Low coronal observations of metric type II associated CMEs by MLSO coronameters

Aims. We have investigated the relationship between coronal mass ejections (CMEs) and coronal type II radio bursts by using type II associated CMEs whose low coronal observations by MLSO MK coronameters (1.08-2.85 solar radii for MK4) were available.Methods. For this we considered all type II burst data at 17:00 UT to 22:00 UT from 1996 to 2003, and then compared them with CME images that were obtained during the same MLSO (Mauna Loa Solar Observatory) observing periods. As a result, we selected 19 type II associated CMEs whose kinematics are well identified. A relationship between CMEs and type IIs has been examined in terms of spatial and temporal closeness without any extrapolation of CME kinematics as well as in terms of CME-streamer interaction.Results. We found that: (1) except one event, all the metric type II events occur simultaneously or after the CME appearance in MK field of view within 30 min, mostly within 10 min after; (2) the distribution of height difference between the CME front and type II formation shows that there are double peaks, one at the CME fronts and the other at about 1 solar radius behind the front; (3) about half of the events (9/19) are identified to have CME-streamer interaction (seven streamer deflection and two overlapping), and the interaction heights are very similar to those of type II formation as well as their interaction times are nearly coincident with those of type II starting; (4) for the other events (10/19), the CME front heights at the starting time of type IIs are comparable to the heights of type II formation.Conclusions. Our low coronal observations of type II associated CMEs suggest that CME front and/or CME-streamer interaction at CME flank are two main mechanisms to generate type II bursts.