A comparison between the CaII(k), H, SOHO/MDI and radio-enhanced temperature regions of the Sun

¹ Tuorla Observatory, 21500 Piikkiö, Finland
² Metsähovi Radio Observatory, Helsinki Univ. of Technology, Espoo, Finland

Corresponding author: A. Riehokainen, alrieho@astro.utu.fi

Received: 4 September 2002
Accepted: 21 January 2003

Abstract

We present a comparison of the enhanced temperature regions (ETRs) in the radio emission of the Sun with other manifestations of solar activity over 5 days. The radio observations at 87 GHz were observed with the Metsähovi Radio Telescope (Finland). We superposed the intensity contours of the full-disk radio maps on the Meudon spectroheliograph CaII and H_α images of the Sun for comparisons between the radio and the optical positions and brightness characteristics of these active areas. A similar comparison to the SOHO satellite's Magnetic Doppler Imager magnetograms was also made. We concentrated on the high and low latitude weak radio ETRs with no discernible connections to sunspots. No distinction was made between radio ETRs inside and outside of coronal holes. A close connection between the radio and the optical activity was found. The average CaII/ H_α brightness of the whole radio ETR is almost always above the disk average. The CaII, the H_α and the radio brightness inside individual ETRs are also correlated. We found that the radio maximum in general coincides either with the brightest CaII/ H_α and strongest magnetic field structures within the ETR area, or with a density enhancement of the less bright CaII/ H_α and less strong magnetic field structures. It is possible that these two cases result from different (unresolvable) fine structures of the radio ETRs. We suggest that the high and the low latitude weak ETRs may have several causes, which explains the lack of one-to-one correlations with other manifestations of solar activity.