HOP 0181

abstract of observational proposal

While the most popular, traditional views attribute the process of active-region development to the emergence of a well-developed, Omega-shaped flux tube, numerical simulations show that an important role can be played by an alternative mechanism related to the MHD action of cellular convection. The very flow topology in a convection cell can ensure the development of a strong bipolar component in the magnetic configuration produced by this cell (see, e.g., A.V. Getling and I.L. Ovchinnikov, 2003 ASP Conf Ser., 286, p. 139; Dobler W., Getling A.V., In: Multi-Wavelength Investigations of Solar Activity, Proc. IAU Symp. 223, 2004, p. 239; and references therein). Presumably, the producers of such magnetic fields could be especially large and energetic cells of a supergranular type.

In broad terms, the aim of the conceived project is to investigate the dynamical coupling between the plasma motion and magnetic field in dense (subphotospheric and photospheric) layers. More specifically, it would be important to elaborate observational criteria to distinguish between the two alternatives and evaluate the actual role of the convective mechanism.

The observations should be aimed at simultaneously obtaining, with a high resolution, full-vector magnetograms and full-vector velocity maps over the area in which an active region develops --- preferably, at early stages of its development. Subsequent analyses of certain correlations between the magnetic field and velocity could give indications for the type of MHD mechanism involved.

request to SOT

*request to SOT*

The SOT is needed to implement the project. It would be important to obtain full-vector magnetograms, Dopplegrams, and LCT maps of the horizontal photospheric velocities simultaneously (during the given observational session).

Specifically, obtaining FGs should be combined with Fast-map SP scans. The same FOV (164" x 164") is needed for both FG and SP observations. The following should be done in the time interval of the session (120 min):

* SP fast scan aimed at obtaining a full-vector magnetogram;
* Dopplergraphy at Fe 5576 A;
* Imaging at 5576 A needed to carry out the LCT procedure and mapping the horizontal velocities.

During a session, 5576-A images and Dopplergrams should follow at a time cadence of 2 min. One SP fast-mode scan with a FOV of 164"x164 takes 31 min, and we would like to start running such SP scans every 40 min (in total, three SP fast maps for one session). If telemetry does not permit doing so, two SP maps for one session would be acceptable.

It would be desirable to repeat such a session every 6 hours (2-h session + 4-h interval) if telemetry permits. If sessions can hardly be repeated during a one-day interval, carrying out new seesion(s) on the next day and on some of subsequent days would be highly desirable.

A very crude estimate of the data volume is as follows:

* for the SP fast scan (3 maps (164" x 164") in one session), 930 Mbits/2h
* for intensity mapping and Dopplergraphy at Fe 5576 A, 225 Mbits/2h (2min cadence, 2 wavelength positions, 164" x 164", 2 x 2 summing)

Total: 1155 Mbits/2h

If two SP fast scans with the FOV of 164"x164" are obtained for 1 session, the data volume will be 845 Mbits/2h in total (=620Mbits/2h for SP fast map and 225Mbits/2h for Dopplergram).

remarks

TIME PERIOD OF PROPOSED OBSERVATIONS:

Ideally, the start and end dates should be determined by the process of development of particular active regions and sunspot groups. If an active region originates in the central part of the disk, observations should be started as early as possible.

Carrying out a few observational sessions of duration about 2 h each in a day appears a desirable minimum. However, obtaining longer data series would be extremely useful in view of studying the evolution of the velocity and magnetic fields in the active region. Since fast oscillations must be eliminated, the data should be subject to either subsonic filtering or averaging over a period several times exceeding 5 min (the averaging procedure could be implemented over a time interval covered by a session).

Preferably, the observational sessions should cover the early evolutionary stage of the active region, but they must not necessarily be on consecutive days.

TIME WINDOW IN DAY:

No coordination with ground-based observations are planned. Short interruptions over the observing periods are admissible.

TARGET OF INTEREST:

Active regions and sunspot groups at early stages of their development near the centre of the disc.