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Register a new user1D Modeling for Temperature-Dependent Upflow in the Dimming Region Observed by Hinode/EIS
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We have previously found a temperature-dependent upflow in the dimming region following a coronal mass ejection (CME) observed by the {it Hinode} EUV Imaging Spectrometer (EIS). In this paper, we reanalyzed the observations along with previous work on this event, and provided boundary conditions for modeling. We found that the intensity in the dimming region dramatically drops within 30 minutes from the flare onset, and the dimming region reaches the equilibrium stage after $sim$1 hour later. The temperature-dependent upflows were observed during the equilibrium stage by EIS. The cross sectional area of the fluxtube in the dimming region does not appear to expand significantly. From the observational constraints, we reconstructed the temperature-dependent upflow by using a new method which considers the mass and momentum conservation law, and demonstrated the height variation of plasma conditions in the dimming region. We found that a super radial expansion of the cross sectional area is required to satisfy the mass conservation and momentum equations. There is a steep temperature and velocity gradient of around 7 Mm from the solar surface. This result may suggest that the strong heating occurred above 7 Mm from the solar surface in the dimming region. We also showed that the ionization equilibrium assumption in the dimming region is violated especially in the higher temperature range.
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A complete understanding of Doppler shift in active region loops can help probe the basic physical mechanism involved into the heating of those loops. Here we present observations of upflows in coronal loops detected in a range of temperature temperatures (log T=5.8 - 6.2). The loop was not discernible above these temperatures. The speed of upflow was strongest at the footpoint and decreased with height. The upflow speed at the footpoint was about 20 km/s in Fe VIII which decreased with temperature being about 13 km/s in Fe X, about 8 km/s in Fe XII and about 4 km/s in FeXIII. To the best of our knowledge this is the first observation providing evidence of upflow of plasma in coronal loop structures at these temperatures. We interpret these observations as evidence of chromospheric evaporation in quasi-static coronal loops.
In order to better understand the possibility of coronal heating by MHD waves, we analyze Fe xii 195.12{AA} data observed with EUV Imaging Spectrometer (EIS) onboard Hinode. We performed a Fourier analysis of EUV intensity and Doppler velocity time series data in the active region corona. Notable intensity and Doppler velocity oscillations were found for two moss regions out of the five studied, while only small oscillations were found for five apexes of loops. The amplitudes of the oscillations were 0.4 - 5.7% for intensity and 0.2 - 1.2 kms-1 for Doppler velocity. In addition, oscillations of only Doppler velocity were seen relatively less often in the data. We compared the amplitudes of intensity and those of Doppler velocity in order to identify MHD wave modes, and calculated the phase delays between Fourier components of intensity and those of Doppler velocity. The results are interpreted in terms of MHD waves as follows: (1) few kink modes or torsional Alfven mode waves were seen in both moss regions and the apexes of loops; (2) upwardly propagating and standing slowmode waves were found inmoss regions; and (3) consistent with previous studies, estimated values of energy flux of the waves were several orders of magnitude lower than that required for heating active regions.
We present the first Hinode/EIS observations of 5 min quasi-periodic oscillations detected in a transition-region line (He II) and five coronal lines (Fe X, Fe XII, Fe XIII, Fe XIV, and Fe XV) at the footpoint of a coronal loop. The oscillations exist throughout the whole observation, characterized by a series of wave packets with nearly constant period, typically persisting for 4-6 cycles with a lifetime of 20-30 min. There is an approximate in-phase relation between Doppler shift and intensity oscillations. This provides evidence for slow magnetoacoustic waves propagating upwards from the transition region into the corona. We find that the oscillations detected in the five coronal lines are highly correlated, and the amplitude decreases with increasing temperature. The amplitude of Doppler shift oscillations decrease by a factor of about 3, while that of relative intensity decreases by a factor of about 4 from Fe X to Fe XV. These oscillations may be caused by the leakage of the photospheric p-modes through the chromosphere and transition region into the corona, which has been suggested as the source for intensity oscillations previously observed by TRACE. The temperature dependence of the oscillation amplitudes can be explained by damping of the waves traveling along the loop with multithread structure near the footpoint. Thus, this property may have potential value for coronal seismology in diagnostic of temperature structure in a coronal loop.
We report on observations of a solar prominence obtained on 26 April 2007 using the Extreme Ultraviolet Imaging Spectrometer on Hinode. Several regions within the prominence are identified for further analysis. Selected profiles for lines with formation temperatures between log(T)=4.7-6.3, as well as their integrated intensities, are given. The line profiles are discussed. We pay special attention to the He II line which is blended with coronal lines. Our analysis confirms that depression in EUV lines can be interpreted by two mechanisms: absorption of coronal radiation by the hydrogen and neutral helium resonance continua, and emissivity blocking. We present estimates of the He II line integrated intensity in different parts of the prominence according to different scenarios for the relative contribution of absorption and emissivity blocking on the coronal lines blended with the He II line. We estimate the contribution of the He II 256.32 line in the He II raster image to vary between ~44% and 70% of the rasters total intensity in the prominence according to the different models used to take into account the blending coronal lines. The inferred integrated intensities of the He II line are consistent with theoretical intensities obtained with previous 1D non-LTE radiative transfer calculations, yielding a preliminary estimate for the central temperature of 8700 K, central pressure of 0.33 dyn/cm^2, and column mass of 2.5 10^{-4} g/cm^2. The corresponding theoretical hydrogen column density (10^{20} cm^{-2}) is about two orders of magnitude higher than those inferred from the opacity estimates at 195 {AA}. The non-LTE calculations indicate that the He II 256.32 {AA} line is essentially formed in the prominence-to-corona transition region by resonant scattering of the incident radiation.
Studying the Doppler shifts and the temperature dependence of Doppler shifts in moss regions can help us understand the heating processes in the core of the active regions. In this paper we have used an active region observation recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) onboard Hinode on 12-Dec-2007 to measure the Doppler shifts in the moss regions. We have distinguished the moss regions from the rest of the active region by defining a low density cut-off as derived by Tripathi et al. (2010). We have carried out a very careful analysis of the EIS wavelength calibration based on the method described in Young et al. (2012). For spectral lines having maximum sensitivity between log T = 5.85 and log T = 6.25 K, we find that the velocity distribution peaks at around 0 km/s with an estimated error of 4-5 km/s. The width of the distribution decreases with temperature. The mean of the distribution shows a blue shift which increases with increasing temperature and the distribution also shows asymmetries towards blue-shift. Comparing these results with observables predicted from different coronal heating models, we find that these results are consistent with both steady and impulsive heating scenarios. However, the fact that there are a significant number of pixels showing velocity amplitudes that exceed the uncertainty of 5 km s$^{-1}$ is suggestive of impulsive heating. Clearly, further observational constraints are needed to distinguish between these two heating scenarios.
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