Examination of Type II Origin with SOHO/LASCO Observations

Details Examination of Type II Origin with SOHO/LASCO Observations Examination of Type II Origin with SOHO/LASCO Observations

May 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmsp23a..10c&link_type=abstract

American Geophysical Union, Spring Meeting 2005, abstract #SP23A-10

Astronomy and Astrophysics

Astrophysics

7500 Solar Physics, Astrophysics, And Astronomy, 7509 Corona, 7513 Coronal Mass Ejections, 7519 Flares, 7534 Radio Emissions

Scientific paper

We examine a possibility that the origin of metric-type II solar radio bursts are coronal mass ejections (CMEs). For this we consider 129 type IIs-flare events from February 1997 to October 2000, and examine their association with SOHO/LASCO CMEs according to their time closeness. Among 129 events, we select 27 limb type II-CME events whose solar surface locations are identified by comparing LASCO and EIT running difference images. In addition, we examine four CMEs observed by LASCO C1 or MLSO Mk4 coronagraph at the time of type II bursts. Under the assumption that the observed type IIs are all generated by CMEs, we determine the formation heights of the CME-associated type IIs using LASCO CME seeds and type II onset times. The criteria for shock formation is assumed that the CME speed is larger than the empirically determined Alfvén speed, and the shock formation height is located within the range taking into account the coronal density effect and the observed type II starting frequencies. From these studies, we have found: (1) the type II bursts associated with CMEs do not strongly depend on longitude but more than 80 % events of the limb events seems to have temporal and spatial association with CMEs; (2) while 61 % (19/31) CMEs (Class I) satisfy the criteria for coronal shock formation, 39% (12/31) CMEs (Class II) violate the criteria; (3) the onset time comparison shows that while the Class I CMEs occurred just before (or nearly simultaneously) the type II onset, the onset time differences (CME - type II) of the Class II CMEs are widely scattered; and (4) the speeds of the Class I CMEs have a much better correlation with coronal shock speeds estimated from type II data than those of the Class II CMEs. Our results show that all type II bursts can not be explained by only CMEs, but large fraction of type IIs have close association with CMEs.

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