Energetics of the solar atmosphere

TL;DR

This paper investigates the energetics of small transient events in the solar corona, using modeling to understand their distribution, impulsive heating, and relation to larger phenomena like flares.

Contribution

It introduces an improved EBTEL model to simulate impulsive coronal events across a wide energy range based on a power-law distribution.

Findings

Impulsive heating is consistent with observed multi-thermal plasma emissions.

Coronal loop modeling suggests impulsive events follow a power-law energy distribution.

Field-aligned flows play a significant role in transition region heating.

Abstract

The excess temperature of the solar corona over the photosphere poses a challenge. Multiple energetic events contribute to maintaining the corona at such high temperatures. The energy released in different events can vary across several orders of magnitude. Large energy events of geomagnetic importance like flares and coronal mass ejections (CMEs) contribute little to the global energetics of the solar corona. Therefore, events with several (9-10) orders of magnitudes of lower energy, with much higher frequency of occurrence, need to be studied in great detail. Observations suggest that these impulsive events with different energies follow a power-law distribution, indicating a common underlying mechanism. We perform observation-motivated modeling of coronal loops (magnetic flux tubes) to understand the energetics of these small transient events and their similarity with impulsive events like flares. This thesis uses the EBTEL code based on the 0D hydrodynamical description of coronal loops. This approach is appropriate for getting quick estimates of the energetics of the system over a wide range of parameters. We then discuss the improvement of EBTEL to make it suitable over a broader range of parameters. This is followed by using improved EBTEL to explore the possibility of simulating impulsive events of different energy generated using a single power-law distribution. Comparison between observed emissions from various components of multi-thermal plasma and hydrodynamical models suggest the heating to be impulsive. Since field-aligned flows induced due to impulsive events are a crucial part of our modeling of coronal loops, we discuss the implications of such flows in the context of transition region heating.