Geoeffectiveness and flare properties of radio-loud CMEs

Abstract

A detailed investigation on geoeffective CMEs associated with meter to Deca-Hectometer (herein after m- and DH-type-II) wavelengths range type-II radio bursts observed during the period 1997–2005 is presented. The study consists of three steps: i) the characteristics of m-and DH-type-II bursts associated with flares and geoeffective CMEs; ii) characteristics of geo and non-geoeffective radio-loud and quiet CMEs, iii) the relationships between the geoeffective CMEs and flares properties. Interestingly, we found that 92 % of DH-type-II bursts are extension of m-type-II burst which are associated with faster and wider geoeffective DH-CMEs and also associated with longer/stronger flares. The geoeffective CME-associated m-type-II bursts have higher starting frequency, lower ending frequency and larger bandwidth compared to the general population of m-type-II bursts. The geoeffective CME-associated DH-type-II bursts have longer duration (P≪1 %), lower ending frequency (P=2 %) and lower drift rates (P=2 %) than that of DH-type-IIs associated with non-geoeffective CMEs. The differences in mean speed of geoeffective DH-CMEs and non-geoeffective DH-CMEs (1327 km s−1 and 1191 km s−1, respectively) is statistically insignificant (P=20 %).However, the mean difference in width (339∘ and 251∘, respectively) is high statistical significant (P=0.8 %). The geo-effective general populations of LASCO CMEs speeds (545 km s−1 and 450 km s−1, respectively) and widths (252∘ and 60∘, respectively) is higher than the non geo-effective general populations of LASCO CMEs (P=3 % and P=0.02 %, respectively). The geoeffective CMEs associated flares have longer duration, and strong flares than non-geoeffective DH-CMEs associated flares (P=0.8 % and P=1 %, respectively). We have found a good correlation between the geo-effective flare and DH-CMEs properties: i) CMEs speed—acceleration (R=−0.78, where R is a linear correlation coefficient), ii) acceleration—flare peak flux (R=−0.73) and, iii) acceleration—Dst index intensity (R=0.75). The radio-rich CMEs (DH-CMEs) produced more energetic storm than the radio-quiet CMEs (general populations of LASCO CMEs). The above results indicate that the DH-type-II bursts tend to be related with flares and geoeffective CMEs, although there is no physical explanation for the result. If the DH-type-II burst is a continuation of m-type-II burst, it could be a good indicator of geoeffective storms, which has important implications for space weather studies.