Lunar conductivity models from the Apollo 12 magnetometer experiment

A number of conductivity models have been investigated for compatibility with the Apollo 12 magnetometer data. Except at the highest frequencies, a simple core-crust model is compatible with the observed dayside transfer function, which is expressed as the ratio of the lunar surface field spectrum to the interplanetary magnetic field spectrum. All conductivity profiles exhibit a peak near 1500 km, when the models are constrained to conform to the observed flat response at the higher frequencies. However, at frequencies above 0.01 Hz the long wavelength limitation of the theoretical model is no longer valid. A combination of dayside and nightside models and data indicate that a conductivity profile with a peak (0.003 mho/m) near 1500 km radius and a core conductivity of about 0.01 mho/m at 1000 km is compatible with the observations, as is a monotonic conductivity profile with 0.0005 mho/m at 1600 km and a core conductivity of 0.01 mho/m at 1000 km radius.A plausible explanation for the difference between the north-south and east-west transfer functions is that it is due to a time varying compression of the remanent (dc) field at the Apollo 12 site by fluctuations in the solar wind plasma. Providing that the spectrum of these compressive fluctuations is not strongly frequency dependent, the result of removing this effect will be to decrease slightly the estimated conductivity.Bellcomm, Inc., 955 L'Enfant Plaza North, S.W. Washington, D.C. 20024, U.S.A.