Sunrise-III near-UV spectroscopy maps multi-frequency oscillatory power in sunspots and active regions

Multi-line Wave Signatures in a Sunspot from Near-UV Sunrise III/SUSI Observations

arXiv:2606.14184v1 Announce Type: new Abstract: Magnetohydrodynamic waves redistribute energy in magnetic structures of the lower solar atmosphere, yet constraints on how wave power and dominant frequencies are organised above sunspots remain limited because most studies use only a few well-separated diagnostics. Here we present multiline wave signatures in a sunspot from near-UV spectroscopy with the Sunrise-III UV Spectropolarimeter and Imager (SUSI). We analyse a two-hour time series of repeated raster scans of a sunspot near disc centre in the 327-329 nm spectral window (> 100 lines). From these, we select 44 lines that radiative-transfer calculations suggest sample effective formation heights within the umbral core from deep photosphere toward the low chromosphere. For each line, we extract line-core intensity and line-of-sight velocity time series using a dedicated multi-line fitting routine and compute Morlet-wavelet power spectra. The refined global wavelet spectra show that most lines (in both intensity and velocity) are genuinely multi-frequency, with a dominant peak and substantial statistically significant power up to 12 mHz. Unsupervised clustering of the normalised spectra groups lines into families with similar spectral shapes and reveals a progression of dominant frequencies from ~2 to ~10 mHz across the ensemble, for both intensity and velocity (not necessarily in the same lines). This behaviour is not reproduced by a simple formation-height ranking, suggesting that uncertainties in the formation-height estimates and line-dependent diagnostic response together shape the ordering. These Sunrise-III/SUSI observations open a new regime for near-UV multi-line wave studies and provide the first systematic characterisation of frequency-structured sunspot wave behaviour in this spectral region.

2 hours ago

Magnetically Structured Oscillatory Power Along an Active-Region Transect in Near-UV Sunrise-III/SUSI Spectroscopy

arXiv:2606.14232v1 Announce Type: new Abstract: We present a multi-line characterisation of how oscillatory power is organised across distinct magnetic environments in an active region using seeing-free, stratospheric near-ultraviolet spectroscopy from the Sunrise-III UV Spectropolarimeter and Imager (SUSI). A two-hour time series of short raster scans in the line-rich 327-329 nm window samples along a single transect that contains the following regions: weak magnetic-field surroundings, a plage, a sunspot, and a pore. From a set of 30 selected, relatively unblended absorption lines, we extract line-core Doppler-velocity time series and compute Morlet-wavelet refined global spectra from which we form band-integrated power maps for three frequency bands (2-4, 4-6, and 6-12 mHz). The stacked, line-resolved maps reveal a clear environment-dependent redistribution of power: 2-4 mHz power is strongest in the weak-field/plage segments but is commonly suppressed in the umbra and pore cores, while 4-6 mHz and 6-12 mHz power becomes relatively enhanced in the strongest-field regions, with line-dependent behaviour in the penumbra and plage. Across the line ensemble, this broad frequency structuring is coherent, but the detailed spatial distribution and relative band ranking are not identical from line to line - even among spectral lines with comparable effective formation depths - demonstrating clear line dependence. This novel result implies that single-line measurements may miss secondary components of the local wave spectrum because different lines weight co-existing perturbations and modes differently; therefore, the SUSI near-UV window provides a uniquely diagnostic-rich mapping of oscillations, offering leverage that is difficult to obtain with traditional one- or two-line approaches.

2 hours ago