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HINODE Operation Plan (HOP)

accepted on


 HOP No.

 HOP title

HOP 0262

Kelvin-Helmholtz instability in coronal loops

plan term


@ @


 name : Antolin, Vissers, van der Voort, Katsukawa, Van Doorsselaere, Verwichte @  e-mail : patrick.antolin[at]nao.ac.jp

contact person in HINODE team

 name : Katsukawa @  e-mail : yukio.katsukawa[at]nao.ac.jp

 abstract of observational proposal
Objective:  To determine the possibility of the Kelvin-Helmholtz instability in coronal loops.

Scientific Background:
High resolution observations of the solar corona in coronal or chromospheric lines (through coronal rain or prominence observations) indicate a tendency of the field to organise itself in fine strand-like structure of a few hundred km widths (Lin et al. 2005, Reale, 2010; Antolin & Roupe van der Voort 2012; Brooks et al., 2013; Peter et al., 2013). Furthermore, small amplitude transverse MHD waves have been shown to permeate the solar corona. These are waves with a few km/s amplitude and periods of a few minutes, propagating or standing in magnetic field structures in the corona, observed in a wide range of wavelengths (De Moortel & Nakariakov, 2012; Lin, 2011; McIntosh et al., 2011; Antolin & Verwichte, 2011; Hillier et al., 2013).

A very recent numerical study suggests a link between the ubiquitous small amplitude transverse MHD oscillations and the small-scale strand-like structure in the corona (Antolin et al., 2014a). This link is based on the fact that a loop subject to transverse oscillations suffers from resonant absorption and  from relatively strong shear motions toward the edges, which can lead to Kelvin-Helmholtz instabilities (Heyvaerts & Priest, 1983; Ofman et al., 1994; Ziegler & Ulmschneider, 1997; Terradas et al., 2008). In the case of the corona, this instability has so far been directly observed on large scales in CMEs (Foullon et al., 2011; Ofman & Thompson, 2011) and on much smaller scales in quiescent prominences (Berger et al., 2010). The KHI generates small scale vortices and current sheets, which, due to line-of-sight effects, appear as strand-like structure in intensity images. The spectral signatures of this model include specific Doppler shifts and line broadening across the loops, with characteristic phase relations with the transverse motion in the plane of the sky (Okamoto et al. 2014, in preparation).

The imaging and spectral signatures predicted by this model can be tested in the context of coronal loops with coronal rain. The high spatial resolution windows offered by the rain allows to detect both strand-like structure and small amplitude transverse MHD waves in the corona (Antolin & Verwichte, 2011). Coordinated observations between IRIS and Hinode allows an excellent temperature coverage of the chromosphere and transition region at high spatial, temporal and spectral resolutions (Antolin et al. 2014b, in preparation). Such combination represents a unique opportunity to determine the possibility of the Kelvin-Helmholtz instability in coronal loops.

 request to SOT
Program number 04cd
- Ca II H at a cadence around 10 sec with exposure times long (1.8s)
- Half CCD for higher cadence
- No 2x2 summing for higher spatial resolution
- ROI 3, include both disk and the off-limb regions. At least 80 arcsec off the limb should be visible at all times.
- E or W pointing (Active region)

Estimated data rate is roughy 2 Gbit / hour

Note: if 1 hour results too heavy for telemetry then please perform 2x2 summing.

 request to XRT
Be_thin, 384x384 high cadence program

 request to EIS
EIS study 434 (VHH_SlowAR_SaS_1h6m), which does a sit and stare, 30 s  exposure time, with the 2h arcsec slit with a slit length of 296 arcsec. Slit should be perpendicular to limb. If possible, make the slit cross at centre of coronal loops (thus aiming for the apexes). Context 40 arcsec slot before / after the sit-and-stare.

 other participating instruments

Request to IRIS:

Target: Off-limb above active region (while keeping always an on-disc portion on the SJI for co-alignment purposes)

1. Observation modes: Sit-and-stare & 2-step raster

2. Slit perpendicular to the limb. Try crossing at the apex of raining loops. The slit should always cross the rain loops above spicular heights: above 20" or so.

3. For the slit do the small line list. For the SJI, do 2796 & 1400 and 2796 & 1330. One hour each per day if possible.

4. Exposure times for the slit should be 8s. For SJI: 18 s. Cadence for 2-step raster should be aimed at being below 30 sec.

6. The sets should be at least 1 hour long.

7. If problems of telemetry are encountered then set the slit to 120" instead of 175".

Tentative OBSIDs: 3820009354 and 3820009454 or 3820009353 and 3820009453

Common request to all instruments:
- Target: Off-limb above active region
- The best observing time at SST is in the morning from UT 07:30 - 12. Please aim at co-observing at that time for at least one uninterrupted hour.

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