HR: 0800h
AN: GP11D-0882    [Abstracts]
TI: Application of CM3 Model in Compilation of Marine Magnetic Anomaly Data of North Pacific
AU: * Ishihara, T
EM: t-ishihara@aist.go.jp
AF: Institute of Geology and Geoinformation, Geological Survey of Japan, AIST, AIST Central 7, Tsukuba, 305-8567 Japan
AB: Marine magnetic data available from the NGDC have a long time span of data collection from 1950s to 2002, and external magnetic fields generally have not been removed from the data. Based on satellite and observatory data, Sabaka et al. (2002) developed a new comprehensive model, CM3, which defines not only the main field but also quiet time external magnetic fields for the period from 1960 to 2002. In this study, the CM3 model was utilized in the compilation of the NGDC marine magnetic data set in the Pacific area east of 140 E of the northern hemisphere. The whole data set amounts to about 6.3 million records with a total line length of about 2.5 million nautical miles. Before applying the CM3 model, the data set was edited. Magnetic anomalies were recalculated by subtracting DGRF reference fields from observed total magnetic intensity values, then bad data were removed by checking all the cross-over errors (COEs) $>$ 300 nT. This data editing reduced total number of data records by 0.5 % (or 1% of track line length), and 10 (including 4 cruises before 1960) out of 870 cruises were excluded from the data set. In order to clarify the effect of CM3 model, two types of new magnetic anomalies were calculated by replacing the DGRF model by: (case 1) only the CM3 main field model and (case 2) both of the main and external field models. Cross-over analysis reveals that the standard deviation (SD) of COEs reduced from about 60 nT for the DGRF model to about 58 nT for the CM3 main field model. The secular variation of main field before 1970 and after 1995 is significantly different between the DGRF and CM3 models in the areas east of 160 W and north of 50 N. Utilization of the CM3 main field model is particularly effective in these areas. Application of CM3 external field model further reduces the SD of COEs to about 50 nT. The external fields have large amplitudes in the area south of 20 N and west of 180, where the magnetic equator passes. Removal of the external fields has a marked effect on reducing COEs particularly in this area: the SD of COEs reduced by about 15 nT. Application of CM3 main and external field models to data collected from various kind of research cruises makes a good compilation of magnetic anomaly map promising, although there are still many data sparse areas.
DE: 9355 Pacific Ocean
DE: 3005 Geomagnetism (1550)
DE: 1532 Reference fields (regional, global)
DE: 1550 Spatial variations attributed to seafloor spreading (3005)
DE: 1555 Time variations--diurnal to secular
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting