# Characteristics of ephemeral coronal holes

## TL;DR

This study systematically identifies and characterizes small, short-lived ephemeral coronal holes on the Sun, analyzing their properties and magnetic features using SDO data from 2010-2015.

## Contribution

First systematic analysis of ephemeral coronal holes, detailing their growth, decay, magnetic properties, and rarity based on SDO observations.

## Key findings

- Ephemeral coronal holes grow rapidly up to 3000 Mm2/hr.
- Decay phases are more gradual than growth phases.
- Mean magnetic flux densities are generally less than 10 G.

## Abstract

Small-scale ephemeral coronal holes may be a recurring feature on the solar disk, but have received comparatively little attention. These events are characterized by compact structure and short total lifetimes, substantially less than a solar disk crossing. We present a systematic search for these events, using Atmospheric Imaging Assembly EUV image data from the Solar Dynamics Observatory, covering the time period 2010 - 2015. Following strict criteria, this search yielded four clear examples of the ephemeral coronal hole phenomenon. The properties of each event are characterized, including their total lifetime, growth and decay rates, and areas. The magnetic properties of these events are also determined using Helioseismic and Magnetic Imager data. Based on these four events, ephemeral coronal holes experience rapid initial growth of up to 3000 Mm2/hr, while the decay phases are typically more gradual. Like conventional coronal holes, the mean magnetic field in each ephemeral coronal hole displays a consistent polarity, with mean magnetic flux densities generally < 10 G. No evidence of a corresponding signature is seen in solar wind data at 1 AU. Further study is needed to determine whether ephemeral coronal holes are under-reported events or a truly rare phenomenon.