HOP 0151

abstract of observational proposal

Goal
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Follow the evolution of magnetic flux in the quiet Sun, to determine the time scales for network and internetwork flux replacement by ephemeral regions and small-scale emerging fields, respectively. This study requires continuous, uninterrupted observations for about 2 days, to track the evolution of the same supergranular cells from birth to death. The study also requires very high signal-to-noise ratios, to detect the weakest signals of the internetwork.

Motivation
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Using MDI measurements, the time needed by ephemeral regions to replace the total flux of the network has been estimated to be 40-70 h (Schrijver et al. 1997), 8-19 h (Hagenaar et al. 2003), or even 1-2 h according to the most recent studies (Hagenaar et al. 2008). A time scale of only 1-2 h implies an enormous amount of magnetic flux being brought to the solar surface by ephemeral regions, and a very
effective way of flux removal, presumably through flux cancellations. However, little is known about these important processes because (a) all the studies are based on MDI data, with moderate angular resolution and cadences on the order of hours, and (b) there exist very few continuous time sequences of the quiet Sun
lasting for 2-3 days, which is the minimum duration needed to observe at least one full lifetime of network cells. The situation is even worse for the internetwork. Indeed, the long-term evolution of internetwork fields is essentially unkwown, as no observations have ever been carried out to address this issue, neither with Hinode nor with other facilities.

We propose to determine the flux emergence and cancellation rates in the network and internetwork with unprecedented accuracy, to study how these processes contribute to the total flux budget of the quiet Sun. The required measurements will push Hinode's capabilities to a limit in terms of sensitivity, cadence, and time coverage. This program demands a significant amount of telemetry and ideally no interruptions, but because of their unique character we anticipate that the measurements will be of interest to many researchers in the field. Also, the questions they address are so fundamental that it seems reasonable to devote all the resources of Hinode for about two days to acquire a unique data set.

request to SOT

Data: Because of telemetry limitations, we will only use FG shutterless IV observations with Ca II.

Parameters:

* NFI Na D1 5896A
* Shutterless Stokes I and V 0.2 sec (Obs ID: 55)
* 8 cycles integration (6.4sec)
* 2 wavelengths: +/- 160 mA from line center
* FrmID 52 (192x512 pixels, 2x2sum, 31"x82")
* 3 ROI loops for FOV of 93"x82"
* JPEG Q65 for I, Q85 for V (to preserve very weak V signals).
(2.3bits/pix for I, 5.1bits/pix for V)
* Repetitions: 2 (to increase SNR)
* Cadence: 2 minutes (for feature tracking)
* Telemetry rate: 24 images every 2 minutes
(2 Stokes x 2 lambdas x 3 ROIs x 2 repetitions)
~250 Mbits/hour
* Best focus for Na D at disk center should be set at the start of the observations
* Use margin factor of 1.30

* Ca II H filtergram every 3 hours for co-alignment

request to EIS

Run the study cor_hole_jet_v1 (#487), which has a 40"x168" FOV and a 6min cadence. Since the FOV is not as wide as that for SOT, center on a strong magnetic element instead of the cell center. This study uses 6.5 kBits/s with DPCM and 4.1 kBits/s with Q85 compression. To run continuously it is likely that the higher compression will be needed.

[Long exposure slot observations in the coolest lines. Raster with 40 arc sec slot to cover SOT FoV of 80"x 90".]

remarks

Aim: Tracking of the same supergranular cell with SOT/NFI. No EIS or XRT observations are required (part of their telemetry could be re-allocated to this program as deemed necessary).

Target: quiet Sun region near disk center with y=0". The initial pointing will be chosen such that the FOV covers the disk center in the middle of the observing period. Tracking solar rotation. Ideally, no re-pointings should be performed during the whole observing period. Interruption must be kept to an absolute minimum and as short as possible. After an interruption, the observations should
be resumed at exactly the same position, to continue the tracking of the same structures.

Duration: at least 40 hours (goal 50 hours), to cover a full flux replacement cycle.

Remarks:
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- To minimize interruptions by OP or table uploads, the observations could be performed over the weekend.

- Synoptic observations could be shifted to accommodate the observations or run when HOP pointing is close to disk center.

- To extend the time sequence as much as possible, it would be advantageous to perform the observations during a period with very good ground-station coverage.

- The goals of this program cannot be achieved with two sequences of about 20 hours separated by 4 hours. The observations must be continuous to follow the evolution of the same supergranular cell.

- It is important to calibrate the line core position as accurately as possible.

- In case of telemetry problems, please contact the proposers to set priorities (FOV, SNR, cadence).