The TEC-GNSS analysis of the paroxysmal eruptive activity of Mt.Etna

The ionosphere is a region of the upper atmosphere (50-1000 km a.s.l.) characterized by free electrons and ions produced mainly by solar radiations (UV, X) and subordinately by cosmic radiations (RAVANELLI, 2021). It’s a very sensitive plasma to energy variations, mostly the F2 layer (240-400 km a.s.l.) that is a region of maximum ionization with an electron density of 10 6 e - /cm 3 . For this reason, the ionosphere (in particular the F region) can be seen as a field of remote sensing monitoring from which to extrapolate various informations by the natural systems that make up our planet.
About this, solid Earth (e.g. litoshpere, internal structure) and fluid Earth (e.g. idrosphere, atmosphere) are two open systems that exchange energy continuously. It means that big dynamic processes (e.g. plate tectonics, genesis of magmas) can release amounts of energy, in the form of earthquakes, volcanic eruptions and correlate phenomena (e.g. tsunami), capable to perturb the earth’s matter at every aggregation state and up to planetay scale with propagation of gravity-acoustic waves. In this field, the ionospheric volcanology is a targered discipline for the study of the effects that great volcanic eruptions (VEI > 3-4) cause to Total Electron Content (TEC) in the ionosphere (F2 level) through propagation of internal gravity waves (0.1 – 2 mHz) and acoustic waves (2 – 10 mHz). The study of the TEC’s variations caused by strong geodynamic events represents a new approach with which to contribute to implementation of the monitoring and research systems in order to mitigate the volcanic and seismic risks.
The method consists to extrapolate the temporal variations of TEC during the volcanic activity period by RINEX and navigational data GNSS registered by RING (Rete Integrata Nazionale GNSS) and local GPS networks. By the way, others outputs can be derived from TEC series such as spectrograms and hodocrones in order to better understand the evolution of the electron activity in ionosphere excited by the volcanic eruption. This study method is applied for some paroxysmal eruptive activities of Mt.Etna analyzing and comparing the volcanological data with TEC outputs. The latter have been processed with VARION (Variometric Approach for Real-time Ionosphere Observation) algorithm, designed within the Geodesy and Geomatics Division of Sapienza University of Rome in 2015. VARION is based on single time differences of geometry-free combination of GNSS carrier-phase measurements, using a standalone GNSS receiver and standard GNSS broadcast products (orbits and clocks correction) that are available in real time. One of the goals to be pursued in the Research is to comprehend the differences between eruptive mechanisms capable to generate gravity waves rather acoustic waves, and how such mechanisms may depend by physical-geometric features of the plumbing system of the volcano and by chemical-physical features of the magma and its amount of gas.