Abstract
Abstract Coronal holes (CHs) are areas of reduced emission in EUV and X-ray images that show bright patches of microwave enhancements (MEs) related to magnetic network junctions inside the CHs. A clear correlation between the CH size and the solar wind (SW) speed is well known, but we have less information about the relationship between MEs and other CH and SW properties. We studied the characteristics of 21 equatorial CHs associated with corotating interaction regions (CIRs) during 1996 to 2005. Our CHs were divided into two groups according to the intensity of the associated geomagnetic storms: Dst≤-100 nT (10 events) and > -100 nT (11 events). Using EUV 284 Å images obtained by SOHO/EIT and 17 GHz microwave images obtained by the Nobeyama Radioheliograph (NoRH), we found a linear correlation not only between the maximum SW speed and the area of EUV CH (r = 0.62), but also between the maximum SW speed and the area of the ME (r = 0.79). We also compared the EUVCH areas with and without an overlapping ME. The area of the CHs with an ME is better correlated with the SW speed (r = 0.71) than the area of those without an ME (r = 0.36). Therefore, the radio ME may play an important role in understanding the origin of SW.
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