Diagnosing the Optically Thick/Thin Features Using the Intensity Ratio of Si iv Resonance Lines in Solar Flares

Abstract In the optically thin regime, intensity ratio of two Si iv resonance lines (1394 and 1403 Å) are theoretically same as their oscillator strengths, which is exactly 2. Here, we study integrated ( R = ∫ I 1394 λ )d /∫ ) at each wavelength point r (Δ )/ )) in solar flares observed by Interface Region Imaging Spectrograph. We find that flare ribbons, ranges from 1.8 to 2.3 would generally decrease when ribbons sweep across slit position. addition, distribution shows a descending trend blue wing red wing. loop cases, line presents wide profile with central reversal. The deviates little 2, but can vary 1.3 near center greater than 2 wings. Hence conclude conditions, varies line, due variation opacity notice that, although could present value result effect center, still close Therefore, caution should be taken using diagnose effect.