Type II radio bursts and their association with coronal mass ejections in solar cycles 23 and 24

Metre wavelength type II solar radio bursts are believed to be the signatures of shock-accelerated electrons in the corona. Studying these bursts can give information about the initial kinematics, dynamics and energetics of CMEs in the absence of white-light observations. In this study, we investigate the occurrence of type II bursts in solar cycles 23 and 24 and their association with coronal mass ejections (CMEs). We also explore the possibility of occurrence of type II bursts in the absence of a CME. We performed statistical analysis of type II bursts that occurred between 200 - 25 MHz in solar cycle 23 and 24 and found the temporal association of these radio bursts with CMEs. We categorised the CMEs based on their linear speed and angular width, and studied the distribution of type II bursts with `fast' ($speed ~\geq 500 km/s$), `slow' ($speed ~< 500 km/s$), `wide' ($width ~\geq 60^o$) and `narrow' ($width ~< 60^o$) CMEs. We explored the type II bursts occurrence dependency with solar cycle phases. Our results suggest that type II bursts dominate at heights $\approx 1.7 - 2.3 \pm 0.3 ~R_{\odot}$ with a clear majority having an onset height around 1.7 $\pm 0.3~R_{\odot}$ assuming the four-fold Newkirk model. The results indicate that most of the type II bursts had a white-light CME counterpart, however there were a few type II which did not have a clear CME association. There were more CMEs in cycle 24 than cycle 24. However, the number of type II radio bursts were less in cycle 24 compared to cycle 23. The onset heights of type IIs and their association with wide CMEs reported in this study indicate that the early CME lateral expansion may play a key role in the generation of these radio bursts.