating solar energetic particle flux and even local particle acceleration. Coherent structures, including CSs and SMIs, play a significant role in the development of secondary stochastic particle acceleration, which changes the observed energetic particle flux time-intensity profiles and increases the final energy level to which energetic particles can be accelerated in the solar wind.

How to cite: Malandraki, O., Khabarova, O., Bruno, R., Zank, G., and Li and the ISSI-405 team, G.: Current sheets, magnetic islands and associated particle acceleration in the solar wind as observed by Ulysses near the ecliptic plane, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3730, https://doi.org/10.5194/egusphere-egu2020-3730, 2020.

D2851 |
Evgeniy Maiewski, Helmi Malova, Roman Kislov, Victor Popov, Anatoly Petrukovich, and Lev Zelenyi

When spacecraft cross the heliospheric plasma sheet (HPS) that separates large-scale magnetic sectors of the opposite direction in the solar wind, multiple rapid fluctuations of a sign of the radial magnetic field component are observed very often, indicating the presence of multiple current sheets occurring within the HPS. Possible mechanisms of formation of these structures in the solar wind are proposed. Taking into accout that the streamer belt in the solar corona is believed to be the main source of the slow solar wind in the heliosphere, we suggest that the effect of the multi-layered HPS is determined by the extension of many streamer-belt-borne thin current sheets oriented along the neutral line of the interplanetary magnetic field. Within the framework of a proposed MHD model, self-consistent distributions of the key solar wind characteristics which depend on streamer propreties are investigated. It is shown that both single and multiple streamers that are capable of reaching a remote boundary surface can form the observed multiple current sheets with azimuthal currents alternating in direction inside the HPS. The implications of these results for the interpretation of observations in the solar wind are discussed.

How to cite: Maiewski, E., Malova, H., Kislov, R., Popov, V., Petrukovich, A., and Zelenyi, L.: Mechanisms of formation of multiple current sheets in the heliospheric plasma sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3945, https://doi.org/10.5194/egusphere-egu2020-3945, 2020.

D2852 |
Spiro Antiochos, Pankaj Kumar, Judy Jarpen, and Joel Dahlin

Jets and mass ejections are ubiquitous features of the Sun’s corona. These explosive dynamics are all believed to be driven by magnetic reconnection at two types of current sheets that form in the solar atmosphere: those that form at magnetic null points and separatrix surfaces, and those, such as the heliospheric current sheet, that form as a result of a large expansion of a bipolar magnetic field. In our breakout model, both types of current sheets are essential for the explosive release of magnetic energy. We report on the first direct observations of reconnection and island formation in a null-point current sheet associated with a large coronal jet. The topology and velocities of the islands are in excellent agreement with our numerical simulations of coronal jets. We discuss the implications of the observations and our models for understanding the energetic particles produced by these events and their release into interplanetary space, as well as the implications for observations by Solar Orbiter and the Parker Solar Probe.

This work was supported by the NASA Living With a Star Program.


How to cite: Antiochos, S., Kumar, P., Jarpen, J., and Dahlin, J.: Observations and Simulations of Reconnecting Current Sheets in the Solar Corona, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5597, https://doi.org/10.5194/egusphere-egu2020-5597, 2020.

D2853 |
Evgenios Pavlos, Olga Malandraki, Olga Khabarova, Leonidas P. Karakatsanis, George P. Pavlos, and George Livadiotis

In this study we use theoretical concepts and computational-diagnostic tools of Tsallis non-extensive statistical theory (Tsallis q-triplet: qsen, qrel, qstat), complemented by other known tools of nonlinear dynamics such as Correlation Dimension and surrogate data, Hurst exponent, Flatness coefficient, and p-modeling of multifractality, in order to describe and understand Small-scale Magnetic Islands (SMIs) structures observed in Solar Wind (SW) with a typical size of ~0.01–0.001 AU at 1 AU. Specifically, we analyze ~0.5 MeV energetic ion time-intensity and magnetic field profiles observed by the STEREO A spacecraft during a rare, widely discussed event. Our analysis clearly reveals the non-extensive character of SW space plasmas during the periods of SMIs events, as well as significant physical complex phenomena in accordance with nonlinear dynamics and complexity theory. As our analysis also shows, a non-equilibrium phase transition parallel with self-organization processes, including the reduction of dimensionality and development of long-range correlations in connection with anomalous discussion and fractional acceleration processes can be observed during SMIs events.

How to cite: Pavlos, E., Malandraki, O., Khabarova, O., Karakatsanis, L. P., Pavlos, G. P., and Livadiotis, G.: Non-Extensive Statistical Analysis of Energetic Particle Flux Enhancements Caused by the Interplanetary Coronal Mass Ejection-Heliospheric Current Sheet Interaction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8461, https://doi.org/10.5194/egusphere-egu2020-8461, 2020.

D2854 |
Elena Parkhomenko, Vladimir Kalegaev, Helmi Malova, Mikhail Panasyuk, Victor Popov, Natalia Vlasova, and Lev Zelenyi

In this work we are studying multicharged oxygen ion acceleration during substorms in the Earth's magnetotail as the source of ring current replenishment by energetic ion population. We used measurements obtained by the CRRES spacecraft for the comparison of experimental spectra of oxygen charge state in the outer region of the ring current and proton radiation belt with model results. We present a numerical model that allows to evaluate acceleration of oxygen ions O+-O+8 in the course of two possible perturbation processes: A) passage of multiple dipolarization fronts in the magnetotail; B) passage of fronts followed by electromagnetic turbulence. It is shown that acceleration processes depend on particle charges and time scale of electric field variations. Oxygen ions O+8 with average initial energies 12 keV are accelerated efficiently during multiple dipolarization processes of type (A) and their energies increased up to 7.4 MeV, whereas ions O+1 with the same energies were energized up to 1.9 МeV. It is shown that oxygen ions O+-O+2 are able to penetrate into the ring/radiation belts region with L between L=4.5 and L=7.5 in the process of plasma transfer on dipolarization fronts. For oxygen O+-O+8 the additional acceleration mechanism is required, such as large-scale electromagnetic turbulence, when the ions can get energies comparable with experimentally observed ones in the indicated range of L shell values. It is shown that the taking into account electromagnetic fluctuations, accompanying magnetic dipolarization, may explain the appearance of oxygen ion flows with energies greater than 3MeV in the near- Earth’s space.

How to cite: Parkhomenko, E., Kalegaev, V., Malova, H., Panasyuk, M., Popov, V., Vlasova, N., and Zelenyi, L.: Earth’s magnetotail as the reservoir of accelerated single- and multicharged oxygen ions replenishing radiation belts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8520, https://doi.org/10.5194/egusphere-egu2020-8520, 2020.

D2855 |
| solicited
Alexander Khokhlachev, Maria Riazantseva, Liudmila Rakhmanova, Yuri Yermolaev, Irina Lodkina, and Georgy Zastenker

The boundaries between large-scale solar wind streams are often accompanied by sharp changes in helium abundance.  Wherein the high value of relative helium abundance is known as a sign of some large-scale solar wind structures ( for example magnetic clouds). Unlike the steady slow solar wind where the helium abundance is rather stable and equals ~5%, in magnetic clouds its value can grow significantly up to 20% and more, and at the same time helium component becomes more variable.  In this paper we analyze the small-scale variations of solar wind plasma parameters, including the helium abundance variations in different large-scale solar wind streams, especially in magnetic clouds and Sheath regions before them. We use rather long intervals of simultaneous measurements at Spektr-R (spectrometer BMSW) and Wind (spectrometer 3DP) spacecrafts.  We choose the intervals with rather high correlation  level of plasma parameters as a whole to be sure that we are deal with the same plasma stream.  The intervals associated with different large scale-solar wind structures are selected by using of our catalog ftp://ftp.iki.rssi.ru/pub/omni/catalog/. For selected intervals we examine cross-correlation function for Spektr-R and Wind measurements  to reveal the local spatial inhomogeneities by helium abundance which can be observed only at one of spacecrafts, and we determine properties of ones. Such inhomogeneities can be generate by turbulence, which is typically getting more intense in the considered disturbed intervals in the solar wind. The work is supported by Russian Science Foundation grant 16-12-10062.

How to cite: Khokhlachev, A., Riazantseva, M., Rakhmanova, L., Yermolaev, Y., Lodkina, I., and Zastenker, G.: Small-scale variations of helium abundance in different large-scale solar wind structures, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9348, https://doi.org/10.5194/egusphere-egu2020-9348, 2020.

D2856 |
| solicited
Joel Dahlin, Spiro Antiochos, and C. Richard DeVore

In highly conducting plasmas, reconnecting current sheets are often unstable to the generation of plasmoids, small-scale magnetic structures that play an important role in facilitating the rapid release of magnetic energy and channeling that energy into accelerated particles. There is ample evidence for plasmoids throughout the heliosphere, from in situ observations of flux ropes in the solar wind and planetary magnetospheres to remote-sensing imaging of plasma ‘blobs’ associated with explosive solar activity such as eruptive flares and coronal jets. Accurate models for plasmoid formation and dynamics must capture the large-scale self-organization responsible for forming the reconnecting current sheet. However, due to the computational difficulty inherent in the vast separation between the global and current sheet scales, previous numerical studies have typically explored configurations with either reduced dimensionality or pre-formed current sheets. We present new three-dimensional MHD studies of an eruptive flare in which the formation of the current sheet and subsequent reconnection and plasmoid formation are captured within a single simulation. We employ Adaptive Mesh Refinement (AMR) to selectively resolve fine-scale current sheet dynamics. Reconnection in the flare current sheet generates many plasmoids that exhibit highly complex, three-dimensional structure. We show how plasmoid formation and dynamics evolve through the course of the flare, especially in response to the weakening of the reconnection “guide field” linked to the global reduction of magnetic shear. We discuss implications of our results for particle acceleration and transport in eruptive flares as well as for observations by Parker Solar Probe and the forthcoming Solar Orbiter.

How to cite: Dahlin, J., Antiochos, S., and DeVore, C. R.: High-Resolution Three-Dimensional MHD Simulations of Plasmoid Formation in Solar Flares, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10039, https://doi.org/10.5194/egusphere-egu2020-10039, 2020.

D2857 |
Olga Khabarova, Valentina Zharkova, Qian Xia, and Olga Malandraki

We present multi-spacecraft observations of pitch-angle distributions (PADs) of suprathermal electrons at ~1 AU which cannot be easily interpreted within the classical paradigm that all suprathermal electrons originate in the solar corona. We suggest that suprathermal electrons accelerated locally in the solar wind are mixed up with the well-known population of electrons of solar origin. Using PIC simulations, we show that key PAD features such as (i) heat flux dropouts and vertical PAD stripes encompassing reconnecting current sheets (RCSs), (ii) bi-directionality of strahls, and (iii) dramatically different PAD patterns observed in different energy channels can be explained by the behavior of electrons accelerated up to hundreds eV directly in the solar wind while thermal particles pass through local RCSs and/or dynamical 3D plasmoids (or 2D magnetic islands).

How to cite: Khabarova, O., Zharkova, V., Xia, Q., and Malandraki, O.: Counterstreaming strahls and dropouts observed in pitch angle distributions of suprathermal electrons as possible signatures of local particle acceleration in the solar wind, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10819, https://doi.org/10.5194/egusphere-egu2020-10819, 2020.

D2858 |
| solicited
Neeraj Jain and Joerg Buechner

Spacecraft observations show the radial dependence of the solar wind temperature to be slower than what is expected from the adiabatic cooling of the solar wind expanding radially outwards from the sun. The most viable process considered to explain the observed slower-than-adiabatic cooling is the heating of the solar wind plasma by dissipation of the turbulent fluctuations. In solar wind which is  a collisionless plasma in turbulent state, macroscopic energy is cascaded down to kinetic scales where kinetic plasma processes can finally dissipate the energy into heat. The kinetic scale plasma processes responsible  for the dissipation of energy are, however, not well understood. A number of observational and simulation studies have shown that the heating is concentrated in and around current sheets self-consistently formed at kinetic scales. The current sheets contain free energy sources for the growth of plasma instabilities which can serve as the mechanism of the collisionless dissipation. A detailed information on the free energy sources contained in these current sheets of plasma turbulence is lacking but essential to understand the role of  plasma instabilities in collisionless dissipation.

We carry out 2-D hybrid simulations of kinetic plasma turbulence to study in detail free energy sources available in the current sheets formed in the turbulence. We focus on three free energy sources, namely, plasma density gradient, velocity gradients for both ions and electrons and ion temperature anisotropy. Our simulations show formation of current sheets in which electric current parallel to the externally applied magnetic field flows in a thickness of the order of an ion inertial length. Inside a current sheet, electron flow velocity dominates ion flow velocity in the parallel direction resulting in a larger cross-gradient of the former. The perpendicular electron velocity inside a current sheet also has variations sharper than the corresponding ion velocity. Cross gradients in plasma density are weak (under 10 % variation inside current sheets). Ion temperature is anisotropic in current sheets. Thus the current in the sheets is primarily due to electron shear flow. A theoretical model to explain the difference between electron and ion velocities in current sheets is developed. Spacecraft observations of electron shear flow in space plasma turbulence will be pointed out.   

These results suggest that the current sheets formed in kinetic plasma turbulence are close to the force free equilibrium rather than the often assumed Harris equilibrium.  This demands investigations of the linear stability properties and nonlinear evolution of force free current sheets with temperature anisotropy. Such studies can provide effective dissipation coefficients to be included in macroscopic model of the solar wind evolution.   

How to cite: Jain, N. and Buechner, J.: Free energy sources in kinetic scale current sheets formed in collisionless plasma turbulence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21518, https://doi.org/10.5194/egusphere-egu2020-21518, 2020.

D2859 |
Gregory Fleishman, Bin Chen, Gary Dale, and Gelu Nita et al.

In the standard model of solar flares, a large-scale reconnection current sheet (RCS) is postulated as the central engine for powering the flare energy release and accelerating particles. However, where and how the energy release and particle acceleration occur remain unclear due to the lack of measurements for the magnetic properties of the RCS. Here we report the first measurement of spatially-resolved magnetic field and flare-accelerated relativistic electrons along a large-scale RCS in a solar flare. The measured magnetic field profile shows a local maximum where the reconnecting field lines of opposite polarities closely approach each other, known as the reconnection X point. The measurements also reveal a local minimum near the bottom of the RCS above the flare loop-top, referred to as a "magnetic bottle". This spatial structure agrees with theoretical predictions and numerical modeling results. A strong reconnection electric field of over 4000 V/m is inferred near the X point. This location, however, shows a local depletion of microwave-emitting relativistic electrons. In contrast, the relativistic electrons concentrate at or near the magnetic bottle structure, where more than 99% of them reside at each instant. Our observations suggest crucial new input to the current picture of high energy electron acceleration.

How to cite: Fleishman, G., Chen, B., Dale, G., and Nita et al., G.: Mapping magnetic field and relativistic electrons along a solar flare current sheet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19937, https://doi.org/10.5194/egusphere-egu2020-19937, 2020.

D2860 |
| solicited
Zixuan Liu, Linghua Wang, Haobo Fu, Krucker Sam, and Wimmer-Schweingruber Robert

We propose a general fitting formula of energy spectrum of suprathermal particles, J=AE-β1[1+(E/E0)α](β1-β2)/α, where J is the particle flux (or intensity), E is the particle energy, A is the amplitude coefficient, E0 represents the spectral break energy, α (>0) describes the sharpness of energy spectral break around E0, and the power-law index β12) gives the spectral shape before (after) the break.  When α tends to infinity (zero), this spectral formula becomes a classical double-power-law (logarithmic-parabola) spectrum. When both β2 and E0 tend to infinity, this formula can be simplified to an Ellison-Ramaty-like equation. Under some other specific parameter conditions, this formula can be transformed to a Kappa or Maxwellian function. Considering  the uncertainties both in particle intensity and energy, we fit this general formula well to the representative energy spectra of various suprathermal particle phenomena including solar energetic particles (electrons, protons,  3He and heavier ions), shocked particles, anomalous cosmic rays, hard X-rays, solar wind suprathermal particles, etc. Therefore, this general spectrum fitting formula would help us to comparatively examine the energy spectrum of different suprathermal particle phenomena and understand their origin, acceleration and transportation.

How to cite: Liu, Z., Wang, L., Fu, H., Sam, K., and Robert, W.-S.: General Spectrum Fitting for Energetic Particles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8189, https://doi.org/10.5194/egusphere-egu2020-8189, 2020.

D2861 |
Primoz Kajdic, Xochitl Blanco-Cano, Tomas Karlsson, and Savvas Raptis

Magnetosheath jets were first discovered by Nemeček et al., 1998 and were defined as events in the magnetosheath that exhibit ion fluxes at least 50 % higher than those in the surrounding plasma. Later authors used different physical quantities in order to study these phenomena, such as velocity, density and dynamic pressure. Magnetosheath jets are usually found in the parts of the magnetosheath that are magnetically connected to the quasi-parallel sections of the Earth's bow-shock, although jets in the so called quasi-perpendicular magnetosheath have also been observed. There are several proposed mechanisms for their formation, the most accepted ones being the formation due to the rippled surface of quasi-parallel shocks, and the transmission of upstream large-amplitude magnetic structures (SLAMS) across the bow-shock. Here we make use of the Magnetospheric Multiscale Mission burst mode data in order to present observations of waves and current sheets inside magnetosheath jets. We show that these phenomena occur commonly and provide additional mechanisms that dissipate the solar wind kinetic energy downstream of the bow-shock.

How to cite: Kajdic, P., Blanco-Cano, X., Karlsson, T., and Raptis, S.: Current sheets and waves inside magnetosheath jets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10694, https://doi.org/10.5194/egusphere-egu2020-10694, 2020.

D2862 |
Helmi Malova, Victor Popov, and Elena Grigorenko

The dynamics of quasi-adiabatic ions in the current sheet (CS) of the Earth's magnetotail during substorms is investigated, when CS is thinned, and the scale of the magnetic inhomogeneity is about proton gyroradius. Experimental data indicate sometimes that the shear magnetic component from the interplanetary magnetic field can penetrate within the magnetosphere and support self-consistent currents. The numerical model of CS is constructed, taking into account the normal magnetic component and shear component of three types: 1) constant profile within CS, 2) bell-shaped and 3) antisymmetric ones. Poincaré maps characterizing quasi-adiabatic dynamics of ions are studied. The jumps of quasi-adiabatic invariant of motion are calculated, and comparison is made with the case of the absent magnetic shear. It is shown that the presence of constant and bell-shaped magnetic components in the current sheet leads to the asymmetric scattering of particles in the North-South direction after their interaction with CS and corresponding differences in the structure of the phase space. It is demonstrated that the jumps of the approximate invariant Iz depend on the location of the plasma source in the Northern or Southern hemispheres.  At the same time, for configurations with anti-symmetric shear component, the particle scattering near the sheet plane is negligible, therefore in this case it is no scattering asymmetry, and the jumps of invariants of motion are smallest; they do not depend on the value of the magnetic field amplitude inside CS. Applications of these results to interpret experimental observations are discussed.

How to cite: Malova, H., Popov, V., and Grigorenko, E.: Peculiarities of quasi-adiabatic dynamics of charged particles in current sheets with magnetic shear, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10698, https://doi.org/10.5194/egusphere-egu2020-10698, 2020.

D2863 |
Victor Popov, Vladimir Domrin, Helmi Malova, Elena Grigorenko, and Anatoly Petrukovich

The self-consistent hybrid model of a thin current sheet with a thickness about several proton gyroradii in a space plasma is proposed, taking into account multicomponent collisionless space plasma. Several plasma components are often presented in planetary magnetotails (Hermean, Martian, Terrestrial and other ones). Influence of heavy oxygen ions with different properties on current sheet structure is analyzed. It is shown that high relative concentrations of oxygen ions, as well as their relatively high temperatures and flow drift speeds lead to a significant thickening of the sheet and a formation of an additional embedding scale. For some real parameters the profiles of self-consistent current densities and magnetic field have symmetrical jumps of derivatives, i.e. sharp changes of gradients. The comparison is made with observations in the Martian magnetosphere. The qualitative agreement of simulation results with observational data is shown.

How to cite: Popov, V., Domrin, V., Malova, H., Grigorenko, E., and Petrukovich, A.: Current sheets with multi-component plasma in planetary magnetospheres , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11700, https://doi.org/10.5194/egusphere-egu2020-11700, 2020.