Development of Coronal Holes Index For Study of Coronal Hole Geo-Effectiveness

Abstract

Coronal holes are expansion regions in the solar corona with lower density and temperature than their surroundings. Coronal holes have open magnetic field structure that radiates out into interplanetary space as the solar wind. During minimum solar activity, coronal holes play important role in space weather because they are sources of high speed-streams. Therefore, studying the geo-effectiveness of coronal holes is very important. This paper presented a development of the coronal holes geo-effectiveness index related to the occurrence of geomagnetic storms. The index which was represented as “G(CH)”, is based on the combination of center position and cross-sectional length of coronal holes surface on latitudinal direction. Using 5 years of data of coronal holes (2015-2020), we analyzed the threshold combinations of the two parameters that can be used to scale the geo-effectiveness of a coronal hole. The results of all CH events with G(CH) > 0 should be considered as geomagnetic storm generator; CH events having the same characteristics as the CME event, i.e. although they have the potential to generate geomagnetic storms, the determining factor is influenced by the behavior and conditions of the solar wind and IMF Bz (-) during reconnection. So, the intensity of geomagnetic storm is strongly influenced by behavior and conditions (value and duration) both solar wind and Bz(-); the duration of CH event with G(CH) > 0 that have the potential to generate geomagnetic storms is a minimum of 6 days after the CH event; CH events accompanied by CIR affect the intensity and duration of the geomagnetic storms they generate, and the minimum value of G(CH) = 2.21.