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Abstract. The paper examines the possible relationship of anomalous variations of different atmospheric and ionospheric parameters observed around the time of a strong earthquake (M w 7.8) which occurred in Mexico (state of Colima) on 21 January 2003. These variations are interpreted within the framework of the developed model of the Lithosphere-Atmosphere-Ionosphere coupling. The main attention is focused on the processes in the near ground layer of the atmosphere involving the ionization of air by radon, the water molecules' attachment to the formed ions, and the corresponding changes in the latent heat. Model considerations are supported by experimental measurements showing the local diminution of air humidity one week prior to the earthquake, accompanied by the anomalous thermal infrared (TIR) signals and surface latent heat flux (SLHF) and anomalous variations of the total electron content (TEC) registered over the epicenter of the impending earthquake three days prior to the main earthquake event. Statistical processing of the data of the GPS receivers network, together with various other atmospheric parameters demonstrate the possibility of an early warning of an impending strong earthquake.Keywords. Atmospheric composition and structure (Ion chemistry of the atmosphere) -Meteorology and atmospheric dynamics (Atmospheric electricity) -Ionosphere (Ionosphere-atmosphere interactions)

This work presents a contribution to the understanding of the ionospheric triggering of L-band scintillation in the region over São Paulo state in Brazil, under high solar activity. In particular, a climatological analysis of Global Navigation Satellite Systems (GNSS) data acquired in 2012 is presented to highlight the relationship between intensity and variability of the total electron content (TEC) gradients and the occurrence of ionospheric scintillation. The analysis is based on the GNSS data acquired by a dense distribution of receivers and exploits the integration of a dedicated TEC calibration technique into the Ground Based Scintillation Climatology (GBSC), previously developed at the Istituto Nazionale di Geofisica e Vulcanologia. Such integration enables representing the local ionospheric features through climatological maps of calibrated TEC and TEC gradients and of amplitude scintillation occurrence. The disentanglement of the contribution to the TEC variations due to zonal and meridional gradients conveys insight into the relation between the scintillation occurrence and the morphology of the TEC variability. The importance of the information provided by the TEC gradients variability and the role of the meridional TEC gradients in driving scintillation are critically described.

Abstract. Ionospheric TEC (Total ElectronContentThis local TEC disturbance arises preparatory to the EQ main shock occurred at 01:32 UT on 06 April 2009, maximizes its amplitude of ~ 0.8 TECu after the shock moment and disappears after it. The TEC disturbance was localized at heights below 160 km, i.e. in the lower ionosphere.

Abstract. About 25,000 total electron content (TEC) values obtained in 2 years from Navy Navigation Satellite System (NNSS) differential Doppler were compared with the corresponding TECs obtained from the Global Positioning System (GPS). The method by which the comparison is effected is also described. The resulting statistics are very effective in showing a good agreement between the two techniques. The GPS TEC results are statistically larger than NNSS TEC, namely, 3 _+ 1 TEC units; the lower quartile of the differences is always greater than zero. IntroductionAn effective tool for calculating total electron content (TEC) is the differential Doppler method. At present, this is practically the only method provided by satellite navigation systems.Basically, this method relies on measuring the differential phase between two coherent carriers transmitted by satellite and scaled to the same nominal frequency. This facility is provided by all satellite navigation systems as a tool for correcting the delays introduced by the ionosphere. In a first-order approximation, a signal of given carrier frequency f undergoes a phase delay resulting from the contribution of two terms: One, due to the nondispersive terms (geometrical distance and troposphere), is proportional to f; the second, the dispersive one, is inversely proportional to f, depending on the electrons contained in a unitary column along the path (TEC). This T tropospheric contribution to the electromagnetic path; TEC total electron content (electrons m-2).A suitable combination of two phases observed at different frequencies, arranged in such a way as to eliminate the nondispersive terms, provides a direct evaluation of the TEC as described bywhere d is the measured differential phase (differential Doppler), /3 is a term resulting from the phase ambiguity, and C a is a constant, depending on the way in which the signals have been combined. Here as follows, phases will be expressed in equivalent TEC units (TEC unit -1016 m-2), so that Ca is 1.It must be emphasized that (1) and, consequently, (2) hold for time spans during which the phases of the two carriers have been observed with continuity without fading (maximum probability of cycle slips) or signal loss: At each occurrence of these events, a new /3 must generally be used. Detection and resolution of such events, in order to arrive at a single value of/3 for the whole satellite pass, are carried out during the preprocessing of the data, and here as follows, it is assumed that this problem has been solved. The only remaining problem in evaluating TEC is the determination of the phase ambiguity/3.Practically all the techniques used to solve this problem assume the possibility of comparing measurements of TEC taken along different paths with a certain common ionospheric quantity. This quantity is the vertical ionospheric content V. The model used in this work, in order to fulfill this requirement, is a simple one, as it assumes that the ionosphere is limited to a slab of infinitesimal width located at a 1071

Abstract. In this paper we focus on the variability of electron concentration in the ionosphere measured by ground based ionosondes and GPS receivers around the time of strong earthquakes. It has been detected and statistically proven that several days before the seismic shock the level of this variability increases at the station closest to the epicenter, a fact which can be regarded as precursory phenomenon. More precisely the localness of this specific kind of ionospheric variability is used for the correlation analysis of data of several observation points. The similarity of geographical location of the observation points leads to the similarity of ionospheric variations registered at these sites during both quiet and disturbed geomagnetic conditions, except in the case of those located at the seismoactive zone. As a rule, the local anomalies in the F2 layer and TEC accompanying the preparation of strong earthquakes show themselves in the breaking of the mutual correlation of the critical frequencies f o F 2 or TEC between stations situated in and outside the seismic zone. The precursory phenomenon appears 1 to 7 days before the time of the seismic shock.

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