Coherent structures and spectral shapes of kinetic Alfvén wave turbulence in solar wind at 1 AU

This paper presents the generation of kinetic Alfv én wave(KAW) coherent structures of magnetic filaments applicable to solar wind at 1 AU, when the background plasma density is modified by parallel ponderomotive force and Joule heating. The inhomogeneity in the magnetic field, which was included as a perturbation in the transverse direction of the magnetic field, takes energy from the main pump KAWs and generates the filamentary structures. When the intensity is high enough, the filaments are broken down and the energy initially confined to low wavenumbers is redistributed to higher wavenumbers, leading to cascades of energy at small scales less than the ion acoustic gyroradius or comparable to electron gyroradius.The magnetic field spectral profile is generated from the numerical simulation results, and its dependence on different directions of the wavevector and initial conditions of the simulation representing the transverse magnetic field inhomogeneity is studied. The relevance of these results with other spacecraft observations and measurements is also pointed out.     

Resonant Heating of Ions by Parallel Propagating Alfvén Waves in Solar Coronal Holes

Resonant heating of H, O+5, and Mg+9 by parallel propagating ion cyclotron Alfven waves in solar coronal holes at a heliocentric distance is studied using the heating rate derived from the quasilinear theory. It is shown that the particle-AlfVen-wave interaction is a significant microscopic process. The temperatures of the ions are rapidly increased up to the observed order in only microseconds, which implies that simply inserting the quasilinear heating rate into the fluid/MHD energy equation to calculate the radial dependence of ion temperatures may cause errors as the time scales do not match. Different species ions are heated by Alfven waves with a power law spectrum in approximately a mass order. To heat O+5 over Mg+9 as measured by the Ultraviolet Coronagraph Spectrometer (UVCS) in the solar coronal hole at a region ≥1.9.R, the energy density of Alfven waves with a frequency close to the O+5-cyclotron frequency must be at least double of that at the Mg+9-cyclotron frequency. With an appropriate wa     

Observations of counter-propagating Alfvénic and compressive fluctuations in the chromosphere

Recent observations have found that chromospheric spicules behave like Alfv′enic fluctuations.Low-frequency Alfv′en waves are predicted to partially reflect in the transition region that has a gradient in the Alfv′en speed,thereby producing inward Alfv′en waves,which may interact nonlinearly with outward Alfv′en waves to generate Alfv′enic turbulence.However,the signature of Alfv′enic turbulence in the chromosphere has not yet been quantitatively analyzed with observations.Here we analyze some characteristics related to Alfv′enic turbulence with the observations from Hinode/SOT.We decompose the height-time diagram of the transverse oscillations to separate the outward and inward propagating Alfv′enic-like signals.The counterpropagating waves are found to have similar amplitude,period and phase speed,suggesting a state having an approximate balance in bi-directional energy fluxes.Counterpropagation of intensity oscillation with lower propagation speed is also presented,probably indicating the presence of slow mode waves.Moreover,we attempt to estimate the Els¨asser spectra of the chromospheric turbulence for the first time.The relative fluctuations in the magnetic field may be measured as the local slope of wave-like shapes in spicules.The resulting low-frequency Els¨asser power spectra look similar to each other without showing a dominant population,which confirms these counterpropagating low-frequency Alfv′enic waves are in a state of balanced flux.These observational results are believed to help us better understand the nature of chromospheric turbulence as well as chromospheric heating.     

Numerical simulations of three-dimensional magnetic swirls in a solar flux-tube

We aim to numerically study evolution of Alfv′en waves that accompany short-lasting swirl events in a solar magnetic flux-tube that can be a simple model of a magnetic pore or a sunspot. With the use of the FLASH code we numerically solve three-dimensional ideal magnetohydrodynamic equations to simulate twists which are implemented at the top of the photosphere in magnetic field lines of the flux-tube. Our numerical results exhibit swirl events and Alfv′en waves with associated clockwise and counterclockwise rotation of magnetic lines, with the largest values of vorticity at the bottom of the chromosphere, and a certain amount of energy flux.     

Long-term transit timing monitoring and homogenous study of WASP-32

We report new photometric observations of the transiting exoplanetary system WASP-32 made by using CCD cameras at Yunnan Observatories and Ho Koon Nature Education cum Astronomical Centre, China from 2010 to 2012. Following our usual procedure, the observed data are corrected for systematic errors according to the coarse decorrelation and SYSREM algorithms so as to enhance the signal of the transit events. Combined with radial velocity data presented in the literature, our newly observed data and earlier photometric data in the literature are simultaneously analyzed to derive the physical parameters describing the system by employing the Markov chain Monte Carlo technique. The derived parameters are consistent with the result published in the original paper about WASP-32b, but the uncertainties of the new parameters are smaller than those in the original paper. Moreover, our modeling result supports a circular orbit for WASP-32b. Through the analysis of all available mid-transit times, we have refined the orbital period of WASP-32b; no evident transit timing variation is found in these transit events.     

Damped large amplitude oscillations in a solar prominence and a bundle of coronal loops

We investigate the evolutions of two prominences(P1, P2) and two bundles of coronal loops(L1, L2), observed with SDO/AIA near the east solar limb on 2012 September 22. It is found that there were large-amplitude oscillations in P1 and L1 but no detectable motions in P2 and L2. These transverse oscillations were triggered by a large-scale coronal wave, originating from a large flare in a remote active region behind the solar limb. By carefully comparing the locations and heights of these oscillating and non-oscillating structures, we conclude that the propagating height of the wave is between 50 Mm and130 Mm. The wave energy deposited in the oscillating prominence and coronal loops is at least of the order of 10~(28) erg. Furthermore, local magnetic field strength and Alfv ′en speeds are derived from the oscillating periods and damping time scales, which are extracted from the time series of the oscillations. It is demonstrated that oscillations can be used in not only coronal seismology, but also to reveal the properties of the wave.     

Observational constraints on the early dark energy model

Dark energy can be studied by its influence on the expansion of the Universe.We investigate current constraints on early dark energy(EDE) achievable by the combined observational data from type Ia supernovae(557),baryon acoustic oscillations,the current cosmic microwave background and the observed Hubble pa-rameter.We find that combining these data sets provides powerful constraints on early dark energy and the best fit values of the parameters in 68% and 95% confidence-level regions are:Ωm0=0.2897 +0.0149+...     

Pulsar timing residuals due to individual non-evolving gravitational wave sources

The pulsar timing residuals induced by gravitational waves from non- evolving single binary sources are affected by many parameters related to the relative positions of the pulsar and the gravitational wave sources. We will analyze the various effects due to different parameters. The standard deviations of the timing residuals will be calculated with a variable parameter fixing a set of other parameters. The or- bits of the binary sources will be generally assumed to be elliptical. The influences of different eccentricities on the pulsar timing residuals will also be studied in detail. We find that the effects of the related parameters are quite different, and some of them display certain regularities.     

Kinetic Alfven Waves in Aurora

On the basis of the differences between ideal MHD Alfven waves and kinetic Alfven waves,the nonlinear kinetic Alfven wave with Poison equation correction and the evolution of kinetic wave have been presented.These results have been used to explain the observation data from Freja satellite and CRITⅡ rocket in aurora.     

Modeling the 2017 September 10 solar energetic particle event using the iPATH model

On 2017 September 10, a fast coronal mass ejection(CME) erupted from the active region(AR)12673, leading to a ground level enhancement(GLE) event at Earth. Using the 2D improved Particle Acceleration and Transport in the Heliosphere(iPATH) model, we model the large solar energetic particle(SEP) event of 2017 September 10 observed at Earth, Mars and STEREO-A. Based on observational evidence, we assume that the CME-driven shock experienced a large lateral expansion shortly after the eruption, which is modeled by a double Gaussian velocity profile in this simulation. We apply the in-situ shock arrival times and the observed CME speeds at multiple spacecraft near Earth and Mars as constraints to adjust the input model parameters. The modeled time intensity profiles and fluence for energetic protons are then compared with observations. Reasonable agreements with observations at Mars and STEREO-A are found. The simulated results at Earth differ from observations of GOES-15. However, the simulated results at a heliocentric longitude 20° west to Earth fit reasonably well with the GOES observation. This can be explained if the pre-event solar wind magnetic field at Earth is not described by a nominal Parker field.Our results suggest that a large lateral expansion of the CME-driven shock and a distorted interplanetary magnetic field due to previous events can be important in understanding this GLE event.     

Three Super Active Regions in the Descending Phase of Solar Cycle 23

We analyze the magnetic configurations of three super active regions, NOAA 10484, 10486 and 10488, observed by the Huairou Multi-Channel Solar Telescope (MCST) from 2003 October 18 to November 4. Many energetic phenomena, such as flares (including a X-28 flare) and coronal mass ejections (CMEs), occurred during this period. We think that strong shear and fast emergence of magnetic flux are the main causes of these events. The question is also of great interest why these dramatic eruptions occurred so close together in the descending phase of the solar cycle.     

Proton and He^2＋ Temperature Anisotropies in the Solar Wind Driven by Ion Cyclotron Waves

We carried out one-dimensional hybrid simulations of resonant scattering of protons and He^2 ions by ion cyclotron waves in an initially homogeneous, collisionless and magnetized plasma. The initial ion cyclotron waves have a power spectrum and propagate both outward and inward. Due to the resonant interaction with the protons and He^2 ions, the wave power will be depleted in the resonance region. Both the protons and He^2 ions can be resonantly heated in the direction perpendicular to the ambient magnetic field and leading to anisotropic velocity distributions, with the anisotropy higher for the He^2 ions than for the protons. At the same time, the anisotropies of the protons and He^2 ions are inversely correlated with the plasma β‖p=8πnpkBT‖p/B0^2, consistent with the prediction of the quasilinear theory (QLT).     

Solar Impulsive Hard X-Ray Emission and Two-Stage Electron Acceleration

Heating and acceleration of electrons in solar impulsive hard X-ray (HXR) flares are studied according to the two-stage acceleration model developed by Zhang for solar 3He-rich events. It is shown that electrostatic H-cyclotron waves can be excited at a parallel phase velocity less than about the electron thermal velocity and thus can significantly heat the electrons (up to 40 MK) through Landau resonance. The preheated electrons with velocities above a threshold are further accelerated to high energies in the flare-acceleration process. The flare-produced electron spectrum is obtained and shown to be thermal at low energies and power law at high energies. In the non-thermal energy range, the spectrum can be double power law if the spectral power index is energy dependent or related. The electron energy spectrum obtained by this study agrees quantitatively with the result derived from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) HXR observations in the flare of 2002 July 23. The total flux and energy flux of electrons accelerated in the solar flare also agree with the measurements.     

An Impulsive Heating Model for the Evolution of Coronal Loops

It was suggested by Parker that the solar corona is heated by many small energy release events generally called microflares or nanoflares. More and more observations showed flows and intensity variations in nonflaring loops. Both theories and observations have indicated that the heating of coronal loops should actually be unsteady. Using SOLFTM (Solar Flux Tube Model), we investigate the hydrodynamics of coronal loops undergoing different manners of impulsive heating with the same total energy deposition. The half length of the loops is 110 Mm, a typical length of active region loops. We divide the loops into two categories: loops that experience catastrophic cooling and loops that do not. It is found that when the nanoflare heating sources are in the coronal part, the loops are in non-catastrophic-cooling state and their evolutions are similar. When the heating is localized below the transition region, the loops evolve in quite different ways. It is shown that with increasing number of heating pulses and inter-pulse time, the catastrophic cooling is weakened, delayed, or even disappears altogether.     

On the line profile changes observed during the X2.2 class flare in the active region NOAA 11158

The solar active region NOAA 11158 produced a series of flares during its passage through the solar disk.The first major flare(of class X2.2) of the current solar cycle occurred in this active region on 2011 February 15 around 01:50 UT.We have analyzed the Dopplergrams and magnetograms obtained by the Helioseismic and Magnetic Imager(HMI) instrument onboard Solar Dynamics Observatory to examine the photospheric velocity and magnetic field changes associated with this flare.The HMI instrument provides high-quality Doppler and magnetic maps of the solar disk with 0.5 spatial scale at a cadence of 45 s along with imaging spectroscopy.We have identified five locations of velocity transients in the active region during the flare.These transient velocity signals are located in and around the flare ribbons as observed by Hinode in the Ca II H wavelength and the footpoints of hard X-ray enhancement are in the energy range 12–25 keV from RHESSI.The changes in shape and width of two circular polarization states have been observed at the time of transients in three out of five locations.Forward modeling of the line profiles shows that the change in atmospheric parameters such as magnetic field strength,Doppler velocity and source function could explain the observed changes in the line profiles with respect to the pre-flare condition.     

Flare evolution and polarization changes in fine structures of solar radio emission in the 2013 April 11 event

The measurement of positions and sizes of radio sources in observations is important for understanding of the flare evolution. For the first time, solar radio spectral fine structures in an M6.5 flare that occurred on 2013 April 11 were observed simultaneously by several radio instruments at four different observatories: Chinese Solar Broadband Radio Spectrometer at Huairou(SBRS/Huairou), Ondˇrejov Radio Spectrograph in the Czech Republic(ORSC/Ondˇrejov), Badary Broadband Microwave Spectropolarimeter(BMS/Irkutsk), and spectrograph/IZMIRAN(Moscow, Troitsk). The fine structures included microwave zebra patterns(ZPs), fast pulsations and fiber bursts. They were observed during the flare brightening located at the tops of a loop arcade as shown in images taken by the extreme ultraviolet(EUV) telescope onboard NASA's satellite Solar Dynamics Observatory(SDO). The flare occurred at 06:58–07:26 UT in solar active region NOAA 11719 located close to the solar disk center. ZPs appeared near high frequency boundaries of the pulsations, and their spectra observed in Huairou and Ondˇrejov agreed with each other in terms of details. At the beginning of the flare's impulsive phase, a strong narrowband ZP burst occurred with a moderate left-handed circular polarization. Then a series of pulsations and ZPs were observed in almost unpolarized emission. After 07:00 UT a ZP appeared with a moderate right-handed polarization.In the flare decay phase(at about 07:25 UT), ZPs and fiber bursts become strongly right-hand polarized.BMS/Irkutsk spectral observations indicated that the background emission showed a left-handed circular polarization(similar to SBRS/Huairou spectra around 3 GHz). However, the fine structure appeared in the right-handed polarization. The dynamics of the polarization was associated with the motion of the flare exciter, which was observed in EUV images at 171 ?A and 131 ?A by the SDO Atmospheric Imaging Assembly(AIA). Combining magnetograms observed by the SDO Helioseismic and Magnetic Imager(HMI) with the homologous assumption of EUV flare brightenings and ZP bursts, we deduced that the observed ZPs correspond to the ordinary radio emission mode. However, future analysis needs to verify the assumption that zebra radio sources are really related to a closed magnetic loop, and are located at lower heights in the solar atmosphere than the source of pulsations.     

The Energetics of White-light Flares Observed by SDO/HMI and RHESSI

White-light(WL) flares have been observed and studied for more than a century since their first discovery. However, some fundamental physics behind the brilliant emission remains highly controversial.One of the important facts in addressing the flare energetics is the spatio-temporal correlation between the WL emission and the hard X-ray(HXR) radiation, presumably suggesting that energetic electrons are the energy sources. In this study, we present a statistical analysis of 25 strong flares(≥M5) observed simultaneously by the Helioseismic and Magnetic Imager(HMI), on board the Solar Dynamics Observatory(SDO),and the Reuven Ramaty High Energy Solar Spectroscopic Imager(RHESSI). Among these events, WL emission was detected by SDO/HMI in 13 flares, associated with HXR emission. To quantitatively describe the strength of WL emission, equivalent area(EA) is defined as the integrated contrast enhancement over the entire flaring area. Our results show that the EA is inversely proportional to the HXR power-law index,indicating that stronger WL emission tends to be associated with a larger population of high energy electrons. However, no obvious correlation is found between WL emission and flux of non-thermal electrons at50 ke V. For the other group of 13 flares without detectable WL emission, the HXR spectra are softer(larger power-law index) than those flares with WL emission, especially for the X-class flares in this group.     

The Modulations of the Electromagnetic Waves near 1/2ω_cH~ in Observations of Freja

In this paper the non-linear parametric resonance is proposed to understand the reason why the observed the electromagnetic ion cyclotron waves in the auroral energization region are usually concentrate in the range close to the half value of the proton gyrofrequency [Gustafsson et at.,1990].The electromagnetic ion cyclotron waves are supposed to exist already at ωcH ,then,the non-linear parametric resonane can predict the peak at 1/2ωc H The parametric resonance is saturated by the non-linear effects and a drift of the resonance frequency is also predicted from     

A coarse-to-fine strategy for the registration of the multi-wavelength high-resolution solar images

The registration of multi-wavelength high-resolution solar images is an important task in the research of solar physics. This paper proposed a coarse-to-fine strategy to realize the accurate registration of high-resolution photospheric images and chromospheric images observed by the New Vacuum Solar Telescope(NVST) whose field-of-view is about 2′～ 3′, and the spatial resolution can reach 0.1′′after image reconstruction. In this strategy, the full-disk solar images with relatively lower resolution taken by other space-or ground-based telescopes are taken as transition images, and the Fourier-Merlin transform,Template matching and a local statistical information based algorithm are used in combination. After registration, the geometric transformation between multi-wavelength images of NVST are corrected at the level of sub-arcseconds, including the rotation, scaling and translation relations. Two sets of data observed in active regions(i.e., the NOAA 11982 and the NOAA 12673) are used to illustrate our method step by step.The result shows that the registration accuracy can reach less than 1′′. Moreover, this work also has facilitated the combination of high-resolution observations of NVST with the continuum, ultraviolet passbands and magnetic field observations of the Solar Dynamic Observation(SDO), which is highly beneficial to the multi-instrument joint measurement of solar activities.     

Historical Evidence for the Birth of the Newly Discovered Pulsar PSR J1833-1034

Stimulated by the recent discovery of PSR J1833-1034 in SNR G21.5-0.9 and its age parameters presented by two groups of discovery, we demonstrate that the PSR J1833-1034 was born 2053 years ago from a supernova explosion, the BC 48 guest star observed in the Western Han (Early Han) Dynasty by ancient Chinese. Based on a detailed analysis of the Chinese ancient record of the BC 48 guest star and the new detected physical parameters of PSR J1833-1034, agreements on the visual position, age and distance between PSR J1833-1034 and the BC 48 guest star are obtained. The initial period P0 of PSR J1833-1034 is now derived from its historical and current observed data without any other extra assumption on P0 itself, except that the factor PP is a constant in its evolution until now.