Research Advances of Solar Corona and Interplanetary Physics in China: 2012–2014

Solar transients and their related interplanetary counterparts have severe effects on the space environments of the Earth. Therefore, the research of solar corona and interplanetary physics has become the focus of study for both solar and space scientists. Considerable progress has been achieved in these aspects by the solar and space physics community of China during 2012–2014, which will be given in this report. The brief report summarizes the research advances of solar corona and interplanetary physics into the following parts: solar wind origin and turbulence, coronal waves and seismology, solar eruptions, solar energetic particle and galactic cosmic ray, magnetic reconnection,Magnetohydrodynamic(MHD) models and their applications, waves and structures in solar wind,propagation of ICMEs/shocks and their arrival time predictions. These research achievements have been achieved by Chinese solar and space scientists independently or via international collaborations.

Research Progress of Interplanetary Physics in China's Mainland

Significant progress has been made by Chinese scientists in research of interplanetary physics during the recent two years(2018–2020).These achievements are reflected at least in the following aspects:Activities in solar corona and lower solar atmosphere;solar wind and turbulence;filament/prominence,jets,flares,and radio bursts;active regions and solar eruptions;coronal mass ejections and their interplanetary counterparts;other interplanetary structures;space weather prediction methods;magnetic reconnection;Magnetohydrodynamic(MHD)numerical modeling;solar energetic particles,cosmic rays,and Forbush decreases;machine learning methods in space weather and other aspects.More than one hundred and forty papers in the academic journals have been published in these research directions.These fruitful achievements are obtained by Chinese scholars in solar physics and space physics either independently or through international collaborations.They greatly improve people’s understanding of solar activities,solar eruptions,the corresponding space weather effects,and the Sun-Earth relations.Here we will give a very brief review on the research progress.However,it must be pointed out that this paper may not completely cover all achievements in this field due to our limited knowledge.

A Brief Review of Interplanetary Physics Research Progress in China' Mainland during 2020-2022

Through independent research by the Chinese scientists or their international collaborations,great achievements have been made in interplanetary physics research in China' Mainland during the past two years(2020-2022).More than 150 papers have been published in academic journals in this field during this period.These achievements can be grouped into the following areas,at least:(i)solar corona;(ii)solar and interplanetary transient phenomena;(iii)radio bursts;(iv)Magnetohydrodynamic(MHD)numerical modeling;(v)solar energetic particles and cosmic rays.These advances have greatly enriched our understanding of interplanetary physics,i.e.our knowledge of solar activities and solar eruptions,their propagation in the interplanetary space,and the corresponding geoeffects on the Earth.In the sense of application,they have also improved the forecasting of space weather.In this paper we will give a very short review about these advances.

Preservation and variation of ion-to-electron temperature ratio in the plasma sheet in geo-magnetotail

The ion-to-electron temperature ratio is a good indicator of the processes involved in solar wind plasma entering and being transported inside Earth’s plasma sheet.In this study,we have demonstrated that patchy magnetic reconnection has the potential to preserve the ion-to-electron temperature ratio under certain conditions.If the charged particles are non-adiabatically accelerated no more than once in a single reconnection,the temperature ratio would be preserved;on the other hand,this ratio would not be preserved if they are accelerated multiple times.Consequently,under a northward interplanetary magnetic field(IMF)condition,the reconnection in the nonlinear phase of the Kelvin-Helmholtz instability is the dominant process for solar-originated plasma entering the Earth’s magnetosphere,and the ion-to-electron temperature ratio is preserved inside the plasma sheet.When the direction of the IMF is southward,the reflection of electrons from the magnetic mirror point,and subsequent multiple non-adiabatic accelerations at the reconnection site,are the primary reasons for the observed low ion-to-electron temperature ratio close to the Earth at midnight.While reconnections that occur in the night-side far tail might preserve the ratio,turbulence on the boundaries of the bursty bulk flows(BBFs)could change the ratio in the far tail through the violation of the frozen-in condition of the ions.The plateau in the contour of the calculated ion-to-electron temperature ratio in the down tail distance between 40 and 60 Earth radii may explain the strong correlation between the ion and electron temperatures in the outer central plasma sheet,which has not been clearly understood till date.

In situ evidence of resonant interactions between energetic electrons and whistler waves in magnetopause reconnection

In this paper,we analyze one reconnection event observed by the Magnetospheric Multiscale(MMS)mission at the earth’s magnetopause.In this event,the spacecraft crossed the reconnection current sheet from the magnetospheric side to the magnetosheath side,and whistler waves were observed on both the magnetospheric and magnetosheath sides.On the magnetospheric side,the whistler waves propagated quasi-parallel to the magnetic field and toward the X-line,while on the magnetosheath side they propagated almost anti-parallel to the magnetic field and away from the X-line.Associated with the enhancement of the whistler waves,we find that the fluxes of energetic electrons are concentrated around the pitch angle 90°when their energies are higher than the minimum energy that is necessary for the resonant interactions between the energetic electrons and whistler waves.This observation provides in situ observational evidence of resonant interactions between energetic electrons and whistler waves in the magnetic reconnection.

Spontaneous growth of the reconnection electric field during magnetic reconnection with a guide field:A theoretical model and particle-in-cell simulations

Reconnection electric field is a key element of magnetic reconnection.It quantifies the change of magnetic topology and the dissipation of magnetic energy.In this work,two-dimensional(2D)particle-in-cell(PIC)simulations are performed to study the growth of the reconnection electric field in the electron diffusion region(EDR)during magnetic reconnection with a guide field.At first,a seed electric field is produced due to the excitation of the tearing-mode instability.Then,the reconnection electric field in the EDR,which is dominated by the electron pressure tensor term,suffers a spontaneous growth stage and grows exponentially until it saturates.A theoretical model is also proposed to explain such a kind of growth.The reconnection electric field in the EDR is found to be directly proportional to the electron outflow speed.The time derivative of electron outflow speed is proportional to the reconnection electric field in the EDR because the outflow is formed after the inflow electrons are accelerated by the reconnection electric field in the EDR and then directed away along the outflow direction.This kind of reinforcing process at last leads to the exponential growth of the reconnection electric field in the EDR.

A comparison of MLT wind between meteor radar chain data and SDWACCM results

A meteor radar chain located along the 120°E meridian in the Northern Hemisphere from low to middle latitudes provides longterm horizontal wind observations of the mesosphere and lower thermosphere(MLT)region.In this study,we report a seasonal variation and its latitudinal feature in the horizontal mean wind in the MLT region observed by six meteor radar instruments located at Mohe(53.5°N,122.3°E),Beijing(40.3°N,116.2°E),Mengcheng(33.4°N,116.5°E),Wuhan(30.6°N,114.4°E),Kunming(25.6°N,108.3°E),and Fuke(19.5°N,109.1°E)stations.In addition,we compare the wind in the MLT region measured by the meteor radar stations with those simulated by the Whole Atmosphere Community Climate Model(WACCM).In general,the WACCM appears to capture well the seasonal and latitudinal variations in the zonal wind component.In particular,the temporal evolution of the eastward zonal wind maximum shifts from July to May as the latitude decreases.However,the simulated WACCM meridional wind exhibits differences from the meteor radar observations.

Spotless days and geomagnetic index as the predictors of solar cycle 25

We study the sunspot activity in relation to spotless days(SLDs)during the descending phase of solar cycles 11-24 to predict the amplitude of sunspot cycle 25.For this purpose,in addition to SLD,we also consider the geomagnetic activity(aa index)during the descending phase of a given cycle.A very strong correlation of the SLD(0.68)and aa index(0.86)during the descending phase of a given cycle with the maximum amplitude of next solar cycle has been estimated.The empirical relationship led us to deduce the amplitude of cycle 25 to be 99.13±14.97 and 104.23±17.35 using SLD and aa index,respectively as predictors.Both the predictors provide comparable amplitude for solar cycle 25 and reveal that solar cycle 25 will be weaker than cycle 24.Further,we predict that the maximum of cycle 25 is likely to occur between February and March 2024.While the aa index has been utilized extensively in the past,this work establishes SLDs as another potential candidate for predicting the characteristics of the next cycle.

A Brief Review of Interplanetary Investigations in China from 2014 to 2016

Great progress has been made in the research of solar corona and interplanetary physics by the Chinese scientists during the past two years(2014—2016).Nearly 100 papers were published in this area.In this report,we will give a brief review to these progresses.The investigations include:solar corona,solar wind and turbulence,superhalo electron and energetic particle in the inner heliosphere,solar flares and radio bursts,Coronal Mass Ejections(CMEs) and their interplanetary counterparts,Magnetohydrodynamic(MHD) numerical modeling,CME/shock arrival time prediction,magnetic reconnection,solar variability and its impact on climate.These achievements help us to better understand the evolution of solar activities,solar eruptions,their propagations in the heliosphere,and potential geoeffectiveness.They were achieved by the Chinese solar and space scientists independently or via international collaborations.

Interplanetary Physics in China's Mainland

During the past two years(2016–2018), great achievements have been made in the Chinese research of interplanetary physics, with nearly 100 papers published in the academic journals. The achievements are including but not limited to the following topics: solar corona; solar wind and turbulence; filament/prominence and jets; solar flare; radio bursts; particle acceleration at coronal shocks; magnetic flux ropes; instability;instrument; Coronal Mass Ejections(CMEs) and their interplanetary counterparts; Magnetohydrodynamic(MHD) numerical modeling; solar energetic particles and cosmic rays. The progress further improves our understanding of the eruptions of solar activities, their evolutions and propagations in the heliosphere, and final geoeffects on our Earth. These results were achieved by the Chinese solar and space scientists independently or via international collaborations. This paper will give a brief review of these achievements.

Propagation and Damping of Two-Fluid Magnetohydrodynamic Waves in Stratified Solar Atmosphere

An extreme ultra-violet（EUV） wave is characterized as a bright pulse that has emanated from the solar eruption source and can propagate globally in the solar corona. According to one leading theory, the EUV wave is a fast magnetoacoustic wave, as the coronal counterpart of the Moreton wave in the chromosphere. However, previous observations have shown that the EUV wave differs significantly from the Moreton wave in both velocity and lifetime. To reconcile these differences, here we analyze the wave characteristics of a two-fluid MHD model in the stratified solar atmosphere with a height-dependent ionization rate. It is found that the collision between neutral and ionized fluids is able to attenuate the wave amplitude, while causing a slight change in its propagation velocity. Because the chromosphere has the lower ionization rate and the stronger magnetic fields than the corona,the velocity of the Moreton wave is much higher than that of the EUV wave. In contrast to the Moreton waves damped strongly by the collision between neutral and ionized fluids, the EUV wave in the fully ionized corona is able to propagate globally on a time scale of several hours. Our results support the previous theory that fast magnetoacoustic waves account for both EUV and Moreteon waves in the different layers of the solar atmosphere.

Study of temporal and spectral characteristics of the X-ray emission from solar flares

Temporal and spectral characteristics of X-ray emission from 60 flares of intensity ≥C class observed by the Solar X-ray Spectrometer （SOXS） during 2003-2011 are presented. We analyze the X-ray emission observed in four and three energy bands by the Si and Cadmium-Zinc-Telluride （CZT） detectors, respectively. The number of peaks in the intensity profile of the flares varies between 1 and 3. We find moderate correlation （R ~=0.2） between the rise time and the peak flux of the first peak of the flare irrespective of energy band, which is indicative of its energy-independent nature. Moreover, the magnetic field complexity of the flaring region is found to be highly anti-correlated （R = 0.61） with the rise time of the flares while positively correlated （R = 0.28） with the peak flux of the flare. The time delay between the peak of the X-ray emission in a given energy band and that in 25-30keV decreases with increasing energy, suggesting conduction cooling is dominant in the lower energies. Analysis of 340 spectra from 14 flares reveals that the peak of differential emission measure （DEM） evolution is delayed by 60-360 s relative to that of the temperature, and this time delay is inversely proportional to the peak flux of the flare. We conclude that temporal and intensity characteristics of flares are dependent on energy as well as the magnetic field configuration of the active region.

Normal-Angle Dependence of the Interaction between Radiation Belt Electrons and Fast Magnetosonic Waves

Fast magnetosonic(MS)waves have been suggested to contribute significantly to radiation belt electron dynamics via Landau resonance and transit time scattering.The corresponding quasi-linear diffusion coefficients in pitch angle,energy and particularly cross-pitch-angle-energy are calculated from the gyro-averaged test-particle simulations.It is found that the cross diffusion coefficient is an effective indicator to differentiate between the contributions of resonant and non-resonant mechanisms.Furthermore,the dependence of diffusion coefficients on the normal angle of MS waves are parametrically investigated.Numerical results show that the increasing normal angle can lead to the shrinking of the Landau resonance region and the expansion of the transit-time scattering region.With the increasing normal angle,the pitch angle diffusion coefficients decrease significantly(by about two orders of magnitude),while the other two diffusion coefficients have a relatively limited decrease(within one order of magnitude).For arbitrary normal angles,the magnitude of cross diffusion coefficients is comparable to the other diffusion coefficients,suggesting that the cross diffusion is indispensable in the kinetic simulation works.

Integration of Electrical Resistivity and Electromagnetic Radiation Methods for Fracture Flow System Detection

An electrical resistivity and electromagnetic emission survey was carried out involving the use of vertical electrical soundings (VES) and natural pulse electromagnetic field of the earth (NPEMFE). The use of this new methodology managed to detect the fracture flow system rupture zones in the underground, also answered the questions about the deferent subsurface water bodies. The present study focuses on Marsaba-Feshcha sub-basin in the northeast of the Dead Sea. Due to the scarcity of boreholes in the study area, several geophysical methods were implanted. The combination of these two methods (VES and NPEMFE) with the field observations and East-West transversal faults with the coordination (624437/242888) was determined, cutting through the anticlines with their mainly impervious cores with fracture length of >400 m. These transversal faults saddle inside Nabi Musa syncline (Boqea syncline), leading to a hydraulic connection between the Lower and the Upper Aquifer. Due to the identified transversal fault, the water of the Upper and Lower Aquifer mixed and emerged as springs at Ein Feshcha group.

Investigation of two coronal mass ejections from circular ribbon source region:Origin,Sun-Earth propagation and Geoeffectiveness

In this article,we compare the properties of two coronal mass ejections(CMEs)that show similar source region characteristics but different evolutionary behaviors in the later phases.We discuss the two events in terms of their near-Sun characteristics,interplanetary evolution and geoeffectiveness.We carefully analyzed the initiation and propagation parameters of these events to establish the precise CMEinterplanetary CME(ICME)connection and their near-Earth consequences.The first event is associated with poor geomagnetic storm disturbance index(Dst≈-20 n T)while the second event is associated with an intense geomagnetic storm of DST≈-119 n T.The configuration of the sunspots in the active regions and their evolution are observed by Helioseismic and Magnetic Imager(HMI).For source region imaging,we rely on data obtained from Atmospheric Imaging Assembly(AIA)on board Solar Dynamics Observatory(SDO)and Hαfiltergrams from the Solar Tower Telescope at Aryabhatta Research Institute of Observational Sciences(ARIES).For both the CMEs,flux rope eruptions from the source region triggered flares of similar intensities(≈M1).At the solar source region of the eruptions,we observed a circular ribbon flare(CRF)for both cases,suggesting fan-spine magnetic configuration in the active region corona.The multi-channel SDO observations confirm that the eruptive flares and subsequent CMEs were intimately related to the filament eruption.Within the Large Angle and Spectrometric Coronograph(LASCO)field of view(FOV)the two CMEs propagated with linear speeds of 671 and 631 km s-1,respectively.These CMEs were tracked up to the Earth by Solar Terrestrial Relations Observatory(STEREO)instruments.We find that the source region evolution of CMEs,guided by the large-scale coronal magnetic field configuration,along with near-Sun propagation characteristics,such as CME-CME interactions,played important roles in deciding the evolution of CMEs in the interplanetary medium and subsequently their geoeffectiveness.

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 and 130 Mm. The wave energy deposited in the oscillating prominence and coronal loops is at least of the order of 10-8 erg. Furthermore, local magnetic field strength and Alfv6n speeds are derived from the oscillating periods and damping time scales, which are extracted from the time series of the oscillations. It is demon- strated that oscillations can be used in not only coronal seismology, but also to reveal the properties of the wave.

Development of technique to detect and classify small-scale magnetic flux cancellation and rapid blue-shifted excursions

We present a set of tools for detecting small-scale solar magnetic cancellations and the disk counterpart of type II spicules（the so-called Rapid Blueshifted Excursions（RBEs））, using line-of-sight photospheric magnetograms and chromospheric spectroscopic observations, respectively. For tracking magnetic cancellation,we improve the Southwest Automatic Magnetic Identification Suite（SWAMIS） so that it is able to detect certain obscure cancellations that can be easily missed. For detecting RBEs, we use a normalized reference profile to reduce false-positive detections caused by the non-uniform background and seeing condition. Similar to the magnetic feature tracking in SWAMIS, we apply a dual-threshold method to enhance the accuracy of RBE detection. These tools are employed to analyze our coordinated observations using the Interferometric BIdimensional Spectrometer at the Dunn Solar Telescope of the National Solar Observatory and Hinode. We present the statistical properties of magnetic cancellations and RBEs, and explore their correlation using this data set.

Quasi-90-day oscillation observed in the MLT region at low latitudes from the Kunming meteor radar and SABER

Observations of a quasi-90-day oscillation in the mesosphere and lower thermosphere(MLT) region from April 2011 to December 2014 are presented in this study. There is clear evidence of a quasi-90-day oscillation in temperatures obtained from the Kunming meteor radar(25.6°N, 103.8°E) and Sounding of the Atmosphere using Broadband Emission Radiometry(SABER), as well as in wind observed by the Kunming meteor radar. The quasi-90-day oscillation appears to be a prominent feature in the temperatures and meridional wind tides and presents quite regular cycles that occur approximately twice per year. The amplitudes and phases of the quasi-90-day oscillation in the SABER temperature show a feature similar to that of upward-propagated diurnal tides, which have a vertical wavelength of ～20 km above 70 km. In the lower atmosphere, a similar 90-day variability is presented in the surface latent heat flux and correlates with the temperature in the MLT region. Similar to the quasi-90-day oscillation in temperature, a 90-day variability of ozone(O3) is also present in the MLT region and is considered to be driven by a similar variability in the upwardly-propagated diurnal tides generated in the lower atmosphere. Moreover, the 90-day variability in the absorption of ultraviolet(UV) radiation by daytime O3 in the MLT region is an in situ source of the quasi-90-day oscillation in the MLT temperature.

Contribution of patchy reconnection to the ion-to-electron temperature ratio in the Earth’s magnetotail

The ion-to-electron temperature ratio is a good indicator of the processes involved in the plasma sheet.Observations have suggested that patchy reconnection and the resulting earthward bursty bulk flows(BBFs)transport may be involved in causing the lower temperature ratios at smaller radial distances during southward IMF periods.In this paper,we estimate theoretically how a patchy magnetic reconnection electric field can accelerate ions and electrons differently.If both ions and electrons are non-adiabatically accelerated only once within each reconnection,the temperature ratio would be preserved.However,when reconnection occurs closer to the Earth where magnetic field lines are shorter,particles mirrored back from the ionosphere can cross the reconnection region more than once within one reconnection;and electrons,moving faster than ions,can have more crossings than do ions,leading to electrons being accelerated more than ions.Thus as particles are transported from tail to the near-Earth by BBFs through multiple reconnection,electrons should be accelerated by the reconnection electric field more times than are ions,which can explain the lower temperature ratios observed closer to the Earth.

Physical Process for the Pick-Up of Minor Ions by Low-Frequency Alfvén Waves

We study the physical process for the pick-up of minor ions by obliquely propagating low-frequency Alfvén waves. It is demonstrated that minor ions can be picked up by the intrinsic low-frequency Alfvén waves observed in the solar wind. When the wave amplitude exceeds the threshold condition for stochasticity, a minor ion can gain a high magnetic moment through the stochastic heating process. Then, the ion with a large magnetic moment can be trapped in the magnetic mirror-like field structures formed by the large-amplitude low-frequency Alfvén waves in the wave frame. As a result, the ion is picked up by the Alfvén waves.