arXiv subjects

Yao Chen

Publications and source records attributed to Yao Chen.

At least 199 records · Page 11Linked to original sources

arXiv2018

Two-sided-loop jets associated with magnetic reconnection between emerging loops and twisted filament threads

Coronal jets are always produced by magnetic reconnection between emerging flux and pre-existing overlying magnetic fields. When the overlying field is vertical/obilique or horizontal, the coronal jet will appear as anemone type or two-sided-loop type. Most of observational jets are of the anemone type, and only a few of two-sided-loop jets have been reported. Using the high-quality data from New Vacuum Solar Telescope, Interface Region Imaging Spectrograph, and Solar Dynamics Observatory, we present an example of two-sided-loop jets simultaneously observed in the chromosphere, transition region, and corona. The continuous emergence of magnetic flux brought in successively emerging of coronal loops and the slowly rising of an overlying horizontal filament threads. Sequentially, there appeared the deformation of the loops, the plasmoids ejection from the loop top, and pairs of loop brightenings and jet moving along the untwisting filament threads. All the observational results indicate there exist magnetic reconnection between the emerging loops and overlying horizontal filament threads, and it is the first example of two-sided-loop jets associated with ejected plasmoids and twisted overlying fields.

astro-ph.SR↗

arXiv2018

Formation of Large Scale Coronal Loops Interconnecting Two Active Regions Through Gradual Magnetic Reconnection and Associated Heating Process

Coronal loops interconnecting two active regions, called as interconnecting loops (ILs), are prominent large-scale structures in the solar atmosphere. They carry a significant amount of magnetic flux, therefore are considered to be an important element of the solar dynamo process. Earlier observations show that eruptions of ILs are an important source of CMEs. It is generally believed that ILs are formed through magnetic reconnection in the high corona (>150-200"), and several scenarios have been proposed to explain their brightening in soft X-rays (SXRs). Yet, the detailed IL formation process has not been fully explored and the associated energy release in the corona still remains unresolved. Here we report the complete formation process of a set of ILs connecting two nearby active regions, with successive observations by STEREO-A on the far side of the Sun and SDO and Hinode on the Earth side. We conclude that ILs are formed by gradual reconnection high in the corona, in line with earlier postulations. In addition, we show evidence supporting that ILs become brightened in SXRs and EUVs through heating at or close to the reconnection site in the corona (i.e., through direct heating process of reconnection), a process that has been largely overlooked in earlier studies on ILs

astro-ph.SR↗

arXiv2018

Random Asynchronous Iterations in Distributed Coordination Algorithms

Distributed coordination algorithms (DCA) carry out information processing processes among a group of networked agents without centralized information fusion. Though it is well known that DCA characterized by an SIA (stochastic, indecomposable, aperiodic) matrix generate consensus asymptotically via synchronous iterations, the dynamics of DCA with asynchronous iterations have not been studied extensively, especially when viewed as stochastic processes. This paper aims to show that for any given irreducible stochastic matrix, even non-SIA, the corresponding DCA lead to consensus successfully via random asynchronous iterations under a wide range of conditions on the transition probability. Particularly, the transition probability is neither required to be independent and identically distributed, nor characterized by a Markov chain.

math.OC↗

arXiv2018

An extreme ultraviolet wave generating upward secondary waves in a streamer-like solar structure

Extreme ultraviolet (EUV) waves, spectacular horizontally propagating disturbances in the low solar corona, always trigger horizontal secondary waves (SWs) when they encounter ambient coronal structure. We present a first example of upward SWs in a streamer-like structure after the passing of an EUV wave. The event occurred on 2017 June 1. The EUV wave happened during a typical solar eruption including a filament eruption, a CME, a C6.6 flare. The EUV wave was associated with quasi-periodic fast propagating (QFP) wave trains and a type II radio burst that represented the existence of a coronal shock. The EUV wave had a fast initial velocity of $\sim$1000 km s$^{-1}$, comparable to high speeds of the shock and the QFP wave trains. Intriguingly, upward SWs rose slowly ($\sim$80 km s$^{-1}$) in the streamer-like structure after the sweeping of the EUV wave. The upward SWs seemed to originate from limb brightenings that were caused by the EUV wave. All the results show the EUV wave is a fast-mode magnetohydrodynamic shock wave, likely triggered by the flare impulses. We suggest that part of the EUV wave was probably trapped in the closed magnetic fields of streamer-like structure, and upward SWs possibly resulted from the release of trapped waves in the form of slow-mode. It is believed that an interplay of the strong compression of the coronal shock and the configuration of the streamer-like structure is crucial for the formation of upward SWs.

astro-ph.SR↗

arXiv2018

New Experimental Limits on Exotic Spin-Spin-Velocity-Dependent Interactions By Using SmCo$_5$ Spin Sources

We report the latest results of searching for possible new macro-scale spin-spin-velocity-dependent forces (SSVDFs) based on specially designed iron-shielded SmCo$_5$ (ISSC) spin sources and a spin exchange relaxation free (SERF) co-magnetometer. The ISSCs have high net electron spin densities of about $1.7\times 10^{21}$ cm$^{-3}$, which mean high detecting sensitivity; and low magnetic field leakage of about $\sim$mG level due to iron shielding, which means low detecting noise. With help from the ISSCs, the high sensitivity SERF co-magnetometer, and the similarity analysis method, new constraints on SSVDFs with forms of $V_{6+7}$, $V_8$, $V_{15}$, and $V_{16}$ have been obtained, which represent the tightest limits in force range of 5 cm -- 1 km to the best of our knowledge.

hep-ex↗

arXiv2018

Harmonics of Solar Radio Spikes at Metric Wavelengths

This paper presents the latest observations from the newly-built solar radio spectrograph at the \emph{Chashan Solar Observatory}. On July 18 2016, the spectrograph records a solar spike burst event, which has several episodes showing harmonic structures, with the second, third, and fourth harmonics. The lower harmonic radio spike emissions are observed later than the higher harmonic bands, and the temporal delay of the second (third) harmonic relative to the fourth harmonic is about 30\ --\ 40 (10) ms. Based on the electron cyclotron maser emission mechanism, we analyze possible causes of the temporal delay and further infer relevant coronal parameters, such as the magnetic field strength and the electron density at the radio source.

astro-ph.SR↗

arXiv2018

Resonant behavior of the generalized Langevin system with tempered Mittag-Leffler memory kernel

The generalized Langevin equation describes anomalous dynamics. Noise is not only the origin of uncertainty but also plays a positive role in helping to detect signal with information, termed stochastic resonance (SR). This paper analyzes the anomalous resonant behaviors of the generalized Langevin system with a multiplicative dichotomous noise and an internal tempered Mittag-Leffler noise. For the system with fluctuating harmonic potential, we obtain the exact expressions of several SR, such as, the first moment, the amplitude and the autocorrelation function for the output signal as well as the signal-noise ratio. We analyze the influence of the tempering parameter and memory exponent on the bona fide SR and the general SR. Moreover, it is detected that the critical memory exponent changes regularly with the increase of tempering parameter. Almost all the theoretical results are validated by numerical simulations.

cond-mat.stat-mech↗

arXiv2018

Two-stage energy release process of a confined flare with double HXR peaks

A complete understanding of the onset and subsequent evolution of confined flares has not been achieved. Earlier studies mainly analyzed disk events so as to reveal their magnetic topology and cause of confinement. In this study, taking advantage of a tandem of instruments working at different wavelengths of X-rays, EUVs, and microwaves, we present dynamic details of a confined flare observed on the northwestern limb of the solar disk on July 24th, 2016. The entire dynamic evolutionary process starting from its onset is consistent with a loop-loop interaction scenario. The X-ray profiles manifest an intriguing double-peak feature. From spectral fitting, it is found that the first peak is non-thermally dominated while the second peak is mostly multi-thermal with a hot (~10 MK) and a super-hot (~30 MK) component. This double-peak feature is unique in that the two peaks are clearly separated by 4 minutes, and the second peak reaches up to 25-50 keV; in addition, at energy bands above 3 keV the X-ray fluxes decline significantly between the two peaks. This, together with other available imaging and spectral data, manifest a two-stage energy release process. A comprehensive analysis is carried out to investigate the nature of this two-stage process. We conclude that the second stage with the hot and super-hot sources mainly involves direct heating through loop-loop reconnection at a relatively high altitude in the corona. The uniqueness of the event characteristics and complete data set make the study a nice addition to present literature on solar flares.

astro-ph.SR↗

arXiv2018

Magnetic braids in eruptions of a spiral structure in the solar atmosphere

We report on high-resolution imaging and spectral observations of eruptions of a spiral structure in the transition region, which were taken with the Interface Region Imaging Spectrometer (IRIS), the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI). The eruption coincided with the appearance of two series of jets, with velocities comparable to the Alfvén speeds in their footpoints. Several pieces of evidence of magnetic braiding in the eruption are revealed, including localized bright knots, multiple well-separated jet threads, transition region explosive events and the fact that all these three are falling into the same locations within the eruptive structures. Through analysis of the extrapolated three-dimensional magnetic field in the region, we found that the eruptive spiral structure corresponded well to locations of twisted magnetic flux tubes with varying curl values along their lengths. The eruption occurred where strong parallel currents, high squashing factors, and large twist numbers were obtained. The electron number density of the eruptive structure is found to be $\sim3\times10^{12}$ cm$^{-3}$, indicating that significant amount of mass could be pumped into the corona by the jets. Following the eruption, the extrapolations revealed a set of seemingly relaxed loops, which were visible in the AIA 94 Å channel indicating temperatures of around 6.3 MK. With these observations, we suggest that magnetic braiding could be part of the mechanisms explaining the formation of solar eruption and the mass and energy supplement to the corona.

astro-ph.SR↗

arXiv2017

The acceleration of high-energy protons at coronal shocks: the effect of large-scale streamer-like magnetic field structures

Recent observations have shown that coronal shocks driven by coronal mass ejections can develop and accelerate particles within several solar radii in large solar energetic particle (SEP) events. Motivated by this, we present an SEP acceleration study including the process that a fast shock propagates through a streamer-like magnetic field with both closed and open field lines in the low corona region. The acceleration of protons is modeled by numerically solving the Parker transport equation with spatial diffusion both along and across the magnetic field. We show that particles can be sufficiently accelerated to up to several hundred MeV within 2-3 solar radii. When the shock propagates through a streamer-like magnetic field, particles are more efficiently accelerated compared to the case with a simple radial magnetic field, mainly due to perpendicular shock geometry and the natural trapping effect of closed magnetic fields. Our results suggest that the coronal magnetic field configuration is an important factor for producing large SEP events. We further show that the coronal magnetic field configuration strongly influences the distribution of energetic particles, leading to different locations of source regions along the shock front where most of high energy particles are concentrated. This work may have strong implications to SEP observations. The upcoming Parker Solar Probe will provide in situ observations for the distribution of energetic particles in the coronal shock region, and test the results of the study.

astro-ph.SR↗

arXiv2017

Frequency responses of the K-Rb-$^{21}$Ne co-magnetometer

The frequency responses of the K-Rb-$^{21}$Ne co-magnetometer to magnetic field and exotic spin dependent forces are experimentally studied and simulated in this paper. Both the relationship between the output amplitude, the phase shift and frequencies are studied. The responses of magnetic field are experimentally investigated. Due to a lack of input methods, others are numerically simulated.

physics.atom-ph↗

arXiv2017

A Solar Radio Dynamic Spectrograph with Flexible Temporal-spectral Resolution

The observation and research of the solar radio emission have unique scientific values in solar and space physics and related space weather forecasting applications, since the observed spectral structures may carry important information about energetic electrons and underlying physical mechanisms. In this study, we present the design of a novel dynamic spectrograph that is installed at the Chashan solar radio station operated by Laboratory for Radio Technologies, Institute of Space Sciences at Shandong University. The spectrograph is characterized by the real-time storage of digitized radio intensity data in the time domain and its capability to perform off-line spectral analysis of the radio spectra. The analog signals received via antennas and amplified with a low-noise amplifier are converted into digital data at a speed reaching up to 32 k data points per millisecond. The digital data are then saved into a high-speed electronic disk for further off-line spectral analysis. Using different word length (1 k - 32 k) and time cadence (5 ms - 10 s) for the off-line fast Fourier transform analysis, we can obtain the dynamic spectrum of a radio burst with different (user-defined) temporal (5 ms - 10 s) and spectral (3 kHz ~ 320 kHz) resolution. This brings a great flexibility and convenience to data analysis of solar radio bursts, especially when some specific fine spectral structures are under study.

astro-ph.IM↗

arXiv2017

Modeling Transport of Energetic Particles in Corotating Interaction Region -- A case Study

We investigate energetic particle transport in Corotating Interaction Regions (CIRs) through a case study. The CIR event we study occurred on $2008$ February $08$ and was observed by both the Advanced Composition Explorer (ACE) and the twin Solar TErrestrial RElations Observatory (STEREO)-B spacecraft. An in-situ reverse shock was observed by STEREO-B ($1.0$ AU) but not ACE ($0.98$ AU). Using STEREO-B observations and assuming the CIR structure does not vary significantly in the corotating frame, we estimate the shock location at later times for both the STEREO-B and ACE observations. Further assuming the accelerated particle spectral shape at the shock does not vary with shock location, we calculate the particle differential intensities as observed by ACE and STEREO-B at two different times by solving the focused transport equation using a Monte-Carlo simulation. We assume that particles move along Parker's field and experience no cross-field diffusion. We find that the modulation of sub-MeV/nucleon particles is significant. To obtain reasonable comparisons between the simulations and the observations by both ACE and STEREO-B, one has to assume that the CIR shock can accelerate more particles at a larger heliocentric distance than at a smaller heliocentric distance.

physics.space-ph↗

arXiv2017

Double Coronal X-ray and Microwave Sources Associated With A Magnetic Breakout Solar Eruption

Double coronal hard X-ray (HXR) sources are believed to be critical observational evidence of bi-directional energy release through magnetic reconnection in a large-scale current sheet in solar ares. Here we present a study on double coronal sources observed in both HXR and microwave regimes, revealing new characteristics distinct from earlier reports. This event is associated with a footpoint-occulted X1.3-class flare (25 April 2014, starting at 00:17 UT) and a coronal mass ejection that are likely triggered by the magnetic breakout process, with the lower source extending upward from the top of the partially-occulted flare loops and the upper source co-incident with rapidly squeezing-in side lobes (at a speed of ~250 km/s on both sides). The upper source can be identified at energies as high as 70-100 keV. The X-ray upper source is characterized by flux curves different from the lower source, a weak energy dependence of projected centroid altitude above 20 keV, a shorter duration and a HXR photon spectrum slightly-harder than those of the lower source. In addition, the microwave emission at 34 GHz also exhibits a similar double source structure and the microwave spectra at both sources are in line with gyro-synchrotron emission given by non- thermal energetic electrons. These observations, especially the co-incidence of the very-fast squeezing-in motion of side lobes and the upper source, indicate that the upper source is associated with (possibly caused by) this fast motion of arcades. This sheds new lights on the origin of the corona double-source structure observed in both HXRs and microwaves.

astro-ph.SR↗

arXiv2017

EUV and Magnetic Activities Associated with Type-I Solar Radio Bursts

Type-I bursts (i.e. noise storms) are the earliest-known type of solar radio emission at the metre wavelength. They are believed to be excited by non-thermal energetic electrons accelerated in the corona. The underlying dynamic process and exact emission mechanism still remain unresolved. Here, with a combined analysis of extreme ultraviolet (EUV), radio and photospheric magnetic field data of unprecedented quality recorded during a type-I storm on 30 July 2011, we identify a good correlation between the radio bursts and the co-spatial EUV and magnetic activities. The EUV activities manifest themselves as three major brightening stripes above a region adjacent to a compact sunspot, while the magnetic field there presents multiple moving magnetic features (MMFs) with persistent coalescence or cancelation and a morphologically similar three-part distribution. We find that the type-I intensities are correlated with those of the EUV emissions at various wavelengths with a correlation coefficient of 0.7-0.8. In addition, in the region between the brightening EUV stripes and the radio sources there appear consistent dynamic motions with a series of bi-directional flows, suggesting ongoing small-scale reconnection there. Mainly based on the induced connection between the magnetic motion at the photosphere and the EUV and radio activities in the corona, we suggest that the observed type-I noise storms and the EUV brightening activities are the consequence of small-scale magnetic reconnection driven by MMFs. This is in support of the original proposal made by Bentely et al. (Solar Phys. 193, 227, 2000).

astro-ph.SR↗

arXiv2017

Localization and ballistic diffusion for the tempered fractional Brownian-Langevin motion

This paper further discusses the tempered fractional Brownian motion, its ergodicity, and the derivation of the corresponding Fokker-Planck equation. Then we introduce the generalized Langevin equation with the tempered fractional Gaussian noise for a free particle, called tempered fractional Langevin equation (tfLe). While the tempered fractional Brownian motion displays localization diffusion for the long time limit and for the short time its mean squared displacement has the asymptotic form $t^{2H}$, we show that the asymptotic form of the mean squared displacement of the tfLe transits from $t^2$ (ballistic diffusion for short time) to $t^{2-2H}$, and then to $t^2$ (again ballistic diffusion for long time). On the other hand, the overdamped tfLe has the transition of the diffusion type from $t^{2-2H}$ to $t^2$ (ballistic diffusion). The tfLe with harmonic potential is also considered.

cond-mat.stat-mech↗

arXiv2017

Interchange reconnection associated with a confined filament eruption: Implications for the source of transient cold-dense plasma in solar winds

The cold-dense plasma is occasionally detected in the solar wind with in situ data, but the source of the cold-dense plasma remains illusive. Interchange reconnections (IRs) between closed fields and nearby open fields are well known to contribute to the formation of solar winds. We present a confined filament eruption associated with a puff-like coronal mass ejection (CME) on 2014 December 24. The filament underwent successive activations and finally erupted, due to continuous magnetic flux cancellations and emergences. The confined erupting filament showed a clear untwist motion, and most of the filament material fell back. During the eruption, some tiny blobs escaped from the confined filament body, along newly-formed open field lines rooted around the south end of the filament, and some bright plasma flowed from the north end of the filament to remote sites at nearby open fields. The newly-formed open field lines shifted southward with multiple branches. The puff-like CME also showed multiple bright fronts and a clear southward shift. All the results indicate an intermittent IR existed between closed fields of the confined erupting filament and nearby open fields, which released a portion of filament material (blobs) to form the puff-like CME. We suggest that the IR provides a possible source of cold-dense plasma in the solar wind.

astro-ph.SR↗

arXiv2017

The Origin of Solar Filament Plasma Inferred from in situ Observations of Elemental Abundances

Solar filaments/prominences are one of the most common features in the corona, which may lead to energetic coronal mass ejections (CMEs) and flares when they erupt. Filaments are about one hundred times cooler and denser than the coronal material, and physical understanding of their material origin remains controversial. Two types of scenarios have been proposed: one argues that the filament plasma is brought into the corona from photosphere or chromosphere through a siphon or evaporation/injection process, while the other suggests that the material condenses from the surrounding coronal plasma due to thermal instability. The elemental abundance analysis is a reasonable clue to constrain the models, as the siphon or evaporation/injection model would predict that the filament material abundances are close to the photospheric or chromospheric ones, while the condensation model should have coronal abundances. In this letter, we analyze the elemental abundances of a magnetic cloud that contains the ejected filament material. The corresponding filament eruption occurred on 1998 April 29, accompanying an M6.8 class soft X-ray flare located at the heliographic coordinates S18E20 (NOAA 08210) and a fast halo CME with the linear velocity of 1374 km s$^{-1}$ near the Sun. We find that the abundance ratios of elements with low and high First Ionization Potential such as Fe/O, Mg/O, and Si/O are 0.150, 0.050, and 0.070, respectively, approaching their corresponding photospheric values 0.065, 0.081, and 0.066, which does not support the coronal origin of the filament plasma.

astro-ph.SR↗