HOP 0503

abstract of observational proposal

Main Objective: Determine the appearance/disappearance rate of ephemeral regions in the polar regions and interactions with pre-existing flux

Scientific Justification: Observing magnetic fields in the polar regions is notoriously difficult. Both high-spatial and temporal resolutions are needed to partially overcome the strong projection effects occurring there and to follow the evolution of the flux as it emerges, interacts with pre-existing fields, and finally disappears from the surface.

As a result, our knowledge of magnetic flux emergence and disappearance at high latitudes is very limited. At low latitudes, flux emergence in the quiet Sun occurs on a wide range of scales from isolated bipolar elements, to medium-size magnetic clusters to fully-fledged ephemeral regions, all of which are relatively well observed. We still do not know if these modes of flux emergence also happen in the polar regions. Ephemeral regions are particularly important, as they are believed to be the result of magnetic flux from decayed active regions and thus it is reasonable to expect few -if any- at high latitudes. This needs to be confirmed.

Another important goal is to study the magnetic network and its evolution near the polar regions. Is the network the same as that observed closer to the active region belt? If a regular magnetic network exists at high latitudes but ephemeral regions do not occur or have a lower appearance rate there, how is it formed? Is it a natural consequence of a small-scale dynamo?

Finally, how does magnetic clusters and ephemeral region appearance near the network contribute to the heating of the solar atmosphere near the poles?

We will try to study these aspects using continuous, high-cadence observations of the South polar region with PHI-HRT, EUI-HRIEUV, and SPICE on Solar Orbiter, just when it attains the maximum southern latitude of almost 17 degrees, thus providing a slightly better view of the polar regions with smaller projection effects.

The Solar Orbiter observations will be taken in coordination with Hinode/SP measurements designed to provide similar spatial resolution, allowing calibrations and magnetic/dynamic stereoscopy to be performed, and Hinode/EIS spectroscopic measurements covering a wider range of lines than is possible with Solar Orbiter. IRIS will provide additional high-cadence spectroscopic and imaging observations to monitor heating events in the chromosphere and transition region.

request to SOT

The requested observing program is identical to that of HOP 459, run on 2023-04-10.

For SOT-SP, we request a series of 8 normal maps, 82" x 82", 1-side, starting on 2024-03.21 at 09:30 UT and ending at 15:30 UT (plus light travel difference). We estimate that each map will take about 45 minutes to complete and will generate 0.3Gb of data.

Solar rotation should be tracked. SOT-SP is the primary instrument for this HOP. In case of insufficient telemetry, the SOT-SP observations should be given priority over EIS and XRT.

remarks

Dates: The observations should be performed on March 21, 2025, when the SOOP is scheduled

Time window: Time window is 09:30-15:30 UT (6 hours).
Ideally Hinode/SP and EIS will cover the full duration of the Solar Orbiter obervations, but depending on the available telemetry Hinode can stop earlier. Short interruptions are also acceptable, but would result in a non-regular cadence.

Target(s) of interest: Target is South polar region, with FOV centered on the central meridian. Limb should be visible at the edge of the FOV

Previous HOPs:
The proposer was the PI of HOP 151, which has produced 24 refereed papers and 2 PhD theses until now. The proposer was also de PI of three HOPs for coordinated observations with Solar Orbiter. The last one, HOP 459, was run successfully, but the overlap between the Hinode/SOT and SO/PHI FOVs was small due to a shift of the Solar Orbiter pointing that is now corrected. The SO/PHI observations have recently been released and are publicly available together with the Hinode/SOT, Hinode/EIS and IRIS datasets.