Spatiotemporal characteristics of cusp latitude spectra

Abstract

In this study we analyze the spatiotemporal characteristics of spectra generated from 754 days of cusp latitude magnetometer data (Longyearbyen and selected Magnetometer Array for Cusp and Cleft Studies (MACCS) stations). In order to distinguish between the presence of spatial (fixed in magnetic local time) and temporal (fixed in universal time) signatures in cusp latitude spectra we develop a simple test using trace power, polarization, and ellipticity spectra. On the basis of this test we find evidence for both spatial and temporal signatures in cusp latitude spectra. We find that the trace power spectrum is dominated by temporal information; however, the polarization and ellipticity spectra contain unambiguous spatial structure. Temporal information in cusp latitude spectra is carried primarily by broadband Pc3 (10–50 mHz) noise, while spatial information is carried by polarized Pc3 (1–10 mHz) pulsations. Additionally, we establish a state‐space measure as a quantitative means of discriminating the spatial passage of the cusp and boundary regions by ground‐based magnetic means. The measure is based on the difference between daily polarization spectra (centered on local magnetic noon) and the mean polarization spectra for a given station. This procedure replaces previous determinations which were made from spectra “by‐eye”.