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Interaction between Granulation and Small-Scale Magnetic Flux Observed by Hinode  

Shuhong Yang   Submitted: 2009-05-11 00:05

With the polarimetric observations obtained by the Spectro-Polarimeter on board Hinode, we study the relationship between granular development and magnetic field evolution in the quiet Sun. 6 typical cases are displayed to exhibit interaction between granules and magnetic elements, and we have obtained the following results. (1) A granule develops centrosymmetrically when no magnetic flux emerges within the granular cell. (2) A granule develops and splits noncentrosymmetrically while flux emerges at an outer part of the granular cell. (3) Magnetic flux emergence as a cluster of mixed polarities is detected at the position of a granule as soon as the granule breaks up. (4) A dipole emerges accompanying with the development of a granule, and the two elements of the dipole root in the adjacent intergranular lanes and face each other across the granule. Advected by the horizontal granular motion, the positive element of the dipole then cancels with pre-existing negative flux. (5) Flux cancellation also takes place between a positive element, which is advected by granular flow, and its surrounding negative flux. (6) While magnetic flux cancellation takes place at a granular cell, the granule shrinks and then disappears. (7) Horizontal magnetic fields enhance at the places where dipoles emerge and where opposite polarities cancel with each other, but only the horizontal fields between the dipolar elements point orderly from the positive element to the negative one. Our results reveal that granules and small-scale magnetic flux influence each other. Granular flow advects magnetic flux, and magnetic flux evolution suppresses granular development. There exist extremely large Doppler blue-shifts at the site of one cancelling magnetic element. This phenomenon may be caused by the upward flow produced by magnetic reconnection below the photosphere.

Authors: Jun Zhang, Shuhong Yang and Chunlan Jin
Projects: Hinode/SOT

Publication Status: Accepted by RAA
Last Modified: 2009-05-11 07:49
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Response of the solar atmosphere to magnetic field evolution in a coronal hole region  

Shuhong Yang   Submitted: 2009-04-16 20:22

Context. Coronal holes (CHs) are deemed to be the sources of the fast solar wind streams that lead to recurrent geomagnetic storms and have been intensively investigated, but not all the properties of them are known well. Aims. We mainly research the response of the solar atmosphere to the magnetic field evolution in a CH region, such as magnetic flux emergence and cancellation for both network (NT) and intranetwork (IN). Methods. We study an equatorial CH observed simultaneously by HINODE and STEREO on July 27, 2007. The HINODE/SP maps are adopted to derive the physical parameters of the photosphere and to research the magnetic field evolution and distribution. The G band and Ca ii H images with high tempo-spatial resolution from HINODE/BFI and the multi-wavelength data from STEREO/EUVI are utilized to study the corresponding atmospheric response of different overlying layers. Results. We explore an emerging dipole locating at the CH boundary. Mini-scale arch filaments (AFs) accompanying the emerging dipole were observed with the Ca II H line. During the separation of the dipolar footpoints, three AFs appeared and expanded in turn. The first AF divided into two segments in its late stage, while the second and third AFs erupted in their late stages. The lifetimes of these three AFs are 4, 6, 10 minutes, and the two intervals between the three divisions or eruptions are 18 and 12 minutes, respectively. We display an example of mixed-polarity flux emergence of IN fields within the CH and present the corresponding chromospheric response. With the increase of the integrated magnetic flux, the brightness of the Ca II H images exhibits an increasing trend. We also study magnetic flux cancellations of NT fields locating at the CH boundary and present the obvious chromospheric and coronal response.We notice that the brighter regions seen in the 171 Å images are relevant to the interacting magnetic elements. By examining the magnetic NT and IN elements and the response of different atmospheric layers, we obtain good positive linear correlations between the NT magnetic flux densities and the brightness of both G band (correlation coeffcient 0.85) and Ca II H (correlation coefficient 0.58).

Authors: S. H. Yang, J. Zhang, C. L. Jin, L. P. Li, and H. Y. Duan

Publication Status: Accepted by A&A
Last Modified: 2009-04-17 08:19
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