General description

1. Focus on Decay of Active regions

Decay of Active regions: see slides in 4-Bellot-Rubio-SAP4_magnetoconvection5_final.pptx:

Decay process of ARs is not well known:

  • Slow, may last a few weeks
  • ARs approach limb and suffer from projection effects
  • Emerging flux starts to reconnect with preexisting flux very soon
  • Appearance of filaments, flux rope eruptions and CMEs in late  phases of decay
  • Sunspot fragmentation by light bridges?
  • Flux erosion by convective flows?
  • Role of moving magnetic features?
  • How is the AR flux dispersed?
  • What is the fate of the flux?

Default SOOP duration: 15 days

Pointing requirements: target pointing and tracking

Triggers: disabled

2. Focus on Thermal Non Equilibrium

Coronal loops in active regions constantly undergo heating and cooling cycles, reflected in the observed intensity variability across the spectrum. The temporal and spatial scales of this variability are key characteristics of the underlying coronal heating mechanisms (SAP The heating mechanisms are expected to occur over short temporal and spatial scales. Footpoint or uniformly distributed heating, and quasi-steady or low frequency heating lead to different global thermal evolution of loops.

A leading theory behind the observed EUV intensity variability over several hours scale in loops is thermal non-equilibrium (TNE), in which the loops are preferentially heated at the footpoints and in a quasi-steady manner. Two key observables of TNE are: (1) long-period EUV intensity pulsations (having periods of up to 15 hours or more) and (2) warm and cool condensations, observable in TR and chromospheric lines. The condensations, which correspond to the coronal rain phenomenon, are partially ionised cool and dense clumps driven by thermal instability of widths down to 0.3’’ that occur in groups and can trace the entire loop during their fall to the lower atmosphere. The presence or absence of rain, the global characteristics of the heating and cooling (TNE) cycles such as the evolution of temperature and density and the period of the cycles, are observables that provide major constraints on the heating properties (SAP,,,, 1.3.1, Furthermore, observations are currently limited to the follow-up of active regions during their passage on-disk, and the length of TNE cycles is constrained by this artificial limitation.

Since Solar Orbiter can, to some approximation, co-rotate with ARs, it allows a longer follow-up, thus allowing to investigate how much can TNE cycles last. In this study we aim at capturing from the unique standpoint and capabilities of Solar Orbiter the major aspects of TNE cycles in the solar corona.

With Solar Orbiter observations we aim to address three main scientific questions:

Q1: How long do they last? How/when do they start and stop?

Q2: Are condensations in prominence-rain hybrids (null-point topologies) due to TNE cycles? Are their counterparts on the solar disk related to the observed quiet Sun long-period EUV pulsations?

Q3: Are these cycles producing elemental abundances variations?


Duration: Follow-up of a region during one observing window (10 days). If possible, 2 consecutive windows, allowing a follow-up of 20 days.

Pointing requirements: AR, prominence-rain hybrids (limb and on-disk), Tracking mode

Preferred execution time / SolO location: Close to perihelion SolO will be able to have a high-resolution view of the off-limb corona. The aim is to follow an AR during a part of its lifetime, from its appearance off-limb, its passage on-disk and disappearance at the other limb over an extended period of time thanks to SolO’s co-rotation. We aim at characterizing the properties of TNE cycles, in terms of periods, total duration, velocities of the coronal flows and condensations, variation in elemental abundances.  

To follow-up the AR we request tracking mode. Since this mode combines observations off-limb and on-disk it combines different observing programs detailed below.


Observations requirement (baseline)

1. Active region decay:

EUIEUV & LYA Coronal hole modes (C) 600 s cadenceEUV + Lyman alpha, FOV and resolution matching PHI


SPICE Dynamics (bracketed by SPICE Composition Mapping)2" slit, 128 slit positions, scan duration 11 minutes
PHIPHI_magnetograph_FDT/HRT_2 HRTFull FOV, 10 min cadence, 5 quantities, 2x2 binning
MetisMETIS standard modes: MAGTOP or GLOBALMetis can potentially provide context data before and after the 15 day SOOP (offpointing during the 15 days)

2. Non thermal equilibrium







FSI Synoptic mode (S)


EUV & LYA Active Region modes (A)

1-2 observing windows

Cadence (for FSI): 10 min

1h per day for HRI



SPICE Dynamics 

Preferred spectral lines: Mg VIII 772, Ne VIII 770, OVI 1032, CII, C III, OV doublet (760.2 & 760.4)

Raster off-limb can be of reduced X


STIX Normal mode

Triggers Active



FDT Synoptic mode

Covering whole observation, 1hr cadence

Full disk

Science objectives

1. Active region decay

SAP objectiveTargetDurationOpportunity
(e.g., orbital requirements, solar cycle phase, quadrature ...)

Operational constraints 

Additional comments AR , complex AR on E limb15 daysPerihelion: to ensure near-co-rotation,
Stereoscopy, which constrains Earth-Sun-SC angle
Duration 15 daysPotentially coordinated with  ground based DKIST/EST/GREGOR/NST for short-term studies What is the distribution of the open magnetic flux?

coronal holes, QS, AR Contribution of flare-like events on all scales

increase cadence; only partially Detect and characterise waves in closed and open structuresplumes

high latitude pointing Magnetic reconnection in the chromosphere, the transition region and the corona

increase cadence
( CME initiation) probably better FDT Track granules and magnetic features to follow their motion and interactions

increase cadence Follow individual magnetic features flux from lower to high latitudes How supergranular flows facilitate/impede transport of magnetic features? 

increase cadence

2. Non thermal equilibrium

SAP Objective




Operational constraints

Additional comments Understand energy release and particle acceleration process

Active Region


Properties of flare energy release


Acceleration relating to the magnetic reconnection process


2 hours

SolO  close to Perihelion

Target tracking?


3.1 How and where are energetic particles accelerated at the Sun?

Active region

2 hours

SolO close to Perihelion Contribution of flare-like events on all scales

Flaring region in AR

2 hours

SolO close to Perihelion Determine whether coronal heating is spatially localized or uniform, and time steady or transient or impulsive for a wide range of magnetic loops with different spatial scales.

Active region

2 hours

SolO close to Perihelion What are the origins of waves, turbulence and small scale structures?

Active region

2 hours




1.3.1 Solar and local origin of Alfvénic fluctuations

Active region loops, spicules above limb

2 hours
 Detect and characterise waves in closed and open structures

Active region loops, spicules at limb

2 hours
 Resolve the geometry of fine elemental loop strands

Active region loops

2 hours

SolO close to Perihelion Magnetic reconnection in the chromosphere, the transition region and the corona

Active region loops

2 hours

SolO close to Perihelion Intensity variability

Active region loops

 Heating in flaring loops and compare to heating in active regions

Active region loops

2 hours




Instances run / planned


2022-03-31 to 04-04 (SOOP coordinators: L. Bellot ) (science objective: Active region decay)


2022-10-16 to 27, 2022-10-29, 2022-11-01 to 06 (SOOP coordinators: S. Parenti, G. Valori) (science objective: Active region decay)

Science outcomes

Ref of paper using the SOOP data

Original SOOP proposers

Luis Bellot-Rubio, Andrzej Fludra, S. Parenti

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  1. SOOP ID in SOOP Kitchen = RS0