Statistical properties of radio flux densities of solar flares

Short timescale flux variations are closely related to the energy release process of magnetic reconnection during solar flares.Radio light curves at 1,2,3.75,9.4,and 17 GHz of 209 flares observed by the Nobeyama Radio Polarimeter from 2000 to 2010 are analyzed with a running smooth technique.We find that the impulsive component(with a variation timescale shorter than 1 s)of 1 GHz emission of most flares peaks at a few tens of solar flux unit and lasts for about 1 minute and the impulsive component of 2 GHz emission lasts a shorter period and peaks at a lower flux level,while at the three high frequency channels the occurrence frequency of flares increases with the decrease of the flux density up to the noise level of the corresponding background.However,the gradual components of these emissions have similar duration and peak flux density distributions.We also derive the power spectrum on different timescales and a normalized wavelet analysis is used to confirm features on short timescales.At a time resolution of 0.1 s,more than^60%of these radio light curves show significant flux variation on 1 s or shorter time scales.This fraction increases with the decrease of frequency and reaches^100%at 1 GHz,implying that short timescale processes are universal in solar flares.We also study the correlation between the impulsive radio flux densities and soft X-ray fluxes obtained with the GOES satellites and find that more than 65%of the flares with an impulsive component have their impulsive radio emission reach a peak value ahead of the soft X-ray fluxes and this fraction increases with the radio frequency.

Observational evidence of magnetic reconnection in a coronal bright point

Magnetic reconnection is considered to be the fundamental process by which magnetic energy is converted into plasma or particle kinetic energy.Magnetic reconnection is a widely applied physics model to explain the solar eruption events,such as coronal bright points(CBPs).Meanwhile,it is an usual way of the solar physics research to look for the observational evidences of magnetic reconnection in the solar eruption events in order to support the model.In this paper,we have explored the evidences of magnetic reconnection in a CBP observed by the Atmospheric Imaging Assembly(AIA)onboard the Solar Dynamics Observatory(SDO)at NOAA No.11163 on 2011 March 5.Our observations show that this event is a small-scale loop system in active regions that have similar size as a traditional CBP and it might shed light on the physics of a traditional CBP.This CBP is bright in all nine AIA wavelengths and displays a flaring development with three bursts intermittently.Each burst exhibits a pair of bi-directional jets almost along a line.They originate from the same position(CBP core),then move in the opposite directions.Our findings are well consistent with the magnetic reconnection process by which the bi-directional plasma outflows are produced and radiate the bi-directional jets detected by SDO/AIA.These facts further support the conclusion that the CBP is produced by the magnetic reconnection process.

The impact of turbulence on electron heating and acceleration near the neutral point of externally driven reconnecting current sheets in solar flares

We aim to investigate the influence of plasma instability on electron acceleration and heating near the neutral point of a turbulent reconnecting current sheet （RCS）.Through numerically solving the one dimensional relativistic Vlasov equation with typical solar coronal parameters and a realistic mass ratio in the presence of a strong inductive electric field E0,we suggest that the wave-particle scattering may produce a flat electron flux spectrum from thermal to nonthermal electrons without a sudden low-energy cutoff in the acceleration region.The ratio between electron heating and acceleration decreases with the increase of the induced electric field.It is about one for E0=1 V cm-1 and one fourth for E0=10 V cm-1.The unstable waves excited by the beam plasma instability first accelerate the electrons,then trap these electrons from further acceleration by an induced electric field through wave-particle resonant interactions.