Comparison Between Radio Loud and Radio Quiet Fast CMEs: A Reason for Radio Quietness

Abstract

It is well known that fast CMEs are mostly associated with magnetohydrodynamic (MHD) shocks in the solar corona, forming type-II radio bursts. However, the absence of type-II radio bursts is not uncommon. Herein, we aim to analyze the differences between the radio loud (RL) and radio quiet (RQ) fast Coronal Mass Ejections (CMEs) (speed ≥ 900 km s⁻¹) during Solar Cycle 24 (2008 – 2021). From the 309 fast CMEs, we could identify 143 events with a known source origin on the visible disk (Earth view). We identified the associated flares/CMEs for 143 events using running-difference images from (i) Solar Dynamic Observatory/Atmospheric Imaging Assembly (SDO/AIA) and (ii) Large Angle Spectrometric Coronagraph (LASCO) observations. Among these 143 events, RQ and RL groups have 70 and 73 events, respectively. CALLISTO and Wind/WAVES observations are used to identify these RL and RQ sets. We analyzed the possibilities of streamer-CME and CME-CME interaction. In this study, we report the important differences between RL and RQ CMEs and the underlying reasons for the radio quietness of fast CMEs. In the LASCO field of view, the majority of RL CMEs (almost 90%) interacted with streamers and/or pre-CMEs, whereas only 25% of RQ CMEs did the same, and there was no pre-CME interaction. The observational evidence led to the conclusion that substantial density perturbation/interaction increases the probability of production of type-II radio emissions by the shock of RL CMEs.