Summary Using 21 equatorial CHs during the solar cycle 23 we studied the correlation of SW velocity with the area of EIT CH and the area of NoRH RBP. SW speed was correlated with both CH (r=0.62) and RBP (r=0.78) areas. When EUV CH area overlapped with RBP, SW velocity was correlated better with the CH area (r=0.69) than when there is no overlap (r=0.38). Therefore RBP may be closely related to the origin of fast SW. ● Kosugi et al., 1986, PASJ, 38, 1 ● Luo et al., 2008, Solar Physics, 250, 159 ● Kundo & Mc.Cullough, 1972, Solar Physics, 24, 133 ● Obridko et al., 2009, Solar Physics, 260, 191 ● Gopalswamy et al., 1999, JGR, 104, 9767 ● Phojolainen et al., 2000, A&A, 143, 227 ● Jian et al., 2006, Solar Physics, 239, 337 ● Richardson et al., 2006, JGR, 111, A07S09 ● Nolte et al., 1976, Solar Physics, 46, 303 Abstract Coronal holes (CHs) identified as areas of reduced emission in EUV and X-ray images show bright patches of microwave enhancements related to magnetic network junctions inside the CHs. Clear correlation between CH size and solar wind (SW) speed is well known, but we have less information for the relationship between CH’s radio bright patch (RBP) and other properties. We study the characteristics of 21 equatorial CHs associated with corotating interaction regions (CIRs) in the interval 1996 to Our data set is divided into two groups according to the size of the 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 Radio Heliograph (NoRH), we found linear correlation of the maximum SW velocity for not only the area of EUV CH (r=0.62) but also the area of RBP (r=0.78). We also compared the EIT CH areas with and without overlapping RBP. The area of CH with RBP was strongly correlated with SW speed (r=0.69) than that without RBP (r=0.38). Therefore the radio enhancements may play an important role in the origin of fast SW. SW speed vs. CH area in EUV and microwave Fig. 2a and 2b are the scatter plots of SW velocity vs. CH and RBP areas. We can see linear correlations of SW speed with CH area (r=0.62) and RBP (r=0.78). The weak storms have a better correlation than the large storms. If the CH area overlapped with RBP, the correlation is better (r= Fig. 2c) compared to the case where there is no overlap (r= Fig. 2d). Introduction CHs and CIR storms CHs are sources of high-speed SW, which result in CIRs in the interplanetary (IP) medium. During solar cycle 23 the majority of CIR-associated storms were weaker (mean Dst = -46 nT) compared to ICME-associated storms (mean Dst = -76 nT) (Richardson et al., 2006). So large CIR storms with Dst ≤ -100 nT were rare events. CH properties influencing the SW speed Nolte et al. (1976) found SW speed correlated with the area of equatorial CH. Recently some reports showed a negative correlation between the intensity of CH and SW speed (Luo et al. 2008; Obridko et al. 2009). CHs and microwave enhancements Radio observations (from 17GHz to 87 GHz) showed RBP in CH (Kundu & McCullough 1972; Kosugi et al. 1986; Pohjolainen et al. 2000). Gopalswamy et al. (1999) pointed out that RBP overlapped with a strong unipolar magnetic flux elements in the network and had a temporal relationship with EIT 304Å observation. In this study we compared CH area and RBP from a standpoint of geomagnetic storms. Sachiko Akiyama 1,2, Nat Gopalswamy 2, and Seiji Yashiro 1,2 1 The Catholic University of America, 2 NASA/GSFC, Study of Coronal Holes Observed by SOHO/EIT and Nobeyama Radio Heliograph Data Analysis Data set We consisted a set of 10 CHs associated with a large storm (min. Dst ≤ -100 nT) (Zhang et al. 2007) and another set of 11 CHs associated with a weak storm (min. Dst ≥ -100 nT) (Jian et al. 2006). Definition of EIT CH and NoRH RBP Using EIT 284Å images we defined CH area as the area enclosing an intensity less than I threshold [median(EIT DISK )×0.5]. A CH’s central meridian (CM) passage time was estimated from the time of the largest area within 10 deg. range from CM. Using NoRH 17GHz images we made the histogram-equalized image to see the RBP distinctly. The area of RBP was defined as the one with brightness temperature more than Tb threshold [median(Histogram(NoRH DISK ))×0.75]. Since the selected area often included active regions, we subtracted the sunspot area from RBP area. The active region was defined from MDI images as the area within 10 pixels (=1.4×10 4 km) radius centered on the strongest magnetic field above B threshold [1 sigma of absolute(MDI DISK )+average(absolute(MDI DISK ))]. We also eliminated areas of opposite polarity within the selected CH area and RBP because, CHs are unipolar regions. We used only selected area within 30 deg. from the Sun center as the equatorial CH and RBP. Interplanetary Data We used interplanetary quantities from SWE/WIND and MFI/WIND. Fig1. Definition of area of CH and RBP Fig2. The plots between SW velocity and each area (a)(b) (c)(d) (a) (b) (c) Discussion Fig. 3a shows the scatter plot between full area of CH and only area of CH with RBP. The area with RBP seems to increase with increasing total CH size. But in case of the weak storms the above trend is not clear. The majority of the CH’s area associated with weak storms also become non-RBP areas. Fig 3b and 3c show the relationship between SW velocity and the corrected average CH’s intensity which is divided by I threshold. We can see almost the same negative correlations in both panels, because RBP may contributes little to EUV intensity (Gopalswamy et al. 1999). Fig3. the differences of CH with/without RBP