An Interplanetary Type IIIb Radio Burst Observed by Parker Solar Probe and Its Emission Mechanism

Abstract

Abstract Type IIIb radio bursts were identified as a chain of quasi-periodic striae in dynamic spectra, drifting from high to low frequencies in a manner similar to type III bursts, which fine structures may provide a clue to a better understanding of emission mechanisms. The approaching observation of the Parker Solar Probe (PSP) spacecraft provides a new chance of probing type IIIb bursts in the vicinity of the Sun. In this Letter, combining the in situ measurement of PSP and the empirical model of solar atmospheres in open magnetic field regions, we analyze in detail a typical event of interplanetary (IP) type IIIb bursts observed by PSP, which was first reported by Pulupa et al. Our results show that the electron cyclotron maser (ECM) emission can probably play an important role in the excitation mechanism of the IP type IIIb burst and the formation of the fine striae structure may be attributed to the modulation of Alfvén waves on the growth rate of the ECM instability.