The Relation Between Large-Scale Coronal Propagating Fronts and Type II Radio Bursts

Abstract

Large-scale, wave-like disturbances in extreme-ultraviolet (EUV) and type II radio bursts are often associated with coronal mass ejections (CMEs). Both phenomena may signify shock waves driven by CMEs. Taking EUV full-disk images at an unprecedented cadence, the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory has observed the so-called EIT waves or large-scale coronal propagating fronts (LCPFs) from their early evolution, which coincides with the period when most metric type II bursts occur. This article discusses the relation of LCPFs as captured by AIA with metric type II bursts. We show examples of type II bursts without a clear LCPF and fast LCPFs without a type II burst. Part of the disconnect between the two phenomena may be due to the difficulty in identifying them objectively. Furthermore, it is possible that the individual LCPFs and type II bursts may reflect different physical processes and external factors. In particular, the type II bursts that start at low frequencies and high altitudes tend to accompany an extended arcshaped feature, which probably represents the 3D structure of the CME and the shock wave around it, rather than its near-surface track, which has usually been identified with EIT waves. This feature expands and propagates toward and beyond the limb. These events may be characterized by stretching of field lines in the radial direction, and be distinct from other LCPFs, which may be explained in terms of sudden lateral expansion of the coronal volume. Neither LCPFs nor type II bursts by themselves serve as necessary conditions for coronal shock waves, but these phenomena may provide useful information on the early evolution of the shock waves in 3D when both are clearly identified in eruptive events.

The Physical Processes of CME/ICME Evolution

“…UVCS gave clear spectroscopic evidence for the presence of shock fronts, while type II radio bursts indicated the presence of shock-accelerated electrons. A connection between type II radio bursts and CME-driven shocks has been established by many studies (e.g., Reiner et al 1998;Liu et al 2009Reames 2013;Nitta et al 2014; MHD simulations also provide predictions of the appearance of CME-driven shocks in a variety of observing modes. Pagano et al (2008) modeled the spectral line signatures of CME-driven shocks as they appear in UVCS, and , simulated the appearance of coronal shocks in synthetic coronagraph images derived from simulations of specific CME events.…”

A Statistical Analysis of the Solar Phenomena Associated with Global EUV Waves

“…Nelson and Melrose, 1985) and as a result the relationship between them and global waves has long been hypothesised and investigated (e.g. Cliver, Webb, and Howard, 1999;Biesecker et al, 2002;Nitta et al, 2014). However, their relationship remains inconclusive.…”

“…More recent work has extended this systematic approach to observations from the Extreme UltraViolet Imager (EUVI; Wuelser et al, 2004) on board STEREO (Muhr et al, 2014;Nitta et al, 2014) and SDO/AIA (Nitta et al, 2013). In each of these cases the global waves were identified using semi-automated techniques; Muhr et al (2014) defined the direction into which the wavefront propagated and used a perturbation profile technique to fit the leading edge of the wavefront while Nitta et al (2013Nitta et al ( , 2014 used 2D intensity stack plots produced by a series of arc sectors to visually identify the leading edge of the wavefront. Each approach requires manual input from the user, potentially making them susceptible to user bias.…”

Global Coronal Waves

“…One simple option is that they are classified as slow EUV waves and fast EUV waves. The second option is that the slower EUV waves can be called "type I EUV waves" and the faster EUV waves be called "type II EUV waves" since the slower EUV waves should be related to type I radio bursts (both of them result from magnetic field reconfiguration) and the faster EUV waves should be related to type II radio bursts (both of them are from the CMEdriven shock, although one may appear without the other, Nitta et al 2014). The third option is that the slower EUV waves can be called "coronal propagating fronts" and the faster EUV waves can be called fast-mode EUV wave/shock wave.…”