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 3.1.1.2.1). 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 1.2.1.3, 1.2.1.7, 1.2.2.3, 1.2.2.5, 1.3.1, 3.1.2.1). 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:

2. Non thermal equilibrium

Science objectives

1. Active region decay

2. Non thermal equilibrium

Instances run / planned

LTP6:

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

LTP9:

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