On the variation of the scaling exponent of the flare fluence with temperature

TL;DR

This study investigates how the distribution of solar flare energy varies across different atmospheric temperatures, revealing a potential trend in the scaling exponent related to the formation region of emission lines.

Contribution

It provides the first comprehensive analysis of flare fluence distributions across multiple temperature-sensitive lines using SDO/EVE data, highlighting a possible temperature-dependent variation in the scaling exponent.

Findings

Scaling exponent decreases from above 2 at lower temperatures to about 1.8 at higher temperatures.

Cold lines show smaller contrast, possibly affecting the observed trend.

Method limitations include noise influence on smaller flares.

Abstract

Solar flares result in an increase of the solar irradiance at all wavelengths. While the distribution of the flare fluence observed in coronal emission has been widely studied and found to scale as f(E) ~ E^{-\alpha}, with \alpha slightly below 2, the distribution of the flare fluence in chromospheric lines is poorly known. We used the solar irradiance measurements observed by the SDO/EVE instrument at a 10s-cadence to investigate if there is a dependency of the scaling exponent on the formation region of the lines (or temperature). We analyzed all flares above the C1 level since the start of the EVE observation (May 2010) to determine the flare fluence distribution in 16 lines covering a large range of temperature, several of which were not studied before. Our results show a small downward trend with the temperature of the scaling exponent of the PDF, going from above 2 at lower temperature (a few 10^4 K) to about1.8 for hot coronal emission (several 10^6 K). However, because colder lines also have smaller contrast, we could not exclude that this behavior is caused by including more noise for smaller flare for these lines. We discuss the method and its limits and tentatively associate this possible trend to the different mechanisms responsible for the heating of the chromosphere and corona during flares.