THE FRONTIER BETWEEN SMALL-SCALE BIPOLES AND EPHEMERAL REGIONS IN THE SOLAR PHOTOSPHERE: EMERGENCE AND DECAY OF AN INTERMEDIATE-SCALE BIPOLE OBSERVED WITH SUNRISE/IMaX
- IAC Instituto de Astrofisica de Canarias, La Laguna, Tenerife E-38200 (Spain)
- IAA Instituto de Astrofisica de Andalucia (CSIC), E-18080 Granada (Spain)
- MPS Max-Planck-Institut fuer Sonnensystemforschung, D-37191 Katlenburg-Lindau (Germany)
- KIS Kiepenheuer-Institut fuer Sonnenphysik, D-79104 Freiburg (Germany)
- HAO High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80307-3000 (United States)
We report on the photospheric evolution of an intermediate-scale ( Almost-Equal-To 4 Mm footpoint separation) magnetic bipole, from emergence to decay, observed in the quiet Sun at high spatial (0.''3) and temporal (33 s) resolution. The observations were acquired by the Imaging Magnetograph Experiment imaging magnetograph during the first science flight of the SUNRISE balloon-borne solar observatory. The bipole flux content is 6 Multiplication-Sign 10{sup 17} Mx, representing a structure bridging the gap between granular scale bipoles and the smaller ephemeral regions. Footpoints separate at a speed of 3.5 km s{sup -1} and reach a maximum distance of 4.5 Mm before the field dissolves. The evolution of the bipole is revealed to be very dynamic: we found a proper motion of the bipole axis and detected a change of the azimuth angle of 90 Degree-Sign in 300 s, which may indicate the presence of some writhe in the emerging structure. The overall morphology and behavior are in agreement with previous analyses of bipolar structures emerging at the granular scale, but we also found several similarities with emerging flux structures at larger scales. The flux growth rate is 2.6 Multiplication-Sign 10{sup 15} Mx s{sup -1}, while the mean decay rate is one order of magnitude smaller. We describe in some detail the decay phase of the bipole footpoints that includes break up into smaller structures, and interaction with preexisting fields leading to cancellation, but it appears to be dominated by an as-yet unidentified diffusive process that removes most of the flux with an exponential flux decay curve. The diffusion constant (8 Multiplication-Sign 10{sup 2} km{sup 2} s{sup -1}) associated with this decay is similar to the values used to describe the large-scale diffusion in flux transport models.
- OSTI ID:
- 22011864
- Journal Information:
- Astrophysical Journal, Vol. 745, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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