Type IV-like Solar Radio Burst Consisting of a Series of Short-time Bursts Observed by PSP

Abstract

Solar and interplanetary radio bursts can reflect the existence and motion of energetic electrons and are therefore a kind of vital phenomenon in solar activities. The present study reported a solar radio storm observed by the Parker Solar Probe (PSP) in its eighth orbital encounter phase, and it lasted about 20 hr in a frequency range of 0.5–15 MHz, called the type IV-like burst. It consists of a series of numerous short-time (ST) bursts with the central frequency drifting slowly from ~5 to ~1 MHz, and each individual ST burst appears at a much faster frequency drifting rate and has a typical frequency range of a few MHz and a short duration of about 1–4 minutes. Based on the empirical models of the solar atmosphere adopted commonly, combining the in situ measurement by PSP, we analyzed and compared some possible mechanisms for the generation of these small-scale ST bursts and proposed that they were generated probably by a group of solitary kinetic Alfvén waves (SKAWs) in a magnetic loop accompanying coronal mass ejection and slowly moving outward, in which the frequency drifting of individual ST burst is caused by the SKAW's propagation and the central frequency drifting may be attributed to the motion of the magnetic loop.