Correction of the temperature effect in calibration of a solar radio telescope

This work analyzes the annual fluctuation of the observation data of the Mingantu Solar radio Telescope(MST)in S,C and X bands.It is found that the data vary with local air temperature as the logarithmic attenuation of equipment increases with temperature and frequency.A simplified and effective calibration method is proposed,which is used to calibrate the MST data in 2018-2020,while the correction coefficients are calculated from data in 2018-2019.For S,C and X bands,the root mean square errors of one polarization are 2.7,5.7 and 20 sfu,and the relative errors are 4%,6%and 8%respectively.The calibration of MUSER and SBRS spectra is also performed.The relative errors of MUSER at 1700 MHz,SBRS at 2800 MHz,3050 MHz and 3350 MHz are 8%,8%,11%and 10%respectively.We found that several factors may affect the calibration accuracy,especially at X-band.The method is expected to work for other radio telescopes with similar design.

Data Matching of Solar Images Super-Resolution Based on Deep Learning

The images captured by different observation station have different resolutions.The Helioseismic and Magnetic Imager(HMI:a part of the NASA Solar Dynamics Observatory SDO)has low-precision but wide coverage.And the Goode Solar Telescope(GST,formerly known as the New Solar Telescope)at Big Bear Solar Observatory(BBSO)solar images has high precision but small coverage.The super-resolution can make the captured images become clearer,so it is wildly used in solar image processing.The traditional super-resolution methods,such as interpolation,often use single image’s feature to improve the image’s quality.The methods based on deep learning-based super-resolution image reconstruction algorithms have better quality,but small-scale features often become ambiguous.To solve this problem,a transitional amplification network structure is proposed.The network can use the two types images relationship to make the images clear.By adding a transition image with almost no difference between the source image and the target image,the transitional amplification training procedure includes three parts:transition image acquisition,transition network training with source images and transition images,and amplification network training with transition images and target images.In addition,the traditional evaluation indicators based on structural similarity(SSIM)and peak signal-to-noise ratio(PSNR)calculate the difference in pixel values and perform poorly in cross-type image reconstruction.The method based on feature matching can effectively evaluate the similarity and clarity of features.The experimental results show that the quality index of the reconstructed image is consistent with the visual effect.

Diagnostic Functions of Solar Coronal Magnetic Fields from Radio Observations

In solar physics,it is a big challenge to measure the magnetic fields directly from observations in the upper solar atmosphere,including the chromosphere and corona.Radio observations are regarded as the most feasible approach to diagnose the magnetic field in solar chromosphere and corona.However,because of the complexity and diversity of the emission mechanisms,the previous studies have only presented the implicit diagnostic functions of the magnetic field for specific mechanism from solar radio observations.This work collected and sorted out all methods for diagnosing coronal magnetic field from solar radio observations,which are expressed as a set of explicit diagnostic functions.In particular,this work supplemented some important diagnostic methods missed in other reviews.This set of diagnostic functions can completely cover all regions of the solar chromosphere and corona,including the quiet region,active region and flaring source regions.At the same time,it also includes incoherent radiation such as bremsstrahlung emission of thermal plasma above the quiet region,cyclotron and gyro-synchrotron emissions of magnetized hot plasma and mildly relativistic nonthermal electrons above the active regions,as well as coherently plasma emission around flaring source regions.Using this set of diagnostic functions and the related broadband spectral solar radio imaging observations,we can derive the magnetic fields of almost all regions in the solar atmosphere,which may help us to make full use of the spectral imaging observations of the new generation solar radio telescopes(such as MUSER,EVOSA and the future FASR,etc.) to study the solar activities,and provide a reliable basis for the prediction of disastrous space weather events.

Evolvement of microwave spike bursts in a solar flare on 2006 December 13

Solar radio spikes are one of the most intriguing spectral types of radio bursts.Their very short lifetimes,small source size and super-high brightness temperature indicate that they should be involved in some strong energy release,particle acceleration and coherent emission processes closely related to solar flares.In particular,for the microwave spike bursts,their source regions are much close to the related flaring source region which may provide the fundamental information of the flaring process.In this work,we identify more than 600 millisecond microwave spikes which recorded by the Solar Broadband Radio Spectrometer in Huairou(SBRS/Huairou)during an X3.4 solar flare on 2006 December 13 and present a statistical analysis about their parametric evolution characteristic.We find that the spikes have nearly the same probability of positive and negative frequency drifting rates not only in the flare rising phase,but also in the peak and decay phases.So we suppose that the microwave spike bursts should be generated by shockaccelerated energetic electrons,just like the terminational shock(TS)wave produced by the reconnection outflows near the loop top.The spike bursts occurred around the peak phase have the highest central frequency and obviously weak emission intensity,which imply that their source region should have the lowest position with higher plasma density due to the weakened magnetic reconnection and the relaxation of TS during the peak phase.The right-handed polarization of the most spike bursts may be due to the TS lying on the top region of some very asymmetrical flare loops.

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.

Systematic investigation of mid-term periodicity of the solar full-disk magnetic fields

The Magnetic Plage Strength Index(MPSI) and the Mount Wilson Sunspot Index(MWSI), which have been measured at Mount Wilson Observatory(MWO) since the 1970 s and which indicate weak and strong magnetic field activity on the solar full disk, respectively, are used to systematically investigate midterm periodicities in the solar full-disk magnetic fields. Multitudinous mid-term periodicities are detected in MPSI and MWSI on timescales of 0.3 to 4.5 yr, and these periodicities are found to fluctuate around several typical periodicities within a small amplitude in different solar cycles or phases. The periodicity of 3.44 yr is found in MPSI, and the periodicities of 3.85 and 3.00 yr are detected in MWSI. Our analysis indicates that they reflect the true oscillating signals of solar magnetic field activity. The typical periodicities are 2.8,2.3 and 1.8 yr in MPSI and MWSI, and possible mechanisms for these periodicities are discussed. A 1.3 yr periodicity is only detected in MPSI, and should be related to meridional flows on the solar surface. The typical annual periodicity of MPSI and MWSI is 1.07 yr, which is not derived from the annual variation of Earth’s heliolatitude. Several periodicities shorter than 1 yr found in MPSI and MWSI are considered to be Rieger-type periodicities.

Periodic variation and phase analysis of grouped solar flare with sunspot activity

Studies on the periodic variation and the phase relationship between different solar activity indicators are useful for understanding the long-term evolution of solar activity cycles.Here we report the statistical analysis of grouped solar flare(GSF) and sunspot number(SN) during the time interval from January 1965 to March 2009.We find that,(1) the significant periodicities of both GSF and SN are related to the differential rotation periodicity,the quasi-biennial oscillation(QBO),and the eleven-year Schwabe cycle(ESC),but the specific values are not absolutely identical;(2) the ESC signal of GSF lags behind that of SN with an average of 7.8 months during the considered time interval,which implies that the systematic phase delays between GSF and SN originate from the inter-solar-cycle signal.Our results may provide evidence about the storage of magnetic energy in the corona.

Energy and spectral analysis of confined solar flares from radio and X-ray observations

The energy and spectral shape of radio bursts may help us understand the generation mechanism of solar eruptions,including solar flares,coronal mass ejections,eruptive filaments,and various scales of jets.The different kinds of flares may have different characteristics of energy and spectral distribution.In this work,we selected 10 mostly confined flare events during October 2014 to investigate their overall spectral behaviour and the energy emitted in microwaves by using radio observations from microwaves to interplanetary radio waves,and X-ray observations of GOES,RHESSI,and Fermi/GBM.We found that:all the confined flare events were associated with a microwave continuum burst extending to frequencies of9.4~15.4 GHz,and the peak frequencies of all confined flare events are higher than 4.995 GHz and lower than or equal to 17 GHz.The median value is around 9 GHz.The microwave burst energy(or nuence)and the peak frequency are found to provide useful criteria to estimate the power of solar flares.The observations imply that the magnetic field in confined flares tends to be stronger than that in 412 flares studied by Nita et al.(2004).All 10 events studied did not produce detectable hard X-rays with energies above~300 keV indicating the lack of efficient acceleration of electrons to high energies in the confined flares.

Solar Radio Burst Automatic Detection Method for Decimetric and Metric Data of YNAO

With the development of solar radio spectrometer, it is difficult to process a large number of observed data quickly by manual detection method. Yunnan astronomical observatories (YNAO) have two solar radio spectrometers with high time and frequency resolution. An automatic detection method of solar radio burst for decimetric and metric data of YNAO is proposed in this paper. The duration of solar radio burst was counted and analyzed. Channel normalization was used to denoise the original solar radio image. Through experimental comparison, Otsu method was selected as a binary method of solar radio spectrum, and open and close operations were used to smooth the binary image. Experiments show that the proposed method for automatic detection of solar radio bursts is effective.

A broadband digital receiving system with large dynamic range for solar radio observation

Solar radio spectra and their temporal evolution provide important clues to understand the energy release and electron acceleration process in the corona,and are commonly used to diagnose critical parameters such as the magnetic field strength.However,previous solar radio telescopes cannot provide high-quality data with complete frequency coverage.Aiming to develop a generalized solar radio observing system,in this study,we designed a digital receiving system that could capture solar radio bursts with a broad bandwidth and a large dynamic range.A dual-channel analog-to-digital converter(ADC)printed circuit board assembly(PCBA)with a sampling rate of 14-bit,1.25 Giga samples per second(GSPS)cooperates with the field-programmable-gate-array(FPGA)chip XC7K410T in the design.This receiver could realize the real-time acquisition and preprocessing of high-speed data of up to 5 GB s^(-1),which ensures high time and spectral resolutions in observations.This receiver has been used in the solar radio spectrometer working in the frequency range of 35 to 40 GHz in Chashan Solar Observatory(CSO)established by Shandong University,and will be further developed and used in the solar radio interferometers.The full-power bandwidth of the PCBA in this receiving system could reach up to 1.5 GHz,and the performance parameters(DC–1.5 GHz)are obtained as follows:spur free dynamic range(SFDR)of 64.7–78.4 dB,signal-to-noise and distortion(SINAD)of 49.1–57.2 dB,and effective number of bits(ENOB)of>7.86 bit.Based on the receiver that we designed,real-time solar microwave dynamic spectra have been acquired and more solar microwave bursts with fine spectral structures are hopeful to be detected in the coming solar maximum.

Orbital parameters and period variation studies of the short-period eclipsing binaries FG Sct, VZ Lib and VZ Psc

We present eight sets of new light curves for binaries FG Sct,VZ Lib and VZ Psc,which are all contact eclipsing binaries with short orbital periods.We carried out our observations from 2016 to 2017 using the 60-cm telescope administered by National Astronomical Observatories,Chinese Academy of Sciences,the Holcomb Observatory at Butler University and the SARA-CT telescope in Chile.We firstly determined the orbital parameters of FG Sct using the O-C method and obtained photometric solutions utilizing the updated W-D program.We also studied its period variation and discovered that its orbital period is decreasing at a rate of 6.39(±0.24)×10^-8 d yr-1,which was likely caused by mass transfer from the primary component to the secondary component or angular momentum interchange between the two components via magnetic interactions.For VZ Lib and VZ Psc,we simultaneously analyzed their BV RI light curves in conjunction with the published radial velocities.In order to obtain the orbital parameters of VZ Lib,we also analyzed its period variation and revised cyclic change,which could be attributed to either the light-time effect due to a tertiary companion or magnetic activity cycle mechanism.We derived the periods of the tertiary component of VZ Lib to be 48.7(±0.1) yr or magnetic cycle to be 46.9(±1.9) yr.Strong emission lines at Ca II H+K,Hα,Hβ,Hγ and Ca II IRT were detected in the LAMOST spectra of VZ Psc,which imply chromospheric activities in this binary system.

An investigation of flare emissions at multiple wavelengths

We report multi-wavelength observations of four solar flares on 2014 July 07.We firstly select these flares according to the soft X-ray(SXR)and extreme ultraviolet(EUV)emissions recorded by the Extreme Ultraviolet Variability Experiment and Geostationary Orbiting Environmental S atellites.Then their locations and geometries are identified from the full-disk images measured by the Atmospheric Imaging Assembly(AIA),and the time delays among the light curves in different channels are identified.The electron number densities are estimated using the differential emission measure method.We find that three of four flares show strong emissions in SXR channels and high temperature(>6 MK)EUV wavelengths during the impulsive phase,i.e.,AIA 131 A and 94 A,and then they emit peak radiation subsequently in the middle temperature(~0.6-3 MK)EUV channels.Moreover,they last for a long time and have smaller electron densities,which are probably driven by the interaction of hot diffuse flare loops.Only one flare emits radiation at almost the same time in all the observed wavelengths,lasts for a relatively short time,and has a larger electron density.It is also accompanied by a typeⅢradio burst.The bright emission at the EUV channel could be corresponding to the associated erupting filament.

Detection and mitigation of RFI in SBRS observation data

In view of the inconsistency of channel gains and a large amount of interference noise in Solar Broadband Radio Spectrometer(SBRS) observation data,they will seriously affect the analysis of SBRS data.In this paper,a method of Radio Frequency Interference(RFI) detection and mitigation for SBRS observation data is reported.Firstly,the SBRS observation data are preprocessed,a part of the observation data was selected to calculate the mean and variance to achieve the normalization of the entire observation data,which can avoid the influence of strong noise on the normalization result.Furthermore,we proposed an adaptive threshold RFI detection method based on fusion wavelet transform reconstruction and an RFI elimination method based on neighborhood weighted filling.It is worth mentioning that to detect RFI interference signals of different magnitudes,we adopted an iterative approach to the RFI detection and mitigation process.Through qualitative analysis of real observation data and quantitative analysis of simulated data,it is shown that the method proposed in this paper can effectively eliminate RFI in SBRS observation data,and improve the quality of observation data for further scientific analysis.

Photometric and spectroscopic study of flares on Ross 15

We conducted photometric and spectroscopic observations of Ross 15 in order to further study the flare properties of this less observed flare star.A total of 28 B-band flares are detected in 128 hr of photometric observations,leading to a total flare rate of 0.22-0.040.04 h-1,more accurate than that provided by previous work.We give the energy range of the B-band flare(1029.5-1031.5 erg) and the flare frequency distribution(FFD) for the star.Within the same energy range,the FFD is lower than that of GJ 1243(M4)and YZ CMi(M4.5),roughly in the middle of those of three M5-type stars and higher than the average FFDs of spectral types> M6.We performed,for the first time for Ross 15,simultaneous high-cadence spectroscopic and photometric observations,resulting in detection of the most energetic flare in our sample.The intensity enhancements of the continuum and Balmer lines with significant correlations between them are detected during the flare,which is the same as those of other deeply studied flare stars with similar spectral type.

Properties of the Main Phases of the Super Geomagnetic Storms(ΔSYM-H≤-250 nT)with Different Heliolongitudes

We studied the properties of the main phases of 24 super geomagnetic storms(SGSs)(ΔSYM-H≤-250 nT)since 1981.We divided the SGSs into two subgroups:SGSs-Ⅰ(-400 nT<ΔSYM-H≤-250 nT)and SGSs-Ⅱ(ΔSYM-H≤-400 nT).Of the 24 SGSs,16 are SGSs-Ⅰand eight are SGSs-Ⅱ.The source locations of SGSs were distributed in the longitudinal scope of[E37,W66].95.8%of the SGSs were distributed in the longitudinal scope of[E37,W20].East and west hemispheres of the Sun had 14 and 10 SGSs,respectively.The durations of the main phases for six SGSs ranged from 2 to 4 hr.The durations of the main phases for the rest 18 SGSs were longer than 6.5 hr.The duration of the SGSs with source locations in the west hemisphere varied from 2.22 to 19.58 hr.The duration for the SGSs with the source locations in the east hemisphere ranged from 2.1 to31.88 hr.The averaged duration of the main phases of the SGSs in the west and east hemispheres are 8.3 hr and13.98 hr,respectively.|ΔSYM-H/Δt|for six SGSs with source locations distributed in the longitudinal area ranging from E15 to W20 was larger than 1.0 nT·minute^(-1),while|ΔSYM-H/Δt|for the rest 18 SGSs was lower than 1.0 nT·minute^(-1).|ΔSYM-H/Δt|for SGSs-Ⅰvaried from 0.18 to 3.0 nT·minute^(-1).|ΔSYM-H/Δt|for eight SGSs-Ⅱvaried from 0.37 to 2.2 nT·minute^(-1)with seven SGSs-Ⅱfalling in the scope from 0.37 to0.992 nT·minute^(-1).

Revisiting the formation mechanism for coronal rain from previous studies

Solar coronal rain is classified generally into two categories:flare-driven and quiescent coronal rain.The latter is observed to form along both closed and open magnetic field structures.Recently,we proposed that some of the quiescent coronal rain events,detected in the transition region and chromospheric diagnostics,along loop-like paths could be explained by the formation mechanism for quiescent coronal rain facilitated by interchange magnetic reconnection between open and closed field lines.In this study,we revisited 38 coronal rain reports from the literature.From these earlier works,we picked 15 quiescent coronal rain events out of the solar limb,mostly suggested to occur in active region closed loops due to thermal nonequilibrium,to scrutinize their formation mechanism.Employing the extreme ultraviolet images and line-of-sight magnetograms,the evolution of the quiescent coronal rain events and their magnetic fields and context coronal structures is examined.We find that six,comprising 40%,of the 15 quiescent coronal rain events could be totally or partially interpreted by the formation mechanism for quiescent coronal rain along open structures facilitated by interchange reconnection.The results suggest that the quiescent coronal rain facilitated by interchange reconnection between open and closed field lines deserves more attention.

Friction compensation for an m-Level telescope based on high-precision LuGre parameters identification

Friction torque severely weakens the tracking accuracy and low-speed stability of an m-level TCS(telescope control system).To solve this problem,a friction compensation method is proposed,based on high-precision LuGre friction model parameters identification.Together with dynamometer calibration,we first design a DOB(disturbance observer)to acquire high-accuracy TCS friction value in real time.Then,the PSO-GA(a hybrid algorithm combined particle swarm optimization algorithm and genetic algorithm)optimization algorithm proposed effectively and efficiently realizes the LuGre model parameters identification.In addition,we design a TCS controller including DOB and LuGre model parameters identification based on double-loop PID controller for practical application.Engineering verification tests indicate that the accuracy of DOB calibrated can reach 96.94%of the real measured friction.When azimuth axis operates in the speed cross-zero work mode,the average positive peak to tracking error reduces from 0.8926"to 0.2252"and the absolute average negative peak to tracking error reduces from 0.8881"to 0.3984".Moreover,the azimuth axis tracking MSE reduces from 0.1155"to 0.0737",which decreases by 36.2%.Experimental results validate the high precision,facile portability and high real-time ability of our approach.

The Ellerman bomb and ultraviolet burst triggered successively by an emerging magnetic flux rope

Ellerman bombs(EBs)and ultraviolet(UV)bursts are common brightening phenomena,which are usually generated in the low solar atmosphere of emerging flux regions.In this paper,we have investigated the emergence of an initial un-twisted magnetic flux rope based on three-dimensional(3 D)magneto-hydrodynamic(MHD)simulations.The EB-like and UV burst-like activities successively appear in the U-shaped part of the undulating magnetic fields triggered by the Parker instability.The EB-like activity starts to appear earlier and lasts for about 80 seconds.Six minutes later,a much hotter UV burstlike event starts to appear and lasts for about 60 seconds.Along the direction vertical to the solar surface,both the EB and UV burst start in the low chromosphere,but the UV burst extends to a higher altitude in the up chromosphere.The regions with apparent temperature increase in the EB and UV burst are both located inside the small twisted flux ropes generated in magnetic reconnection processes,which are consistent with the previous 2 D simulations that most hot regions are usually located inside the magnetic islands.However,the twisted flux rope corresponding to the EB is only strongly heated after it floats up to an altitude much higher than the reconnection site during that period.Our analyses show that the EB is heated by the shocks driven by the strong horizontal flows at two sides of the U-shaped magnetic fields.The twisted flux rope corresponding to the UV burst is heated by the driven magnetic reconnection process.

DSC based Dual-Resunet for radio frequency interference identification

Radio frequency interference(RFI)will pollute the weak astronomical signals received by radio telescopes,which in return will seriously affect the time-domain astronomical observation and research.In this paper,we use a deep learning method to identify RFI in frequency spectrum data,and propose a neural network based on Unet that combines the principles of depthwise separable convolution and residual,named DSC Based Dual-Resunet.Compared with the existing Unet network,DSC Based Dual-Resunet performs better in terms of accuracy,F1 score,and MIoU,and is also better in terms of computation cost where the model size and parameter amount are 12.5%of Unet and the amount of computation is 38%of Unet.The experimental results show that the proposed network is a high-performance and lightweight network,and it is hopeful to be applied to RFI identification of radio telescopes on a large scale.

Automatic Detection of Solar Radio Spectrum Based on Codebook Model

Space weather can affect human production and life,and solar radio burst will seriously affect space weather.Automatic detection of solar radio bursts in real time has a positive effect on space weather warning and prediction.Codebook model is used to simulate solar background radio to achieve automatic detection of solar radio bursts in this paper.Firstly,channel normalization was used to eliminate channel difference of original radio data.Then,a new automatic detection method for solar radio bursts based on codebook model was proposed to detect radio bursts.Finally,morphological processing was implemented to obtain burst parameters by detecting binary burst area.The experimental results show that the proposed method is effective.