Several observing campaigns have been carried out with the IRIS mission in coordination with other observatories to target solar prominences and prominence-like tornadoes. We focus here on observations between 2014 and 2016. The observational data is being complemented by a grid of non-LTE radiative transfer models producing synthetic Mg II line profiles. An algorithm is used to automatically extract relevant line profile parameters from the optically thick Mg II h and k lines, both on the observed and synthetic profiles. This allows us to study a large set of profiles and provide statistical results. We present our most recent findings from the combined analysis of synthetic spectra and of Mg II spectra acquired by IRIS, in terms of plasma parameters, magnetic fields, and dynamics, with the help of data from other observatories such as SDO, Hinode, the Meudon Solar Tower, and THEMIS. Implications for future high-resolution instruments are discussed.

1. Nic Labrosse – High-resolution observations of tornado-prominences – EWASS18
High-resolution diagnostics of
solar prominences and
prominence-like tornadoes
Nicolas Labrosse1, Peter Levens1, Brigitte Schmieder2,
Arturo López Ariste3, Maciej Zapiór4
1. School of Physics and Astronomy, University of Glasgow, UK
2. LESIA, Observatoire de Paris Meudon, FR
3. IRAP, CNRS - Université de Toulouse, FR
4. Academy of Sciences of the Czech Republic, CZ
With thanks to Anna Fumagalli, Jiangdan Li,
Eric McNeil, Holly Waller

2. Nic Labrosse – High-resolution observations of tornado-prominences – EWASS18
What are “giant tornadoes”?
Su et al 2012
Su et al 2012
Li et al 2012
Levens et al 2012
Yang et al 2018

3. Nic Labrosse – High-resolution observations of tornado-prominences – EWASS18
15 July 2014
observations
AIA 171
THEMIS He I D3 and B strength
SOT Ca II H
Levens et al (2016, 2017)

4. Nic Labrosse – High-resolution observations of tornado-prominences – EWASS18
Quantile analysis
𝜆 𝐶 = 2796.32
𝑊 = 386 mÅ
𝑆 = −0.059
𝜆 𝐶 = 2796.32
𝑊 = 382 mÅ
𝑆 = 0.014
(2796.34 Å)
15 July 2014
observations
• Robust method, no assumption on line
profile shape, applied on observed and
synthetic spectra
• Similar to quartile analysis of Mg II h & k
line profile shapes by Kerr et al (2015) in
flares
• Quantiles used are Q1=12%, Q2=50%, and
Q3=88% of total intensity to derive
𝜆 𝑐 = 𝑄2: line centroid position
𝑊 = 𝑄3 − 𝑄1: line width (=FWHM for Gaussian profile)
𝑆 =
𝑄3−𝑄2 − 𝑄2−𝑄1
𝑊
: profile asymmetry

5. Nic Labrosse – High-resolution observations of tornado-prominences – EWASS18
Models
Two examples of k line profile
showing result of convolution with
instrumental profile + rebinning to
IRIS spectral pixel size
New 1D plane-parallel non-LTE radiative
transfer code to compute Mg II lines
• prominence to corona transition region
(PCTR)
• detailed incident radiation from IRIS
Similar to recent 1D prominence Mg II models
by Heinzel et al (2014,2015) but with finer grid
of parameters
⇒Study line formation mechanisms
⇒ Explore model grid to compare with
observations

6. Nic Labrosse – High-resolution observations of tornado-prominences – EWASS18
Observations and models
No correlation between Mg II line
parameters and B strength
Observed line widths larger than
synthetic line widths
k/h ratio in good agreement,
points towards models with low
pressures

7. Nic Labrosse – High-resolution observations of tornado-prominences – EWASS18
What else did we learn?
Schmieder et al (2017): “The spiral-like structure of the prominence
observed in the plane of the sky is mainly due to the projection
effect of long arches of threads (up to 8×104 km). Knots run along
more or less horizontal threads with velocities reaching 65 km s-1.”
Schmieder et al (2016): “The Hα Doppler
maps show a pattern with alternatively
blueshifted and redshifted areas of 5 to
10′′ wide. Over time the blueshifted areas
become redshifted and vice versa, with a
quasi-periodicity of 40 to 60 min.
The Doppler pattern observed in Hα
cannot be interpreted as rotation of the
cool plasma inside the tornado.”

8. Nic Labrosse – High-resolution observations of tornado-prominences – EWASS18
Prominence ALMA observations
• Single pointing observations in Band 3 and
Band 6 (17 April)
• Mosaic in Band 3 (19 April)
• Support from IRIS, Hinode, GBOs…
Goals
(1) To measure brightness temperatures at
several frequencies to infer the global
thermal structure of the prominence plasma
(2) To characterise its evolution over short
temporal and spatial scales.
Rodger & Labrosse (2017)
Next steps in high-
resolution observations

9. Nic Labrosse – High-resolution observations of tornado-prominences – EWASS18
Summary
Magnetic field mostly horizontal everywhere
Similar Mg II line features in both structures
• Observations point to pressures  0.1 dyn cm-2 in tornado
Simple static 1D models unable to explain observed widths
• Need to consider other models, most likely inclusion of a number of 2D moving threads
along line-of-sight (e.g. Gunár et al 2007, 2008; Labrosse & Rodger 2016) - See also
discussion in Heinzel et al 2015
IRIS observations allow us to probe small scales but more will be learned with other high-
resolution observations: e.g. ALMA (e.g Rodger & Labrosse 2017), CLASP, EST, …
High-resolution observations require advanced models