Visibility and Origin of Compact Interplanetary Radio Type IV Bursts

Nasrin Talebpour Sheshvan,Silja Pohjolainen

doi:10.1007/s11207-018-1371-9

Nasrin Talebpour Sheshvan, Silja Pohjolainen

Open Access

https://doi.org/10.1007/s11207-018-1371-9

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Journal: Solar Physics	Publication Date: Oct 30, 2018
Citations: 6	License type: open-access

Affiliation: University of Turku

Abstract

We have analyzed radio type IV bursts in the interplanetary (IP) space at decameter–hectometer (DH) wavelengths to determine their source origin and a reason for the observed directivity. We used radio dynamic spectra from the instruments on three different spacecraft, STEREO-A, Wind, and STEREO-B, which were located approximately 90 degrees apart from each other in 2011 – 2012, and thus gave a 360 degree view of the Sun. The radio data were compared to white-light and extreme ultraviolet (EUV) observations of flares, EUV waves, and coronal mass ejections (CMEs) in five solar events. We find that the reason that compact and intense DH type IV burst emission is observed from only one spacecraft at a time is the absorption of emission in one direction and that the emission is blocked by the solar disk and dense corona in the other direction. The geometry also makes it possible to observe metric type IV bursts in the low corona from a direction where the higher-located DH type IV emission is not detectable. In the absorbed direction we found streamers, and they were estimated to be the locations of type II bursts, caused by shocks at the CME flanks. The high-density plasma was therefore most probably formed by shock–streamer interaction. In some cases, the type II-emitting region was also capable of stopping later-accelerated electron beams, which were visible as type III bursts that ended near the type II burst lanes.

Highlights

Coronal mass ejections (CMEs) are large-scale phenomena of plasma and magnetic field eruption from the Sun into the interplanetary (IP) medium
An extreme ultraviolet (EUV) wave occurred on the backside, observed by STEREO-A/EUVI, and it originated from the active region located at ∼ W50 in this field of view
The first brightening phase of the EUV wave started at 06:30 UT, after which a dimming phase was observed at 06:50 UT

Summary

Introduction

Coronal mass ejections (CMEs) are large-scale phenomena of plasma and magnetic field eruption from the Sun into the interplanetary (IP) medium. Solar events such as flares and CMEs accelerate particles with different mechanisms, and cause them to propagate from the solar corona into the IP space. Type II bursts are thought to be due to propagating shock fronts that accelerate electrons, and type III bursts are caused by propagating electron beams Both types of emission are produced when suprathermal electrons interact with the surrounding plasma. The particles in type III bursts are typically flare-accelerated electrons traveling along coronal magnetic field lines (Krupar et al, 2018), while type II bursts have been associated with CME-induced shock waves (Cane, 1984; Leblanc et al, 2001)

Results

Discussion

Conclusion