Abstract
Abstract 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 (41o06′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.
Highlights
We are at a new era in the history of measuring the geomagnetic field by scientific instruments
Geomagnetic Secular Variation at the Seafloor It has been confirmed that the short-period temporal variations observed at NWP are compatible with those predicted by the existing geomagnetic observatory network
Summary Here we reported details of the seafloor geomagnetic observation being conducted in the northwest Pacific, where needs to fill the gap in the existing geomagnetic observatory network have been keen for decades
Summary
We are at a new era in the history of measuring the geomagnetic field by scientific instruments. A series of geomagnetic satellites carrying fluxgate magnetometers and highly accurate positioning instruments have been recently launched into Low Earth Orbit (LEO) to form a miniconstellation which includes Ørsted (Neubert et al, 2001), CHAMP (Reigber et al, 2002) and SAC-C. The launch of these long-life geomagnetic satellites was an epoch-making event because it had been a long wait since the launch of the previous LEO vector geomagnetic satellite, MAGSAT (Langel et al, 1980). Our knowledge of the ionospheric current system is much improved by a combination of land-based and satellite geomagnetic data It is essential for a better understanding of the geomagnetic field to collect both Earth-locked and Sun-locked view of the field at the same time. Because the seafloor geomagnetic data range from August, 2001 through July, 2003, the candidate models to be compared are restricted to
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