Coronal Holes and Open Magnetic Flux over Cycles 23 and 24

TL;DR

This study analyzes coronal holes and their evolution over solar cycles 23 and 24 using multi-instrument EUV observations, revealing hemispheric asymmetries and distinct latitudinal behaviors.

Contribution

It provides a comprehensive automatic detection and characterization of coronal holes over two solar cycles, highlighting hemispheric asymmetries and latitudinal differences.

Findings

Hemispheric asymmetry in polar coronal holes

Distinct latitudinal behavior of coronal hole areas

Lag between hemispheres in polar coronal hole appearance

Abstract

As the observational signature of the footprints of solar magnetic field lines open into the heliosphere, coronal holes provide a critical measure of the structure and evolution of these lines. Using a combination of Solar and Heliospheric Observatory / Extreme ultraviolet Imaging Telescope (SOHO/EIT), Solar Dynamics Observatory / Atmospheric Imaging Assembly (SDO/AIA) and Solar Terrestrial Relations Observatory / Extreme Ultraviolet Imager (STEREO/EUVI A/B) extreme ultraviolet (EUV) observations spanning 1996-2015 (nearly two solar cycles), coronal holes are automatically detected and characterized. Coronal hole area distributions show distinct behavior in latitude, defining the domain of polar and low-latitude coronal holes. The northern and southern polar regions show a clear asymmetry, with a lag between hemispheres in the appearance and disappearance of polar coronal holes.