New Insights into the Relation Between Coronal Mass Ejections and Nonthermal Radio Emissions
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Date
2016-04
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Addis Ababa University
Abstract
Coronal Mass Ejections (CMEs) are the main space weather drivers. Studying CME kinematics and associated events is important to be able to make predications before a CME arrival and make proper arrangements. Type II bursts are signatures of energetic CMEs. By studying type II bursts, it is possible to probe the information on the associated CME remotely since they are electromagnetic waves, which arrive at Earth in ~ 8 minutes but the CME arrival time is not less than a day. In this research, we report on the complex type II radio burst of 2012 January 19 and its association with a CME. The dynamic spectrum shows a pair of type II bursts with fundamental – harmonic structures, one confined to decameter-hectometric (DH) and the other extending to kilometric (km) wavelengths. By comparing the CME and shock speeds, the coronal density obtained from white-light polarization brightness images with that inferred from the fundamental component of the type II burst, we show that the radio sources of the DH-km and the DH come from the region above the flank and near the nose of the shock, respectively. We report also on an unusual drifting feature in the radio dynamic spectrum at frequencies below 14 MHz that occurred on 2001 September 27 observed by the Radio and Plasma Waves (WAVES) experiment on board the Wind spacecraft. We call this feature a “Diffuse Interplanetary Radio Emission (DIRE)”. It occurred in association with a regular type II burst. It is observed at higher frequency than the associated type II burst, with no harmonic relationship with the type II burst. We identified the source of the DIRE is the flank. Study on DIRE statistics showed DIREs have slightly larger drift rates than the regular type II bursts. Their onset is generally delayed from the onset of the regular type II bursts. DIREs are mostly associated with fast-halo and disk centered CMEs. Finally, we revisit the hierarchical relationship between the different wavelength ranges of the type II bursts from Wind/WAVES and the associated CME kinetic energy reported previously. We consider pure DH, m-DH and DH-km as separate groups, which are previously included under a single DH (DH: decameter-hectometric; m: metric; km: kilometric). We find that the kinetic energy of CMEs organizes the hierarchal relationship of type II bursts. Collectively, our results give a new way to look at nonthermal radio emission from CMEs, which can be used to improve predictions of CME travel in the interplanetary medium
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Nonthermal Radio Emissions