A characterization of periodicity in the voltage time series of a riometer

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Space Physics 125(7), (2020): e2019JA027160, doi:10.1029/2019JA027160.This paper reveals unprecedented periodicity in the voltage series of relative ionospheric opacity meters (riometers) of the Canadian Riometer Array (CRA). In quiet times, the riometer voltage series is accurately modeled by a stochastic process whose components include both a six term expansion in harmonic functions and some amplitude modulated modes of lower signal to noise ratio (SNR). In units of cycles per sidereal day (cpsd), the frequencies of the six harmonic functions lie within 0.01 cpsd of an integer. Earth's rotation induces a splitting of the low SNR components, resulting in the appearance of nine multiplets in standardized power spectrum estimates of the considered CRA voltage series. A second feature of these spectrum estimates is a 6 min periodic element appearing in both the CRA voltage series and the proton mass density series of the Advanced Composition Explorer (ACE). Spectral peak frequencies have been detected, which lie near established solar mode frequency estimates. In addition, some of these peak frequency estimates are coincident with peak frequency estimates of the standardized power spectra for the time series of proton mass density and interplanetary magnetic field strength (IMF) at ACE.“Marshall_Francois_Supporting_Information_JGR_2019.pdf” contains a summary of the supporting information. The 1 hr sampled F10.7 series was obtained from DRAO (National Research Council, 2017). The three MAG time series of IMF strength were acquired from The ACE Science Center (2007), while the SWEPAM time series of proton mass density was acquired from Space Weather Prediction Center, National Oceanic and Atmospheric Administration (2018). The relevant data sets for the analysis of this paper are included in Marshall (2019). This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC), Canadian Statistical Sciences Institute (CANSSI), Bonneyville Power Authority, and Queen's University. David J. Thomson, the official holder of the grants and contracts, provided research and conference funding to advance this project. Special thanks to Ken F. Tapping (DRAO of NRCan) for his guidance in finding the data sets relevant to solar radio emissions. Glen Takahara, of the Department of Mathematics and Statistics at Queen's University, suggested exploring different data sets to confirm the modal origin of spectral peaks observed in the Ottawa riometer of the CRA. Alessandra A. Pacini of the Arecibo Observatory recommended checking to see if some of the modes could have been driven by the harmonics of Earth's rotation. Frank Vernon of the Institute of Geophysics and Planetary Physics at Scripps Institution of Oceanography confirmed how seismic data could be expected to reveal coincident spectral peaks at the detected frequencies in the riometer standardized spectra.2020-10-2