Statistical Analysis of Wave Propagation Properties of Equatorial Noise Observed at Low Altitudes

0559224 - ÚFA 2023 RIV US eng J - Journal Article
Hanzelka, Miroslav - Němec, F. - Santolík, Ondřej - Parrot, M.
Statistical Analysis of Wave Propagation Properties of Equatorial Noise Observed at Low Altitudes.
Journal of Geophysical Research-Space Physics. Roč. 127, č. 7 (2022), č. článku e2022JA030416. ISSN 2169-9380. E-ISSN 2169-9402
EU Projects: European Commission(XE) 870452 - PAGER
Institutional support: RVO:68378289
Keywords : Earth's magnetosphere * plasma waves * equatorial noise * ray tracing * DEMETER spacecraft
OECD category: Fluids and plasma physics (including surface physics)
Impact factor: 2.8, year: 2022
Method of publishing: Open access
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022JA030416

Equatorial noise is an electromagnetic emission with line spectral structure, predominantly located in the vicinity of the geomagnetic equatorial plane at radial distances ranging from 2 to 8 Earth's radii. Here we focus on the rare events of equatorial noise occurring at ionospheric altitudes during periods of strongly increased geomagnetic activity. We use multicomponent electromagnetic measurements from the entire 2004-2010 DEMETER spacecraft mission and present a statistical analysis of wave propagation properties. We show that, close to the Earth, these emissions experience a larger spread in latitudes than they would at large radial distances and that their wave normals can significantly deviate from the direction perpendicular to local magnetic field lines. These results are compared to ray tracing simulations, in which whistler mode rays with initially nearly perpendicular wave vectors propagate down to the low altitudes with wave properties corresponding to the observations. We perform nonlinear fitting of the simulated latitudinal distribution of incident rays to the observed occurrence and estimate the distribution of wave normal angles in the source. The assumed Gaussian distribution provides the best fit with a standard deviation of 2 degrees from the perpendicular direction. Ray tracing analysis further shows that small initial deviations from the meridional plane can rapidly increase during the propagation and result in deflection of the emissions before they can reach the altitudes of DEMETER.
Permanent Link: https://hdl.handle.net/11104/0332611