Probing the Large-Scale Structure and Dynamics of the Ionosphere: An Analysis of Low-Latitude TEC

Abraham C. Stern and Eric Altshuler, Patricia H. Doherty, Cesar E. Valladares

Peer Reviewed

Abstract:	We present an analysis of the average temporal and spatial variation of six years of total electron content (TEC) measurements derived from the Low-Latitude Ionospheric Sensor Network (LISN). Fundamentally, our analysis enables us to decompose the observed variation in TEC into individual contributions which we can then characterize by frequency, shape, and time evolution. By employing a combined approach using spherical harmonic basis together with a spectral analysis, we are able to isolate and describe the variation associated with underlying processes. For example, the diurnal, annual and semiannual variation are readily identifiable. Moreover, we are able to reconstruct in time and space the specific variation associated with an identified mode for characterization. Our analysis reveals contributions which arise from solar rotation and Earth’s transit through the solar magnetic field. These modes show up as peaks in the frequency domain with respective periods of 27.0 and 14.7 days. The effects of solar rotation and the interplanetary magnetic field on the topside ionosphere have been documented previously [1,2], however, it is our belief that this study represents the first observation of these phenomena using a GPS receiver network. We then demonstrate that the contributions identified by our analysis can be used to construct a simple climatological model. Our model allows for individual modes to be reconstructed and analyzed with respect to the overall total electron content. We include a discussion of this unique perspective which is provided by our method. In particular, we characterize the ionospheric effects arising from solar rotation and the solar magnetic field. Our aim is to present the approach that we used to identify several fundamental contributions to ionospheric TEC and to characterize these in terms of understanding the average observable ionosphere. Along the way, we describe how we construct a climatological model that captures the average behavior of the ionosphere, especially near and in the equatorial region. We provide a preliminary characterization of residuals and assess model performance, especially as it relates to its use in compensating for atmospheric errors. It is our hope that accounting for the average behavior of the fundamental contributions will aid researchers and engineers in determining better performing estimates and error models near geographic transition regions as well as equatorial ionospheric threat models.
Published in:	Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015) September 14 - 18, 2015 Tampa Convention Center Tampa, Florida
Pages:	3525 - 3533
Cite this article:	Stern, Abraham C., Altshuler, Eric, Doherty, Patricia H., Valladares, Cesar E., "Probing the Large-Scale Structure and Dynamics of the Ionosphere: An Analysis of Low-Latitude TEC," Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015), Tampa, Florida, September 2015, pp. 3525-3533.
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