The Astrophysical Journal
We have examined images from the Precision Solar Photometric Telescope (PSPT) at the Mauna Loa Solar Observatory (MLSO) in search of latitudinal variation in the solar photospheric intensity. Along with the expected brightening of the solar activity belts, we have found a weak enhancement of the mean continuum intensity at polar latitudes (continuum intensity enhancement 0.1%Y0.2%, corresponding to a brightness temperature enhancement of 2.5 K). This appears to be thermal in origin and not due to a polar accumulation of weak magnetic elements, with both the continuum and Ca ii K intensity distributions shifted toward higher values with little change in shape from their midlatitude distributions. Since the enhancement is of low spatial frequency and of very small amplitude, it is difficult to separate from systematic instrumental and processing errors.We provide a thorough discussion of these and conclude that the measurement captures real solar latitudinal intensity variations.
Rast, Mark P.; Ortiz, Ada; and Meisner, Randle W., "Latitudinal Variation of the Solar Photospheric Intensity" (2008). Astrophysical & Planetary Sciences Faculty Contributions. 17.