Heating Mechanisms and Radio Response from the Solar Chromosphere to Corona

TL;DR

This paper reviews heating mechanisms in the solar atmosphere, proposes a new magnetic-gradient pumping mechanism, and discusses how broadband radio observations can distinguish among these mechanisms to understand the corona's physics.

Contribution

It introduces the magnetic-gradient pumping heating mechanism and links specific radio spectral signatures to different heating processes in the solar atmosphere.

Findings

Different heating mechanisms produce distinct radio spectral signatures.

Radio observations can be used to identify and verify the dominant heating process.

The proposed MGP mechanism offers a potential solution to longstanding heating problems.

Abstract

Heating mechanism in the solar atmosphere (from chromosphere to corona) is one of the top-challenges in modern astronomy. The classic mechanisms can be divided into two categories: wave heating (W) and magnetic reconnection heating (X). Both of them still face some problems currently difficult to overcome. Recently, we proposed a new mechanism, called magnetic-gradient pumping heating (MGP, or P) which seems to overcome those difficulties, but still lacks sufficient observational evidence. Which one really explained the physics of hot corona exactly? How can observations be used to identify and verify the heating mechanism? Since different heating mechanism will generate non-thermal particles from different accelerations and experience different propagations, they will have different response on the broadband spectral radio observations. Among them, the non-thermal electrons from W mechanisms are closely related to shock-wave acceleration, and their radio response should be group of spike bursts with random distribution of drifting rates; the non-thermal electrons from X mechanisms are accelerated by reconnecting electric field with bidirectional flow, and their radio response should be type III pairs or spike pairs; P mechanism will produce energetic particle upflows, and their radio response should be unidirectional fiber bursts with moderate negative drifting rates. Therefore, the heating mechanism can be identified and verified from the the broadband dynamic spectral radio observations. Additionally, using high-resolution radioheliographs and spectral-imaging observations, the heating mechanisms in different regions can be identified and verified separately, thereby demonstrating the physical essence of hot corona.