HR: 0800h
AN: P51B-0486    [Abstracts]
TI: Modeling Lunar Borehole Temperature in order to Reconstruct Historical Total Solar Irradiance and Estimate Surface Temperature in Permanently Shadowed Regions
AU: * Wen, G
EM: wen@climate.gsfc.nasa.gov
AF: NASA/Goddard Space Flight Center, 8800 Greenbelt Rd., Greenbelt, MD 20771, United States
AU: * Wen, G
EM: wen@climate.gsfc.nasa.gov
AF: University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, United States
AU: Cahalan, R F
AF: NASA/Goddard Space Flight Center, 8800 Greenbelt Rd., Greenbelt, MD 20771, United States
AU: Miyahara, H
EM: miyahara@eps.s.u-tokyo.ac.jp
AF: University of Tokyo, University of Tokyo, Tokyo, 113-0033, Japan
AU: Ohmura, A
EM: atsumu.ohmura@env.ethz.ch
AF: Institute for Atmospheric and Climate Science, Swiss Federal Institute of Technology (ETH), Zurich, 8092, Swaziland
AB: The Moon is an ideal place to reconstruct historical total solar irradiance (TSI). With undisturbed lunar surface albedo and the very low thermal diffusivity of lunar regolith, changes in solar input lead to changes in lunar surface temperature that diffuse downward to be recorded in the temperature profile in the near-surface layer. Using regolith thermal properties from Apollo, we model the heat transfer in the regolith layer, and compare modeled surface temperature to Apollo observations to check model performance. Using as alternative input scenarios two reconstructed TSI time series from 1610 to 2000 (Lean, 2000; Wang, Lean, and Sheeley 2005), we conclude that the two scenarios can be distinguished by detectable differences in regolith temperature, with the peak difference of about 10 mK occuring at a depth of about 10 m (Miyahara et al., 2007). The possibility that water ice exists in permanently shadowed areas near the lunar poles (Nozette et al., 1997; Spudis et al, 1998), makes it of interest to estimate surface temperature in such dark regions. "Turning off" the Sun in our time dependent model, we found it would take several hundred years for the surface temperature to drop from ~~100K immediately after sunset down to a nearly constant equilibrium temperature of about 24~~38 K, with the range determined by the range of possible input from Earth, from 0 W/m² without Earth visible, up to about 0.1 W/m² at maximum Earth phase. A simple equilibrium model (e.g., Huang 2007) is inappropriate to relate the Apollo-observed nighttime temperature to Earth's radiation budget, given the long multi- centennial time scale needed for equilibration of the lunar surface layer after sunset. Although our results provide the key mechanisms for reconstructing historical TSI, further research is required to account for topography of lunar surfaces, and new measurements of regolith thermal properties will also be needed once a new base of operations is established. References Huang, S., (2007), Surface Temperatures at the Nearside of the Moon as a Record of the Radiation Budget of Earth's Climate System, Advances in Space Research, doi:10.1016/j.asr.2007.04.093. Lean, J., Geophys. Res. Lett., (2000), 27(16), 2425-2428. Miyahara, H., G. Wen, R. F. Cahalan, and A. Ohmura, (2007), Deriving Historical Total Solar Irradiance from Lunar Borehole Temperatures, submitted to Geophy. Res. Lett. Nozette, S., E. M. Shoemaker, P. D. Spudis, and C. L. Lichtenberg, The possibility of ice on the Moon, Science, 278, 144-145, 1997. Spudis, P.D., T. Cook, M. Robinson, B. Bussey, and B. Fessler, Topography of the southe polar region from Clementine stereo imaging, New views of the Moon, Integrated remotely sensed, geophysical, and sample datasets, Lunar Planet. Inst., [CD-ROM], abstract 6010, 1998. Wang, Y. M., J. L. Lean and N. R. Sheeley (2005), Astrophys. J., 625, 522-538.
DE: 5430 Interiors (8147)
DE: 6250 Moon (1221)
DE: 6297 Instruments and techniques
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting