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Simulations of ultra-long wavelength interferometers in Earth orbit and on the lunar surface

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Research in Astronomy and Astrophysics 2015年第3期15卷 443-452页

作者： Mo Zhang Mao-Hai huang yi-hua yan Key Laboratory of Space Astronomy and Technology National Astronomical ObservatoriesChinese Academy of Sciences Key Laboratory of Solar Activity National Astronomical Observatories Chinese Academy of Sciences

We present simulations of interferometers in Earth orbit and on the lunar surface to guide the design and optimization of space-based ultra-long wavelength missions, such as those pioneered by China＇s Chang＇e Program. We choose parame- ters and present simulations using simulated data to identify inter-dependencies and constraints on science and engineering parameters. A regolith model is created for the lunar surface array simulation, and the results show that the lunar regolith will have an undesirable effect on the observations. We estimate data transmission requirements, calculate sensitivities for both cases, and discuss the trade-off between brightness tem- perature sensitivity and angular resolution for the Earth orbit array case.

关键词： techniques: interferometric -- Moon -- methods: data analysis

The importance of source positions during radio fine structure observations

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Research in Astronomy and Astrophysics 2014年第7期14卷 831-842页

作者： Guennadi P.Chernov yi-hua yan Qi-Jun Fu Key Laboratory of Solar Activity National Astronomical ObservatoryChinese Academy of Sciences Pushkov Institute of Terrestrial Magnetism Ionosphere and Radio Wave PropagationRussian Academy of Sciences (IZMIRAN)TroitskMoscow region142190Russia

The measurement of positions and sizes of radio sources in the observations of the fine structure of solar radio bursts is a determining factor for the selection of the radio emission mechanism. The identical parameters describing the radio sources for zebra structures（ZSs） and fiber bursts confirm there is a common mechanism for both structures. It is very important to measure the size of the source in the corona to determine if it is distributed along the height or if it is point-like. In both models of ZSs（the double plasma resonance（DPR） and the whistler model） the source must be distributed along the height, but by contrast to the stationary source in the DPR model, in the whistler model the source should be moving. Moreover, the direction of the space drift of the radio source must correlate with the frequency drift of stripes in the dynamic spectrum. Some models of ZSs require a local source, for example,the models based on the Bernstein modes, or on explosive instability. The selection of the radio emission mechanism for fast broadband pulsations with millisecond duration also depends on the parameters of their radio sources.

关键词： solar flare -- radio emission -- zebra-pattern -- spike-bursts

Solar image deconvolution by generative adversarial network

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Research in Astronomy and Astrophysics 2020年第11期20卷 182-190页

作者： Long Xu Wen-Qing Sun yi-hua yan Wei-Qiang Zhang Key Laboratory of Solar Activity National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China College of Mathematics and Statistics Shenzhen UniversityShenzhen 518060China

With aperture synthesis(AS)technique,a number of small antennas can be assembled to form a large telescope whose spatial resolution is determined by the distance of two farthest antennas instead of the diameter of a single-dish *** contrast from a direct imaging system,an AS telescope captures the Fourier coefficients of a spatial object,and then implement inverse Fourier transform to reconstruct the spatial *** to the limited number of antennas,the Fourier coefficients are extremely sparse in practice,resulting in a very blurry *** remove/reduce blur,“CLEAN”deconvolution has been widely used in the ***,it was initially designed for a point *** an extended source,like the Sun,its efficiency is *** this study,a deep neural network,referring to Generative Adversarial Network(GAN),is proposed for solar image *** experimental results demonstrate that the proposed model is markedly better than traditional CLEAN on solar *** main purpose of this work is visual inspection instead of quantitative scientific *** believe that this will also help scientists to better understand solar phenomena with high quality images.

关键词： deep learning(DL)generative adversarial network(GAN)solar radio astronomy

Editorial: solar radiophysics—recent results on observations and theories

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Research in Astronomy and Astrophysics 2014年第7期14卷 I0001-I0006页

作者： Valery M.Nakariakov Larisa K.Kashapova yi-hua yan Centre for Fusion Space and AstrophysicsDepartment of PhysicsUniversity of WarwickCV47ALUK School of Space Research Kyung Hee UniversityYongin446-701GyeonggiKorea Central Astronomical Observatory at Pulkovo of RAS St Petersburg 196140Russia Institute of Solar-Terrestrial Physics Russian Academy of SciencesSiberian Branch126a Lermontov st.664033IrkutskRussia Key Laboratory of Solar Activity National Astronomical ObservatoriesChinese Academy of Sciences

Solar radiophysics is a rapidly developing branch of solar physics and plasma astrophysics. Solar radiophysics has the goal of analyzing observations of radio emissions from the Sun and understanding basic physical processes operating in quiet and active regions of the solar corona. In the near future, the commissioning of a new generation of solar radio observational facilities, which include the Chinese Spectral Radio Heliograph（CSRH） and the upgrade of the Siberian Solar Radio Telescope（SSRT）, and the beginning of solar observations with the Atacama Large Millimeter/submillimeter Array（ALMA）, is expected to bring us new breakthrough results of a transformative nature. The Marie-Curie International Research Staff Exchange（MC IRSES） “RadioSun” international network aims to create a solid foundation for the successful exploitation of upcoming solar radio observational facilities, as well as intensive use of the existing observational tools, advanced theoretical modeling of relevant physical processes and observables, and training a new generation of solar radio physicists. The RadioSun network links research teams from China,Czech Republic, Poland, Russia and the UK. This mini-volume presents research papers based on invited reviews and contributed talks at the 1st RadioSun workshop in China. These papers cover a broad range of research topics and include recent observational and theoretical advances in solar radiophysics, MHD seismology of the solar corona, physics of solar flares, generation of radio emission, numerical modeling of MHD and plasma physics processes, charged-particle acceleration and novel instrumentation.

关键词： editorials notices -- Sun: corona -- Sun: radio radiation -- Sun: flares

Are Homologous Radio Bursts Driven by Solar Post-Flare Loops?

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Chinese Journal of Astronomy and Astrophysics 2007年第4期7卷 477-486页

作者： Min Wang Rui-Xiang Xie yi-hua yan Yu-ying Liu National Astronomical Observatories/Yunnan Observatory Chinese Academy of Sciences Kunming 650011 National Astronomical Observatories Chinese Academy of Sciences Beijing 100012

Three particularly complex radio bursts （2001 October 19, 2001 April 10 and 2003 October 26） obtained with the spectrometers （0.65-7.6GHz） at the National Astronomical Observatories, Chinese Academy of Sciences （NAOC, Beijing and Yunnan） and other instruments （NoRH, TRACE and SXT） are presented. They each have two groups of peaks occurring in different frequency ranges （broad-band microwave and narrow-band decimeter wavelengths）. We stress that the second group of burst peaks that occurred in the late phase of the flares and associated with post-flare loops may be homologous radio bursts. We think that they are driven by the post-flare loops. In contrast to the time profiles of the radio bursts and the images of coronal magnetic polarities, we are able to find that the three events are caused by the active regions including main single-bipole magnetic structures, which are associated with multipole magnetic structures during the flare evolutions. In particular, we point out that the later decimetric radio bursts are possibly the radio counterparts of the homologous flares （called ＂homologous radio bursts＂ by us）, which are also driven by the single-bipole mag- netic structures. By examining the evolutions of the magnetic polarities of sources （17 GHz）, we could presume that the drivers of the homologous radio bursts are new and/or recurring appearances/disappearances of the magnetic polarities of radio sources, and that the triggers are the magnetic reconnections of single-bipole configurations.

关键词： Sun: radio radiation - Sun: magnetic fields

Energy spectral property in an isolated CME-driven shock

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Research in Astronomy and Astrophysics 2016年第2期16卷 105-112页

作者： Xin Wang yi-hua yan Ming-De Ding Na Wang Hao Shan Xinjiang Astronomical Observatory Chinese Academy of Sciences Key Laboratory of Solar Activity National Astronomical Observatories Chinese Academy of Sciences Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University) Ministry of Education Key Laboratory of Radio Astronomy Chinese Academy of Sciences

Observations from multiple spacecraft show that there are energy spectral ＂breaks＂ at 1-10 MeV in some large CME-driven shocks. However, numerical models can hardly simulate this property due to high computational expense. The present paper focuses on analyzing these energy spectral ＂breaks＂ by Monte Carlo particle simulations of an isolated CME-driven shock. Taking the 2006 Dec 14 CME-driven shock as an example, we investigate the formation of this energy spectral property. For this purpose, we apply different values for the scattering time in our isolated shock model to obtain the highest energy ＂tails,＂ which can potentially exceed the ＂break＂ energy range. However, we have not found the highest energy ＂tails＂ beyond the ＂break＂ energy range, but instead find that the highest energy ＂tails＂ reach saturation near the range of energy at 5 MeV. So, we believe that there exists an energy spectral ＂cut off＂ in an isolated shock. If there is no interaction with another shock, there would not be formation of the energy spectral ＂break＂ property.

关键词： acceleration of particles -- shock waves -- Sun coronal mass ejections (CMEs) -- solar wind-- methods numerical

Antenna system characteristics and solar radio burst observations

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Research in Astronomy and Astrophysics 2015年第11期15卷 1917-1930页

作者： Sha Li yi-hua yan Zhi-Jun Chen Wei Wang Dong-Hao Liu Key Laboratory of Solar Activity National Astronomical Observatories Chinese Academy of Sciences Key Laboratory of Radio Astronomy Chinese Academy of Sciences University of Chinese Academy of Sciences

The Chinese Spectral Radio Heliograph（CSRH） is an advanced aperture synthesis solar radio heliograph, independently developed by National Astronomical Observatories, Chinese Academy of Sciences. It consists of 100 reflector antennas,which are grouped into two antenna arrays（CSRH-I and CSRH-II） for low and high frequency bands respectively. The frequency band of CSRH-I is 0.4–2 GHz and that for CSRH-II is 2–15 GHz. In the antenna and feed system, CSRH uses eleven feeds to receive signals coming from the Sun. The radiation pattern has a lower side lobe and the back lobe of the feed is well illuminated. The characteristics of gain G and antenna noise temperature T affect the quality of solar radio imaging. For CSRH, the measured G is larger than 60 d Bi and T is less than 120 K. After CSRH-I was established, we successfully captured a solar radio burst between 1.2–1.6 GHz on 2010 November12 using this instrument and this event was confirmed through observations with the Solar Broadband Radio Spectrometer at 2.84 GHz and the Geostationary Operational Environmental Satellite. In addition, an image obtained from CSRH-I clearly revealed the profile of the solar radio burst. The other observational work involved the imaging the Fengyun-2E geosynchronous satellite which is assumed to be a point *** indicate that the data processing method applied in this study for deleting errors in a noisy image could be used for processing images from other sources.

关键词： captured burst noisy antenna reflector aperture instrument coordinates Solar independently

Observational Characteristics of Radio Emission Related to Multi-polar Magnetic Configuration

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Chinese Journal of Astronomy and Astrophysics 2005年第5期5卷 508-518页

作者： Min Wang Rui-Xiang Xie Chun Xu Shuo-Biao Shi yi-hua yan National Astronomical Observatories Yunnan Observatory Chinese Academy of SciencesKunming 650011 National Astronomical Observatories Chinese Academy of Sciences Beijing 100012

We present a large complex radio burst and its associated fast time structures observed on 2001 April 10 in the frequency range of 0.65-7.6 GHz. The NoRH radio image observation shows very complex radio source structures which include preexisting, newly emerging, submerging/cancelling polarities and a bipolar, a tripolar （a ＇bipolar ＋ remote unipolar＇）, and a quadrupolar structure. This suggests that the radio burst is generated from a very complicated loop structure. According to the spectral and image observations, we assume that the beginning of this flare was caused by a single bipolar loop configuration with a ‘Y-type＇ re- connection structure. A composite of radio continuum and fast time structures is contained in this flare. The various fast radio emission phenomena include normal and reverse drifting type Ⅲ bursts, and slowly drifting and no-drift structures. The tripolar configurations may form a double-loop with a ＇three-legged＇ struc- ture, which is an important source of the various types of fast time structures. The two-loop reconnection model can lead simultaneously to electron acceleration and corona heating. We have also analyzed the behaviors of coronal magnetic polarities and the emission processes of different types radio emission qualitatively. Interactions of a bipolar or multi-polar loop are consistent with our observational results. Our observations favor the magnetic reconnection configurations of the ‘inverted Y-type＇（bipolar） and the ‘three-legged＇ structures （tripolar or quadrupo- lar）.

关键词： Sun: radio radiation - Sun: activity - Sun: flares

An agile very low frequency radio spectrum explorer

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Research in Astronomy and Astrophysics 2021年第4期21卷 139-148页

作者： Lin-Jie Chen yi-hua yan Qiu-Xiang Fan Li-Hong Geng Susanta Kumar Bisoi Key Laboratory of Solar Activity National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China School of Astronomy and Space Sciences University of Chinese Academy of SciencesBeijing 100049China Institute of Automation Chinese Academy of SciencesBeijing 100190China National Institute of Technology Rourkela 769008India

The very low frequency(VLF)regime below 30 MHz in the electromagnetic spectrum has presently been drawing global attention in radio astronomical research due to its potentially significant science outcomes exploring many unknown extragalactic sources,transients,and so ***,the nontransparency of the Earth’s ionosphere,ionospheric distortion and artificial radio frequency interference(RFI)have made it difficult to detect the VLF celestial radio emission with ground-based instruments.A straightforward solution to overcome these problems is a space-based VLF radio telescope,just like the VLF radio instruments onboard the Chang’E-4 *** building such a space telescope would be inevitably costly and technically *** alternative approach would be then a ground-based VLF radio ***,in the period of post 2020 when the solar and terrestrial ionospheric activities are expected to be in a’calm’state,it will provide us a good chance to perform VLF ground-based radio *** such an opportunity,we built an agile VLF radio spectrum explorer co-located with the currently operational Mingantu Spectra Radio Heliograph(MUSER).The instrument includes four antennas operating in the VLF frequency range 1-70 *** with them,we employ an eight-channel analog and digital receivers to amplify,digitize and process the radio signals received by the *** present in the paper this VLF radio spectrum explorer and the instrument will be useful for celestial studies of VLF radio emissions.

关键词： very low frequency instrumentation:polarimeters methods:data analysis