Solar surges related to UV bursts. Characterization through k-means, inversions, and density diagnostics

Nóbrega-Siverio, D.; Guglielmino, S. L.; Sainz Dalda, A.
Bibliographical reference

Astronomy and Astrophysics

Advertised on:
11
2021
Number of authors
3
IAC number of authors
1
Citations
6
Refereed citations
6
Description
Context. Surges are cool and dense ejections typically observed in chromospheric lines and closely related to other solar phenomena such as UV bursts or coronal jets. Even though surges have been observed for decades now, questions regarding their fundamental physical properties such as temperature and density, as well as their impact on upper layers of the solar atmosphere remain open.
Aims: Our aim is to address the current lack of inverted models and diagnostics of surges, as well as to characterize the chromospheric and transition region plasma of these phenomena.
Methods: We have analyzed an episode of recurrent surges related to UV bursts observed with the Interface Region Imaging Spectrograph (IRIS) in April 2016. The mid- and low-chromosphere of the surges were unprecedentedly examined by getting their representative Mg IIh&k line profiles through the k-means algorithm and performing inversions on them using the state-of-the-art STiC code. We have studied the far-UV spectra focusing on the O IV 1399.8 Å and 1401.2 Å lines, which were previously unexplored for surges, carrying out density diagnostics to determine the transition region properties of these ejections. We have also used numerical experiments performed with the Bifrost code for comparisons.
Results: Thanks to the k-means clustering, we reduced the number of Mg IIh&k profiles to invert by a factor 43.2. The inversions of the representative profiles show that the mid- and low-chromosphere of the surges are characterized, with a high degree of reliability, by temperatures mainly around T = 6 kK at −6.0 ≤ log10(τ)≤ − 3.2. For the electronic number density, ne, and line-of-sight velocity, VLOS, the most reliable results from the inversions are within −6.0 ≤ log10(τ)≤ − 4.8, with ne ranging from ∼1.6 × 1011 cm−3 up to 1012 cm−3, and VLOS of a few km s−1. We find, for the first time, observational evidence of enhanced O IV emission within the surges, indicating that these phenomena have a considerable impact on the transition region even in the weakest far-UV lines. The O IV emitting layers of the surges have an electron number density ranging from 2.5 × 1010 cm−3 to 1012 cm−3. The numerical simulations provide theoretical support in terms of the topology and location of the O IV emission within the surges.

Movie associated with Fig. 2 is available at https://www.aanda.org
Related projects
Example of state of the art 3-D simulation of the Sun
The Whole Sun Project: Untangling the complex physical mechanisms behind our eruptive star and its twins

The Sun is a magnetically active star with violent eruptions that can hit Earth´s magnetosphere and cause important perturbations in our technology-dependent society. The objective of the Whole Sun project is to tackle in a coherent way for the first time key questions in Solar Physics that involve as a whole the solar interior and the atmosphere

Fernando
Moreno Insertis
Solar Eruption
Numerical Simulation of Astrophysical Processes

The general aim of this project is the investigation of astrophysical processes through the use of state­of­the­art numerical codes on massively parallel computers. More specifically, the research in many astrophysical fields requires an understanding of gas dynamical, magnetic, radiative transfer and gravitational phenomena not accessible to