Analyzing Doublet Type II Radio Bursts During Solar Cycles 23 and 24: Key Characteristics and Trends

This paper presents a statistical analysis of doublet type II radio bursts, specifically the first type II (type II1) and the second type II (type II2), during solar cycles 23 and 24. The study focuses on radio-rich CMEs that are accompanied by type II solar radio bursts, covering a period of 15 years from November 1997 to December 2015. The characteristics of these doublet type II radio bursts were analyzed using data from the Culgoora radio spectrograph. Key parameters such as lifetime, start frequency, end frequency, bandwidth, drift rate, and estimated shock speed (ESS) of both the types of radio burst were examined. During solar cycles 23 and 24, the start frequencies of first type II bursts were generally higher than those of the second type II bursts, suggesting different driving mechanisms for the two types. A good correlation was found between start frequency and drift rate throughout the study period, with correlation coefficients of $$r = 0.5$$ for solar cycle 23 and $$r \cong 0.9$$ for solar cycle 24. This indicates that doublet type II radio bursts consistently drift from a high start frequency to a low end frequency, reflecting the rapid propagation of the shock away from the sun. However, the correlation between other solar parameters, such as lifetime, bandwidth, drift rate, and ESS was weak, implying that various drivers or mechanisms might influence the occurrence of these radio bursts. Additionally, the ESS of the first type II bursts was observed to be greater than that of the second type II bursts suggesting that doublet type II radio bursts may originate from eruptions of different structures.