Photospheric Diameter Measurements and Variations in the Solar Luminosity
Abstract
The size of the Sun and its temporal variation, if any, have been of historical interest. Recently, helioseismic (SOHO/MDI) and photometric (Solar Disk Monitor) data have been used to show that the photospheric radius is about 300 km smaller than what had been the standard for a quarter century. The change in the Sun's size through the solar cycle has also been carefully studied. From Solar Diameter Monitor data covering the decline of cycle 21, Brown and Christensen-Dalsgaard (1998) determined that the average annual radii are consistent to within their measurement errors of about 40 km. SOHO/MDI data covering the rising phase of cycle 23 have been used to show the upper limit on annual changes is an order of magnitude smaller. Such values imply a negligible contribution of the radius change to the variation of the Sun's irradiance. We use SOHO/MDI data to discuss the relative roles, in the radius changes, of the magnetic field's growth with increasing activity, and/or a relative decrease in subphotospheric temperature and/or an equivalent decrease in the turbulent energy.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2001
- Bibcode:
- 2001AGUSM..SP31B06G
- Keywords:
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- 7522 Helioseismology;
- 7524 Magnetic fields;
- 7536 Solar activity cycle (2162);
- 7537 Solar and stellar variability