Field-Line Resonances

Welcome to probably the most comprehensive guide to field-line resonances on the entire web.

This presentation is accompanied by various postscript slides which may be viewed by those lucky enough to have viewers which can handle post-script.

Field-line resonances are long duration ULF waves in the magnetic field of the Earth. They can be set up in many ways - for example the Kelvin-Helmholtz instability. My work involves looking for ways of detecting field-line resonances given time-series readings of the Earth's magnetic field read from devices known as magnetometers. There are several methods of locating field-line resonances. All of these methods involve the creation of Power Spectra of the time series sampled from the Earth's magnetic field. Some processing must be used on the time series in order to produce this power series. Several such power series may be combined to produce the Dynamic or 2D power spectrum. The 2D power spectrum has many uses but is not useful for detecting field-line resonances.

One method which is related to the power spectrum is the cross-phase spectrum. This detects field-line resonances through frequency-space phase difference. The cross-phase technique requires even more processing than the power spectrum. Processing techniques include the setting of a minimum power rejection level and some simple image processing.

Another method is the Gradient Method. This works due to the amplitude and frequency fall off characteristics of FLRs. A final method is H/D power division.

There are several problems related to FLR detection. A major problem is Geoelectric Inhomogeneity.

Further work to be done in this area involves automating a process to look for static and dynamic field-line resonances in months of field-readings. The saga continues.

Read a brief summary of FLR detection techniques if you wish.

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