What solar photometric properties are best studied at activity minimum?
The standard model is incomplete, as it excludes nonmagnetic sources of irradiance variation. These other sources are best studied at activity minimum, when noise from magnetic structures is least. Nonmagnetic sources include known photospheric structures such as convective cells and acoustic oscillations and inferred structures such as pole-equator temperature gradients and global variations of effective temperature. We expect that all measurable sources of irradiance variation will have distinct spatial patterns over the solar disk, just as surface magnetic fields and convection cells have. Variation of TSI will occur from an unbalanced summation of the local contrasts. For example, the correlation of TSI with the disk-integrated magnetic flux is nil, while the correlation with the sum of the local magnetic signals is high. Therefore we propose to use bolometric images to understand the localized sources of irradiance variation. The above figure, generated from a SOHO/MDI magnetic an
