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HINODE Operation Plan (HOP)

accepted on


 HOP No.

 HOP title

HOP 0252

Transition Region Explosive Events

plan term




 name : Kankelborg, Jaeggli, McKenzie, Tarbell    e-mail :

contact person in HINODE team

 name : McKenzie    e-mail : mckenzie[at]solar.physics.montana.edu

 abstract of observational proposal
OBJECTIVE: To determine the causes and energetics of explosive events in the solar transition region, and to look for coupling of these events to the chromosphere and corona.

SCIENTIFIC BACKGROUND: Explosive events are ubiquitous, reconnection-driven line broadenings in the transition region, 1.5-5 Mm in size, lasting from a few seconds to a few minutes (Dere et al. 1991; Innes et al. 1997; and references therein). Few have been imaged, but there is evidence that EEs are much more complex than the bipolar jet model (Fox, Kankelborg & Thomas 2010; Innes & Teriaca 2013).  Some preliminary IRIS observations are shown in figure 1. This IRIS campaign would spatially and temporally resolve many events, observe events down to $sim 300$,km scales, and look for chromospheric and coronal coupling. Explosive events are observed in a variety of different solar conditions, but they often involve small bipoles and/or occur near neutral lines. We hope to determine what magnetic situations give rise to reconnection, the rates and timescales of reconnection, how much energy is released, and the degree to which the events couple to the corona and the chromosphere.
Explosive events are a laboratory to probe reconnection physics. Since the reconnection occurs in transition region plasma, the emission measure is high, the event is localized along the line of sight, and it should be possible to observe the reconnection region itself, as well as inflows and outflows, routinely. We anticipate a very high event rate for this study. Figure 2 compares a cartoon of tearing mode reconnection to observations obtained with the MOSES rocket payload in February 2006 (Fox et al. 2010).
The magnetic context is essential to understanding the nature of these events. Ideally, the magnetic field would be measured in the chromosphere, where it is presumed to be nearly force free, so that extrapolation to the transition region and corona will be more accurate.
Observations are desired with approximately 1-hr duration in a variety of solar conditions, particularly near neutral lines in both quiet sun and quiescent active regions. We particularly desire observations in May (to collect data that will be used by REU students at MSU beginning June 9) and August (coordinated with the MOSES-II rocket flight, launch date TBD, near noon MDT).

Dere, K. P., Bartoe, J., Brueckner, G. E., Ewing, J., & Lund, P. 1991, J. Geophys. Res., 96, 9399

Fox, J. L., Kankelborg, C. C., & Thomas, R. J. 2010, ApJ, 719, 1132

Innes, D. E. & Teriaca, L. 2013, Sol. Phys., 282, 453

Innes, D. E., Inhester, B., Axford, W. I., & Wilhelm, K. 1997a, Nature, 386, 811

 request to SOT
We will use HINODE-SOT data to get information about the magnetic field and the dynamics of the chromosphere during the explosive events. If the telemetry allows, we request a combination of FG and SP observation.  

NFI: Chromospheric magnetograms and Dopplergrams at Mg Ib 5172.7 Å, or
       Chromospheric fields at Na I D 5896.0 Å. 31''x80'', Sh-less IV (FG 0x4c9).
These should use ROI # 2 shifted down on the CCD by 25 arcseconds to get better image quality.

BFI: Chromospheric intensity filtergram at Ca II H 3968.5 Å.

SP: Fast map mode. FOV large enough to cover the target region with margin, at least one map for context before and after IRIS observations. If telemetry permits, run repeated fast maps of the IRIS target region during IRIS observing time; these may be much smaller in FOV than the large context maps, but with minimum height of 82”.

 request to XRT
XRT, in combination with AIA, will allow us to learn whether and to what extent the explosive events are coupled to the corona. We request fastest possible cadence with a single filter, full resolution, small FOV. Disable flare patrol (FLD) and Flare mode (FL-CTRL) during the 1-hr duration of this HOP, if and only if there are no actively flaring regions within the XRT full FOV.

・FOV: 384"x384"
・Filter: Al-Poly
・Cadence: 15-20s desired, 30s acceptable.
・Compression: Q98
・Full resolution; no binning.

 request to EIS
EIS should run the following sequence:  PRY_slot_context_v3 (ID: 353, 3m 29s) Cor_Hole_Jet_v1 (ID: 512; 6m 31s, 40"x168")

PRY_slot_context_v3  Cor_Hole_Jet_v1 should be repeated continuously to fill the available time-slot. The sequence should run continuously through SAA periods. The pointing for Cor_Hole_Jet_v1 should be centered on the IRIS field-of-view.

 other participating instruments
IRIS will allow us to identify the explosive events by line broadening in C II and Si IV, and to observe the dynamics in the transition region and chromosphere. SJI images in FUV (1400) will provide morphological information, including the extent of each event and its relationship to nearby structures, as well as skyplane motions correlated with the line shifts observed by the spectrograph. Observing parameters:
・Sit & stare
・Large or Very Large FOV is best, but could trim it down based on available memory.
・Solar rotation tracking off (let it drift to slowly sample a region).
・Exposures deep x2
・SJI: SiIV only
・Standard compression
・SJI cadence 10x faster
・FUV spectrally rebinned x2 (save memory, lines of interest are broad)
・Flare line list (Includes CII, SiIV, OIV, and enough wings to capture large doppler shifts).
E.g., OBSID 3864255603.

We request a special run of the explosive event IHOP in coordination with the anticipated launch of the Multi-Order Solar EUV Spectrograph (MOSES) sounding rocket in August, 2014. MOSES will obtain snapshot maps of intensity, doppler shift, and line width in Ne VII 46.5 nm, with arc second spatial resolution, over a FOV of 20' x 10', at a cadence of around 10-30 s. The launch window will be one hour in duration near noon MDT, and the actual obseving time will be approximately 5 minutes.

Our targets will be a variety of mixed-polarity regions likely to host transition region magnetic reconnection events, including active regions and quiet sun near neutral lines. Coordinates will typically be at the discretion of the SOT planners, as their planning cycle is longer than that of IRIS. For the August sounding rocket coordination, the MOSES team will announce target coordinates in advance to facilitate coordination.

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