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tokens: plotted the intensity increase and decrease in Figure 6 (a). The base-subtracted images show that strong coronal dimming appears in the west of the active region from 03:10 UT, which is 18 minutes after the GOES peak time. The dimming reached the peak at 04:10 UT, which is 78 minutes after the GOES peak time. Coronal mass ejections (CMEs) are often associated with coronal dimming (Sterling Hudson 1997 ). Therefore, in this case, a CME was likely to occur as well, even though the CME catalog 3 3 https://cdaw.gsfc.nasa.gov/CME_list/ by the SOHO /Large Angle and Spectrometric COronagraph (LASCO; Brueckner et al. 1995 ) does not show any CME. Figure 6. (a) Spatially integrated intensity increase (thick black) and decrease (dashed red) of the 195 Å intensity measured on EIS 195 Å images from 01:46:55 UT. The vertical dotted line indicates the GOES peak time at 02:52 UT. (b) Intensity and base-subtracted maps of EIT 195 Å. The observation time is shown at the top right of each image. The base-subtracted images are the difference from the image at 01:46:55 UT shown in the top plot. The red boxes show the field of view of Figure 3 . 5. Summary and Discussions In this section, we summarize our results from the statistical and event studies and discuss the chance to observe the linear polarization in H α and its origin. 5.1. Infrequent Occurrence of Significant Linear Polarization at H<italic>α</italic> in Solar Flares We found only one event that showed significant linear polarization signals among 71 H α flares including 64 GOES flares with the spatial and temporal samplings of 10′′ × 10′′ and 40 s, respectively. Many preceding papers reported the characteristics of the linear polarization in H α only for the events that show significant polarization signals. In the cases where the polarization was not detected, it has been considered that the sensitivity of the polarimetry was insufficient. On the other hand, Bianda et al. ( 2005 ) reported that they did not find significant linear polarization signals in 30 flares, even though they used a high-sensitivity instrument. Based on their preliminary analysis of dozens of flares, Hanaoka ( 2004 , 2005 ) also found that one flare showed significant linear polarization signals, while most other flares showed none. In our study, we used the polarimeter with higher accuracy described in the papers by Hanaoka ( 2004 , 2005 ) and confirmed their preliminary results. Furthermore, although the analyzed samples include some large flares such as 4 X- and 13 M-class events, the results are basically negative. The high-frequency modulation techniques reduce spurious signals caused by the seeing effect and by flaring structures evolving in time, and data obtained by these techniques are more reliable than data that were taken by low-frequency modulation techniques. Thus, our results proved that the linear polarization does not appear in most of the flares, but there are a few flares that actually show the polarization.