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U.S. Geological Survey, Geomagnetism Program

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Magnetotelluric (MT) method is a branch of geophysics that employs very large-scale natural sources from the solar wind and lightning. Modern-day MT uses state-of-the-art instrumentation, data processing and analysis tools to provide valuable information about deep Earth structure, complimentary to that of seismic data. These days, MT data also serve as a primary resource for estimation of geomagnetically induced currents, hazardous to modern infrastructure. However, there is a real need to modernize deeply historic MT data formats to a common standard that is fully documented, platform-independent, extensible, and accessible to the broader community of geoscientists. In the past decade, we have led just such an...
A revised version of the storm-time disturbance index Dst is calculated using hourly-mean magnetic-observatory data from four standard observatories and collected over the years 1958–2007. The calculation algorithm is a revision of that established by Sugiura et al., and which is now used by the Kyoto World Data Center for routine production of Dst. The most important new development is for the removal of solar-quiet variation. This is done through time and frequency-domain band-stop filtering – selectively removing specific Fourier terms approximating stationary periodic variation driven by the Earth’s rotation, the Moon’s orbit, the Earth’s orbit around the Sun, and their mutual coupling. The resulting non-stationary...
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Movie-maps of low-latitude horizontal-intensity magnetic disturbance are derived from magnetic vector time series data collected at multiple ground-based observatories. Using a technique similar to that used in the calculation of Dst, a quiet time baseline is subtracted from the time series from each observatory. The remaining disturbance time series are shown in a polar coordinate system that accommodates both Earth rotation and the universal time dependence of magnetospheric disturbance. Each magnetic storm recorded in the movie-maps is different. While some standard interpretations about the storm time equatorial ring current appear to apply to certain moments and certain phases of some storms, the movie-maps...
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