Observation And Wave-Propagation Simulations On The Source Of Solar Radio Bursts

In solar activities,the energy accumulation and eruption process are often accompanied by the generation of high-energy electrons.The high-energy electrons transporting through the plasma in the solar atmosphere and interplanetary can produce strong electromagnetic(EM)radiation by coherent radiation mechanism,namely solar radio bursts whose bright temperature can reach 1015k.The analysis on the solar radio bursts emission can help understanding the particle acceleration process in the solar eruption activities.Solar radio bursts also provides a unique perspective to diagnose the source region of solar eruptions and the interplanetary space environment.However,due to the lack of in-situ observations,the specific details of the emission mechanism and EM wave propagation of solar radio bursts remain unclear,which requires more data analyses,high-resolution observations,and the simulations on the influences of wave propa-gation effect on the observation features,so as to infer the radiation mechanism and the physical process happening in the source region.In this thesis,the generation and propagation of solar radio bursts are studied with the method of observation and simulation.The main results are as follows:Extract Information from Type ? Burst ObservationFirstly,we designed an event recognition analysis system that can automatically detect solar Type ? radio burst and extract the key parameters of the burst from the dynamic spectra observation.These parameters include the time of occurrence,the starting and stopping frequencies,the frequency driftline,and the frequency drift rate of the burst.We run this system on the NDA data of half solar cycle from 2012 to 2017,and estimate the exciter speed using three corona density models.The statistical results show that there is not any significant dependence of the drift rate on the cycle of solar activity.The exciter electrons may experience weak acceleration in the corona in the corresponding height range(1.5-2.0 solar radii)of decameter Type ? bursts(between 80MHz and 10MHz).Then,we proposed a forward modeling method to measure the speed,and trajectory of interplanetary Type ? bursts.This method uses the arrival time of the radio waves at multiple spacecraft(STEREO-A,B/WAVES and WIND/WAVES)in dynamic spectrum,by fitting the observation data to the model of Type ? radio burst exciter,we can obtain the speed and trajectory of the exciter.The reliability of this method is verified by a few interplanetary Type ? burst events with know source location,showing that this method is reliable.Dominant Factor of the Duration of Type ? Solar Radio BurstsWith tied array beamformed imaging of LOFAR(the LOw Frequency ARray),the source positions of different time and frequency points in the spectrum of Type ?bursts is semantically analyzed.There factors that may affect the duration of Type ?radio burst are discussed:(1)electron density fluctuations,(2)velocity dispersion in the electron beam,and(3)propagation effect of radio wave.Based on the quantitative analyses of the source region position,the final conclusion is that the dominant factor of the duration in single frequency channel of the Type ? radio burst in the 30-40MHz frequency band is the velocity dispersion of the electron beam.Fine Structures in The Solar Radio BurstsSolar S bursts is studied with LOFAR-HBA's high-resolution spectroscopy.A fine drift variation pattern was found in the structure of S-bursts.have a quasiperiodic segmented pattern,and the relative flux intensity tends to be large when the frequency drift rate is relatively large.We propose that the fine structure is due to the density fluc-tuations of the background coronal density.We performed a simulation based on this theory that can reproduce the shape and relative flux intensity of the fine structures of S-bursts.The properties of solar Type ?-?b is analysed with high spatial resolution interferometric imaging.It is found that the source of fundamental emission has a large visual velocity(>3.5c)and the visual area expansion rate can reach 382 arcmin2/s,while the source of harmonic emission is very static,the visual speed is about 0.01c,the expansion rate is smaller than 0.5 arcmin2/s.Simulation of the Wave Propagation EffectWe performed systematic ray tracing simulations on the wave propagation effects with anisotropic background density model.the size,duration,offset,visual speed,area expansion rate,and the brightness of the radio burst source is reconstructed from the statistical of the final position and wave vector of the photons.By comparing the source properties in the simulation and observation,the scattering rate and level of anisotropy is estimated.The simulation results indicate that,the anisotropic scattering can effectively explain the phenomena such as the size,duration of the observed source region and the Cospatial phenomena of the fundamentalharmonic pair in given frequency.From the simulation,we found that,the wave propagation effect can cause visual motion and expansion of the observed source.In the simulation results,the visual speed of the source can reach 1.5c and the expansion rate can reach 442 arcmin2/s.Moreover,the propagation effect can cause a large attenuation of the brightness of the fundamental frequency source,which requires higher efficiency of the radio wave excitation in the radiation mechanism.In this thesis,we present a serial of work including data analyses and modeling,observation and simulation.With these works,more effective information can be extracted from the radio burst observation with the method of automatic identification and data modeling.The parameters and fine structures of radio bursts are analyzed with high-resolution observations.Finally,the relationship between the observation and the real source is established through ray tracing simulation,which provides a reference for the following study of the source property diagnostics and radiation mechanism quantification of solar radio bursts.