Earth Planets Space, Vol. 58 (No. 6), pp. 697-705, 2006
H. Toh1, Y. Hamano2, and M. Ichiki3
1Department of Earth Sciences, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan
2Department of Earth and Planetary Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
3Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-Cho, Yokosuka, Kanagawa 237-0061, Japan
(Received May 2, 2005; Revised November 24, 2005; Accepted November 24, 2005; Online published June 2, 2006)
For two years, geomagnetic variations have been measured at the seafloor in the northwest Pacific. The seafloor data consist of the geomagnetic vector field measured by a three-component fluxgate magnetometer and the absolute scalar total force measured by an Overhauser (1953) magnetometer with attitude measurements for both orientation and tilt. Using the attitude data, the geomagnetic data at a site in the northwest Pacific (41°06´08″N, 159°57´47″E, -5580 m), hereafter referred to as NWP, were converted into the same reference frame as land and satellite measurements. Short-period variations of the converted vector data were examined by Hamano's (2002) global time domain analysis method, which showed compatibility of the seafloor geomagnetic observatory data with the existing land observatory network. The smooth and gradual change of the Earth's main field (i.e., the geomagnetic secular variation) was also found consistent with those predicted by the latest International Geomagnetic Reference Field (IGRF-10; IAGA, 2005) and by Ørsted Satellite (Olsen, 2002) for not only the scalar field but also the vector field. This means that observation of the geomagnetic vector secular variation is now feasible on the seafloor.
Key words: Long-term seafloor geomagnetic observation, secular variation, IGRF, satellite measurements, the Earth's main field, attitude data, scalar and vector geomagnetic fields.