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

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