Global asymmetry of the sun observed in the extreme ultraviolet radiation

We report on observations of the solar luminosity variations in the Fe xii line (195 Angstrom) over the period 1996-1999, which corresponds to the min imum and rising phase of the current 23rd solar cycle. The relatively or ra ther high temporal cadence and spatial resolution of the Extreme-ultraviole t Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory ( SOHO) allowed a nearly continuous measurement of intensity of different str uctures on the Sun. We find that a significant contribution to the longitud inal asymmetry, and thus to the 27-day variability of the solar EUV radiati on, is produced by the numerous intermediate brightness elements that are g lobally distributed over large areas (up to about similar to 2/3 of the who le surface of the Sun). When activity is low, this component even becomes d ominant over the contribution from localized active regions and bright poin ts. This suggests that weak magnetic field areas outside active regions con stitute an important factor through which solar activity modulates the sola r EUV luminosity.