Helioseismic Inversion method applied to Stokes data
Abstract
As light travels through an atmosphere, it interacts with the medium through absorption, emission and scattering processes. Given a light spectra, inferring the physical properties (for example T, Pg, velocity) of the atmosphere it traversed, is called an inversion problem. To infer the unknown atmosphere, one usually starts with a depth-dependent guess atmospheric model and perturbs it until the synthesized spectra through this model match the observed spectra. The desired perturbations are computed using response functions which is a measure of the sensitivity of spectra to changes in atmospheric variables. Due to the ill-posed nature of inverse problems, the solutions are non-unique and highly oscillatory. Thus, nodes are used to obtain a smooth solution. These nodes are a small number of evenly spaced depth locations where the perturbations are calculated. Perturbations at remaining depth points are interpolated using these nodal values. The final model has a depth resolution set by the number of nodes, independent of the information content of the spectra. The solution thus obtained, most likely, does not have the optimal depth resolution.
The OLA inversion method used in helioseismology does not suffer from the limited resolution issues with nodes. In this method, the response functions are linearly combined in order to obtain a highly localized, average response kernel at a given target depth. The width of the kernel corresponds to the vertical resolution at that depth, and its limit mostly depends on the amount of spectral information. The inverted physical parameter then corresponds to this kernel averaged quantity. The process is repeated for all depths and a smooth inverted solution is obtained. In this work, we aim to apply the OLA method to spectroscopic data. To facilitate this, we used SIR code to synthesize spectra through the 1D smooth temperature profiles from MURaM. To this 1D model, we added a Gaussian perturbation. The goal of the project is how well can we invert for this perturbed atmosphere using OLA method and how do the results compare to the SIR inversion code.- Publication:
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Solar Heliospheric and INterplanetary Environment (SHINE 2019)
- Pub Date:
- May 2019
- Bibcode:
- 2019shin.confE.132A