2026-10-14T06:49:58Z https://api.figshare.com/v2/oai

oai:figshare.com:article/33971410 2026-09-23T06:24:23Z category_57 portal_316 item_type_2 month_year_09_2026

Video 1_Formation-height diagnostics across a sunspot: a comparison of Lightweaver radiative transfer and NICOLE inversions using the Ca ii 8542Å line.mp4 Timothy J. Duckenfield (24221946) David B. Jess (10506041) Shahin Jafarzadeh (13547428) Luc Rouppe van der Voort (25094857) Vasco M. J. Henriques (25094860) Cosmology chromosphere radiative transfer spectropolarimetric inversions Sun: magnetohydrodynamics sunspots <p>The Ca ii 8542Å line is widely used by modern instruments such as SST/CRISP and DKIST to probe the highly structured and dynamic chromosphere. However, interpreting observations in this line requires a characterisation of the effective height ranges sampled by each spectral tuning, particularly when geometric height is obtained from inversion atmospheres that assume hydrostatic equilibrium. Using high resolution observations of a sunspot, we present a direct comparison between formation-height diagnostics derived from non-LTE radiative-transfer calculations and the geometric heights returned by NICOLE inversions, covering atmospheres corresponding to the umbra, umbral–penumbral boundary, penumbra, and the penumbral–quiet sun boundary. Formation-height probability distributions are computed from Lightweaver contribution functions evaluated in the inversion atmospheres, and convolved with the SST/CRISP transmission profile. We then identify the optical-depth layers whose associated geometric-height distributions from the inversions best match these formation-height probability distributions. We find that the optical-depth range sampled by the line remains broadly stable across the sunspot, whilst the corresponding geometric heights vary systematically in the radial direction. Across the modelled annuli, the selected optical depth intervals remain broadly stable, whilst the corresponding model geometric heights vary with radius. Within the adopted inversion framework, the resulting mapping relates CRISP spectral tunings to optical depth and model geometric height and provides a practical guide for interpreting Ca ii 8542Å observations of chromospheric waves and dynamics, particularly in the era of next-generation facilities such as DKIST.</p> 2026-09-23T06:24:23Z Dataset Media 10.3389/fspas.2026.1873920.s002 https://figshare.com/articles/media/Video_1_Formation-height_diagnostics_across_a_sunspot_a_comparison_of_Lightweaver_radiative_transfer_and_NICOLE_inversions_using_the_Ca_ii_8542_line_mp4/33971410 CC BY 4.0