[논문]COMPARISON OF LOS DOPPLER VELOCITIES AND NON-THERMAL LINE WIDTHS IN THE OFF-LIMB SOLAR CORONA MEASURED SIMULTANEOUSLY BY COMP AND HINODE/EIS

Lee, Jae-Ok; Lee, Kyoung-Sun; Seough, Jungjoon; Cho, Kyung-Suk

doi:10.5303/jkas.2021.54.2.49

COMPARISON OF LOS DOPPLER VELOCITIES AND NON-THERMAL LINE WIDTHS IN THE OFF-LIMB SOLAR CORONA MEASURED SIMULTANEOUSLY BY COMP AND HINODE/EIS 원문보기

Journal of the Korean astronomical society = 천문학회지, v.54 no.2, 2021년, pp.49 - 60

Lee, Jae-Ok (Korea Astronomy and Space Science Institute) , Lee, Kyoung-Sun (Department of Physics and Astronomy, Seoul National University) , Seough, Jungjoon (Korea Astronomy and Space Science Institute) , Cho, Kyung-Suk (Korea Astronomy and Space Science Institute)

Abstract ▼ AI-Helper

Observations of line of sight (LOS) Doppler velocity and non-thermal line width in the off-limb solar corona are often used for investigating the Alfvén wave signatures in the corona. In this study, we compare LOS Doppler velocities and non-thermal line widths obtained simultaneously from two different instruments, Coronal Multichannel Polarimeter (CoMP) and Hinode/EUV Imaging Spectrometer (EIS), on various off-limb coronal regions: flaring and quiescent active regions, equatorial quiet region, and polar prominence and plume regions observed in 2012-2014. CoMP provides the polarization at the Fe xiii 10747 Å coronal forbidden lines which allows their spectral line intensity, LOS Doppler velocity, and line width to be measured with a low spectral resolution of 1.2 Å in 2-D off limb corona between 1.05 and 1.40 RSun, while Hinode/EIS gives us the EUV spectral information with a high spectral resolution (0.025 Å) in a limited field of view raster scan. In order to compare them, we make pseudo raster scan CoMP maps using information of each EIS scan slit time and position. We compare the CoMP and EIS spectroscopic maps by visual inspection, and examine their pixel to pixel correlations and percentages of pixel numbers satisfying the condition that the differences between CoMP and EIS spectroscopic quantities are within the EIS measurement accuracy: ±3 km s-1 for LOS Doppler velocity and ±9 km s-1 for non-thermal width. The main results are summarized as follows. By comparing CoMP and EIS Doppler velocity distributions, we find that they are consistent with each other overall in the active regions and equatorial quiet region (0.25 ≤ CC ≤ 0.7), while they are partially similar to each other in the overlying loops of prominences and near the bottom of the polar plume (0.02 ≤ CC ≤ 0.18). CoMP Doppler velocities are consistent with the EIS ones within the EIS measurement accuracy in most regions (≥ 87% of pixels) except for the polar region (45% of pixels). We find that CoMP and EIS non-thermal width distributions are similar overall in the active regions (0.06 ≤ CC ≤ 0.61), while they seem to be different in the others (-0.1 ≤ CC ≤ 0.00). CoMP non-thermal widths are similar to EIS ones within the EIS measurement accuracy in a quiescent active region (79% of pixels), while they do not match in the other regions (≤ 61% of pixels); the CoMP observations tend to underestimate the widths by about 20% to 40% compared to the EIS ones. Our results demonstrate that CoMP observations can provide reliable 2-D LOS Doppler velocity distributions on active regions and might provide their non-thermal width distributions.

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표/그림 (9)

그림 Figure 1. Raster scan CoMP and EIS intensity maps for all coronal regions. The panels show the flaring active region (a), quiescent active regions (b and c), equatorial quiet region (d), polar prominence regions (e and f), and polar plume region (g). These are corresponding to event Nos. 1−7 in Table 1. In each raster scan map, the y direction shows spatial variations at a given time, while the x direction represents temporal and spatial variations. Green and blue contours show the regions where CoMP intensities are equal to 20% and 50% of their maximum intensities, respectively. In panel (c), all pixels have values higher than 20% of the maximum intensities. The gray continuous (dashed) partial circle lines indicate the solar disk (CoMP occulting disk). In panels (e−g), the yellow and yellow-dotted arrows indicate the observed prominence and polar plume, respectively. The horizontal and vertical gray lines represent the observed CoMP FOV in its pseudo raster scan. Limitations of the CoMP FOVs in solar x direction are caused by CoMP data gaps during the EIS raster scan observations as shown in columns 4 and 12 of Table 1. The data gaps are caused by limitations on the available time windows due to geographic and weather conditions of the ground-based CoMP observations.
그림 Figure 2. Raster scan CoMP and EIS Doppler maps. Each panel shows the same events as in Figure 1. We only present CoMP Doppler velocities for locations where the CoMP intensity is higher than 20% of the maximum intensity, and EIS velocities where the EIS measurement error is below the measurement accuracy (±3 km s⁻¹). In panels (e−g), black arrows indicate specific regions where the LOS Doppler velocity patterns are similar in both CoMP and EIS observations. The gray partial circle (dashed circle) and horizontal (vertical) gray lines are the same as those in Figure 1.
그림 Figure 3. CoMP vs. EIS LOS Doppler velocities. Each panel shows the same event as the corresponding panel of Figure 1. The dashed lines indicate equality of the two spectroscopic quantities, while the upper and lower dotted lines indicate the EIS measurement accuracy for determining Doppler velocities (±3 km s⁻¹). Since the systematic differences between CoMP and EIS Doppler velocity observations are estimated as 4, −2, −2, and −2 km s⁻¹ shown in Figure 4b, e, f, and g, respectively, we shift the equality and EIS measurement accuracy lines in panels b, e, f, and g accordingly. CC and RMSE indicate correlation coefficient and root mean square error, respectively. The red and blue symbols indicate relatively bright and faint structures as described in Section 2.2. The Doppler velocities of bright structures overlap with those of faint structures.
그림 Figure 4. Histograms of the differences between CoMP and EIS LOS Doppler velocities with a bin size of 2 km s⁻¹. The pixel numbers within vertical lines indicate that the difference between CoMP and EIS Doppler velocities are within the EIS measurement accuracy. The systematic differences between CoMP and EIS Doppler velocity observations are estimated as 4, −2, −2, and −2 km s⁻¹ in panels b, e, f, and g, respectively. These are corrected for estimating the percentages of pixels measured to within the EIS measurement accuracy. The percentages are presented in each histogram. "Std" indicates standard deviation. The red and blue symbols are the same as those in Figure 2.
그림 Figure 5. Raster scan CoMP and EIS non-thermal width maps. We only present CoMP non-thermal widths where CoMP intensities are higher than 20% of the maximum intensity, and EIS non-thermal widths where its measurement error is within the measurement accuracy (±9 km s⁻¹) and its line width is larger than the sum of thermal and instrumental widths. The gray partial circle (dashed circle) and horizontal (vertical) gray lines are the same as those in Figure 1.
그림 Figure 6. CoMP vs. EIS non-thermal widths. Each panel shows the same events as in Figure 1. The dashed lines indicate equality of the two spectroscopic quantities, while the upper and lower dotted lines indicate the EIS measurement accuracy for determining line widths (±9 km s⁻¹). The non-thermal widths of bright structures overlap with those of faint structures. CC, RMSE, red symbols, and blue symbols are the same as in Figure 3.
그림 Figure 7. Histograms of the differences between CoMP and EIS LOS non-thermal widths with a bin size of 6 km s⁻¹. Each panel shows the same events in Figure 1. The pixel numbers within vertical lines indicate that the difference between CoMP and EIS non-thermal widths are within the EIS measurement accuracy. The red and blue symbols are the same as in Figure 3. The percentages and Std are the same as those in Figure 4.
그림 Figure 8. Histograms of the ratios of CoMP and EIS LOS non-thermal widths with a bin size of 0.2. Each panel shows the same events as in Figure 1. The red and blue symbols are the same as in Figure 3. Std is the same as in Figure 4.
표 Table 1 EIS and CoMP observations.

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