11institutetext: INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00078
Monte Porzio Catone, Italy 22institutetext: ASI Agenzia Spaziale Italiana, via
della Ricerca Scientifica, Roma, Italy 33institutetext: INAF—Osservatorio
Astronomico di Trieste, Via Giambattista Tiepolo, 11, 34131 Trieste, Italy
44institutetext: INAF—Osservatorio Astrofisico di Catania, Via S. Sofia 78,
95123 Catania, Italy 55institutetext: INAF—Osservatorio Astrofisico di
Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy 66institutetext: National
Solar Observatory, 3665 Discovery Drive, Boulder CO 80303, USA

# IBIS-A: The IBIS data Archive ††thanks: Research supported by the H2020
SOLARNET grant no. 824135,

High resolution observations of
the solar photosphere and chromosphere with contextual data

Ilaria Ermolli 11 Fabrizio Giorgi 11 Mariarita Murabito 11 Marco Stangalini
2211 Vincenzo Guido 11 Marco Molinaro 33 Paolo Romano 44 Salvatore L.
Guglielmino 44 Giorgio Viavattene 11 Gianna Cauzzi 5566 Serena Criscuoli 66
Kevin P. Reardon 66 Alexandra Tritschler 66<EMAIL_ADDRESS>
(Received x y 2021/ Accepted z w j)

###### Abstract

Context. The IBIS data Archive (IBIS-A) stores data acquired with the
Interferometric BIdimensional Spectropolarimeter (IBIS), which was operated at
the Dunn Solar Telescope of the US National Solar Observatory from June 2003
to June 2019. The instrument provided series of high-resolution narrow-band
spectro-polarimetric imaging observations of the photosphere and chromosphere
in the range 5800$-$8600 Å and co-temporal broad-band observations in the same
spectral range and with the same field-of-view of the polarimetric data.

Aims. We present the data currently stored in IBIS-A, as well as the interface
utilized to explore such data and facilitate its scientific exploitation. To
this purpose we also describe the use of IBIS-A data in recent and undergoing
studies relevant to Solar Physics and Space Weather research.

Methods. IBIS-A includes raw and calibrated observations, as well as science-
ready data. The latter comprise maps of the circular, linear, and net circular
polarization, and of the magnetic and velocity fields derived for a
significant fraction of the series available in the archive. IBIS-A
furthermore contains links to observations complementary to the IBIS data,
such as co-temporal high-resolution observations of the solar atmosphere
available from the instruments onboard the Hinode and IRIS satellites, and
full-disc multiband images from INAF solar telescopes.

Results. IBIS-A currently consists of 30 TB of data taken with IBIS during 28
observing campaigns performed in 2008 and from 2012 to 2019 on 159 days. 29%
of the observations are released as Level 1 data calibrated for instrumental
response and compensated for residual seeing degradation, while 10% of these
data is also available as Level 1.5 format as multi-dimensional arrays of
circular, linear, and net circular polarization maps, and line-of-sight
velocity patterns. 81% of the photospheric calibrated series present Level 2
data with the view of the magnetic and velocity fields of the targets, as
derived from data inversion with the Very Fast Inversion of the Stokes Vector
code (VFISV). Metadata and movies of each calibrated and science-ready series
are also available to help users evaluating observing conditions.

Conclusions. IBIS-A represents a unique resource for investigating the plasma
processes in the solar atmosphere and the solar origin of Space Weather
events. The archive presently contains 454 different series of observations. A
recently undertaken effort to preserve IBIS observations is expected to lead
in the future to an increase of the raw measurements and fraction of processed
data available in IBIS-A.

###### Key Words.:

Sun: atmosphere – Sun: photosphere – Sun: chromosphere – Methods: data
analysis – Astronomical databases: miscellaneous

††offprints: I. Ermolli,

##  1 Introduction

The solar atmosphere is a highly structured, complex, and strongly dynamic
environment produced by the continuous interplay between un-magnetized and
magnetized plasmas that permeate it (e.g. Rempel & Schlichenmaier 2011; Stein
2012; Cheung & Isobe 2014; van Driel-Gesztelyi & Green 2015; Bellot Rubio &
Orozco Suárez 2019; Wiegelmann & Sakurai 2021). Such interplay drives the
Sun’s activity and radiative variability on time scales from seconds to
centuries. Besides, it imposes electromagnetic forces in the whole
heliosphere, by modulating the solar particulate and magnetic flux (e.g.
Kilpua et al. 2017; Temmer 2021). The same interplay also holds a fundamental
role in hugely diverse astrophysical systems. For example, in addition to
being responsible for the evolution of magnetic features, coronal heating and
wind acceleration in the solar and stellar atmospheres (e.g. Schmelz 2003), it
is responsible for the acceleration of jets from active galactic nuclei and
gamma ray bursts (e.g. Blandford et al. 2019), and for the heating of the
warm-ionized medium of galaxies (e.g. Padoan & Nordlund 2011). In all these
systems, un-magnetized and magnetized plasmas interrelate at small spatial and
temporal scales that are still beyond those achievable with current
telescopes. However, these scales will be accessible soon in the Sun’s
atmosphere with the upcoming 4-m class solar telescopes, e.g. the National
Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST, Rimmele et al.
2020; Rast et al. 2021) and European Solar Telescope (EST, Collados et al.
2013; Schlichenmaier et al. 2019).

Nevertheless, analysis of high-resolution multi-wavelength spectro-
polarimetric observations of the Sun’s atmosphere performed over the past two
decades have already yielded a wealth of information on the interaction
between un-magnetized and magnetized plasmas (e.g. van Driel-Gesztelyi & Green
2015; Jess et al. 2015; Borrero et al. 2017; Bellot Rubio & Orozco Suárez
2019). These observations include data acquired with the Interferometric
BIdimensional Spectrometer (IBIS, Cavallini 2006), which combined dual,
tunable Fabry-Perot interferometers with a high-order adaptive optics system
and short exposures to perform high-resolution solar studies.

IBIS was developed at the INAF Arcetri Astrophysical Observatory with
contributions from the Universities of Florence and Rome “Tor Vergata”. It was
installed at the Dunn Solar Telescope (DST) of the National Solar Observatory
(NSO) in New Mexico (USA) in June 2003, on an optical bench fed by a high-
order adaptive optics system. It was operated there by INAF and NSO from 2005
to 2019 as a facility instrument. In 2019 the instrument was dismantled for
refurbishing in light of its re-installation at a different telescope (Ermolli
et al. 2020).

From 2003 to 2019 IBIS has provided data of the solar photosphere and
chromosphere at high spectral, spatial and temporal resolution over a
relatively large field-of-view (FOV, hereafter). Find more details in Sect.
2.2. These data have often been acquired simultaneously to those from other
instruments installed at the DST, e.g. the Rapid Oscillations in the Solar
Atmosphere (ROSA, Jess et al. 2010) and the Facility Infrared Spectrometer
(FIRS, Jaeggli et al. 2012). Besides, IBIS has often observed co-temporally
with other instruments in the framework of coordinated observing campaigns,
with space-borne telescopes, e.g., Solar and Heliospheric
Observatory/Michelson Doppler Imager (SOHO/MDI, Scherrer et al. 1995),
Hinode/Solar Optical Telescope (Hinode/SOT, Tsuneta et al. 2008), Solar
Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI, Scherrer et
al. 2012), SDO/Atmospheric Imaging Assembly (SDO/AIA, Lemen et al. 2012),
Interface Region Imaging Spectrograph (IRIS, De Pontieu et al. 2014), and
ground-based telescopes, e.g., New Solar Telescope (NST, Cao et al. 2010) and
Atacama Large Millimeter/submillimeter Array (ALMA, Wedemeyer et al. 2020).
With the DST located in the mountains above the White Sands Missile Range,
IBIS also co-observed with many solar sounding rocket payloads launched from
the range, including Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS,
Brosius et al. 2014), High Resolution Coronal Imager (Hi-C, Kobayashi et al.
2014), Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP, Narukage et al.
2016), and Very high Angular resolution Ultraviolet Telescope (VAULT,
Vourlidas et al. 2016). Instead, due to different time zones and telescope
operations, there are few if any co-temporary observations between IBIS and
other spectro-polarimetric instruments installed at the solar telescopes on
Canary Islands, e.g. the CRisp Imaging Spectro-Polarimeter (CRISP, Scharmer et
al. 2008) and the CHROMospheric Imaging Spectrometer (CHROMIS, Scharmer et al.
2019) operating at the Swedish 1-m Solar Telescope (SST, Scharmer et al.
2003).

Given the versatility of the instrument, IBIS data have been used to study a
variety of topics, including: temporal evolution and 3D nature of plasma flow
in quiet regions (Del Moro et al. 2007) and large-scale magnetic features
(Giordano et al. 2008; Sobotka et al. 2012, 2013); turbulent solar convection
(Viavattene et al. 2020, 2021); structure and brightness of small- (Viticchié
et al. 2009, 2010; Romano et al. 2012) and large-scale magnetic features
(Criscuoli et al. 2012); dissipation of magnetic energy by current sheets
above sunspot umbrae (Tritschler et al. 2008); identification, formation and
decay of active regions (Ermolli et al. 2017; Zuccarello et al. 2009; Murabito
et al. 2016, 2017; Schilliro & Romano 2021); formation, atmospheric
stratification and brightening in penumbral regions (Romano et al. 2013, 2014;
Murabito et al. 2019, 2020a; Romano et al. 2020); acoustic oscillations and
MHD wave propagation in the solar atmosphere (Vecchio et al. 2007, 2009;
Stangalini et al. 2011, 2012, 2013; Sobotka et al. 2016; Abbasvand et al.
2020; Houston et al. 2020) and in sunspots (Stangalini et al. 2018, 2021a,
2021b, 2021c); First Ionization Potential (FIP) effect (Baker et al. 2021);
magnetic flux emergence from the photosphere to the chromosphere (Murabito et
al. 2020a); chromospheric vortices (Murabito et al. 2020b); flares (Kowalski
et al. 2015; Capparelli et al. 2017; Romano et al. 2017); sensitivity of
spectral line diagnostics to temperature variations and small-scale magnetic
fields (Criscuoli et al. 2013) and new spectroscopic diagnostics of the solar
chromosphere (Cauzzi et al. 2008; Straus et al. 2008; Cauzzi et al. 2009;
Reardon et al. 2009; Judge et al. 2010; Lipartito et al. 2014; Molnar et al.
2019).

Recently an effort has been undertaken to collect to best effort the data
acquired by the IBIS instrument and to preserve them in the permanent IBIS-
Archive (IBIS-A). In this paper, we describe the public release of the data
available in IBIS-A. We introduce the IBIS observations and their processing
in Sect. 2. We present the data available in IBIS-A and their quality in Sect.
3. We give an outline of the data access and examples of unexplored data
available in IBIS-A in Sects. 4 and 5, respectively. Finally, we summarize
this work and draw our conclusions in Sect. 6.

##  2 Observations and data processing

###  2.1 IBIS

The IBIS instrument (Cavallini 2006) basically consisted of two tunable Fabry-
Pérot interferometers (hereafter referred to as FPs) and narrow band
interference filters (hereafter referred to as pre-filters) operating in a
classical mount over the spectral range 5800$-$8600 Å (later extended down to
5400 Å). During operations, the combination of the FPs, pre-filters and
instrument control allowed tuning the instrument transmission in wavelength
sequentially through spectral lines isolated by the pre-filters. The number of
wavelength points sampled per line, as well as the number of lines used in
sequence, were defined by the observer depending on science target and
available pre-filters.

It is worth noting that the layout and optical components of the IBIS
instrument underwent improvements in time. For example, the addition of a
polarimetric unit in 2006 allowed to expand measurements at the spectral
positions sampled by the instrument to all the Stokes polarization states (I,
Q, U, V). After this upgrade, the instrument also underwent the implementation
of new detectors and control software in 2010. However, these changes did not
affect the main characteristics of the instrument described above. Moreover,
from 2011 to 2019 the instrument had a rather stable condition with only minor
modifications that did not significantly change the main characteristics of
the data acquired by the instrument.

A thorough evaluation of the optical performance of IBIS is provided by
Reardon & Cavallini (2008) and Righini et al. (2010). In brief, the instrument
had a transmission profile with full width at half maximum (FWHM) of 24.0 mÅ
at 6328 Å (Reardon & Cavallini 2008) and a pixel scale of 0.082 arcsec per
pixel (until 2010) or 0.098 arcsec per pixel (after 2010). These values
allowed observations at the diffraction limit of the DST ($\approx$ 0.16
arcsec at 5800 Å). Find further details concerning the IBIS data in Sect. 2.2.

###  2.2 Observing campaigns

A typical IBIS data set consists of measurements taken in sequence over
multiple spectral lines (two or three lines, e.g. Fe I at 6302 Å, Fe I at 6173
Å, and Ca II at 8542 Å), with each line sampled at several spectral positions
(often between 10 and 30 positions), each position at six polarimetric
modulation states (I$\pm\mathrm{[Q,U,V]}$) and each state with either single
exposure or multiple exposures. The data are characterized by a high spectral
(R $>$ 200000), spatial ($\approx$ 0.16 – 0.24 arcsec), and temporal (8 – 15
frames per second) resolution, over a relatively large FOV (minimum linear
dimension $>$ 40 arcsec, find more details in the following). IBIS ensured a
high wavelength stability in time of the instrumental profile (with a drift of
the order of 10 m/s over 10 hours), short exposure times to partially freeze
the Earth’s atmospheric seeing (tens of ms), and nearly diffraction limited
resolution over the whole FOV.

The instrument could be operated in both the spectroscopic and spectro-
polarimetric modes. It also allowed for a hybrid mode where full-Stokes
measurements were taken in some of the selected spectral lines while only
spectral Stokes-I measurements were acquired for other lines. In standard
spectroscopic mode the FOV was often circular with a diameter of $\approx$ 95
arcsec, as defined by a circular mask inserted in the entrance focal plane of
the instrument. In standard spectro-polarimetric mode the FOV was rectangular
with a dimension of $\approx$ 40$\times$95 arcsec2, as a result of the
rectangular mask inserted in the focal entrance plane of the instrument so
that the two orthogonally linear polarized beams could be imaged onto the same
detector.

Both the spectroscopic and spectro-polarimetric observational modes were
operated with acquisition of broad-band (hereafter referred to as BB) images
simultaneous to the narrow-band (hereafter referred to as NB) data produced by
the two FPs. The BB images allow for post-facto compensation of residual
seeing degradation with enhancement of the image quality (Löfdahl 2016).

Figure 1 shows examples of IBIS data acquired in the standard spectroscopic
and spectro-polarimetric observational modes after instrumental calibrations
and further processing described in Sect. 2.3. In particular, we show the
spectroscopic observation at the photospheric Fe I 6173 Å line of a large
sunspot region with umbral and penumbral areas imaged near the disc center,
and the Stokes-I, -Q, -U, and -V measurements of a smaller sunspot region
observed closer to the limb.

Figure 1: From left to right: Examples of IBIS data acquired in standard
spectroscopic and spectro-polarimetric modes at the Fe I 6173 Å line with
circular (1000$\times$1000 pixels2) and rectangular (350$\times$800 pixels2)
FOV on 25 October 2014, 15:32 UT and 13 May 2016, 13:38 UT at disc positions
$\mathrm{\mu}$=0.85 and $\mathrm{\mu}$=0.68, respectively. The spectroscopic
and spectro-polarimetric Stokes I observations were taken in the line
continuum, while the spectro-polarimetric Stokes Q and Stokes U and V data
were acquired in the line core and line blue wing, respectively. We show here
the Level 1 data derived from the instrumental calibrations and MOMFBD
restoration. See Sects. 2.2 and 3.1 for more details.

Figure 2: Pie charts of the fraction (in %) of : panel a) spectroscopic and
spectro-polarimetric data available in IBIS-A, panel b) spectral lines (in Å)
acquired during the observations, panel c) duration (in minutes) of the
observational sequences, and panel d) $\mathrm{\mu}$ disc position of the FOV,
for all the Level 0 data stored in the archive. $\mathrm{\mu=cos\theta}$ where
$\mathrm{\theta}$ is the heliocentric angle. Table 1:  Overview of the Level 0
data available in IBIS-A.

Year | N Series |  Target(a) [%] |  N Data sets for each spectral line(b)
---|---|---|---
|  | PO | SP | QS | L | K I | Fe I | Ca II |  H$\alpha$ | Fe I | Fe I | Na I D1 | He I
|  |  |  |  |  | 7699 | 6173 | 8542 | 6563 | 630.2 | 7090 | 5896 | 5875
2012 | 33 | 51.5 | 30.3 | 15.2 | 0 | 0 | 33 | 33 | 0 | 33 | 0 | 0 | 0
2013 | 81 | 8.7 | 48.1 | 28.4 | 14.8 | 0 | 25 | 52 | 31 | 0 | 4 | 5 | 0
2014 | 64 | 14.1 | 54.2 | 10.3 | 20.4 | 0 | 45 | 27 | 52 | 0 | 7 | 0 | 5
2015 | 45 | 28.8 | 46.7 | 24.4 | 0 | 0 | 37 | 40 | 21 | 16 | 0 | 0 | 0
2016 | 26 | 19.2 | 46.2 | 34.6 | 0 | 0 | 17 | 26 | 17 | 0 | 0 | 1 | 0
2017 | 20 | 40 | 35 | 25 | 0 | 0 | 16 | 20 | 10 | 10 | 0 | 4 | 0
2018 | 136 | 8.8 | 0.7 | 69.8 | 20.6 | 25 | 14 | 127 | 104 | 0 | 0 | 27 | 0
2019 | 47 | 32 | 0 | 63.4 | 4.3 | 0 | 1 | 46 | 37 | 0 | 0 | 8 | 0

> Notes. (a) PO: pore, SP: sunspot, QS: quiet sun, L: Limb region. (b) Line
> core is given in Å.

Table 2:  Overview of the Level 1.5 and Level 2 data available in IBIS-A.

Date | Time |  Target(a) | Scans |  $\mu$ (b) | Cadence |  Data(c) |  Other data(c) | Ref |  Level(d)
---|---|---|---|---|---|---|---|---|---
YY-MM-DD | [UT] |  |  |  | [s] | processed | available |  |
2012-04-17 | 13:58:43 | PO | 56 | 0.94 | 67 | Fe I 6173 | Fe I 6302, Ca II 8542 (I) | 1 | 2.0
2012-04-17 | 15:09:06 | PO | 68 | 0.94 | 67 | Fe I 6173 | Fe I 6302, Ca II 8542 (I) |  | 2.0
2012-04-17 | 18:43:40 | PO | 100 | 0.94 | 67 | Fe I 6173 | Fe I 6302, Ca II 8542 (I) |  | 2.0
2013-10-07 | 17:39:08 | SP | 130 | 0.96 | 33 | Fe I 6173 | Na I D1 5896 |  | 2.0
2014-04-21 | 14:15:33 | PO | 15 | 0.98 | 116 | Fe I 6173 | Ca II 8542 |  | 2.0
2014-10-14 | 15:15:57 | PO | 238 | 0.44 | 50 | Fe I 6173 |  Ca II 8542, H$\alpha$ 6563 (I) |  | 2.0
2015-04-10 | 14:34:25 | SP | 237 | 0.88 | 23 | Fe I 6173 | Ca II 8542 |  | 2.0
2015-04-11 | 14:14:40 | PO | 19 | 0.69 | 131 | Fe I 6173 | Ca II 8542 |  | 2.0
2015-04-11 | 15:01:55 | PO | 18 | 0.88 | 131 | Fe I 6173 | Ca II 8542 |  | 2.0
2015-04-30 | 13:52:44 | QS | 290 | 1.00 | 27 | Fe I 6173 | Ca II 8542 (I) |  | 2.0
2015-05-01 | 14:17:52 | QS | 58 | 1.00 | 48 | Fe I 6173, Ca II 8542 |  | 2 | 1.5, 2.0
2015-05-02 | 14:25:34 | QS | 50 | 1.00 | 44 | Fe I 6173, Ca II 8542 |  |  | 1.5, 2.0
2015-05-02 | 15:08:33 | QS | 20 | 0.99 | 44 | Fe I 6173, Ca II 8542 |  |  | 1.5, 2.0
2015-05-02 | 15:27:31 | QS | 79 | 0.98 | 44 | Fe I 6173, Ca II 8542 |  |  | 1.5, 2.0
2015-05-03 | 14:28:42 | SP | 85 | 0.74 | 44 | Fe I 6173, Ca II 8542 |  |  | 1.5, 2.0
2015-05-03 | 17:15:05 | SP | 25 | 0.75 | 44 | Fe I 6173, Ca II 8542 |  |  | 1.5, 2.0
2016-05-13 | 13:38:48 | SP | 50 | 0.67 | 42 | Fe I 6173, Ca II 8542 |  |  | 1.5, 2.0
2016-05-13 | 14:15:05 | SP | 58 | 0.67 | 42 | Fe I 6173, Ca II 8542 |  |  | 1.5, 2.0
2016-05-13 | 15:00:27 | PO | 163 | 0.88 | 42 | Fe I 6173, Ca II 8542 |  |  | 1.5, 2.0
2016-05-19 | 13:37:43 | SP | 100 | 0.98 | 42 | Fe I 6173, Ca II 8542 |  |  | 1.5, 2.0
2016-05-20 | 13:53:06 | SP | 319 | 0.99 | 48 | Fe I 6173, Ca II 8542 |  | 3, 4, 5 | 1.5, 2.0
2016-10-11 | 16:04:17 | QS | 29 | 1.00 | 49 | Fe I 6173 |  Ca II 8542, H$\alpha$ 6563 (I) |  | 2.0
2016-10-11 | 16:33:07 | QS | 31 | 1.00 | 49 | Fe I 6173 |  Ca II 8542, H$\alpha$ 6563 (I) |  | 2.0
2016-10-12 | 14:53:30 | QS | 100 | 1.00 | 49 | Fe I 6173 |  Ca II 8542, H$\alpha$ 6563 (I) |  | 2.0
2017-05-05 | 14:06:00 | PO | 85 | 0.82 | 40 | Fe I 6173, Ca II 8542 |  |  | 1.5, 2.0
2017-05-05 | 15:37:49 | QS | 107 | 0.81 | 40 | Fe I 6173, Ca II 8542 |  |  | 1.5, 2.0
2017-05-12 | 13:34:16 | QS | 40 | 1.00 | 40 | Fe I 6173, Ca II 8542 |  |  | 1.5, 2.0

> Notes. (a) Target: PO: pore, SP: sunspot, QS: quiet sun. (b) $\mu$ :
> $\mu=cos\theta$, where $\theta$ is the heliocentric angle. (c) Spectral
> lines observed with IBIS. Line core is given in Å. (I) specifies
> spectroscopic data. (d) Level: 1.5 and 2.0 science-ready data described in
> the main text. 1: Ermolli et al. (2017), 2: Murabito et al. (2020b), 3:
> Stangalini et al. (2018), 4: Murabito et al. (2019), 5: Houston et al.
> (2020).

###  2.3 Data processing

IBIS-A includes the camera data as originally generated by instrument as well
as processed data. The latter were obtained with a reduction package built on
the IBIS calibration pipeline (Criscuoli & Tritschler 2014) released by
NSO111https://nso.edu/telescopes/dunn-solar-telescope/dst-pipelines/ and with
other codes. The NSO pipeline includes calibration for the dark, flat-field
response, and gain of the detectors, computation of the detector image scale
and orientation, compensation for the artificial polarization introduced by
the instrumentation and by the telescope, calibrations for the systematic
wavelength shift across the FOV due to the collimated mounting of the FPs, and
for residual effects of the seeing. Besides, the data available in IBIS-A were
calibrated for pre-filters transmission curves and residual polarization
cross-talk between Stokes-I and Stokes-Q, -U, -V data. Moreover, the BB data
were processed for image restoration by using the outcomes of the Multi-Object
Multi-Frame Blind Deconvolution (MOMFBD, Löfdahl 2012; van Noort et al. 2005),
in order to enhance the image quality over the full FOV. The package employed
to process the data is written in IDL222Interactive Data Language, Harris
Geospatial Solutions, Inc., and it is run under a Linux Ubuntu distribution.
The codes are run in a semi-automatic mode, which requires inputs from the
user at two steps, in order to select the FOV for alignment of NB and BB
images and to compute the residual polarization cross-talk. At present the
MOMFBD restoration, which is written in C++, is not integrated in the data
reduction package.

The IBIS measurements processed for the above steps form the Level 1 data in
IBIS-A. At present, there are 133 calibrated series out of the 454 series of
raw IBIS observations stored in the archive.

A subset of the Level 1 observations was further processed to generate Level
1.5 data. This subset consists of the calibrated spectro-polarimetric
observations acquired at the photospheric Fe I 6173 Å and chromospheric Ca II
8542 Å lines under homogeneous instrumental setup (i.e. same observing mode
and spectral sampling).

The Level 1.5 data comprise maps of the mean circular polarization (CP), mean
linear polarization (LP), and net circular polarization (NCP), and of the
line-of-sight ($\mathrm{los}$) velocity field ($\mathrm{V_{los}}$). The mean
CP signal was estimated by using two methods: 1) by computing the maximum
amplitude of the Stokes-V spectral profile as reported in Stangalini et al.
(2021a) with the formula:

$\mathrm{CP1=\frac{|V_{max}|}{I_{cont}}\cdot sign\leavevmode\nobreak\
(V_{max})}$ (1)

where $\mathrm{V_{max}}$ is the maximum amplitude of the Stokes-V parameter in
the measured profile, and $\mathrm{I_{cont}}$ the local continuum intensity,
and 2) by considering all the values of the Stokes-V profile as set out by
Martínez Pillet et al. (2011). The latter method was adapted to account for
the actual number $\mathrm{n}$ of spectral points sampled during the
observations. In particular, we applied the formula:

$\mathrm{CP2=\frac{1}{n\leavevmode\nobreak\ \langle
I_{c}\rangle}\sum_{i=1}^{n}\epsilon_{i}\leavevmode\nobreak\ |V_{i}|}$ (2)

where $\mathrm{\epsilon}$ = 1 for the spectral positions of the line sampling
on the blue wing of the line, $\mathrm{\epsilon}$ = -1 for the spectral
positions on the red wing, and $\mathrm{\epsilon}$ = 0 for the line center
position, $\mathrm{n=21}$ is the number of sampled spectral positions, and $i$
runs from the $\mathrm{1st}$ to the $21st$ wavelength position.
$\mathrm{\langle I_{c}\rangle}$ and $\mathrm{V_{i}}$ are the values of the
average line continuum intensity in a quiet Sun region within the FoV and of
the Stokes-$\mathrm{V}$ parameter at the wavelength position $\mathrm{i}$.

We also estimated the LP signal with the method set out by Martínez Pillet et
al. (2011), by using the formula:

$\mathrm{LP=\frac{1}{n\leavevmode\nobreak\ \langle
I_{c}\rangle}\sum_{i=1}^{n}\sqrt{\leavevmode\nobreak\
Q^{2}_{i}\leavevmode\nobreak\ +\leavevmode\nobreak\ U^{2}_{i}}}$ (3)

where $\mathrm{Q_{i}}$ and $\mathrm{U_{i}}$ are the values of the
Stokes-$\mathrm{Q}$ and Stokes-$\mathrm{U}$ parameters at the wavelength
position $\mathrm{i}$.

The NCP, which is a measure of the asymmetry of the Stokes-V polarization
signal, was estimated from the integral of the measured Stokes-V profile
following Solanki & Montavon (1993). In particular, we applied the formula:

$\mathrm{NCP=\int_{\lambda_{1}}^{\lambda_{n}}d\lambda\leavevmode\nobreak\
V(\lambda)}$ (4)

where the $\mathrm{\lambda}$, $\mathrm{\lambda_{1}}$, and
$\mathrm{\lambda_{n}}$ represent the wavelength, and wavelengths at the
$\mathrm{1st}$ and $\mathrm{21st}$ spectral positions of the sampled line,
respectively. We computed $\mathrm{V_{los}}$ by using the phase cross-
correlation of Fourier transform as set out in Sect. 2.4 of Schlichenmaier &
Schmidt (2000).

The Level 1.5 data were computed by utilizing the Matplotlib (Hunter 2007),
Scipy (Virtanen et al. 2020), and Numpy (Harris et al. 2020) libraries written
in Python language. At present, there are 14 different series of Level 1.5
data available in the archive.

Finally, the Level 1 series from spectro-polarimetric observations at the Fe I
6173 Å line were further considered to generate Level 2 data. In particular,
all the scans of the above series were processed with inversion techniques.
The core of these techniques relies on inference of the dynamics, magnetic and
thermodynamics properties of the imaged atmosphere from the measured Stokes
profiles of single or multiple spectral lines that form at different heights
in the solar atmosphere. This is achieved by solving the radiative transfer
equation through codes aimed at working the inverse problem (del Toro Iniesta
& Ruiz Cobo 2016). The Level 2 data in IBIS-A were obtained with the Very Fast
Inversion of the Stokes Vector code (VFISV, Borrero et al. 2011), version 4.0,
which performs a Milne-Eddington inversion of measured Stokes profiles. At
present, 31 data series have been inverted and a total of 2902 scans
processed, which let more than 80% of the calibrated Fe I 6173 Å line
observations stored in the archive to also be available as Level 2 data.

The FOV size of Level 1 data333Currently available only for spectro-
polarimetric series. is 500$\times$1000 pixels2, while the size of both the
science-ready Level 1.5 and 2.0 data cover 350$\times$800 pixels2, or
$\approx$ 34$\times$78 arcsec2.

##  3 IBIS-A data

The IBIS observing campaigns varied depending on instrumental setup, observer,
target, and science goals, thus the acquired data are very heterogeneous.
However, almost all the IBIS data sets include the sampling of a photospheric
line and a chromospheric line, either Ca II 8542 Å or H${\alpha}$ 6563 Å, and
sometimes of both these latter lines. From 2013 to 2017 the chromospheric Ca
II 8542 Å observations were frequently carried out in spectro-polarimetric
mode.

Figure 2 summarizes the main characteristics of the IBIS data available in
IBIS-A. Figure 2 panels a) and b) show the fraction of spectroscopic and
spectro-polarimetric series, and the spectral lines sampled in the
observations, respectively. The spectro-polarimetric data are 37% of the
available measurements (in terms of number of sets). Over 19%, 6%, 4% of the
data refer to the photosphere sampled at the Fe I 6173 Å and 6302 Å, and Na I
at 5896 Å lines, respectively; 38% and 27% of the data report observations of
the chromosphere at the Ca II 8542 Å and H${\alpha}$ 6563 Å lines,
respectively. Figure 2 panels c) and d) display the fraction of sequences in
the archive depending on their duration and solar disc position of the target,
respectively. Almost 56% of the data consist of sequences of observations
lasting less than 30 minutes, but more than 12% of the available data report
on long-duration observations exceeding 1 hour. Besides, it is worth noting
that duration in this statistics refers to the length of individual series.
However, sometimes multiple series were run with minimal delay between each
other and could thus be considered as a “continuous” observing block. About
53% of the observations were taken at disc center ($\mu$¿ 0.85, where
$\mu=cos\theta$ and $\theta$ is the heliocentric angle), while over 40% of the
data image the solar atmosphere at intermediate disc locations
(0.25¡$\mu$¡0.85) and about 4% very close to the limb (0.04¡$\mu$¡0.1) or
above it.

Figure 3 (top panel) describes the IBIS-A data in terms of the median value of
the “quality image” parameter q. This quantity is a measure of the image
resolution in arcsec due to the seeing. It is is generated by the DST control
system from the monitoring of the variability of the Sun’s light intensity
during the observing run; see Seykora (1993) for more details. Figure 3 shows
that more than 77% of the IBIS-A data were taken under very good and average
seeing conditions, i.e. image resolution $<$ 1 arcsec, while about 4% of the
observations image the solar atmosphere at medium spatial resolution with
image resolution $>$ 1.5 arcsec. About 18% of the data are characterized by a
resolution in the range 1-1.5 arcsec.

Figure 3 (bottom panel) provides information on the homogeneity of the data
sets available in the archive. Here we show the number of data sets depending
on the homogeneity of the “image quality” parameter q during the observing
run, for observations of given duration d. The distribution of values in Fig.
3 (bottom panel) shows that a large fraction of the short duration data sets
available in IBIS-A were taken under stable excellent and good seeing
conditions, but this also holds for a significant number of observations
exceeding one hour.

Figure 3: Top panel: Pie chart of the IBIS-A data divided for the median value
of the “quality image” parameter q (in arcsec) during acquisition of Level 0
data. See Sect. 3.1 for more details. Bottom panel: Number of Level 0 data
sets depending on their duration d and homogeneity of the “quality image”
parameter q during observations. The homogeneity of the data set is described
by the standard deviation of the q values measured during the observing run.

###  3.1 Data format

IBIS-A includes the data generated by the instrument, those processed for
instrumental calibration and seeing restoration, and those further elaborated
to derive physical quantities and science-ready data. These diverse sets,
which form the Level 0, Level 1, Level 1.5, and Level 2 data, respectively,
are stored in the archive with different formats.

The Level 0 data ($\approx$ 25 TB of data) are archived as extended FITS
format files in a main folder comprising two sub-directories. These include
the NB and BB data, respectively, containing data for both science and
instrumental calibrations. The name of the files describes the nature of the
data (Science, Dark, Flat-Field, etc.). Each file comprises the data from a
single iteration of all pre-filters and wavelengths used during observations.
General information about the data, which is common to the whole observing
run, is stored in the primary FITS header, while information specific of a
single exposure (acquisition time, wavelength position, exposure time,
telescope pointing, polarization state, etc) is stored in the extended FITS
headers. Figures 8 and 9 in Appendix A give examples of such information. Each
FITS file consists of a four-dimensional array with
$\mathrm{(x,y,\lambda,Pol)}$-axes, where the spatial $\mathrm{x}$ and
$\mathrm{y}$ axes describe the instrument FOV, the $\mathrm{\lambda}$ axis
covers the wavelength spectral points along the sampled line and the
$\mathrm{Pol}$ axis represents the six polarimetric states (I+Q, I‐Q, I+V,
I‐V, I+U, and I‐U) measured by the instrument. The above structure and
labelling of the Level 0 data follow the IBIS data definition and file
arrangement given at the DST.

Table 1 gives an overview of the Level 0 data currently available in IBIS-A,
with information on the number of data sets, the fraction of observations
depending on the target and sampled spectral lines. The information is
provided per year from 2012 to 2019. Table 1 shows that there is a variety of
observations at different lines, and targets available in IBIS-A, the latter
including quiet Sun, sunspots, pores, and limb regions. Some of the data also
relate to plages and filaments.

The Level 1 data ($\approx$ 4 TB of data) are stored in the archive using the
.sav format generated by the IDL pipeline applied to the Level 0 observations.
The Level 1 files consist of four dimensional arrays with
$\mathrm{(x,y,\lambda,Stokes)}$-axes, where the spatial $\mathrm{x}$ and
$\mathrm{y}$ axes describe the instrument FOV, the $\mathrm{\lambda}$ axis
renders the wavelength of the line sampling during the observation, and the
$\mathrm{Stokes}$ axis represents the $\mathrm{(I,Q,U,V)}$ polarimetric states
of the measurements. Each Level 1 file also contains information about the
data in the info$\\_$nb variable, which is a structure with several tags and
values. Figure 10 in Appendix A lists the fields included in the info$\\_$nb
variable. The Level 1 data are stored with the naming convention llll-
nbsss.pc.sav and llll-nbsss.sav for the spectro-polarimetric and purely
spectroscopic data, respectively, where “llll” is the wavelength in Å , and
“sss” is the scan number in the corresponding Level 0 data. Each .sav file
thus reports the data at the given time $t$ of the “sss” scan during the
sequence of observations. The structure and naming of the Level 1 data follow
the ones set in the NSO calibration pipeline.

Table LABEL:tablev1 in Appendix A summarizes key information on the Level 1
data currently available in IBIS-A, with details on targets, lines and number
of spectral points sampled during observations, number of measurements at each
spectral point and number of line scans. Table LABEL:tablev1 makes it clear
that most of these data currently include observations of the chromosphere at
the Ca II 8542 Å and H$\alpha$ 6563 Å lines. It is worth noting that the Level
1 data of IBIS-A can be accessed with the CRIsp SPectral EXplorer (CRISPEX)
graphical user interface (Vissers & Rouppe van der Voort 2012; Löfdahl et al.
2021), version 1.7.4, which was developed to manage the CRISP and CHROMIS
data. To this purpose, the IBIS data format needs to be adapted to the FITS
format accepted by the CRISPEX interface with a code available at the IBIS-A
site specified in the following. The pipeline to reduce Level 0 data is also
available at the archive site. Other codes are available, e.g. to convert
Level 1 data from .sav to .FITS format.

Level 1.5 and Level 2 data ($\approx$ 15 GB and 20 GB of data, respectively)
are stored in the archive in FITS format files444At present, FITS Standard
Version 3 using CFITSIO Version 3.47. as multi-dimensional arrays with
$\mathrm{(x,y,var)}$-axes, where $\mathrm{x}$ and $\mathrm{y}$ are the spatial
coordinates in the FOV, and $\mathrm{var}$ indicates the physical quantities
derived from the line measurements and VFISV data inversion, respectively. The
physical quantities obtained from line measurements include estimates of the
CP555From both the above-mentioned calculations applied., LP, NCP and
$\mathrm{V_{los}}$, while those from the VFISV data inversion comprise the
magnetic field strength ($\mathrm{B}$), the inclination ($\mathrm{B_{inc}}$)
and azimuth ($\mathrm{B_{azi}}$) angles of the magnetic field, the
longitudinal component of the velocity field ($\mathrm{V_{los}}$), and the
magnetic filling factor ($\mathrm{F_{fact}}$). Field azimuth ambiguity is
unresolved.

The Level 1.5 and Level 2 data comprehend metadata information in the form of
FITS header keywords that are stored in a primary header and two extended
headers. The primary header contains information derived from the Level 0 data
to describe the observations with regard to telescope pointing as Stonyhurst
Heliographic solar coordinates (in degrees), solar $\mathrm{P0,L0,B0}$
ephemeris (in degrees), apparent solar photospheric disc radius (in arcsec),
Seykora scintillation monitor value (the “quality image” parameter given in
arcsec), and duration of the line scan (in seconds). The information stored in
the first and second extended headers concerns the physical quantities
available in the data and spectral sampling of the observations employed to
estimate them, respectively. Since Level 1.5 data are obtained from
observations taken at the Fe I 6173 Å and Ca II 8542 Å lines, the latter
extended header of Level 1.5 data includes information on both the sampled
lines, while it only refers to Fe I 6173 Å spectral measurements for Level 2
data. It is worth noting that the metadata information delivered in the Level
1.5 and Level 2 data is compliant with the SOLARNET recommendations (Haugan &
Fredvik 2015, 2020). In particular, a number of keywords employed in primary
and extended headers address the SOLARNET recommendations, e.g., the keywords
specifying date and time of data series, wavelength, observing mode, exposure
time, instrument and telescope employed, frame dimension, solar ephemeris,
telescope pointing, data author, data version, name of the procedures applied
to the data, origin and level of the data.

Figures 11, 12, and 13 in Appendix A give examples of keywords in the FITS
header of the Level 1.5 and Level 2 data. Level 1.5 and Level 2 files are
stored in the archive with the naming convention
$IBIS\\_l\\_YYYYMMDD\\_HHMMSS$, where ”$l$” shows the data level, $YYYYMMDD$
and $HHMMSS$ the date and time of the related observations. This file naming
convention also addresses the SOLARNET recommendations.

Table 2 summarizes the main characteristics of the Level 1.5 and Level 2 data
available in IBIS-A. There is a variety of targets in science-ready data,
including pores, sunspots, and quiet Sun regions. Besides, a few series have
further co-temporal observations available than the Fe I 6173 Å and Ca II 8542
Å ones considered to produce the Level 1.5 and Level 2 data, obtained at e.g.
the photospheric Fe I 6302 Å and chromospheric H$\alpha$ 6563 Å lines. Table
LABEL:tablev2a in Appendix A summarizes key information on the Level 2 data
currently available in IBIS-A and further co-temporal spectral lines observed
with IBIS.

Figure 4: Examples of contextual data available in IBIS-A. Full-disc
observations of the solar chromosphere acquired on 22 October 2014 at the
H$\alpha$ (top left panel) and Ca II K (top right panel) lines by the INAF
Catania and Rome/PSPT telescopes, respectively, zoom of the Hinode/SOT
observation (Level 1) of the central region of NOAA AR 12192 (bottom left
panel), also imaged by the IBIS data available in IBIS-A (bottom right
panels).

###  3.2 Contextual and coordinated observations

The data stored at IBIS-A are characterized by the large volume of each target
observation and the challenging analysis that is typical of any spectro-
polarimetric measurements. Nevertheless, the literature is rich in novel
results derived from analysis of data either belonging to or similar to those
in IBIS-A. Almost all these studies, as well as the ones listed in Sect. 1,
clearly show that combining spectro-polarimetric measurements such as those in
IBIS-A with data from other instruments greatly enhances the return of the
scientific analysis of the former observations, by expanding the FOV and range
of atmospheric heights that can be investigated. In this light, the IBIS-A
archive offers to its users links to observations complementary to the IBIS
series available in the archive, such as those from co-temporal and near co-
temporal high-resolution observations of the solar atmosphere available from
the instruments onboard the Hinode/SOT (Tsuneta et al. 2008) and IRIS (De
Pontieu et al. 2014) satellites, and full-disc filtergrams from INAF solar
telescopes (Ermolli et al. 2011; Romano et al. 2022).

Figure 4 shows examples of contextual data available in IBIS-A for the IBIS
data set obtained on 22 October 2014 observing the active region (AR) NOAA
12192. The contextual data include full-disc observations of the solar
photosphere (not shown) and chromosphere at the H$\alpha$ 6563 Å and Ca II K
3933 Å lines acquired by the INAF Catania and Rome/PSPT telescopes on the same
day of the IBIS observations, and zoom of the central region of AR NOAA 12192
from Hinode/SOT observations almost co-temporal with the IBIS measurements
stored in IBIS-A. The latter pertain the inner part of the AR during the
occurrence of a X1.6 flare. It is worth noting that at present users are only
provided with direct links to the Hinode/SOT and IRIS data complementary to
those available for each series in IBIS-A, without any processing to e.g.
scale and target observations from the diverse instruments.

##  4 Data access

The IBIS-A data are stored on a RS24S3 SuperNAS server (96 TB, 64 GB Ram, 2
CPU Haswell 4C E5-2623V3 3G) at the INAF Osservatorio Astronomico di Roma
666The IBIS-A data can be accessed at http://ibis.oa-roma.inaf.it/IBISA/..

The metadata of the Level 0 files were ingested into a MySQL database (DB
hereafter) by using a Python application. The Python Django framework has been
used both to define the relational table schema using its object-relational
internal mapping and to provide the web pages with simple query search
interface.

The IBIS-A archive, so built, works on the server running Python 2.7.6, with
Django version 1.9.1 on a MySQL 5.5 server. It has recently been tested (to
update the query service) on a test machine running Python 3.9.1, Django 3.2.9
and a MySQL 8.0 server.

The interface permits searching data according to various criteria: solar
target, disc position, observational mode, data range; criteria can be
combined in order to refine searches. Based on the metadata stored on the
IBIS-A DB, the data search dynamically generates a HTML page with information
about the available data. The HTML tabular output is prepared using Django
views for the search results and formatted in HTML using the internal Django
template tools. The products of the data search also include movies and plots
of the atmospheric seeing during observations, as basic information to allow
users to assess the data quality. The movies for quick look purposes were
created by using the 2D plotting library Matplotlib (version 1.5.2).

Browsing IBIS-A does not require authentication, but users have to register
and login in order to be able to request and download IBIS-A data.

Figure 5: Examples of Level 1 data of chromospheric flaring regions available
in IBIS-A. The data were acquired along the H$\alpha$ 6563 Å line, in the wing
(panel A) and core (panel B) of the line, on 10 October 2014, 14:20 UT at disc
position $\mu$=0.43, and along the Ca II 8542 Å line, in the far wing (panel
C) and line core (panel D), on 13 May 2016, 15:00 UT, at disc position
$\mu$=0.9. White lines in right-most panels show contours of magnetic pore
regions corresponding to $I_{c}(x,y)=0.8\times I_{c}(quiet)$, where
$I_{c}(x,y)$ and I${}_{c}(quiet)$ are values of the line continuum intensity
at the given position $(x,y)$ and in quiet region.

Figure 6: Examples of Level 1, Level 1.5, and Level 2 data available in IBIS-A
for the flaring region with magnetic pores shown in Fig. 5. The observations
were taken on 13 May 2016 at 15:00 UT. Top panels display Level 1 (panel A)
and Level 2 (panels B-D) data, while bottom panels show Level 1.5 (panels E-H)
data. Top panels, from left to right: maps of the intensity measured on the
FOV at the Fe I 6173 Å line continuum and of the magnetic field strength,
azimuth and inclination angles derived from the VFISV inversion of the Fe I
6173 Å line data. Bottom panels, from left to right: maps of the linear and
circular polarization estimated from the photospheric Fe I 6173 Å line data,
circular polarization from the chromospheric Ca II 8542 Å observations, and
$los$ velocity field at photopheric heights from Fe I 6173 Å measurements. See
caption of Fig. 5 for more details.

Figure 7: Examples of Level 1, Level 1.5, and Level 2 data available in IBIS-A
for the sunspot region observed on 13 May 2016, 13:38 UT at disc position
$\mu$=0.68 shown in Fig. 1. Top panels display Level 1 (panel A) and Level 2
(panels B-D) data, while bottom panels show Level 1.5 (panels E-H) data. See
captions of Figs. 5 and 6 for more details.

##  5 A glimpse at science with IBIS-A

A significant fraction of the observations stored in IBIS-A are still
scientifically unexplored. Figure 5 displays examples of these data. They
concern calibrated observations of flaring regions obtained at the
photospheric Fe I 6173 Å line and at the chromospheric H$\alpha$ 6563 Å (the
latter is shown in Fig. 5 panels A and B at two different wavelengths) and Ca
II 8542 Å (Fig. 5 panels C and D) lines on 10 October 2014, 14:25 UT and 13
May 2016, 15:00 UT, at disc positions $\mu$=0.47 and $\mu$=0.89, respectively.
The observations of both these flaring regions exceed 100 minutes.

The atmosphere imaged in the wing of Ca II 8542 Å (Fig. 5 panel C) is typical
of the middle photosphere, with a clear pattern of reversed granulation.
Instead, both the wing of H$\alpha$ 6563 Å, and the core of both H$\alpha$
6563 Å and Ca II 8542 Å (Fig. 5 panels A, B, D) show various parts of the
chromosphere, with the typical dazzling variety of features such as surges,
bundles of arch filament systems, spicules, and localized and extended bright
regions. Figure 6 shows several science-ready data available in IBIS-A for the
flaring region with pores shown in panels C and D of Fig. 5. In the left side
of the FOV, the maps of CP derived from the photospheric Fe I 6173 Å and
chromospheric Ca II 8542 Å data (Fig. 6 panels F and G, respectively), and the
map of the field inclination obtained from the VFISV data inversion (Fig. 6
panel D) reveal magnetic field concentrations with opposite polarity with
respect to that in the pores. At the same location, the chromospheric
observations at the Ca II line core (Fig. 5 panel D) display a filament and a
footpoint of the flaring region (see X=[0,100], Y=[300,400]). Magnetic
signatures of these structures are also found in the chromospheric CP map from
Ca II 8542 Å data (Fig. 6 panel G). The maps of the magnetic field strength
derived from inversion of the photospheric Fe I 6173 Å data (Fig. 6 panels B,
C, and A, respectively) show values up to 1.4 kG in the pores, and field
strength in the range of 0.4-0.6 kG in their surrounding area. There the maps
of the photopsheric LP and Vlos from the Fe I 6173 Å data (Fig. 6 panels E and
H, respectively) show horizontal magnetic fields and velocity field with
strong upflows.

Figure 7 displays examples of the Level 1, Level 1.5, and Level 2 data
available in IBIS-A for the spectro-polarimetric observations of a sunspot
region shown in Fig. 1. That region was observed on 13 May 2016, 15:38 UT at
disc position $\mathrm{\mu}$=0.67. It is worth noting that both Figs. 6 and 7
show values of the field inclination derived from data inversion in quiet Sun
areas peaked around 90∘. As reported by Borrero & Kobel (2011), these values
result from inversion of LP measurements characterized by a signal to noise
ratio lower than 4.5. A more accurate estimate of the magnetic field
inclination in quiet Sun regions is however beyond the scope of the present
work, which aims to provide quick-look science-ready data to IBIS-A users.

##  6 Summary and conclusions

This paper presents the IBIS-A archive, which currently includes 30 TB of data
taken with the Interferometric BIdimensional Spectropolarimeter (IBIS) during
28 observing campaigns carried across 2008 to 2019 on 159 days. This
presentation of the archive is meant to facilitate and foster the scientific
usage of the IBIS-A data with examples of the data quality and their
application in recent and undergoing studies relevant to solar processes and
Space Weather science.

Indeed, since the implementation of IBIS-A in 2016, the raw data available in
the archive have increased, as well as the fraction of calibrated
measurements. Also, links have been added pointing to complementary data of
the solar atmosphere available from coordinated measurements performed with
the instruments onboard the Hinode and IRIS satellites, and the full-disc red
continuum, Ca II K, and H$\alpha$ observations of the photosphere and
chromosphere from the INAF synoptic solar telescopes.

Furthermore, the archive has been populated with higher level products from
inversion of the calibrated data. Multi-dimensional arrays with maps of
circular, linear, and net circular polarization, and $\mathrm{los}$ velocity
patterns from calibrated photospheric Fe I 6173 Å and chromospheric Ca II 8542
Å series are also offered to registered users. Besides, more than 80% of the
calibrated Fe I 6173 Å photospheric series have already been inverted with the
VFISV code to offer a quick-look view of the magnetic and velocity fields in
the archived targets. A further milestone will be reached from inversion of
the remaining photospheric data and of the chromospheric series with the new
NLTE DeSIRe code (Ruiz Cobo et al. 2022). The IBIS-A team will also ingest
more data in the archive when they will be available to it.

IBIS-A data include metadata for proper interpretation and archiving of the
observations available in the archive. At present, the keywords employed in
the header of FITS Level 1.5 and Level 2 data are partly compliant777Following
the definition in relevant documents. with the recently formulated SOLARNET
recommendations. The complete standardization of the metadata information
provided by the IBIS-A data planned in the near future will facilitate their
usage by users with limited knowledge of the spectro-polarimetric
observations. Besides, it will allow easy inclusion of IBIS-A data in future
Solar Virtual Observatories.

IBIS-A represents a unique resource for investigating the plasma processes in
the solar atmosphere and the solar origin of Space Weather events. Besides, it
represents the prototype of the archive that will host the data acquired with
the updated version of the IBIS instrument, named IBIS 2.0, which is under
development for installation at the Osservatorio del Roque de Los Muchachos in
the Canary Islands.

Browsing the IBIS-A does not require authentication, but users have to
register and login in order to be able to request and download data. The
IBIS-A team is open for technical support and help with the data analysis to
foster the use of data stored in the archive in new science projects. In this
respect, note that IBIS-A is currently maintained by the H2020 SOLARNET High-
resolution Solar Physics Network project, which aims at integrating the major
European infrastructures in the field of high-resolution solar physics.
Therefore, any publication that uses data contained in IBIS-A should
acknowledge the above support by reporting “This study makes use of data
collected in the IBIS-A archive, which has received funding from the European
Union’s Horizon 2020 research and innovation programme under Grant Agreements
No 824135 (SOLARNET).”

###### Acknowledgements.

The authors thank Doug Gilliam and Mike Bradford for acquisition of IBIS data
throughout the years. They also thank Juan Manuel Borrero and Han Uitenbroek
for their work on IBIS data. The authors are grateful to the referee for
carefully reading of the paper and for her/his comments. This research has
received funding from the European Union’s FP7 Capacities program under grant
agreement No 312495 (SOLARNET) and from the European Union’s Horizon 2020
Research and Innovation program under grant agreements No 824135 (SOLARNET)
and No 739500 (PRE-EST). This work was also supported by the Italian MIUR-PRIN
grant 2017 ”Circumterrestrial Environment: Impact of Sun–Earth Interaction”
and by the INAF Istituto Nazionale di Astrofisica. The Level 2 data available
in IBIS-A were obtained from access to servers of the Italian CINECA and INAF.
IBIS has been designed and constructed by the INAF Osservatorio Astrofisico di
Arcetri with contributions from the Universitá di Firenze, the Universitá di
Roma Tor Vergata, and upgraded with further contributions from National Solar
Observatory (NSO) and Queens University Belfast. IBIS was operated with
support of the NSO. The NSO is operated by the Association of Universities for
Research in Astronomy, Inc., under cooperative agreement with the National
Science Foundation. This research made use of NASA’s Astrophysics Data System.

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##  Appendix A Data summary and Metadata information

Figure 8: Example of metadata information stored in the FITS primary header of
the Level 0 data available in IBIS-A for the observations taken on 28 May 2012
at 13:38:43 UT.  Figure 9: Example of metadata information stored in the FITS
extended header of the Level 0 data available in IBIS-A for the observations
taken on 28 May 2012 at 13:38:43 UT.  Figure 10: Example of the several fields
with information stored in the info$\\_$nb variable, which is relevant to the
Level 1 data derived from the spectro-polarimetric observations taken at the
Fe I 617.3 nm line on 13 May 2016 at 13:38:48 UT.  Figure 11: Example of
metadata information stored in the FITS primary header of the Level 1.5 data
available in IBIS-A for the observations taken on 13 May 2016 at 13:38:48 UT.
Figure 12: Example of metadata information stored in the FITS extended header
of the Level 1.5 data available in IBIS-A for the observations taken on 13 May
2016 at 13:38:48 UT.

Figure 13: Example of metadata information stored in the FITS header of the
Level 2 data available in IBIS-A for the observations taken on 13 May 2016 at
13:38 UT.

Table LABEL:tablev1 summarizes information on the Level 1 data available in
IBIS-A. These data consist of the observations processed for instrumental
calibrations and restored for residual image degradation by seeing using the
MOMFBD method. Table LABEL:tablev2a summarizes information on the Level 2 data
available in IBIS-A. These data consist of the observations processed for data
inversion using the VFISV code. Find more details concerning the Level 1 and
Level 2 data in Sect. 2.3.

Figures 8 and 9 show examples of metadata information provided in the keywords
of the primary and extended headers of FITS files of the Level 0 data
available in IBIS-A. Figure 10 gives an example of the fields with information
stored in the variable info$\\_$nb relevant to Level 1 data. Figures 11 and 12
show examples of metadata information provided in the keywords of the primary
and extended headers of FITS files of the Level 1.5 data, respectively. Figure
13 displays same information for Level 2 data. See Sect. 3.1 for more details.

Table 3:  Overview of the Level 1 data available in IBIS-A. Date | Time | Target(a) | Lambda(b) Points(c) | Scans
---|---|---|---|---
YY-MM-DD | [UT] |  |  |
2008-10-15 | 16:30:00 | PO | 6173 IQUV (21), 8542 I (21) | 80
2012-04-17 | 13:58:43 | PO | 6302 IQUV (30), 6173 IQUV (24) 8542 I (25) | 56
| 15:09:06 | PO | 6302 IQUV (30), 6173 IQUV (24) 8542 I (25) | 68
| 18:13:40 | PO | 6302 IQUV (30), 6173 IQUV (24) 8542 I (25) | 100
2013-02-05 | 18:18:21 | SP | 6173 IQUV (5), 6563 I (14), 8542 IQUV (25) | 61
2013-10-07 | 17:39:08 | SP | 6173 IQUV (10), 5896 IQUV (23) | 137
2013-10-20 | 15:14:22 | SP | 6173 IQUV (10), 7090 I (10), 8542 IQUV (11) | 175
| 17:37:20 | QS | 5896 IQUV (10) | 157
| 18:11:51 | QS | 5896 IQUV (10) | 137
2014-04-15 | 14:41:21 | PO | 6173 IQUV (5), 8542 I (11) | 300
2014-04-21 | 14:15:33 | PO | 6173 IQUV (10x6), 8542 IQUV (11x6) | 15
| 15:17:03 | PO | 6173 IQUV (10x6), 8542 IQUV (11x6), | 15
2014-10-14 | 15:15:57 | PO | 6173 IQUV (20), 6563 I (25), 8542 IQUV (25) | 238
2014-10-22 | 14:29:34 | SP | 6173 IQUV (20), 6563 I (25), 8542 IQUV (25) | 84
| 15:46:24 | SP | 6173 IQUV (20), 6563 I (25), 8542 IQUV (25) | 17
| 16:05:36 | SP | 6173 IQUV (20), 6563 I (25), 8542 IQUV (25) | 37
| 17:43:40 | PO | 6173 IQUV (20), 6563 I (25), 8542 IQUV (25) | 31
2015-04-10 | 14:34:25 | SP | 6173 IQUV (10), 8542 IQUV (11), | 237
2015-04-11 | 14:14:40 | PO | 6173 IQUV (10x6), 8542 IQUV (11x6) | 19
| 15:01:55 | PO | 6173 IQUV (10x6), 8542 IQUV (11x6) | 18
2015-04-30 | 13:52:44 | QS | 6173 IQUV (21), 8542 I (21) | 290
2015-05-01 | 14:17:52 | QS | 6173 IQUV (21), 8542 IQUV (21) | 58
2015-05-02 | 14:25:34 | QS | 6173 IQUV (21), 8542 IQUV (21) | 50
| 15:08:33 | QS | 6173 IQUV (21), 8542 IQUV (21) | 20
| 15:27:31 | QS | 6173 IQUV (21), 8542 IQUV (21) | 79
2015-05-03 | 14:28:42 | SP | 6173 IQUV (21), 8542 IQUV (21) | 85
| 17:15:05 | SP | 6173 IQUV (21), 8542 IQUV (21) | 25
2015-05-18 | 16:38:19 | SP | 6173 IQUV (24), 6302 IQUV (30), 8542 I (25), 6563 I (17) | 20
2016-05-13 | 13:38:48 | SP | 6173 IQUV (21), 8542 IQUV (21) | 50
| 14:15:09 | SP | 6173 IQUV (21), 8542 IQUV (21) | 58
| 15:00:27 | PO | 6173 IQUV (21), 8542 IQUV (21) | 163
2016-05-19 | 13:37:43 | SP | 6173 IQUV (21), 8542 IQUV (21) | 100
2016-05-20 | 13:53:06 | SP | 6173 IQUV (21), 8542 IQUV (21) | 319
2016-10-05 | 15:06:58 | PO | 8542 IQUV (11), 6563 I (14) | 200
2016-10-06 | 15:58:20 | QS | 8542 IQUV (11), 6563 I (14) | 200
| 16:55:16 | QS | 8542 IQUV (11), 6563 I (14) | 176
2016-10-10 | 17:12:08 | PO | 8542 IQUV (11), 6563 I (14) | 200
| 18:07:47 | PO | 8542 IQUV (11), 6563 I (14) | 100
2016-10-11 | 16:04:17 | QS | 6173 IQUV (20), 8542 IQUV (25), 6563 I (14) | 29
| 16:33:07 | QS | 6173 IQUV (20), 8542 IQUV (25), 6563 I (14) | 31
2016-10-12 | 14:53:30 | QS | 6173 IQUV (20), 8542 IQUV (25), 6563 I (14) | 100
| 16:31:47 | SP | 8542 IQUV (11), 6563 I (14) | 5
| 16:38:46 | SP | 8542 IQUV (11), 6563 I (14) | 200
| 17:32:08 | SP | 8542 IQUV (11), 6563 I (14) | 85
2016-10-14 | 14:53:57 | QS | 6173 IQUV (20), 5896 IQUV (10), 6563 I (14) | 150
| 16:25:24 | SP | 8542 IQUV (11), 6563 I (14) | 228
2016-10-17 | 15:24:24 | QS | 6173 IQUV (20), 8542 IQUV (25), 6563 I (14) | 74
2016-10-18 | 15:12:40 | QS | 6173 IQUV (20), 8542 IQUV (25), 6563 I (14) | 58
2016-10-21 | 16:00:14 | QS | 6173 IQUV (20), 8542 IQUV (25), 6563 I (14) | 60
| 17:00:34 | PO | 8542 IQUV (11), 6563 I (14) | 232
2017-05-05 | 14:06:00 | PO | 6173 IQUV (21), 8542 IQUV (21) | 85
| 15:37:49 | QS | 6173 IQUV (21), 8542 IQUV (21) | 107
2017-05-12 | 13:34:16 | QS | 6173 IQUV (21), 8542 IQUV (21) | 40
2017-11-10 | 15:12:46 | QS | 8542 I (30), 5896 I (19) | 347
2018-02-01 | 17:06:03 | QS | 8542 I (30), 5896 I (19) | 149
| 17:44:02 | QS | 8542 I (30), 5896 I (19) | 147
2018-04-11 | 16:05:05 | QS | 8542 I (30), 5896 I (19) | 293
2018-04-26 | 15:48:38 | PO | 8542 I (27), 5896 I (24) | 199
2018-05-18 | 14:01:10 | PO | 8542 I (30), 6563 I (17), 5896 I (19) | 365
2018-05-19 | 14:01:17 | PO | 8542 I (29), 6563 I (27), 5896 I (19) | 215
2018-06-20 | 13:53:05 | SP | 8542 I (29), 6563 I (27), 5896 I (19) | 185
2018-06-21 | 13:57:00 | QS | 8542 I (29), 6563 I (27) | 315
| 15:22:32 | QS | 8542 I (29), 6563 I (27) | 10
| 15:53:12 | QS | 8542 I (29), 6563 I (27) | 10
| 16:21:09 | QS | 8542 I (29), 6563 I (27) | 10
| 16:32:05 | QS | 8542 I (29), 6563 I (27) | 10
2018-06-21 | 14:29:32 | QS | 8542 I (29), 6563 I (27) | 182
| 15:18:55 | QS | 8542 I (29), 6563 I (27) | 253
2018-06-25 | 14:31:04 | QS | 8542 I (30), 6563 I (27) | 190
| 15:22:10 | QS | 8542 I (30), 6563 I (27) | 182
| 16:13:17 | QS | 8542 I (30), 6563 I (27) | 127
2018-06-26 | 13:35:58 | QS | 8542 I (30), 6563 I (27) | 179
| 14:25:00 | QS | 8542 I (30), 6563 I (27) | 180
| 15:13:44 | QS | 8542 I (30), 6563 I (27) | 177
| 16:02:50 | QS | 8542 I (30), 6563 I (27) | 130
2018-06-27 | 13:40:50 | QS | 8542 I (30), 6563 I (27) | 213
| 14:41:01 | QS | 8542 I (30), 6563 I (27) | 190
| 15:36:14 | QS | 8542 I (30), 6563 I (27) | 213
| 16:51:11 | QS | 8542 I (30), 6563 I (27) | 5
| 16:54:46 | QS | 8542 I (30), 6563 I (27) | 5
| 17:10:40 | QS | 8542 I (30), 6563 I (27) | 5
| 17:14:48 | QS | 8542 I (30), 6563 I (27) | 5
2018-07-05 | 14:11:11 | QS | 8542 I (30), 6563 I (27) | 68
| 14:35:16 | QS | 8542 I (30), 6563 I (27) | 5
| 14:41:09 | QS | 8542 I (30), 6563 I (27) | 5
| 14:46:33 | QS | 8542 I (30), 6563 I (27) | 5
| 14:54:33 | QS | 8542 I (30), 6563 I (27) | 5
2018-06-16 | 13:53:21 | QS | 8542 I (30), 6563 I (27) | 106
| 14:50:04 | QS | 8542 I (30), 6563 I (27) | 106
2018-07-17 | 13:33:46 | QS | 8542 I (30), 6563 I (27) | 122
| 14:28:21 | QS | 8542 I (30), 6563 I (27) | 116
2018-07-23 | 14:02:33 | QS | 8542 I (30), 6563 I (27) | 3
| 14:03:41 | QS | 8542 I (30), 6563 I (27) | 139
| 14:41:02 | QS | 8542 I (30), 6563 I (27) | 151
2018-08-16 | 14:15:34 | QS | 8542 I (30) | 573
2018-08-17 | 14:01:21 | QS | 8542 I (30) | 582
2018-09-24 | 14:34:27 | QS | 8542 I (30), 6563 I (27) | 201
| 15:33:56 | QS | 8542 I (30), 6563 I (27) | 141
2018-09-25 | 14:09:52 | QS | 8542 I (30), 6563 I (27) | 196
| 15:32:27 | QS | 8542 I (30), 6563 I (27) | 145
2018-10-04 | 20:29:11 | QS | 8542 I (30), 6563 I (27) | 22
2018-10-10 | 15:06:09 | QS | 8542 I (30), 6563 I (27) | 146
2018-11-02 | 15:11:37 | QS L | 8542 I (25) | 900
| 16:28:55 | QS L | 8542 I (25) | 509
2018-11-03 | 15:35:59 | QS L | 8542 I (25) | 900
| 16:45:31 | QS L | 8542 I (25) | 900
| 17:54:54 | QS L | 8542 I (25) | 900
2018-11-04 | 15:00:54 | QS L | 8542 I (25) | 619
| 15:54:45 | QS L | 8542 I (25) | 900
| 17:04:22 | QS L | 8542 I (25) | 900
| 18:13:46 | QS L | 8542 I (25) | 175
| 18:38:28 | QS L | 8542 I (25) | 99
2018-11-15 | 15:16:49 | PO | 8542 I (30), 6563 I (27) | 316
| 17:20:28 | QS | 8542 I (30), 6563 I (27) | 190
| 15:05:40 | PO | 8542 I (30), 6563 I (27) | 31
2018-11-16 | 15:13:26 | PO | 8542 I (30), 6563 I (27) | 189
| 16:10:14 | QS | 8542 I (30), 6563 I (27) | 188
2018-11-19 | 15:33:04 | PO | 8542 I (30), 6563 I (27) | 163
| 16:09:27 | PO | 8542 I (30), 6563 I (27) | 266
2018-11-27 | 16:58:08 | QS | 8542 I (30), 6563 I (27) | 244
2018-11-29 | 15:35:31 | QS | 8542 I (30), 6563 I (27) | 126
2018-12-04 | 16:28:59 | QS | 8542 I (30), 6563 I (27) | 279
2018-12-20 | 15:55:00 | QS L | 8542 I (21), 6563 I (23) | 15
| 16:04:54 | QS | 8542 I (21), 6563 I (23) | 10
| 17:25:17 | QS | 8542 I (21), 6563 I (23) | 100
2018-12-23 | 15:15:32 | QS | 8542 I (21), 6563 I (23) | 120
| 17:19:24 | QS | 8542 I (21), 6563 I (23) | 120
| 17:53:06 | QS | 8542 I (21), 6563 I (23) | 120
| 18:25:34 | QS | 8542 I (21), 6563 I (23) | 120
2019-01-25 | 15:40:56 | PO | 8542 I (30), 6563 I (27), 5896 I (19) | 25
| 15:52:35 | PO | 8542 I (30), 6563 I (27), 5896 I (19) | 160
| 17:27:47 | PO | 8542 I (30), 6563 I (27), 5896 I (19) | 48
| 17:46:32 | PO | 8542 I (30), 6563 I (27), 5896 I (19) | 55
2019-02-18 | 15:39:03 | QS | 8542 I (30), 6563 I (27) | 127
2019-02-25 | 14:52:08 | QS L | 8542 I (30), 6563 I (27) | 130
| 15:25:23 | QS L | 8542 I (30), 6563 I (27) | 146
Table 3: continued.

> Notes. (a) Target: PO: pore, SP: sunspot, QS: quiet sun, QS L: Quiet Sun
> Limb. (b) Lambda: Spectral lines observed with IBIS. (c) Points describes
> the number of spectral positions sampled in the line. Observing modes with
> multiple exposures at each point are reported as $n\times m$, where $n$ and
> $m$ are the number of spectral points and the number of exposures at each
> point, respectively.

Table 4:  Overview of the Level 2 data available in IBIS-A. Date | Time | Target(a) | Data(b) | Other data(c) | Scans
---|---|---|---|---|---
YY-MM-DD | [UT] |  | from 6173 Å IUQV | available |
2012-04-17 | 13:58:43 | PO | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 6302 IUQV, 8542 I | 56
2012-04-17 | 15:09:06 | PO | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 6302 IUQV, 8542 I | 68
2012-04-17 | 18:43:40 | PO | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 6302 IUQV, 8542 I | 100
2013-10-07 | 17:39:08 | SP | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 5896 IUQV | 130
2014-04-21 | 14:15:33 | PO | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 15
2014-10-14 | 15:15:57 | PO | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV, 6563 I | 238
2015-04-10 | 14:34:25 | SP | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 237
2015-04-11 | 14:14:40 | PO | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 19
2015-04-11 | 15:01:55 | PO | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 18
2015-04-30 | 13:52:44 | QS | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 I | 290
2015-05-01 | 14:17:52 | QS | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 58
2015-05-02 | 14:25:34 | QS | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 50
2015-05-02 | 15:08:33 | QS | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 20
2015-05-02 | 15:27:31 | QS | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 79
2015-05-03 | 14:28:42 | SP | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 85
2015-05-03 | 17:15:05 | SP | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 25
2016-05-13 | 13:38:48 | SP | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 50
2016-05-13 | 14:15:05 | SP | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 58
2016-05-13 | 15:00:27 | PO | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 163
2016-05-19 | 13:37:43 | SP | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 100
2016-05-20 | 13:53:06 | SP | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 319
2016-10-11 | 16:04:17 | QS | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV, 6563 I | 29
2016-10-11 | 16:33:07 | QS | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV, 6563 I | 31
2016-10-12 | 14:53:30 | QS | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV, 6563 I | 100
2017-05-05 | 14:06:00 | PO | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 85
2017-05-05 | 15:37:49 | QS | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 107
2017-05-12 | 13:34:16 | QS | $\mathrm{B,B_{inc},B_{azi},F_{fact},V_{los}}$ | 8542 IUQV | 40
Table 4: continued.

> Notes. (a) Target: PO: pore, SP: sunspot, QS: quiet sun, QS L: Quiet Sun
> Limb. (b) Data: Level 2 data from Fe I 6173 Å IUQV observations.
> $\mathrm{B,B_{inc},B_{azi}}$, and $\mathrm{F_{fact}}$ refer to the magnetic
> field strength, inclination, azimuth, and filling factor, respectively.
> $\mathrm{V_{los}}$ is the longitudinal component of the velocity field. (c)
> Other data available: Other spectral lines observed with IBIS. Line core is
> given in Å.