Complex shock wave signatures associated with CME on September 27/28, 2012

Immanuel Christopher Jebaraj, Royal Observatory of Belgium

Eruptive events such as Coronal mass ejections (CMEs) and flares can accelerate particles and generate shock waves. Tracking of shock waves and predicting their arrival at the Earth is an important scientific goal. Space based radio observations provide us the unique opportunity to track shock waves in the inner heliosphere. We present study of the CME/flare event on September 27/28, 2012. The GOES C3.7 flare that originated from NOAA AR 1577 was associated with a full-halo CME (first seen in the SOHO/LASCO C2 field of view at 23:47 UT) and white light shock wave observed by all three spacecraft STEREO A, STEREO B, and SOHO. The associated radio event shows a group of type III bursts and two somewhat unusual type II bursts with significantly different starting frequencies. To understand the origin of the two shock waves we performed multi-wavelength and radio triangulation study. For the radio triangulation we used goniopolarimetric measurements from STEREO/WAVES and WIND/WAVES instruments. We also model propagation of the CME using the data-driven EUHFORIA cone model (EUropean Heliospheric FORecasting Information Asset) and compared results with in-situ observations. Results of this study indicate that, although temporal association between the shocks and the CME is good, the low frequency type II burst occurs significantly higher in the solar corona than the associated CME and has therefore unclear origin. Our analysis indicates that the interaction of the shock wave and the nearby streamer, situated close to the southern polar coronal hole, is the most probable source of the observed low frequency type II burst. We also demonstrate the importance of radio triangulation studies in understanding the relationship between the CMEs and associated radio emissions.