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HINODE Operation Plan (HOP)

accepted on

22-mar-2018


 HOP No.

 HOP title

HOP 0355

ALMA+IRIS+Hinode observations of thermal non-equilibrium and coronal rain

plan term

2018/04/26-2018/04/26
2018/04/29-2018/04/29
2018/08/30-2018/08/30

@ @

proposer

 name : Antolin @  e-mail : patrick.antolin[at]st-andrews.ac.uk

contact person in HINODE team

 name : Savage, Watanabe, De Pontieu
@  e-mail : sabrina.savage[at]nasa.gov, watanabe[at]uvlab.mtk.nao.ac.jp, bdp[at]lmsal.com

 abstract of observational proposal
Main Objective:
Constraining the properties of coronal heating mechanisms based on the observed plasma cooling characteristics

Scientific Justification:
Numerical simulations and observations have shown that coronal loops, the building blocks of coronae, undergo heating and cooling cycles (Goldsmith 1971, Antiochos 1999) over large portions of the active corona (Froment et al. 2015). Footpoint heating produces chromospheric evaporation leading to dense, strongly radiating loops, which end up cooling catastrophically, a thermal non-equilibrium process that sets the corona in a dynamic and strong thermally inhomogeneous state. The cooling phase is driven by thermal instability, and produces a partially ionised, dense, multi-thermal (ranging 2,000 K to 150,000 K) and clumpy plasma that accretes towards the solar surface (Antolin & Rouppe van der Voort 2012). This phenomenon is known as coronal rain and is deeply linked to coronal heating and thermal instability (Leroy 1972, Antolin et al. 2012). In this project we aim at investigating the cool side of the corona, the degree of spatial and thermal inhomogeneity, and use the advantages of studying cold material to gain insight into the nature of coronal heating.

Through the thermometer and high resolution capability of ALMA in Cycle 5, the atmosphere above an active region can be probed for thermal bremsstrahlung from the rain (Wedemeyer et al. 2016). Through coordination with the instruments from the SDO and IRIS missions, and other observatories from the ground (SST, BBSO), the full temperature range of the rain, from 2000 K to 200,000 K, can be covered, which allows to follow and characterise the evolution of thermal instability in active region loops. In turn this allows to firmly assess the rainfs role in the chromosphere-corona mass and energy cycle of the solar atmosphere.

Furthermore, at the very high cadence offered by ALMA, we can observe and directly measure the triggering of thermal instability, the formation process of coronal rain, and follow its impact into the lower solar atmosphere. Following catastrophic cooling, as the plasma recombines from coronal down to chromospheric temperatures (in a timescale of minutes), the MHD thermal mode (also known as the entropy mode, a solution to the MHD equations) is expected to be triggered and act as seed for neighbouring rain clumps. The progressive cooling in time (as the clumps fall) and further (cascade-like) triggering of catastrophic cooling along neighbouring field lines can be captured at the very high cadence of ALMA. The formation process and tracing of the rain is therefore a perfect test ground into the limits of MHD validity in the solar corona.

For ALMA:
4 scheduling blocks, 2 hour each, 2 bands (band 3 & 6): 2 modes:
-LF mode: Large FOV: 60 x 120 arcsec^2 (bands 3 & 6)

duration: 2 hours x 2, cadence: <15 min
-HC mode: High cadence mode: 60x60 (band 3), 25x25 (band 6)

duration: 2 hours x 2, cadence: 2 s
1 mode / day preferable (bands 3 & 6 for same target).

For all instruments: Pointing is based on ALMA target.  Please point Hinode so SOT (after correcting for the SOT offset) is at the limb adjacent to the ALMA target; this is an exception to the usual 15 arcsec inside the limb rule.  XRT and EIS may use internal offsets to match the center of the ALMA FOV.

 request to SOT
Point Hinode so that SOT (after correcting for the SOT offset) is at the limb, at R_sun, adjacent to the ALMA pointing; this is an exception to the usual 15 arcsec rule.

Set SP ROI 2 to be centered 20 arcsec above the limb.  

Run the following program during both HC and LF modes, continuing 2 hours after the ALMA observing period, if telemetry permits.

*0x01f3  HOP 355, set ROI 2 to 20arcsec for off-limb, repeats

Use a low margin factor, perhaps 0.5 (exact value to be determined from program tests).

 request to XRT
NOTE: LF & HC modes are listed in the ALMA coordination calendar.

Both LF & HC:
Continuous high-cadence time series of X-ray images
Al-poly+Open or similar filter
1x1 pixel, FOV 128"x128" (384"x384", if telemetry available with high cadence)
Fixed exposure appropriate to solar conditions
highest possible time cadence (shorter than 8 sec)

 request to EIS
Not available at present. If it is operational at the time of observation please perform the following:

NOTE: LF & HC modes are listed in the ALMA coordination calendar.

LF mode:
High cadence repeated scans during the time window.
One possible study is ID: 360 cam_artb_lite_v2
40h (slit 2h x 20 positions) scan x 120 pixels width (slit parallel to limb)
Exposure 10 sec. Context 40 arcsec slot before / after the sit-and-stare.

HC mode:
Modified EIS study 434 (VHH_SlowAR_SaS_1h6m), which does a sit and stare, 10 s exposure time, with the 2h arcsec slit. Modified slit length of 175 arcsec. Slit parallel to limb. Context 40
arcsec slot before / after the sit-and-stare.

 other participating instruments
ALMA: #870
(SST & BBSO to be coordination)
IRIS:
Slit parallel to surface
LF: Raster (OBS ID 3620110460)
HC: Sit-and-stare (OBS ID 3620110404)
These programs have been previously performed in IRIS+SST coordination (June 2017)

 remarks
Dates: April 2018, subject to ALMA cycle 5 C43-3 observing dates

Time window: 4 ALMA scheduling blocks have been requested, which amounts to 8 hours. We request continuous coverage within this time frame. Please refrain from stopping at SAAs.

Target(s) of interest: Active region off-limb. The specific target will be provided roughly 3 days before the observing date (unknown at present).
For all instruments: Pointing is based on ALMA target.  Please point Hinode so SOT (after correcting for the SOT offset) is at the limb adjacent to the ALMA target; this is an exception to the usual 15 arcsec inside the limb rule.  XRT and EIS may use internal offsets to match the center of the ALMA FOV.

Previous HOP information: HOPs 234, 248, 262

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