Distinctions between the characteristics of before and after DH CMEs associated flares

Abstract

A detailed analysis of characteristics of coronal mass ejections and flares associated with deca-hectometer wavelength type-II radio bursts (DH-CMEs and DH-flares) observed in the period 1997-2008 is presented. A sample of 62 limb events is divided into two populations known as after-flare CMEs (AF-CMEs) and before-flare CMEs (BFCMEs) based on the relative timing of the flare and CME onsets. On average, AF-CMEs (1589 km s −1 ) have more speed than the BF-CMEs (1226 km s −1 ) and the difference between mean values are highly significant (P ∼ 2%). The average CME nose height at the time of type-II start is at larger distance for AF-CMEs than the BF-CMEs (4.89 and 3.84 R o , respectively). We found a good anti-correlation for accelerating (R a = −0.89) and decelerating (R d = −0.78) AF-CMEs. In the case of decelerating BF-CMEs, the correlation seems to be similar to that for decelerating AF-CMEs (R d = −0.83). The number of decelerating AF-CMEs is 51% only; where as, the number of decelerating BF-CMEs is 83%. The flares associated with BF-CMEs have shorter rise and decay times than flares related to AF-CMEs. We found statistically significant differences between the two sets of associated DH-type-II bursts characteristics: starting frequency (P ∼ 4%), drift rate (P ∼ 1%), and ending frequency (P ∼ 6%). The delay time analysis of DH-type-II start and flare onset times shows that the time lags are longer in AF-CME events than in BF-CME events (P 1%). From the above results, the AF-CMEs which are associated O. Prakash ( ) · S. Umapathy