Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmgp61a1017m&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #GP61A-1017
Physics
1515 Geomagnetic Induction, 1545 Spatial Variations (All Harmonics And Anomalies), 1555 Time Variations: Diurnal To Secular, 4255 Numerical Modeling, 4275 Remote Sensing And Electromagnetic Processes (0689)
Scientific paper
Sea water is an electrical conductor. As it is moved by ocean flow through the Earth's magnetic field, electrical currents are induced. These currents generate secondary magnetic fields which have now been identified for the first time in CHAMP satellite magnetic data. From the first 2 years of CHAMP total field magnetic measurements we select magnetically quiet periods by using only the night time data (22:00 to 6:00 local time) and discarding periods with a magnetic activity index Kp > 2. The analysis is restricted to track segments of -60o to 60o geomagnetic latitude. After subtracting a main field model 05m-02 [Olsen, 2002] and a lithospheric field model MF1 [Maus et al., 2002], we remove long wavelength magnetospheric and ionospheric contributions by subtracting best-fitting external and internal spherical harmonic degree-1 fields, separately for each track. In the future, this filtering can possibly be substituted by a joint inversion of multiple satellite and ground observatory data. For a first demonstration of this effect we focus on tidal ocean flow because periodic signals are readily separable from steady contributions to the magnetic field, the lithospheric magnetization in particular. For the strong lunar M2 tidal constituency, we find an ocean magnetic signal with a filtered amplitude in the range of +/-1 nT at CHAMP altitude (380-470 km). A global map of the signal agrees remarkably well with fully independently derived model predictions. The identification of this ocean dynamo signal has important implications: In broader terms, it encourages future studies to assess the feasibility of monitoring ocean flow from space using magnetic field satellites. A more immediate consequence, however, is that oceanic signals must be incorporated into geomagnetic field models. Indeed, with recent advances in internal/external field separation the ocean flow signal is now the strongest remaining signal in the low latitude magnetic residuals which has not yet been modeled. Correcting magnetic readings for predictable ocean flow signals could significantly raise the detectability of small scale crustal magnetization. References:\Olsen, N., Geophys. J. Int., 149, 454-462, 2002.\Maus et al., Geophys. Res. Lett., 29, 14, 10.1029/2001GL013685, 2002.
Luehr Herman
Maus Stefan
Tyler Helene R.
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