An Iterative OLA Method for Inversion of Solar Spectropolarimetric Data. I. Single- and Multiple-variable Inversions of Thermodynamic Quantities
This paper describes an adaptation of the Optimally Localized Averaging (OLA) inversion technique, originally developed for geo- and helioseismological applications, to the interpretation of solar spectroscopic data. It focuses on inverting the thermodynamical properties of the solar atmosphere, ass...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2023-01-01
|
| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/aca536 |
| _version_ | 1797701263706554368 |
|---|---|
| author | Piyush Agrawal Mark P. Rast Basilio Ruiz Cobo |
| author_facet | Piyush Agrawal Mark P. Rast Basilio Ruiz Cobo |
| author_sort | Piyush Agrawal |
| collection | DOAJ |
| description | This paper describes an adaptation of the Optimally Localized Averaging (OLA) inversion technique, originally developed for geo- and helioseismological applications, to the interpretation of solar spectroscopic data. It focuses on inverting the thermodynamical properties of the solar atmosphere, assuming that the atmosphere and radiation field are in local thermodynamic equilibrium (LTE). We leave inversions of magnetic field and non-LTE inversions for future work. The advantage with the OLA method is that it computes solutions that are optimally depth resolved with minimal crosstalk error between variables. Additionally, the method allows for direct assessment of the vertical resolution of the inverted solutions. The primary challenges faced when adapting the method to spectroscopic inversions originate with the possible large-amplitude differences between the atmospheric model used to initiate the inversion and the underlying atmosphere it aims to recover, necessitating the development of an iterative scheme. Here, we describe the iterative OLA method we have developed for both single and multivariable inversions and demonstrate its performance on simulated data and synthesized spectra. We note that, when carrying out multivariable inversions, employing response function amplification factors can address the inherent spectral sensitivity bias that makes it hard to invert for less spectrally sensitive variables. The OLA method can, in most cases, reliably invert as well as or better than the frequently employed Stokes Inversion based on Response functions (SIR) scheme, but some difficulties remain. In particular, the method struggles to recover large-scale offsets in the atmospheric stratification. We propose future strategies to improve this aspect. |
| first_indexed | 2024-03-12T04:33:54Z |
| format | Article |
| id | doaj.art-7bba354b19724b0997cd7753d37741f7 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-12T04:33:54Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-7bba354b19724b0997cd7753d37741f72023-09-03T09:58:12ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-01944111110.3847/1538-4357/aca536An Iterative OLA Method for Inversion of Solar Spectropolarimetric Data. I. Single- and Multiple-variable Inversions of Thermodynamic QuantitiesPiyush Agrawal0https://orcid.org/0000-0001-6514-8944Mark P. Rast1https://orcid.org/0000-0002-9232-9078Basilio Ruiz Cobo2https://orcid.org/0000-0001-9550-6749Department of Astrophysical and Planetary Sciences, University of Colorado , Boulder, CO, USA ; piyush.agrawal@colorado.edu; Laboratory for Atmospheric and Space Physics, University of Colorado , Boulder, CO, USA ; mark.rast@lasp.colorado.edu; Southwest Research Institute , Boulder, CO 80302, USADepartment of Astrophysical and Planetary Sciences, University of Colorado , Boulder, CO, USA ; piyush.agrawal@colorado.edu; Laboratory for Atmospheric and Space Physics, University of Colorado , Boulder, CO, USA ; mark.rast@lasp.colorado.eduInstituto de Astrofisica de Canarias , La Laguna, Tenerife, E-38200, Spain ; basilio.ruiz@iac.es; Departamento de Astrofísica, Univ. de La Laguna , La Laguna, Tenerife, E-38205, SpainThis paper describes an adaptation of the Optimally Localized Averaging (OLA) inversion technique, originally developed for geo- and helioseismological applications, to the interpretation of solar spectroscopic data. It focuses on inverting the thermodynamical properties of the solar atmosphere, assuming that the atmosphere and radiation field are in local thermodynamic equilibrium (LTE). We leave inversions of magnetic field and non-LTE inversions for future work. The advantage with the OLA method is that it computes solutions that are optimally depth resolved with minimal crosstalk error between variables. Additionally, the method allows for direct assessment of the vertical resolution of the inverted solutions. The primary challenges faced when adapting the method to spectroscopic inversions originate with the possible large-amplitude differences between the atmospheric model used to initiate the inversion and the underlying atmosphere it aims to recover, necessitating the development of an iterative scheme. Here, we describe the iterative OLA method we have developed for both single and multivariable inversions and demonstrate its performance on simulated data and synthesized spectra. We note that, when carrying out multivariable inversions, employing response function amplification factors can address the inherent spectral sensitivity bias that makes it hard to invert for less spectrally sensitive variables. The OLA method can, in most cases, reliably invert as well as or better than the frequently employed Stokes Inversion based on Response functions (SIR) scheme, but some difficulties remain. In particular, the method struggles to recover large-scale offsets in the atmospheric stratification. We propose future strategies to improve this aspect.https://doi.org/10.3847/1538-4357/aca536Radiative transferSpectropolarimetryHelioseismologySolar physics |
| spellingShingle | Piyush Agrawal Mark P. Rast Basilio Ruiz Cobo An Iterative OLA Method for Inversion of Solar Spectropolarimetric Data. I. Single- and Multiple-variable Inversions of Thermodynamic Quantities The Astrophysical Journal Radiative transfer Spectropolarimetry Helioseismology Solar physics |
| title | An Iterative OLA Method for Inversion of Solar Spectropolarimetric Data. I. Single- and Multiple-variable Inversions of Thermodynamic Quantities |
| title_full | An Iterative OLA Method for Inversion of Solar Spectropolarimetric Data. I. Single- and Multiple-variable Inversions of Thermodynamic Quantities |
| title_fullStr | An Iterative OLA Method for Inversion of Solar Spectropolarimetric Data. I. Single- and Multiple-variable Inversions of Thermodynamic Quantities |
| title_full_unstemmed | An Iterative OLA Method for Inversion of Solar Spectropolarimetric Data. I. Single- and Multiple-variable Inversions of Thermodynamic Quantities |
| title_short | An Iterative OLA Method for Inversion of Solar Spectropolarimetric Data. I. Single- and Multiple-variable Inversions of Thermodynamic Quantities |
| title_sort | iterative ola method for inversion of solar spectropolarimetric data i single and multiple variable inversions of thermodynamic quantities |
| topic | Radiative transfer Spectropolarimetry Helioseismology Solar physics |
| url | https://doi.org/10.3847/1538-4357/aca536 |
| work_keys_str_mv | AT piyushagrawal aniterativeolamethodforinversionofsolarspectropolarimetricdataisingleandmultiplevariableinversionsofthermodynamicquantities AT markprast aniterativeolamethodforinversionofsolarspectropolarimetricdataisingleandmultiplevariableinversionsofthermodynamicquantities AT basilioruizcobo aniterativeolamethodforinversionofsolarspectropolarimetricdataisingleandmultiplevariableinversionsofthermodynamicquantities AT piyushagrawal iterativeolamethodforinversionofsolarspectropolarimetricdataisingleandmultiplevariableinversionsofthermodynamicquantities AT markprast iterativeolamethodforinversionofsolarspectropolarimetricdataisingleandmultiplevariableinversionsofthermodynamicquantities AT basilioruizcobo iterativeolamethodforinversionofsolarspectropolarimetricdataisingleandmultiplevariableinversionsofthermodynamicquantities |