The Lunar Terrestrial Observatory: Observing the Earth using photometers on the Moon’s surface

The Earth’s albedo is one of the least studied fundamental climate parameters. The albedo is a bi-directional variable, and there is a high degree of anisotropy in the light reflected from a given terrestrial surface. However, simultaneously observing from all points on Earth at all reflecting angles is a practical impossibility. Therefore, all measurements from which albedo can be inferred require assumptions and/or modeling to derive a good estimate. Nowadays, albedo measurements are taken regularly either from low Earth orbit satellite platforms or from ground-based measurements of the earthshine from the dark side of the Moon. But the results from these different measurements are not in satisfactory agreement. Clearly, the availability of different albedo databases and their inter-comparisons can help to constrain the assumptions necessary to reduce the uncertainty of the albedo estimates. In recent years, there has been a renewed interest in the development of robotic and manned exploration missions to the Moon. Returning to the Moon will enable diverse exploration and scientific opportunities. Here we discuss the possibility of a lunar-based Earth radiation budget monitoring experiment, the Lunar Terrestrial Observatory, and evaluate its scientific and practical advantages compared to the other, more standard, observing platforms. We conclude that a lunar-based terrestrial observatory can enable advances in Earth sciences, complementary to the present efforts, and to our understanding of the Earth’s climate.     

Evolution of the sun''s near-surface asphericities over the activity cycle

Solar oscillations provide the most accurate measures of cycle dependent changes in the sun, and the Solar and Heliospheric Observatory/Michelson Doppler Imager (MDI) data are the most precise of all. They give us the opportunity to address the real challenge — connecting the MDI seismic measures to observed characteristics of the dynamic sun. From inversions of the evolving MDI data, one expects to determine the nature of the evolution, through the solar cycle, of the layers just beneath the sun's surface. Such inversions require one to guess the form of the causal perturbation — usually beginning with asking whether it is thermal or magnetic. Matters here are complicated because the inversion kernels for these two are quite similar, which means that we don't have much chance of disentangling them by inversion. However, since the perturbation lies very close to the solar surface, one can use synoptic data as an outer boundary condition to fix the choice. It turns out that magnetic and thermal synoptic signals are also quite similar. Thus, the most precise measure of the surface is required.

We argue that the most precise synoptic data come from the Big Bear Solar Observatory (BBSO) Solar Disk Photometer (SDP). A preliminary analysis of these data implies a magnetic origin of the cycle-dependent sub-surface perturbation. However, we still need to do a more careful removal of the facular signal to determine the true thermal signal.