Identifying candidate models for transition region features from chromospheric inversions

Background

The transition region is the height in the solar atmosphere where heating occurs from a few tens of thousands of degrees to hundreds of thousands. It is a highly dynamic and highly spatially structured region. Complete models that account for its three-dimensional character are, so far, lacking. This is partially due to the break down of the complete redistribution assumption used to generate chromospheric line profiles, and partially due to the difficulty in obtaining complete sets of observations that adequately constrain the solar atmosphere at all heights for the highly dynamic fine structures there present.

Sunspots are large scale structures offering some preservation of character across multiple layers. Some of the dynamic phenomena observed in sunspots, such as umbral flashes, have recently been detected across the chromospheric and transition region layers ( eg. Madsen et al. ). Sunspots are both interesting candidates from a scientific point of view being one of the primary manifestations of magnetism in the Sun and one of the best places to attempt extensions of spatially dependent chromospheric semi-empirical models.

Goal

The primary goal of the project is to identify semi-empirical models that reproduce transition region line profiles. A secondary goal is to find profiles for which the chromospheric models fail completely, indicating a large departure across layers.

Method

1. Convert an inverted three-dimensional model from NICOLE, obtained from the 8542 line and including a transition region, to a format usable by the RH code.

Routines to extract the models into IDL, such as read_model.pro, are trivially obtainable with

git clone https://github.com/hsocasnavarro/NICOLE.git

cd NICOLE/idl

Python routines are also available and locally provided.

2. Run the full model through RH 1.5D by Pereira and Uitenbroek (2015)

Lines to be synthesized are, in this order of priority (roughly from lower to upper in height): Mg h/k, C II 1335 ? triplet, and Si IV 1402 ?

Compare these profiles with those of the provided in IRIS data. The exact position of the profiles needs to be identified using the aligned slit-jaw images and the fiduciary mark position along the slit. Known scale and crop transformations for both sets are necessary. For which features do the profiles match the best? Is there any one adjustment to the model atmospheres that would lead to better fits for a class of features? For what features are the profiles the most different?

Consider quiescent umbra, flashing umbra, penumbra and any transient brightenings. Umbra and penumbra can be differentiated with a simple intensity threshold. Flashing and quiescent umbra pixels can be differentiated by a threshold in the inner blue wing of the provided 8542 profiles. For this project any transient brightenings can be looked at and identified case-by-case manually selecting pixels that look exceptional at different wavelength mappings.