Nanoflare Activity in the Solar Chromosphere

TL;DR

This study uses high-resolution ground-based imaging to detect subtle intensity fluctuations in the solar chromosphere, providing evidence for frequent nanoflare activity that may significantly contribute to chromospheric heating.

Contribution

It demonstrates that nanoflare activity in the chromosphere is more prevalent than in the corona, using Monte Carlo simulations to interpret intensity asymmetries as impulsive events.

Findings

Negative intensity fluctuation excess indicates impulsive events.

Nanoflares occur approximately every 360 seconds in a 10,000 km^2 area.

Chromospheric nanoflares are about 50 times more frequent than coronal ones.

Abstract

We use ground-based images of high spatial and temporal resolution to search for evidence of nanoflare activity in the solar chromosphere. Through close examination of more than 10^9 pixels in the immediate vicinity of an active region, we show that the distributions of observed intensity fluctuations have subtle asymmetries. A negative excess in the intensity fluctuations indicates that more pixels have fainter-than-average intensities compared with those that appear brighter than average. By employing Monte Carlo simulations, we reveal how the negative excess can be explained by a series of impulsive events, coupled with exponential decays, that are fractionally below the current resolving limits of low-noise equipment on high-resolution ground-based observatories. Importantly, our Monte Carlo simulations provide clear evidence that the intensity asymmetries cannot be explained by photon-counting statistics alone. A comparison to the coronal work of Terzo et al. (2011) suggests that nanoflare activity in the chromosphere is more readily occurring, with an impulsive event occurring every ~360s in a 10,000 km^2 area of the chromosphere, some 50 times more events than a comparably sized region of the corona. As a result, nanoflare activity in the chromosphere is likely to play an important role in providing heat energy to this layer of the solar atmosphere.