Wavelet Analysis and Correlation Study of Multipoint Auroral Magnetic Field Measurements

Computer Science – Sound

Scientific paper

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2704 Auroral Phenomena (2407)

Scientific paper

The Enstrophy sounding rocket, launched at 0645~UT on 11~Feb~99, flew through a nightside active auroral zone, to the dynamic current region --- the poleward edge of the arc --- and into the polar cap. Four Free-Flying-Magnetometers (FFMs) were deployed from the rocket and multipoint measurements of magnetic field fluctuations were made. The largest magnetic perturbations were seen near apogee (1070~km), in the poleward edge region, and were observed for about 50 seconds by the FFMs, with a spatial separation of ~1-2~km between FFMs. The field aligned current density was calculated using a Taylor series expansion of the curl of B to the first order from the multipoint measurements. Signatures consistent with both spatial structures and temporal variations were observed. In order to separate spatial and temporal signatures, wavelet transformations were applied to each component of the multipoint timeseries of magnetic field observations. Next, a correlation study at variable delay times was performed at each scale of the wavelet transform, between each pair of payloads. The correlation study of the measurements after the wavelet transformation between different payloads shows that structures of different scalesizes (frequencies) were moving relative to each other at different velocities, which is consistent with the camera observations made in a nearby region. The interpretation of the wavelet analysis results was guided by comparing these results to an application of the same wavelet analysis method on the known data of a model consisting of multiple moving current sheets. In addition to the component analysis, the non-zero perturbations observed in the in magnetic field magnitude show the presence of compressional Alfven waves. A similar wavelet analysis and correlation study should provide information on the phase velocity of the waves involved.

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