MAGNETIC RECONNECTION BETWEEN SMALL-SCALE LOOPS OBSERVED WITH THE NEW VACUUM SOLAR TELESCOPE

AbstractBased on the New Vacuum Solar Telescope observations, some new results about the solar activities are obtained. (1) In the Hα line, a flux rope tracked by filament activation is detected for the first time. There may exist some mild heating during the filament activation. (2) The direct observations illustrate the mechanism of confined flares, i.e., the flares are triggered by magnetic reconnection between the emerging loops and the pre-existing loops and prevented from being eruptive by the overlying loops. (3) The solid observational evidence of magnetic reconnection between two sets of small-scale loops is reported. The successive slow reconnection changes the conditions around the reconnection area and leads to the rapid reconnection. (4) An ensemble of oscillating bright features rooted in a light bridge is observed and given a new name, light wall. The light wall oscillations may be due to the leakage of p-modes from below the photosphere.

Download Full-text

Ion Dynamics in the Meso-scale 3-D Kelvin–Helmholtz Instability: Perspectives From Test Particle Simulations

Frontiers in Astronomy and Space Sciences ◽

10.3389/fspas.2021.758442 ◽

2021 ◽

Vol 8 ◽

Author(s):

Xuanye Ma ◽

Peter Delamere ◽

Katariina Nykyri ◽

Brandon Burkholder ◽

Stefan Eriksson ◽

...

Keyword(s):

Magnetic Field ◽

Magnetic Reconnection ◽

Test Particle ◽

Acoustic Waves ◽

Particle Simulation ◽

Three Dimensions ◽

Small Scale ◽

Physical Processes ◽

Length Scales ◽

Ion Species

Over three decades of in-situ observations illustrate that the Kelvin–Helmholtz (KH) instability driven by the sheared flow between the magnetosheath and magnetospheric plasma often occurs on the magnetopause of Earth and other planets under various interplanetary magnetic field (IMF) conditions. It has been well demonstrated that the KH instability plays an important role for energy, momentum, and mass transport during the solar-wind-magnetosphere coupling process. Particularly, the KH instability is an important mechanism to trigger secondary small scale (i.e., often kinetic-scale) physical processes, such as magnetic reconnection, kinetic Alfvén waves, ion-acoustic waves, and turbulence, providing the bridge for the coupling of cross scale physical processes. From the simulation perspective, to fully investigate the role of the KH instability on the cross-scale process requires a numerical modeling that can describe the physical scales from a few Earth radii to a few ion (even electron) inertial lengths in three dimensions, which is often computationally expensive. Thus, different simulation methods are required to explore physical processes on different length scales, and cross validate the physical processes which occur on the overlapping length scales. Test particle simulation provides such a bridge to connect the MHD scale to the kinetic scale. This study applies different test particle approaches and cross validates the different results against one another to investigate the behavior of different ion species (i.e., H+ and O+), which include particle distributions, mixing and heating. It shows that the ion transport rate is about 1025 particles/s, and mixing diffusion coefficient is about 1010 m2 s−1 regardless of the ion species. Magnetic field lines change their topology via the magnetic reconnection process driven by the three-dimensional KH instability, connecting two flux tubes with different temperature, which eventually causes anisotropic temperature in the newly reconnected flux.

Download Full-text

Why are CMEs large-scale coronal events: nature or nurture?

Annales Geophysicae ◽

10.5194/angeo-26-3077-2008 ◽

2008 ◽

Vol 26 (10) ◽

pp. 3077-3088 ◽

Cited By ~ 24

Author(s):

L. van Driel-Gesztelyi ◽

G. D. R. Attrill ◽

P. Démoulin ◽

C. H. Mandrini ◽

L. K. Harra

Keyword(s):

Magnetic Reconnection ◽

Large Scale ◽

Observational Evidence ◽

Angular Width ◽

Small Scale ◽

Apparent Contradiction ◽

Lower Corona ◽

Magnetic Structures ◽

Source Regions ◽

Scale Response

Abstract. The apparent contradiction between small-scale source regions of, and large-scale coronal response to, coronal mass ejections (CMEs) has been a long-standing puzzle. For some, CMEs are considered to be inherently large-scale events – eruptions in which a number of flux systems participate in an unspecified manner, while others consider magnetic reconnection in special global topologies to be responsible for the large-scale response of the lower corona to CME events. Some of these ideas may indeed be correct in specific cases. However, what is the key element which makes CMEs large-scale? Observations show that the extent of the coronal disturbance matches the angular width of the CME – an important clue, which does not feature strongly in any of the above suggestions. We review observational evidence for the large-scale nature of CME source regions and find them lacking. Then we compare different ideas regarding how CMEs evolve to become large-scale. The large-scale magnetic topology plays an important role in this process. There is amounting evidence, however, that the key process is magnetic reconnection between the CME and other magnetic structures. We outline a CME evolution model, which is able to account for all the key observational signatures of large-scale CMEs and presents a clear picture how large portions of the Sun become constituents of the CME. In this model reconnection is driven by the expansion of the CME core resulting from an over-pressure relative to the pressure in the CME's surroundings. This implies that the extent of the lower coronal signatures match the final angular width of the CME.

Download Full-text

ViDA: a Vlasov–DArwin solver for plasma physics at electron scales

Journal of Plasma Physics ◽

10.1017/s0022377819000631 ◽

2019 ◽

Vol 85 (5) ◽

Cited By ~ 3

Author(s):

Oreste Pezzi ◽

Giulia Cozzani ◽

Francesco Califano ◽

Francesco Valentini ◽

Massimiliano Guarrasi ◽

...

Keyword(s):

Plasma Physics ◽

Magnetic Reconnection ◽

Spatial Scales ◽

Collisionless Plasma ◽

Low Noise ◽

Numerical Code ◽

Small Scale ◽

Diffusion Region ◽

Plasma Dynamics ◽

Algorithm Efficiency

We present a Vlasov–DArwin numerical code (ViDA) specifically designed to address plasma physics problems, where small-scale high accuracy is requested even during the nonlinear regime to guarantee a clean description of the plasma dynamics at fine spatial scales. The algorithm provides a low-noise description of proton and electron kinetic dynamics, by splitting in time the multi-advection Vlasov equation in phase space. Maxwell equations for the electric and magnetic fields are reorganized according to the Darwin approximation to remove light waves. Several numerical tests show that ViDA successfully reproduces the propagation of linear and nonlinear waves and captures the physics of magnetic reconnection. We also discuss preliminary tests of the parallelization algorithm efficiency, performed at CINECA on the Marconi-KNL cluster. ViDA will allow the running of Eulerian simulations of a non-relativistic fully kinetic collisionless plasma and it is expected to provide relevant insights into important problems of plasma astrophysics such as, for instance, the development of the turbulent cascade at electron scales and the structure and dynamics of electron-scale magnetic reconnection, such as the electron diffusion region.

Download Full-text

Ionospheric ions in the magnetosphere: Important at large and small scales

10.5194/egusphere-egu2020-3653 ◽

2020 ◽

Author(s):

Mats André ◽

Sergio Toledo-Redondo ◽

Andrew W Yau

Keyword(s):

Electric Field ◽

Magnetic Reconnection ◽

Energy Transport ◽

Small Scale ◽

Diffusion Region ◽

Positive Ions ◽

Small Scales ◽

Outflow Rate ◽

Long Time ◽

Cold Ions

Cold (eV) ions of ionospheric origin dominate the number density of most of the volume of the magnetosphere during most of the time. Supersonic flows of cold positive ions are common and can cause a negatively charged wake behind a positively charged spacecraft. The associated induced electric field can be observed and can be used to study the cold ions. We present observations from the Cluster and MMS spacecraft showing how a charged satellite, and also individual charged wire booms of &#160;an electric field instrument, can be used to investigate cold ion populations. Ionospheric ions affect large scales, including the Alfv&#233;n velocity and &#160;thus energy transport with waves and the magnetic reconnection rate. These ions also affect small-scale kinetic plasma physics, including the Hall physics and wave instabilities associated with magnetic reconnection. Concerning large scales, we summarize observations from several spacecraft and show that a typical total outflow rate of ionospheric ions is 1026 ions/s and that many of these ions stay cold also after a long time in the magnetosphere.&#160; Concerning small scales, we show examples of how cold ions modify the Hall physics of thin current sheets, including magnetic reconnection separatrices. On small kinetic scales the cold ions introduce a new length-scale, a gyro radius between the gyro radii of hot (keV) ions and electrons. The Hall currents carried by electrons can be partially cancelled by the cold ions when electrons and the magnetized cold ions ExB drift together. Also, close to a reconnection X-line an additional diffusion region can be formed (regions associated with hot and cold ions, and with electrons, total of three).

Download Full-text

The Relationship Between Electron-Only Magnetic Reconnection and Turbulence in Earth’s Magnetosheath

10.5194/egusphere-egu2020-5692 ◽

2020 ◽

Author(s):

Julia E. Stawarz ◽

Jonathan P. Eastwood ◽

Tai Phan ◽

Imogen L. Gingell ◽

Alfred Mallet ◽

...

Keyword(s):

Magnetic Reconnection ◽

Power Spectra ◽

Theoretical Work ◽

Small Scale ◽

Current Sheets ◽

The Earth ◽

Recent Theoretical Work ◽

Magnetospheric Multiscale ◽

Scale Turbulence ◽

The Relationship

The Earth&#8217;s magnetosheath is filled with small-scale current sheets arising from turbulent dynamics in the plasma. Previous observations and simulations have provided evidence that such current sheets can be sites for magnetic reconnection. Recently, observations from the Magnetospheric Multiscale (MMS) mission have revealed that a novel form of &#8220;electron-only&#8221; reconnection can occur at these small-scale, turbulence-driven current sheets, in which ions do not appear to couple to the reconnected magnetic field to form ion jets. The presence of electron-only reconnection may facilitate dissipation of the turbulence, thereby influencing the partition of energy between ions and electrons, and can alter the nonlinear dynamics of the turbulence itself. In this study, we perform a survey of turbulent intervals in the Earth&#8217;s magnetosheath as observed by MMS in order to determine how common magnetic reconnection is in the turbulent magnetosheath and how it impacts the small-scale turbulent dynamics. The magnetic correlation length, which dictates the length of the turbulent current sheets, is short enough in most of the examined intervals for reconnection with reduced or absent ion jets to occur. Magnetic reconnection is found to be a common feature within these intervals, with a significant fraction of reconnecting current sheets showing evidence of sub-Alfv&#233;nic ion jets and super- Alfv&#233;nic electron jets, consistent with electron-only reconnection. Moreover, a subset of the intervals exhibit changes in the behavior of the small-scale magnetic power spectra, which may be related to the reconnecting current sheets. The results of the survey are compared with recent theoretical work on electron-only reconnection in turbulent plasmas.

Download Full-text

New solar telescope in Big Bear: evidence for super-diffusivity and small-scale solar dynamos?

Physica Scripta ◽

10.1088/0031-8949/86/01/018402 ◽

2012 ◽

Vol 86 (1) ◽

pp. 018402 ◽

Cited By ~ 5

Author(s):

Philip R Goode ◽

Valentyna Abramenko ◽

Vasyl Yurchyshyn

Keyword(s):

Small Scale ◽

Solar Telescope

Download Full-text

Turbulence and dynamo interlinks

Proceedings of the International Astronomical Union ◽

10.1017/s174392131300272x ◽

2012 ◽

Vol 8 (S294) ◽

pp. 337-348

Author(s):

E. M. de Gouveia Dal Pino ◽

R. Santos-Lima ◽

G. Kowal ◽

D. Falceta-Gonçalves

Keyword(s):

Magnetic Fields ◽

Magnetic Flux ◽

Magnetic Reconnection ◽

Small Scale ◽

Low Density ◽

Mhd Turbulence ◽

Turbulent Dynamo ◽

Dynamo Process

AbstractThe role of turbulence in astrophysical environments and its interplay with magnetic fields is still highly debated. In this lecture, we will discuss this issue in the framework of dynamo processes. We will first present a very brief summary of turbulent dynamo theories, then will focus on small scale turbulent dynamos and their particular relevance on the origin and maintenance of magnetic fields in the intra-cluster media (ICM) of galaxies. In these environments, the very low density of the flow requires a collisionless-MHD treatment. We will show the implications of this approach in the turbulent amplification of the magnetic fields in these environments. To finalize, we will also briefly address the connection between MHD turbulence and fast magnetic reconnection and its possible implications in the diffusion of magnetic flux in the dynamo process.

Download Full-text

Project of the Large Solar Telescope with mirror 3 m in diameter

Solar-Terrestrial Physics ◽

10.12737/stp-62202002 ◽

2020 ◽

Vol 6 (2) ◽

pp. 14-29 ◽

Cited By ~ 2

Author(s):

Victor Grigoryev ◽

Mikhail Demidov ◽

Dmitriy Kolobov ◽

Vasiliy Pulyaev ◽

Valery Skomorovsky ◽

...

Keyword(s):

Adaptive Optics ◽

Near Infrared ◽

Solar Physics ◽

Solar Observatory ◽

Spectral Lines ◽

Small Scale ◽

Solar Telescope ◽

Rotating Platform ◽

Solar Telescopes ◽

Under Construction

One of the most important problems of modern solar physics is the observation of the small-scale structure of the solar atmosphere at various heights (including the chromosphere and corona) in different spectral lines. Such observations can be made only with large solar telescopes whose main mirror has a diameter of at least 3 m. Currently, several large solar telescopes are under construction or development in the world. In 2013 in Russia, the work began on the development of a national large solar telescope with a mirror 3 m in diameter (LST-3), which is a part (subproject) of the National Heliogeophysical Complex of the Russian Academy of Sciences. The telescope is planned to be located in the Sayan Solar Observatory at an altitude of more than 2000 m. The choice was made in favor of the classic axisymmetric Gregory optical layout on an alt-azimuth mount. The scientific equipment of LST-3 will consist of several systems of narrow-band tunable filters and spectrographs for various wave ranges. The equipment will be placed both in the main coude focus on a rotating platform and in the Nasmyth focus. To achieve a diffraction resolution, high-order adaptive optics (AO) will be used. It is assumed that with a certain modification of the optical configuration, LST-3 will work as a 0.7 m mirror coronograph in near infrared lines and can also be used for observing astrophysical objects in the nighttime.

Download Full-text

Numerical Simulation of the Explosive Events in the Solar Atmosphere

International Astronomical Union Colloquium ◽

10.1017/s0252921100028955 ◽

1993 ◽

Vol 141 ◽

pp. 134-137

Author(s):

Shu-Ping Jiu

Keyword(s):

Numerical Simulation ◽

Magnetic Flux ◽

Magnetic Reconnection ◽

Solar Atmosphere ◽

Plasma Flow ◽

Small Scale ◽

Flare Activity ◽

Specific Location ◽

Mhd Simulations ◽

Explosive Events

AbstractExplosive events are the earliest indicators of flare activity and potentially predict the imminent occurrence of a flare at a specific location. They are highly energetic small-scale phenomena which are frequently detected throughout the quiet and active sun. The observations show that explosive events are related to emerging magnetic flux and tend to occur on the edges of high photospheric magnentic field regions. The cancellation of photospheric magnetic flux are the manifestation of explosive events, so that they are identified as the magnetic reconnection of flux elements. We assume that emerging flux are convected to the network boundaries with the typical velocity of intranetwork elements. Two-dimension (2D) compressible MHD simulations are performed to explore the reconnection process between emerging intranework flux and network field. The numerical results clearly show the cancellation of magnetic flux and the acceleration of the plasma flow.

Download Full-text