The 10.7 cm solar radio flux （F10.7）, the value of the solar radio emission flux density at a wavelength of 10.7 cm, is a useful index of solar activity as a proxy for solar extreme ultraviolet radiation. It is mean...The 10.7 cm solar radio flux （F10.7）, the value of the solar radio emission flux density at a wavelength of 10.7 cm, is a useful index of solar activity as a proxy for solar extreme ultraviolet radiation. It is meaningful and important to predict F10.7 values accurately for both long-term （months-years） and short-term （days） forecasting, which are often used as inputs in space weather models. This study applies a novel neural network technique, support vector regression （SVR）, to forecasting daily values of F10.7. The aim of this study is to examine the feasibility of SVR in short-term F10.7 forecasting. The approach, based on SVR, reduces the dimension of feature space in the training process by using a kernel-based learning algorithm. Thus, the complexity of the calculation becomes lower and a small amount of training data will be sufficient. The time series of F10.7 from 2002 to 2006 are employed as the data sets. The performance of the approach is estimated by calculating the norm mean square error and mean absolute percentage error. It is shown that our approach can perform well by using fewer training data points than the traditional neural network.展开更多
This review covers the most recent experimental results and theoretical research on zebra patterns （ZPs） in solar radio bursts. The basic attention is given to events with new peculiar elements of zebra patterns rec...This review covers the most recent experimental results and theoretical research on zebra patterns （ZPs） in solar radio bursts. The basic attention is given to events with new peculiar elements of zebra patterns received over the last few years. All new properties are considered in light of both what was known earlier and new theoretical models. Large-scale ZPs consisting of small-scale fiber bursts could be explained by simultaneous inclusion of two mechanisms when whistler waves ＂high- light＂ the levels of double plasma resonance （DPR）. A unique fine structure was observed in the event on 2006 December 13： spikes in absorption formed dark ZP stripes against the absorptive type Ⅲ-like bursts. The spikes in absorption can appear in accordance with well known mechanisms of absorptive bursts. The additional injection of fast particles filled the loss-cone （breaking the loss-cone distribution）, and the generation of the continuum was quenched at these moments. The maximum absorptive effect occurs at the DPR levels. The parameters of millisecond spikes are determined by small dimensions of the particle beams and local scale heights in the radio source. Thus, the DPR model helps to understand severai aspects of unusual elements of ZPs. However, the simultaneous existence of several tens of the DPR levels in the corona is impossible for any realistic profile of the plasma density and magnetic field. Three new theories of ZPs are examined. The formation of eigenmodes of transparency and opac- ity during the propagation of radio waves through regular coronal inhomogeneities is the most natural and promising mechanism. Two other models （nonlinear periodic space - charge waves and scattering of fast protons on ion-sound harmonics） could happen in large radio bursts.展开更多
Based on Dulk and Marsh＇s approximate theory about nonthermal gyrosyn- chrotron radiation, one simple impulsive microwave burst with a loop-like structure is selected for radio diagnostics of the coronal magnetic fie...Based on Dulk and Marsh＇s approximate theory about nonthermal gyrosyn- chrotron radiation, one simple impulsive microwave burst with a loop-like structure is selected for radio diagnostics of the coronal magnetic field and column density of non- thermal electrons, which are calculated from the brightness temperature, polarization degree, and spectral index, as well as the turnover frequency, observed by using the Nobeyama Radioheliograph and the Nobeyama Radio Polarimeters, respectively. Very strong variations （up to one or two orders of magnitude） of the calculated transverse and longitudinal magnetic fields with respect to the line-of-sight, as well as the cal- culated electron column density, appear in the looptop and footpoint sources during the burst. The absolute magnitude and varied range of the transverse magnetic field are evidently larger than those of the longitudinal magnetic field. The time evolution of the transverse magnetic field is always anti-correlated with that of the longitudi- nal magnetic field, but positively correlated with that of the electron column density. These results strongly support the idea that quantifying the energy released in a flare depends on a reconstruction of the coronal magnetic field, especially for the trans- verse magnetic field, and they are basically consistent with the recent theoretical and observational studies on the photospheric magnetic field in solar flares.展开更多
Solar type III radio bursts are an important diagnostic tool in the understanding of solar accelerated electron beams. They are a signature of propagating beams of nonthermal electrons in the solar atmosphere and the ...Solar type III radio bursts are an important diagnostic tool in the understanding of solar accelerated electron beams. They are a signature of propagating beams of nonthermal electrons in the solar atmosphere and the solar system. Consequently, they provide information on electron acceleration and transport, and the conditions of the background ambient plasma they travel through. We review the observational properties of type III bursts with an emphasis on recent results and how each property can help identify attributes of electron beams and the ambient background plasma. We also review some of the theoretical aspects of type III radio bursts and cover a number of numerical efforts that simulate electron beam transport through the solar corona and the heliosphere.展开更多
By applying the state-of-the-art mathematical apparatus, the wavelet transformation, we explore the possibility of a dynamic cleaning of raw data ob- tained with the Chinese solar radio spectrographs over a wide wa...By applying the state-of-the-art mathematical apparatus, the wavelet transformation, we explore the possibility of a dynamic cleaning of raw data ob- tained with the Chinese solar radio spectrographs over a wide wavelength range (from 0.7 to 7.6 GHz). We consider the problem of eliminating the interference caused by combination rates of data sampling (10-20 ins), and the low-frequency interference (4-30 s) caused by the receiving equipment changing its characteristics with time. It is shown that the best choice to reconstruct a signal suffering from amplitude, frequency and phase instabilities, is by means of wavelet transformation at both high and low frequencies. We analysed observational data which contained interferences of nonsolar origin such as instrumental effects and other man-made signals. A subsequent comparison of the reference data obtained with the acousto- optical receiver of the Siberian Solar Radio Telescope (SSRT) with the 'cleaned' spectra confirms the correctness of this approach.展开更多
In the physics of solar flares, it is crucial to diagnose the physical conditions near the flare energy- release sites. However, so far it is unclear how to diagnose these physical conditions. A solar microwave type I...In the physics of solar flares, it is crucial to diagnose the physical conditions near the flare energy- release sites. However, so far it is unclear how to diagnose these physical conditions. A solar microwave type III burst is believed to be a sensitive signature of primary energy release and electron accelerations in solar flares. This work takes into account the effect of the magnetic field on the plasma density and develops a set of formulas which can be used to estimate the plasma density, temperature, magnetic field near the magnetic reconnection site and particle acceleration region, and the velocity and energy of electron beams. We apply these formulas to three groups of microwave type III pairs in an X-class flare, and obtained some reasonable and interesting results. This method can be applied to other microwave type III bursts to diagnose the physical conditions of source regions, and provide some basic information to understand the intrinsic nature and fundamental processes occurring near the flare energy-release sites.展开更多
The 2.6-3.8 GHz, 4.5-7.5 GHz, 5.2-7.6 GHz and 0.7-1.5 GHz componentspectrometers of Solar Broadband Radio Spectrometer (SBRS) started routine observations,respectively, in late August 1996, August 1999, August 1999, a...The 2.6-3.8 GHz, 4.5-7.5 GHz, 5.2-7.6 GHz and 0.7-1.5 GHz componentspectrometers of Solar Broadband Radio Spectrometer (SBRS) started routine observations,respectively, in late August 1996, August 1999, August 1999, and June 2000. They just managed tocatch the coming 23rd solar active maximum. Consequently, a large amount of microwave burst datawith high temporal and high spectral resolution and high sensitivity were obtained. A variety offine structures (FS) superimposed on microwave bursts have been found. Some of them are known, suchas microwave type Ⅲ bursts, microwave spike emission, but these were observed with more detail;some are new. Reported for the first time here are microwave type U bursts with similar spectralmorphology to those in decimetric and metric wavelengths, and with outstanding characteristics suchas very short durations (tens to hundreds ms), narrow bandwidths, higher frequency drift rates andhigher degrees of polarization. Type N and type M bursts were also observed. Detailed zebra patternand fiber bursts at the high frequency were found. Drifting pulsation structure (DPS) phenomenaclosely associated with CME are considered to manifest the initial phase of the CME, andquasi-periodic pulsation with periods of tens ms have been recorded. Microwave 'patches', unlikethose reported previously, were observed with very short durations (about 300 ms), very high fluxdensities (up to 1000 sfu), very high polarization (about 100% RCP), extremely narrow bandwidths(about 5%), and very high spectral indexes. These cannot be interpreted with the gyrosynchrotronprocess. A superfine structure in the form of microwave FS (ZPS, type U), consisting of microwavemillisecond spike emission (MMS), was also found.展开更多
文摘The 10.7 cm solar radio flux （F10.7）, the value of the solar radio emission flux density at a wavelength of 10.7 cm, is a useful index of solar activity as a proxy for solar extreme ultraviolet radiation. It is meaningful and important to predict F10.7 values accurately for both long-term （months-years） and short-term （days） forecasting, which are often used as inputs in space weather models. This study applies a novel neural network technique, support vector regression （SVR）, to forecasting daily values of F10.7. The aim of this study is to examine the feasibility of SVR in short-term F10.7 forecasting. The approach, based on SVR, reduces the dimension of feature space in the training process by using a kernel-based learning algorithm. Thus, the complexity of the calculation becomes lower and a small amount of training data will be sufficient. The time series of F10.7 from 2002 to 2006 are employed as the data sets. The performance of the approach is estimated by calculating the norm mean square error and mean absolute percentage error. It is shown that our approach can perform well by using fewer training data points than the traditional neural network.
基金the Russian Foundation of Basic Research (RFBR), grant Nos. 08-02-00270 and 11-02-91151
文摘This review covers the most recent experimental results and theoretical research on zebra patterns （ZPs） in solar radio bursts. The basic attention is given to events with new peculiar elements of zebra patterns received over the last few years. All new properties are considered in light of both what was known earlier and new theoretical models. Large-scale ZPs consisting of small-scale fiber bursts could be explained by simultaneous inclusion of two mechanisms when whistler waves ＂high- light＂ the levels of double plasma resonance （DPR）. A unique fine structure was observed in the event on 2006 December 13： spikes in absorption formed dark ZP stripes against the absorptive type Ⅲ-like bursts. The spikes in absorption can appear in accordance with well known mechanisms of absorptive bursts. The additional injection of fast particles filled the loss-cone （breaking the loss-cone distribution）, and the generation of the continuum was quenched at these moments. The maximum absorptive effect occurs at the DPR levels. The parameters of millisecond spikes are determined by small dimensions of the particle beams and local scale heights in the radio source. Thus, the DPR model helps to understand severai aspects of unusual elements of ZPs. However, the simultaneous existence of several tens of the DPR levels in the corona is impossible for any realistic profile of the plasma density and magnetic field. Three new theories of ZPs are examined. The formation of eigenmodes of transparency and opac- ity during the propagation of radio waves through regular coronal inhomogeneities is the most natural and promising mechanism. Two other models （nonlinear periodic space - charge waves and scattering of fast protons on ion-sound harmonics） could happen in large radio bursts.
基金Supported by the National Natural Science Foundation of China(Grant Nos. 10773032,11073058 and 10833007)the National Basic Research Program of China (973 program,No. 2011CB811402)
文摘Based on Dulk and Marsh＇s approximate theory about nonthermal gyrosyn- chrotron radiation, one simple impulsive microwave burst with a loop-like structure is selected for radio diagnostics of the coronal magnetic field and column density of non- thermal electrons, which are calculated from the brightness temperature, polarization degree, and spectral index, as well as the turnover frequency, observed by using the Nobeyama Radioheliograph and the Nobeyama Radio Polarimeters, respectively. Very strong variations （up to one or two orders of magnitude） of the calculated transverse and longitudinal magnetic fields with respect to the line-of-sight, as well as the cal- culated electron column density, appear in the looptop and footpoint sources during the burst. The absolute magnitude and varied range of the transverse magnetic field are evidently larger than those of the longitudinal magnetic field. The time evolution of the transverse magnetic field is always anti-correlated with that of the longitudi- nal magnetic field, but positively correlated with that of the electron column density. These results strongly support the idea that quantifying the energy released in a flare depends on a reconstruction of the coronal magnetic field, especially for the trans- verse magnetic field, and they are basically consistent with the recent theoretical and observational studies on the photospheric magnetic field in solar flares.
基金supported by a SUPA Advanced Fellowship (Hamish Reid)the European Research Council under the SeismoSun Research Project No. 321141 (Heather Ratcliffe)the Marie Curie PIRSESGA- 2011-295272 RadioSun project
文摘Solar type III radio bursts are an important diagnostic tool in the understanding of solar accelerated electron beams. They are a signature of propagating beams of nonthermal electrons in the solar atmosphere and the solar system. Consequently, they provide information on electron acceleration and transport, and the conditions of the background ambient plasma they travel through. We review the observational properties of type III bursts with an emphasis on recent results and how each property can help identify attributes of electron beams and the ambient background plasma. We also review some of the theoretical aspects of type III radio bursts and cover a number of numerical efforts that simulate electron beam transport through the solar corona and the heliosphere.
文摘By applying the state-of-the-art mathematical apparatus, the wavelet transformation, we explore the possibility of a dynamic cleaning of raw data ob- tained with the Chinese solar radio spectrographs over a wide wavelength range (from 0.7 to 7.6 GHz). We consider the problem of eliminating the interference caused by combination rates of data sampling (10-20 ins), and the low-frequency interference (4-30 s) caused by the receiving equipment changing its characteristics with time. It is shown that the best choice to reconstruct a signal suffering from amplitude, frequency and phase instabilities, is by means of wavelet transformation at both high and low frequencies. We analysed observational data which contained interferences of nonsolar origin such as instrumental effects and other man-made signals. A subsequent comparison of the reference data obtained with the acousto- optical receiver of the Siberian Solar Radio Telescope (SSRT) with the 'cleaned' spectra confirms the correctness of this approach.
基金support by the National Natural Science Foundation of China(Grant Nos.11273030,11221063,11373039 and 11433006)MOST Grant(2014FY120300,CAS XDB09000000)+3 种基金the National Major Scientific Equipment R&D Project(ZDYZ 2009-3)support by the Grant P209/12/00103(GA CR)the research project(RVO:67985815)of the Astronomical Institute ASsupported by the Marie Curie PIRSES-GA-295272-RADIOSUN project
文摘In the physics of solar flares, it is crucial to diagnose the physical conditions near the flare energy- release sites. However, so far it is unclear how to diagnose these physical conditions. A solar microwave type III burst is believed to be a sensitive signature of primary energy release and electron accelerations in solar flares. This work takes into account the effect of the magnetic field on the plasma density and develops a set of formulas which can be used to estimate the plasma density, temperature, magnetic field near the magnetic reconnection site and particle acceleration region, and the velocity and energy of electron beams. We apply these formulas to three groups of microwave type III pairs in an X-class flare, and obtained some reasonable and interesting results. This method can be applied to other microwave type III bursts to diagnose the physical conditions of source regions, and provide some basic information to understand the intrinsic nature and fundamental processes occurring near the flare energy-release sites.
基金Supported by the National Natural Science Foundation of China
文摘The 2.6-3.8 GHz, 4.5-7.5 GHz, 5.2-7.6 GHz and 0.7-1.5 GHz componentspectrometers of Solar Broadband Radio Spectrometer (SBRS) started routine observations,respectively, in late August 1996, August 1999, August 1999, and June 2000. They just managed tocatch the coming 23rd solar active maximum. Consequently, a large amount of microwave burst datawith high temporal and high spectral resolution and high sensitivity were obtained. A variety offine structures (FS) superimposed on microwave bursts have been found. Some of them are known, suchas microwave type Ⅲ bursts, microwave spike emission, but these were observed with more detail;some are new. Reported for the first time here are microwave type U bursts with similar spectralmorphology to those in decimetric and metric wavelengths, and with outstanding characteristics suchas very short durations (tens to hundreds ms), narrow bandwidths, higher frequency drift rates andhigher degrees of polarization. Type N and type M bursts were also observed. Detailed zebra patternand fiber bursts at the high frequency were found. Drifting pulsation structure (DPS) phenomenaclosely associated with CME are considered to manifest the initial phase of the CME, andquasi-periodic pulsation with periods of tens ms have been recorded. Microwave 'patches', unlikethose reported previously, were observed with very short durations (about 300 ms), very high fluxdensities (up to 1000 sfu), very high polarization (about 100% RCP), extremely narrow bandwidths(about 5%), and very high spectral indexes. These cannot be interpreted with the gyrosynchrotronprocess. A superfine structure in the form of microwave FS (ZPS, type U), consisting of microwavemillisecond spike emission (MMS), was also found.
