Correlation of Coronal Hole Area Indices and Solar Wind Speed

TL;DR

This study investigates the relationship between coronal hole area indices and solar wind speed, finding strong correlations with specific indices and highlighting the importance of catalog selection for reliable solar wind predictions.

Contribution

It identifies specific coronal hole area indices that strongly correlate with solar wind speed and compares different catalogs to assess their reliability for this purpose.

Findings

1-year averaged CH areas within 30° of solar equator correlate with solar wind speed at 0.9

Correlation strength varies significantly between different CH catalogs

Time-latitude diagrams of correlation can help identify source regions of high-speed streams

Abstract

Coronal holes (CHs) are widely considered as the main sources of high-speed solar wind streams. We validate this thesis comparing the smoothed time series of solar wind speed measured by Advanced Composition Explorer (ACE) and various indices of CH areas constructed from the CH catalog compiled at the Kislovodsk Mountain Astronomical Station for the period 2010-2025. The main result is that we find specific indices of CH areas that give a strong correlation with smoothed solar wind speed variations. As an example, 1-year averaged areas of CHs located within 30 degrees of the solar equator yield a correlation of 0.9 with 1-year averaged solar wind speed. This strong correlation is a feature of the particular CH catalog, and considering an alternative CH catalog obtained using the Spatial Possibilistic Clustering Algorithm (SPoCA) from the Heliophysics Event Knowledgebase (HEK), the same index provides a correlation of only 0.3. Although the fact that the correlation significantly depends on the catalog requires a separate discussion, we conclude that if some of the catalogs can be used to construct a reliable indicator of solar wind speed variations, then this methodology should be maintained further. Additionally, we present time-latitude diagrams of rolling correlation between CHs areas and solar wind speed, which, in our opinion, can be used to reveal source CHs for high-speed solar wind streams.