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HINODE Operation Plan (HOP)

accepted on

30-nov-2017


 HOP No.

 HOP title

HOP 0347

Long period pulsations of plasma velocity and density in loops

plan term

ToO

@ @

proposer

 name : Pelouze, Auchere, Bocchialini, Parenti @  e-mail : gabriel.pelouze[at]ias.u-psud.fr, frederic.auchere[at]ias.u-psud.fr, karine.bocchialini[at]ias.u-psud.fr, susanna.parenti[at]ias.u-psud.fr

contact person in HINODE team

 name : Culhane @  e-mail : j.culhane[at]ucl.ac.uk

 abstract of observational proposal
Main Objective: To detect and characterise plasma downflows in loop footpoints that are associated with long-period intensity pulsations.

Scientific Justification: Long-period intensity pulsations have been recently detected in coronal loops with EUV images of both SoHO/EIT (Auchere et al., 2014) and SDO/AIA (Froment et al., 2015). They are observed with periods ranging from 3 to 16 h, and in loops at coronal temperatures, thus visible at EUV wavelengths. These pulsations have been interpreted as resulting from thermal non-equilibrium (TNE), thus providing a signature of a highly-stratified and quasi-constant heating at the loops footpoints (Froment et al., 2017; Auchere et al., 2016). Recent observations have permitted the unification of this phenomenon with coronal rain (Auchere et al., 2018, in prep.). Depending on the adequacy between the geometry of the loop and the characteristics of the heating, this can result in either complete (at chromospheric temperatures, i.e. those of coronal rain) or incomplete (> 1 MK) condensation and evaporation cycles, that are responsible for the observed intensity pulsations.

Various simulation studies indicate that TNE may occur in coronal loops where the heating is highly-stratified and quasi-constant. Using 1D hydrodynamic simulations, Froment et al. (2017) were able to reproduce the observed intensity, temperature, and density pulsations, with incomplete condensation for the active region studied in their previous paper. However, the simulations also predict periodic plasma upflows and downflows along the loops, with velocities up to 40 km/s. Detecting these velocities is thus necessary in order to confirm that the observed intensity pulsations are indeed due to TNE. In addition, spectral measurements would help refine the temperature and density diagnostics for such events.

In order to detect these pulsations, continuous observations of the same region during several periods are required. This translates to several days for periods around 10 h. First, we tried to find such datasets in the EIS archive.  For 3181 pulsation events detected with SDO/AIA between 2010 and 2016 (see Auchere et al., 2014, for the detection method and Froment, 2016, for the events), we systematically searched for sets of EIS rasters such that:

- the FOV of all rasters intersected with the AIA event;
- the set covered more than 3 pulsation periods;
- the gaps between the rasters werenft too long nor too frequent;
- the FOV of the rasters was greater than 55 arcsec;
- all rasters had the same study numbers.

After filtering out events with too faint pulsations, we obtained 8 datasets.  However, none was perfect, because they still contained lots of gaps, had short exposure times, or lacked lines essential for density diagnostics. From these datasets, we could identify variations in density, but the expected pulsations in velocity could not be detected.  We thus need better datasets, mainly with less data gaps and better signal to noise ratio.
Hence the present HOP proposal. This study aims at tracking an active region during most of its lifetime, from the east limb to the west limb. Such observations will allow us to characterise the long term variations of the plasma velocity, temperature and density in the loops. Given that these events appear to be common in active regions (Auchere et al., 2014), it is highly probable to observe pulsations in any active region.

 request to SOT
None

 request to XRT
None

 request to EIS
In order to study these long term variations, we request observations of the same AR spanning over at least 2 days just before, or centered on the passage of the AR at the central meridian. Study 571 (ar_vel_fast_scan) should be repeated during that time period, thus resulting in a raster being captured every 40 min.

These first 2 days of observation should allow us to assess wheter pulsations are visible in the observed loops. Depending on this and on the EIS schedule, we might request longer observations.

 other participating instruments
IRIS Request: The FOV should be centered in one of the loops footpoints. The observations would allow to capture coronal rain associated with the plasma flows, and to measure velocities with the Fe XII 1349.4 A line.

Program 1:
3630173662  |  Very large coarse 64-step raster 126x175 64s  Si IV Deep x 30 Spatial   |    2022.14    |     410.37    |       0.3     | 31.6+/-0.0 | 2022+/-0   |  0.0+/-0.0 | 31.6+/-0.0 |  0.0+/-0.0 |  0.0+/-0.0

Repeat during the entire EIS observation time.

 remarks
Dates:  2 consecutive days are required. The observations should happen outside of the eclipse seasons of Hinode and IRIS.

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