Title: Global asymmetry of the Sun observed in the extreme ultraviolet radiation
Author: Igor. S. Veselovsky
Affil: Institute of Nuclear Physics, Moscow State University
Email: veselov@dec1.sinp.msu.ru
Authors: A. N. Zhukov (1), A. V. Dmitriev (1), M. V. Tarsina (1), F. Clette (2), P. Cugnon (2), J.-F. Hochedez (2)
Affils: (1) Institute of Nuclear Physics, Moscow State University (2) Royal Observatory of Belgium
Abstract: We report on observations of the solar luminosity variations in the Fe XII line over the period 1996 - 1999, which corresponds to the minimum and rising phase of the current 23rd solar cycle. The relatively high temporal cadence and spatial resolution of the Extreme-ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO) allowed nearly continuous intensity measurements of different structures on the Sun. We find that a significant contribution to the longitudinal asymmetry, and thus to the 27-day variability of the solar EUV radiation, is produced by the numerous intermediate-brightness elements that are globally distributed over large areas (up to about 2/3 of the whole solar surface). When activity is low, this component even becomes dominant over the contributions from localized magnetic structures, like active regions and bright points. This suggests that weak magnetic field areas outside active regions constitute an important factor through which solar activity modulates the solar EUV luminosity.