Fan Loops Observed by IRIS, EIS, and AIA

Ghosh, Avyarthana; Tripathi, Durgesh; Gupta, G. R.; Polito, Vanessa; Mason, H. E.; Solanki, S. K.

doi:10.3847/1538-4357/835/2/244

Cited by 20 publications

(18 citation statements)

References 61 publications

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“…A I denotes the relative intensity amplitudes in AIA 171Å channel, measured at the bottom of the selected loop segments. ues obtained here are of the same order of those found from spectroscopic observations of fan loops (Ghosh et al 2017 In a couple of loops, the temperature perturbations do not possess sufficient amplitudes to estimate γ, ∆φ obs , and ∆φ S , which therefore, are left blank.…”

Section: Analysis and Resultssupporting

confidence: 71%

The Polytropic Index of Solar Coronal Plasma in Sunspot Fan Loops and Its Temperature Dependence

Prasad

Raes

Doorsselaere

et al. 2018

ApJ

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Observations of slow magneto-acoustic waves have been demonstrated to possess a number of applications in coronal seismology. Determination of the polytropic index (γ) is one such important application. Analysing the amplitudes of oscillations in temperature and density corresponding to a slow magneto-acoustic wave, the polytropic index in the solar corona has been calculated and based on the obtained value it has been inferred that thermal conduction is highly suppressed in a very hot loop in contrast to an earlier report of high thermal conduction in a relatively colder loop. In this study, using SDO/AIA data, we analysed slow magneto-acoustic waves propagating along sunspot fan loops from 30 different active regions and computed polytropic indices for several loops at multiple spatial positions. The obtained γ values vary from 1.04±0.01 to 1.58±0.12 and most importantly display a temperature dependence indicating higher γ at hotter temperatures. This behaviour brings both the previous studies to agreement and perhaps implies a gradual suppression of thermal conduction with increase in temperature of the loop. The observed phase shifts between temperature and density oscillations, however, are substantially larger than that expected from a classical thermal conduction and appear to be influenced by a line-of-sight integration effect on the emission measure.

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Section: Analysis and Resultssupporting

confidence: 71%

The Polytropic Index of Solar Coronal Plasma in Sunspot Fan Loops and Its Temperature Dependence

Prasad

Raes

Doorsselaere

et al. 2018

ApJ

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“…We choose the 171 Å image for the identification of fan loops as they are best seen at temperature of log [T/K] = 5.80 (e.g. Brooks et al 2011;Ghosh et al 2017). We note that each slit is four pixels wide.…”

Section: Data Analysis and Resultsmentioning

confidence: 99%

“…A possible reason for this may be the broad temperature response of the AIA channels. Fan loops are structures of typically 1 MK; therefore, it may be that the emissions from the lower-temperature components are contributing to these different AIA EUV emissions (Ghosh et al 2017), thereby giving similar phase speeds. Our result shows that the PIDs have longer detection length (≈5.9−7.35 Mm) in 171 Å and 193 Å, whereas a shorter detection length (≈2.9 Mm) in 131 Å and 211 Å.…”

Section: Discussionmentioning

confidence: 99%

“…Similar intensity oscillations in coronal fan loops were first detected by Berghmans & Clette (1999) using the Extreme ultraviolet Imaging Telescope (EIT, Delaboudinière et al 1995) on board SOHO in 195 Å channel, and later confirmed by De Moortel et al (2000) in the observations recorded by Transition Region and Coronal Explorer (TRACE, Handy et al 1999) in the 171 Å channel. Fan loops are magnetic plasma structures in the corona with temperature between 0.6-1 MK (Reale 2010;Ghosh et al 2017). They are found at the edges of active regions, and are mostly rooted in the umbra and umbra-penumbra boundaries of sunspots.…”

Section: Introductionmentioning

confidence: 99%

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Wave amplitude modulation in fan loops as observed by AIA/SDO

Sharma

Tripathi

Erdélyi

et al. 2020

A&A

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Aims. We perform a detailed analysis to understand the evolution and dynamics of propagating intensity disturbances observed in a fan loop system. Methods. We performed multiwavelength time-distance analysis of a fan loop system anchored in an isolated sunspot region (AR 12553). The active region was observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. We measured the phase speeds of the propagating intensity disturbances by employing cross-correlation analysis, and by obtaining the slopes in xt-plots. We obtained original and detrended light curves at different heights of the time-distance maps and characterised them by performing Fourier and wavelet analysis, respectively. Results. The time-distance maps reveal clear propagation of intensity oscillations in all the coronal extreme ultraviolet (EUV) channels except AIA 94 and 335 Å. We determine the nature of the intensity disturbances as slow magneto-acoustic waves by measuring their phase speeds. The time-distance maps, as well as the detrended light curves, show an increase and decrease in the amplitude of propagating 3 min oscillations over time. The amplitude variations appear most prominently in AIA 171 Å, though other EUV channels also show such signatures. The Fourier power spectrum yields the presence of significant powers with several nearby frequencies in the range of 2–3 min (5–8 mHz), along with many other smaller peaks between 2–4 min. Wavelet analysis shows an increase and decrease of oscillating power around 3 min simultaneous to the amplitude variations. We obtain the modulation period to be in the range of 20–30 min. Conclusions. Our results provide the viability of occurrence of phenomenon like “Beat” among the nearby frequencies giving rise to the observed amplitude modulation. However, we cannot at this stage rule out the possibility that the modulation may be driven by variability in an underlying unknown source.

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“…The spectroscopic observations do show larger blueshifts for the spectral lines formed at higher temperatures (Del Zanna et al 2006a). Such effects have also been seen at the footpoints of loops in quiescent active regions and are interpreted as evidence of nanoflares occurring in the corona (see e. g., Tripathi et al 2009b;Ghosh et al 2017, and references therein).…”

Section: Introductionmentioning

confidence: 90%

Observation and Modeling of Chromospheric Evaporation in a Coronal Loop Related to Active Region Transient Brightening

Gupta

Sarkar

Tripathi

2018

ApJ

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Using the observations recorded by Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO), the Interface Region Imaging Spectrograph (IRIS) and the Extreme-ultraviolet Imaging Spectrometer (EIS) and X-Ray Telescope (XRT) both on-board Hinode, we present the evidence of chromospheric evaporation in a coronal loop after the occurrence of two active region transient brightenings (ARTBs) at the two footpoints. The chromospheric evaporation started nearly simultaneously in all the three hot channels of AIA such as 131 Å, 94 Å and 335 Å, which was observed to be temperature dependent, being fastest in the highest temperature channel. The whole loop became fully brightened following the ARTBs after ≈ 25 s in 131 Å, ≈ 40 s in 94 Å, and ≈ 6.5 min in 335 Å. The DEM measurements at the two footpoints (i.e., of two ARTBs) and the loop-top suggest that the plasma attained a maximum temperature of ∼10 MK at all these locations. The spectroscopic observations from IRIS revealed the presence of redshifted emission of ∼20 km s −1 in cooler lines like C II and Si IV during the ARTBs that was co-temporal with the evaporation flow at the footpoint of the loop. During the ARTBs, the line width of C II and Si IV increased nearly by a factor of two during the peak emission. Moreover, enhancement in the line width preceded that in the Doppler shift which again preceded enhancement in the intensity. The observed results were qualitatively reproduced by 1-D hydrodynamic simulations where energy was deposited at both the footpoints of a monolithic coronal loop that mimicked the ARTBs identified in the observations.

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Fan Loops Observed by IRIS, EIS, and AIA

Cited by 20 publications

References 61 publications

The Polytropic Index of Solar Coronal Plasma in Sunspot Fan Loops and Its Temperature Dependence

The Polytropic Index of Solar Coronal Plasma in Sunspot Fan Loops and Its Temperature Dependence

Wave amplitude modulation in fan loops as observed by AIA/SDO

Observation and Modeling of Chromospheric Evaporation in a Coronal Loop Related to Active Region Transient Brightening

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