Abstract
The high temporal, spatial and spectral resolution of Interface Region Imaging Spectrograph (IRIS) has provided new insights into the understanding of different small-scale processes occurring at the chromospheric and transition region (TR) heights. We study the dynamics of high-frequency oscillations of an active region (AR 2376) moss as recorded by simultaneous imaging and spectral data of IRIS. Wavelet transformation, power maps generated from slit-jaw images in Si\,IV\,1400\,\AA~passband, and sit-and-stare spectroscopic observations of Si\,IV\,1403\,\AA~spectral line reveal the presence of high-frequency oscillations with $\sim$1--2\,minutes periods in the bright moss regions. The presence of such low periodicities is further confirmed by intrinsic mode functions (IMFs) as obtained by empirical mode decomposition (EMD) technique. We find the evidence of the presence of slow waves and reconnection-like events, and together they cause the high-frequency oscillations in the bright moss regions.
Highlights
Understanding the processes responsible for the heating of the upper atmosphere is the central problem in solar physics
We study high-frequency dynamics of active region moss by using high spatially and spectrally resolved observations of Interface Region Imaging Spectrograph (IRIS), with the fast cadence of 13 s for imaging and 3.3 s for spectral data
The techniques of wavelet and empirical mode decomposition (EMD) analysis are employed in conjunction to explore the characteristics of the high-frequency oscillations
Summary
Understanding the processes responsible for the heating of the upper atmosphere is the central problem in solar physics. Using the High-resolution Coronal Imager [Hi-C; Kobayashi et al (2014)] data, Testa et al (2013) observed variability on time-scales of 15–30 s to be present in the moss regions as observed in the upper TR, which they found to be mostly located at the foot-points of coronal loops They regarded such oscillations as the signatures of heating events associated with reconnection occurring in overlying hot coronal loops, i.e., impulsive nano-flares. From the Chromospheric Lyα SpectroPolarimeter (CLASP; Kano et al, 2012) observations, Ishikawa et al (2017) reported short temporal variations in the solar chromosphere and TR emission of an active region with periodicities of ∼10–30 s They attributed these intensity variations to waves or jets from the lower layers instead of nano-flares. The joint imaging and spectroscopic observations of IRIS at high cadence provide us with a unique opportunity to have a detailed analysis of different characteristics and mechanisms involved in the generation of high-frequency oscillations in TR moss regions
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