学术文献库

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 sets of populations based on the observation period: i) 235 events belong to SC 23 (August 1996 - December 2008) and ii) 144 events belong to SC 24 (January 2009 - December 2019). The average residual acceleration of RL CMEs in SC 24 (--17.39 $\pm$ 43.51 m s$^{-2}$) is two times lower than that of the RL CMEs in SC 23 (--8.29 $\pm$ 36.23 m s$^{-2}$), which means that deceleration of RL CMEs in SC 24 is twice as fast as in SC 23. RL CMEs of SC 23 (1443 $\pm$ 504 km s$^{-1}$; 13.82 $\pm$ 7.40 \emph{R}$_{\circledcirc}$) reach their peak speed at higher altitudes than RL CMEs of SC 24 (1920 $\pm$ 649 km s$^{-1}$; 12.51 $\pm$ 7.41 \emph{R}$_{\circledcirc}$).We also observed that the mean apparent widths of RL CMEs in SC 23 are less than in SC 24which is statistically significant. SC 23 has a lower average CME nose height (3.85 \emph{R}$_{\circledcirc}$) at the start time of DH type II bursts than that of SC 24 (3.46 \emph{R}$_{\circledcirc}$). The starting frequencies of DH type II bursts associated with RL CMEs for SC 24 are significantly larger (formed at lower heights) than that of SC 23. We found that there is a good correlation between the drift rates and the mid-frequencies of DH type II radio bursts for both the solar cycles (\emph{R} = 0.80, $ε$ = 1.53). Most of the RL CMEs kinematics and their associated solar flare properties are found similar for SC 23 and SC 24. 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 SC 23.