Microflares and the Statistics of X-ray Flares

TL;DR

This review discusses the statistical properties of solar X-ray microflares, revealing their similarities to larger flares, and examines their implications for coronal heating and flare distributions.

Contribution

It provides new insights from RHESSI data on microflares, highlighting their characteristics and challenging their role in coronal heating.

Findings

Microflares resemble larger flares in many aspects.

Microflares occur only within active regions.

Microflares do not significantly contribute to coronal heating.

Abstract

This review surveys the statistics of solar X-ray flares, emphasising the new views that RHESSI has given us of the weaker events (the microflares). The new data reveal that these microflares strongly resemble more energetic events in most respects; they occur solely within active regions and exhibit high-temperature/nonthermal emissions in approximately the same proportion as major events. We discuss the distributions of flare parameters (e.g., peak flux) and how these parameters correlate, for instance via the Neupert effect. We also highlight the systematic biases involved in intercomparing data representing many decades of event magnitude. The intermittency of the flare/microflare occurrence, both in space and in time, argues that these discrete events do not explain general coronal heating, either in active regions or in the quiet Sun.