Application of a new method for calculation of low-frequency wave vectors

Abstract

The problem of resolving spatial and temporal properties of waves, so-called "space-time ambiguity", is a longstanding issue of single-spacecraft measurements. The general case can be insoluble, but in special cases in which certain assumptions hold, such as when each frequency corresponds to a single wave vector, the ambiguity can be resolved. Recently a method has been proposed to obtain wave vectors from single-spacecraft measurements of Alfvén wave-modulated magnetic fields and currents [Bellan, 2016], through application of the Wiener-Khinchin theorem to cross-correlation of the current density J and magnetic field B, and to the autocorrelation of B. We apply this method to spacecraft data, obtained by culling, from a large database of inertial Alfvén waves observed by the FAST satellite, two case study intervals during which extraordinarily large modulated currents were measured by the FAST particle detectors in burst mode. Results of this analysis for at least one of the two case studies appear consistent with known properties of ionospheric inertial Alfvén waves and pass error and consistency checks within the analysis method.