Kinematic Study of Radio-Loud CMEs Associated with Solar Flares and DH Type-II Radio Emissions During Solar Cycles 23 and 24

Abstract

We have statistically analyzed 379 radio-loud (RL) CMEs and their associated flares during the period 1996 - 2019 covering both Solar Cycles (SC) 23 and 24. We classified them into two populations based on the observation period: i ) 235 events that belong to SC 23 (August 1996 - December 2008) and ii ) 144 events that belong to SC 24 (January 2009 - December 2019). For both cycles, the mean sky-plane speed, projection corrected speed (space speed), and initial acceleration of RL CMEs are found to be similar. Moreover, the average residual acceleration of RL CMEs in SC 24 (−17.39 ±43.51 m s⁻²) is twice lower than that of the RL CMEs in SC 23 (−8.29 ±36.23 m s⁻²), which means that the deceleration of RL CMEs in SC 24 is twice as fast as in SC 23. RL CMEs reach their peak speed at higher altitudes in SC 23 (1443 ±504 km s⁻¹; 13.82 ±7.40 R_⊙) than SC 24 (1920 ±649 km s⁻¹; 12.51 ±7.41 R_⊙). We also observed that the mean apparent widths of RL CMEs in SC 23 are less than in SC 24, which is statistically significant. SC 23 has a lower average CME nose height (3.85 R_⊙) at the start time of DH type-II bursts than that of SC 24 (3.46 R_⊙). The starting frequencies of DH type-II bursts associated with RL CMEs for SC 24 are significantly larger (formed at lower heights) than those of SC 23. We found that there is a good correlation between the drift rates and the midfrequencies of DH type-II radio bursts for both of these solar cycles (R² = 0.80, ε = 1.53). Most of the RL CMEs kinematics and their associated solar-flare properties are found to be similar for SC 23 and SC 24. The annual variations for the general population of CMEs are well consistent with the mean sunspot number but small variations in halo and RL CMEs are observed. We concluded that the reduced total pressure in the heliosphere for SC 24 enables RL CMEs to expand wider and decelerate faster, resulting in DH type-II radio emissions at lower heights than for SC 23.