HOP 0140

abstract of observational proposal

The purpose of this project is to study 3D structures of magnetic field and velocity field at magnetic flux cancellation sites from multi-line observations. The magnetic flux cancellation is a descriptive term to indicate a mutual flux loss due to the apparent collision of the oppositepolarity magnetic elements. The flux cancellation has the key to understanding the dissipation of the magnetic flux from the photosphere. We plan joint observations with the IBIS (Cavallini 2006) and Hinode, and our proposal to the IBIS has been already accepted.

Two major possible processes have been proposed to explain the observed flux cancellation (Zwaan 1987): submergence (retract) of Ω-shaped loops or emergence of U-shaped loops across the photosphere. The approaches to understanding the physical process of magnetic flux cancellation could be categorized into two types. One is to examine the motion of the photospheric horizontal magnetic field between the canceling magnetic elements from the vector field measurements. The horizontal field with the downward motion should be observed in the submerging Ω-loop model, and the observation of the emerging horizontal field is expected in the emerging U-loop model. Another approach is to investigate the relative timing of disappearance of the photospheric and chromospheric magnetic flux from a time series of line-of-sight magnetograms like Harvey et al. (1999). When the chromospheric magnetic flux disappears before the photospheric magnetic flux, some submerging activities are suggested at the cancellation site, and vice versa.

We expect two new results from our proposed joint observations. (1) We will improve the Harvey et al. (1999) study. The cadence of their study was about 14 minutes, which was insufficient to detect the dynamic motion of magnetic field lines at the cancellation sites. The IBIS can provide us the photospheric and chromospheric magnetic flux (Fe I 630.2 nm, Na I D 589.6 nm, and Ca II 854.2 nm) with about a 90 second cadence. We request the Hinode/NFI to observe Mg I b 517.2 nm with the similar cadence in order to complement our IBIS observations. If the evolution of photospheric/chromospheric transverse fields would be detected at the cancellation site, it is much helpful to understand the physical process of the flux cancellation. However, we can examine the relative timing of the magnetic flux disappearance from only the longitudinal fields. (2) We will also investigate the consistency between the timing of the photospheric/chromospheric (line-ofsight) magnetic flux disappearances and the motion of the photospheric horizontal fields. For this purpose, we propose the repeat scans by the Hinode/SP. The SP is necessary for the accurate measurements of the photospheric horizontal fields between the canceling magnetic elements, and is helpful for the calibration of Stokes IQUV images of Fe I 630.2 nm with the IBIS.

request to SOT

Before 14:00UT
SP – Fast map, FOV=50”x110”, Q75, 1-side
→ 64 Mbits

14:00UT – 17:00UT
(1) Active region case: Mg I b shutterless IQUV at 3 wavelength positions (line cetnter & line center +-11.4 nm) – FOV = 38”x80”, sum=2x2, cadence=fastest (~2 minutes), integration=4.8sec, Q75
→ 90 Mbits/hour
SP – Fast map, FOV=20”x82”, Q75, 2-side, repeat (4 min/map)
→ 570 Mbits/hour
Total = 2000 Mbits /day

(2) Quiet region case
Mg I b shutterless IQUV at 3 wavelength positions (line cetnter & line center +-114 nm) – FOV= 38”x80”, sum=2x2, cadence=fastest (~2 minutes), integration=4.8sec, Q75
→ 90 Mbits/hour
SP – Normal map, FOV=10”x82”, Q75, 2-side, repeat (5.5min/map),
→ 840 Mbits/hour
Total = 2900 Mbits/day

remarks

Magnetic flux cancellations are observed everywhere on the Sun, and their size has a wide range from a flux tube scale to a sunspot scale. We can carry out our observations independently of solar activities. However the magnetic flux cancellations at scales of several arcseconds (pores, larger magnetic elements in the network…) are better target. The excellent seeing is needed for the IBIS
observations to resolve granular-scale cancellations, and the horizontal fields really produced by the cancellation process are hardly distinguished from penumbral horizontal fields in the cancellation of sunspots. Considering the recent low solar activates, the flux cancellations in an active region are higher priority as our observing target.

(1) Active region case: If an active region is located on the disk, we plan to track the active region during the whole observing period. We will observe a part of the active region where high canceling activities are expected (e.g. boundary of two emerging flux regions, polarity inversion line below a dark
filament, moat boundary).

(2) Quiet region case: Our target will be a region with higher magnetic activities (ephemeral regions, network fields, etc) around the disk center. When we obtain a data set around the disk center on the good seeing condition, we plan to observe the similar region far from the disk center. The magnetic field measurements from a different view angle are helpful to know the 3D structure of magnetic field.