An innovative methodology for locating ionosphere layer height:&#160;case study on 2011 Tohoku-Oki earthquake and tsunami
Authors: Ravanelli Michela , Occhipinti Giovanni 
Published: March 2021

&lt;p&gt;One of the main issues in GNSS ionosphere seismology is to localize the exact height of the single thin layer (H&lt;sub&gt;ion&lt;/sub&gt;) with which the ionosphere is approximated. H&lt;sub&gt;ion&lt;/sub&gt; is generally assumed to be the altitude of the maximum ionospheric ionization (hmF2), i.e., in the ionospheric F-layer. In this sense, H&lt;sub&gt;ion&lt;/sub&gt; is often&amp;#160; be presumed from physical principles or ionospheric models. The determination of &amp;#160;H&lt;sub&gt;ion &lt;/sub&gt;is, therefore, fundamental since it affects the coordinates of the ionospheric pierce point (IPP) and subsequentely of the sub-ionospheric pierce point (SIP).&lt;/p&gt;&lt;p&gt;In this work, we present a new developed methodology to determine the exact localization of H&lt;sub&gt;ion.&lt;/sub&gt; We tested this approach on the TIDs (Travelling ionospheric disturbances) connected with the 2011 Tohoku-Oki earthquake and tsunami [1]. In detail, we computed the slant Total Electron Content (sTEC) variations at different H&lt;sub&gt;ion &lt;/sub&gt;(in the range from 100 to 600 km) with the VARION (Variometric Approach for Real-Time Ionosphere Observation) algorithm [2,3], then we interpolated the different pattern in sTEC values related to different waves detected in the ionosphere (AGW&lt;sub&gt;epi&lt;/sub&gt;, IGW&lt;sub&gt;tsuna&lt;/sub&gt; and AW&lt;sub&gt;Rayleigh&lt;/sub&gt;) finding the mean velocity value of these waves. Subsequentely, the minimized difference between the estimated propagation velocity and the values from physical models fix us the correct H&lt;sub&gt;ion.&lt;/sub&gt;&lt;/p&gt;&lt;p&gt;Our results show a H&lt;sub&gt;ion &lt;/sub&gt;of 370 km, while ionopshere model IRI 2006 located the maximum of ionospheric ionization at an height of 270 km. This difference is important to understand how a different H&lt;sub&gt;ion&lt;/sub&gt; can impact on the location of the sTEC perturbation, affecting the shape and the extent of the source from TEC observations.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;[1] https://earthquake.usgs.gov/earthquakes/eventpage/official20110311054624120_30/executive&lt;/p&gt;&lt;p&gt;[2] Giorgio Savastano, Attila Komjathy, Olga Verkhoglyadova, Augusto Mazzoni, Mattia Crespi, Yong Wei, and Anthony J Mannucci, &amp;#8220;Real-time detection of tsunami ionospheric disturbances with a stand-alone gnss receiver: A preliminary feasibility demonstration, &amp;#8221;Scientific reports, vol. 7, pp. 46607, 2017.&lt;/p&gt;&lt;p&gt;[3] Giorgio Savastano, Attila Komjathy, Esayas Shume, Panagiotis Vergados, Michela Ravanelli, Olga Verkhoglyadova, Xing Meng, and Mattia Crespi, &amp;#8220;Advantages of geostationary satellites for ionospheric anomaly studies: Ionospheric plasma depletion following a rocket launch,&amp;#8221;Remote Sensing, vol. 11, no. 14, pp. 1734, 2019&lt;/p&gt;