Association of radio polar cap brightening with bright patches and coronal holes

Selhorst, C. L., Simões, P. J.A. , Oliveira e Silva, A. J., Giménez de Castro, C.G., Costa, J. E.R. and Valio, A. (2017) Association of radio polar cap brightening with bright patches and coronal holes. Astrophysical Journal, 851(2), 146. (doi: 10.3847/1538-4357/aa992b)

152372.pdf - Accepted Version



Radio-bright regions near the solar poles are frequently observed in Nobeyama Radioheliograph (NoRH) maps at 17 GHz, and often in association with coronal holes. However, the origin of these polar brightenings has not been established yet. We propose that small magnetic loops are the source of these bright patches, and present modeling results that reproduce the main observational characteristics of the polar brightening within coronal holes at 17 GHz. The simulations were carried out by calculating the radio emission of the small loops, with several temperature and density profiles, within a 2D coronal hole atmospheric model. If located at high latitudes, the size of the simulated bright patches are much smaller than that of the beam size and they present the instrument beam size when observed. The larger bright patches can be generated by a great number of small magnetic loops unresolved by the NoRH beam. Loop models that reproduce bright patches contain denser and hotter plasma near the upper chromosphere and lower corona. On the other hand, loops with increased plasma density and temperature only in the corona do not contribute to the emission at 17 GHz. This could explain the absence of a one-to-one association between the 17 GHz bright patches and those observed in extreme ultraviolet. Moreover, the emission arising from small magnetic loops located close to the limb may merge with the usual limb brightening profile, increasing its brightness temperature and width.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Simoes, Dr Paulo
Authors: Selhorst, C. L., Simões, P. J.A., Oliveira e Silva, A. J., Giménez de Castro, C.G., Costa, J. E.R., and Valio, A.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
Publisher:IOP Publishing
ISSN (Online):1538-4357
Published Online:21 December 2017
Copyright Holders:Copyright © 2017 The American Astronomical Society
First Published:First published in Astrophysical Journal 851(2):146
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
631581Consolidated grant in solar and astrophysical plasmasLyndsay FletcherScience & Technology Facilities Council (STFC)ST/L000741/1S&E P&A - PHYSICS & ASTRONOMY