Influence of Polar Coronal Holes on Solar Wind Characteristics at the Activity Minimum between Solar Cycles 24 and 25

Abstract

The SDO/AIA 193 A and ACE/SWEPAM data acquired in 2019 are used to compare the effects of polar and equatorial coronal holes (CHs) on solar wind (SW) characteristics under conditions of low solar activity. As expected, most geomagnetic storms in this period were caused by high-speed SW streams ( $${>}500{-}600$$ km s $${}^{-1}$$ ) originating from equatorial CHs. At the same time, it has been shown that at a deep solar activity minimum polar CHs can exert a noticeable influence on SW characteristics at the Earth’s orbit. A correlation with a correlation coefficient of 0.8 has been found for the integrated polar CH area and the SW speed in the investigated period. The southern polar CH, for which a correlation with the SW speed with a correlation coefficient of 0.82 was found in the spring of 2019 (in the period when the south solar pole was maximally tilted to the Earth), exerted a particularly significant influence on the SW speed. The northern polar CH had virtually no effect on the SW speed. An anticorrelation of the polar CH area with the SW speed at the Earth’s orbit was found in the fall of 2019, in the period when the north solar pole was tilted to the Earth. We discuss a possible mechanism for the influence of polar CHs on SW characteristics and propose an interpretation of the results obtained.