HOP 0098

abstract of observational proposal

To detect the (propagating) fast magnetoacoustic wave and Alfven wave in polar plumes, and to determine the fundamental physical parameters (morphology, density, temperature profile, composition, flows) of these plumes using multi-wavelength observations from several satellites.

Science Case
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This Joint Observing Programme between Hinode, STEREO, TRACE and SoHO aims to investigate the nature of oscillations in solar polar plumes. Polar plumes are denser than the surrounding material and so are natural wave guides for the three MHD modes, namely Alfven, fast and slow magnetoacoustic waves. However, so far only one of the three modes has been detected (the slow mode) (DeForest & Gurman 1998). This HOP/JOP aims to detect these two 'missing' modes using high spatial and temporal resolution imaging and spectroscopy. In addition, we will obtain a significant improvement to our understanding of the morphology, density, temperature profile and composition of polar plumes.

Such an investigation is of high scientific value for three reasons. Firstly, the two missing modes are theoretically predicted and so their detection would be a significant contribution to the study of MHD wave theory, and validation of its application. Secondly, this HOP/JOP will significantly improve current estimates (DeForest et al. 1997) of the properties of polar plumes (such fundamental properties are essential in order to accurately interpret and evaluate the modes). Thirdly, these wave modes feed directly into the fast solar wind. Thus, a detailed understanding of their properties is needed to accurately determine their energy flux contribution and their role in the acceleration of the fast solar wind.

This aims of this HOP/JOP are:
1) To determine the fundamental properties of polar plumes.
2) To detect the fast magnetoacoustic and Alfven waves in polar plumes.
3) To investigate the underlying driving mechanism of these wave motion (are the modes coupled to oscillations in the lower atmosphere, or driven by reconnection events).
4) To uncover what governs the lifecycle of polar plumes (how and where do they form, are they created by jets, what physical processes govern when they disappear).

We propose a two part campaign taking both spectroscopic and imaging data at multiple wavelengths. This will consist of a "lifetime campaign" for 6 hours (lower resolution, mostly synoptic), followed by a "high cadence campaign" for two hours followed by a second "lifetime campaign" for 24 hours. The high resolution part of this JOP gives us the best chance of observing wave motions, and the data on either side will allow us to investigate the entire life cycle (addressing how and where do plumes form, and what physical processes govern when they disappear) and overall evolution.

The 2 hour, high-cadence part of the campaign aims to detect wave motions. To detect the fast waves, we shall use TRACE (30 second cadence and 1'' spatial resolution) and both STEREO/EUVI instruments (30 second cadence, 1.6''). The unique stereoscopic view points of the STEREO satellites will allow us to determine if the fast waves propagate with 3D motion, e.g. helical kink motions. We expect the fast wave to have a period of the order of several minutes, so 30 second cadence should be sufficient for a conclusive detection. To detect the Alfven wave, we will look for evidence of non-thermal line broadening using SoHO/CDS and Hinode/EIS. We shall also observe slow waves (as in DeForest & Gurman 1998) and aim to improve the statistics of their properties in plumes, and to investigate their relation to slow waves in coronal loops.

In addition, data from Hinode/SOT will allow us to glimpse the chromospheric motions within plumes, shedding light on the underlying physical driving mechanism. A photospheric vector magnetogram taken with Hinode/NFI will allow realistic theoretical modelling in order to directly compare with observations. Hinode/XRT will give critical insights into the heating profile and we will look for evidence that reconnection jets are the precursors to plume formation (Raouafi et al. 2008). Finally, we shall use SoHO/EIT to give context to our whole campaign: Plumes are most easily identified using EIT (and thus its involvement is essential) and the original slow wave detection was made using this instrument (repeating and improving the original work on the slow modes will be the first part of our data analysis).

Previous observational results also provide some tantalising suggestions that Alfven and fast modes are supported in polar plumes. The observations of DeForest et al. (1997) hinted of a ripply appearance (sub-resolution behaviour of the propagating fast kink wave) and there is indirect spectral evidence for the (unresolved) presence of Alfven waves (O'Shea et al. 2003).

Finally, we have never before had the overlap of such unique and high-resolution observations and we now have the full suite of instruments necessary to address all of our scientific aims. In addition, plumes are most clearly observed at solar minimum, and right now the Sun is in one of the deepest ever recorded minima, which we believe makes the timing of this HOP/JOP proposal ideal.

request to SOT

Lifetime Campaign:
NFI: Na I D IVDG mode (Stokes I, Stokes V, and dopplergrams), line-center tuning, 2k x 2k (110" x 110") 2x2 summed, cadence 5 minutes.

SP: three Fast map 120" x 164", one taken every two hours (assuming lifetime campaign starts at 00:00UT, then the three fast maps should be taken at 00:00 UT, then 02:00 UT, then 04:00 UT.
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NOTE 1: If additional memory is needed to fit in the SP Fast map at 06:00 UT (see high cadence campaign below), then drop the earlier SP map at 00:00 UT.

NOTE 2: After 08:00 UT, the lifetime campaign resumes. If data allocation allows, then:
NFI: Na I D IVDG mode (Stokes I, Stokes V, and dopplergrams), line-center tuning, 4k x 2k (220" x 110") 2x2 summed, cadence 5 minutes.
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High Cadence Campaign:
BFI: Ca II H-line 2k x 2k (110" x 110") 2x2 summed, spatial resolution 0.22", exposure time 500 milliseconds , cadence 10 seconds.

SP: one Fast map 120" x 164" at 06:00 UT (i.e. Make one vector magnetogram raster with spectro-polarimeter at beginning of high cadence observations).
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NOTE 3: If additional memory is needed to fit in the SP Fast map at 06:00 UT, then drop the earlier SP map at 00:00 UT.
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request to EIS

High Cadence Campaign:
Context raster should point at coronal polar hole with target plume central in fov. Target plume will be chosen by James McLaughlin (i.e. he will choose a “nice” target plume. If not possible, then please choose a "nice" target plume yourselves. Same one as CDS please!). Plume footpoints must be in fov - and as much of the plume length as possible should be observed.

Run sta_plume_context, once at start of observation before 2 hour high cadence observations
4/5 repeats of sta_plume_slot, to fill 2 hour high cadence period
Run sta_plume_context, at end of observation after 2 hour high cadence period

sta_plume_slot. Area 40x512", 4" slot, exposure time 30 seconds, number of repeats 50, cadence 28 minutes, 16 seconds, compression jpeg 75, data rate 17.2982 kbits/s, data volume 29333.33 kbits, emission lines Fe XI (188.23), Ca XVII (192.82), Fe XII (195.12), Fe XIII (202.04), Fe XIII (203.83), He II (256.32), Fe XVI (262.98), Mg VI (269.00), Fe XIV (274.20), Si VII (275.35), Fe XV (284.16)

sta_plume_context. Area of raster 120x512", 2" slit, locations per raster 60, step size 2", exposure time per step 60 seconds, cadence 1 hour 5 minutes 20 seconds, compression DPCM, data rate 12.2949 kbits/s, data volume 48200.84 kbits, emission lines Fe XII (186.75), Fe XI (188.23), O V (192.90), Fe XII (195.12), Fe XIII (202.04), Fe XIII (203.83), He II (256.32), Fe XIV (274.20), Fe XV (284.16)

remarks

Pointing & Target Selection
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The south or north coronal hole, with preference given to the coronal hole that has the larger spatial extent. However, the primary aim of this HOP/JOP is to observe polar plumes and so, above all else, the target coronal hole must contain a target polar plume.

Proposed Observation Dates
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The south coronal hole will be slightly more tilted towards Earth in February and March. Thus, if there exists a south coronal hole that also contains plumes in February or March, then this would be an ideal observing time. Apart from this, then anytime would be acceptable, only noting that it is only during solar minimum that we can clearly observe plumes in fully developed coronal holes and, since the Sun is currently in one of the deepest recorded minima, that the timing right now is ideal.

Specific Instrument Requirements
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Assuming campaign starts at 00:00 UT, then campaign consists of “lifetime campaign” from 00:00 UT - 06:00 UT, then “high cadence campaign” from 06:00 UT - 08:00 UT, then resumes “lifetime campaign” from 08:00 UT - 08:00 UT following day. At 08:00 UT following day, the JOP/HOP ends. Total observing time = 32 hours.

Lifetime Campaign (6 hours before and 24 hours after high cadence campaign, e.g. Assuming campaign starts at 00:00 UT, then lifetime campaign is 00:00 UT - 06:00 UT, then resumes 08:00 UT - 08:00 UT following day)

High Cadence Campaign (2 hours, i.e. assuming lifetime campaign starts at 00:00 UT, then high cadence campaign is 06:00 UT – 08:00 UT)