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On the background of seasonal and helio-geomagnetic disturbances, disturbances of the ionization density near noon connected to earthquakes are investigated. The study is performed for some tens of earthquakes with magnitudes M>5 and depths hR=exp(M)+150 km. The analysis is performed using data registered by the three sounding stations every hour during 30 years. Especially methods of the statistical analysis are applied to search for regularities in the lithospheric-ionospheric links before and after earthquakes. The growth of the mean ionization density N at the F-layer electron density maximum Fof2 five-three days before earthquakes, and the decrease of N approaching the eruption and during a few days after the earthquake is investigated in dependence on both the magnitude of the earthquake M and the ionization density N near the F-layer maximum. It is found that some days before earthquakes the decrease of the ionization density ΔN is proportional to the values of M and N. After the earthquakes, ΔN depends much weaker on the magnitude M, and it is not influenced by the ionization density N. The variations of the ionization density three days before earthquakes do not depend on N and M (within the same order of approximation).

The paper objective is to demonstrate the possibility of studying irregular variations of the total electron content (TEC) of the ionosphere using GPS data of single-frequency measurements. This is considered by the example of registering the time behavior of the oblique TEC during the 20 March 2015 solar eclipse. As the initial data, we used single-frequency and dual-frequency phase and code measurements from the station MORP which is a part of the International IGS Network. As a result, by comparing the data of TEC time courses for two modes it is shown both qualitative agreement (TEC significant decrease during the eclipse) and quantitative agreement of results after appropriate treatment.

In the past few years, precise point positioning (PPP) has become an important positioning method for many practical applications. It is based on ionosphere-free carrier phase combination measurements, in which only first-order ionospheric error is removed. Past research has shown that high-order ionospheric effect can affect PPP performance. In this study, the effect of high-order ionospheric error, the second-order one, on PPP has been evaluated in Hong Kong, a low latitude area. First, a method regarding how to calculate second-order ionospheric error is introduced and the evaluation method is also discussed. After that, the numerical results are shown. Based on the results, it is found that the effect of the second-order ionospheric error on ionosphere-free carrier phase combination measurements reached up to the cm level in 2001 and the effect of the second-order ionospheric error on both kinematic and static PPP also reached the cm level. Further, it is also demonstrated that the effect of second-order ionospheric error on PPP is closely related to solar activity.

The data, obtained for the first time, permit the conclusion to be drawn, with a high degree of probability, that large meteors similar to the Chelyabinsk meteor, while entering the Earth’s atmosphere, are able to cause perturbations within the whole ionospheric stratum, rather than only at the sporadic Es layer altitudes, as previously thought.

This paper presents the results of modeling the ionospheric effect of the seismogenic electrostatic field (SEF) seen at the earth’s surface as a perturbation of the vertical atmospheric electrostatic field in the earthquake preparation zone. The SEF distribution at ionospheric altitudes is obtained as an analytical solution of the continuity equation for the electric current density. It is shown that at night, the horizontally large scale SEF can efficiently penetrate into the ionosphere and produce noticeable changes in the horizontal distribution of the F region electron density. The results suggest that the seismogenic electrostatic field could be a possible source for the ionospheric variations observed over Taiwan before the strong Chi Chi earthquake of September 21, 1999.

The electric field strength of three broadcasting stations - CLT (189 kHz, Sicily, Italy), MCO (216 kHz, France) and of CZE (270 kHz, Czech Republic) - has been monitored since 1997 with a sampling frequency of ten minutes at two sites, named AS and PE, located in the Central Apennines (Central Italy). The strongest seismic activity occurring in Central Italy during the last decade was the 1997–1998 Umbria-Marche seismic sequence; over a period of eight months, seven earthquakes with magnitudes greater than 5.0 occurred. The distances of the epicentres from the radio receivers were over 100 km. Unfortunately, at the PE site there were problems with both the power supply and saturation of the recorded signals so we could not use the data from this receiver in this study. At the AS measurement site, no anomalies were evident in the signals received from the three broadcasting stations before the main seismic event (M=5.9) of September 26, 1997. However, during February 1998, we observed a significant increase in the electric field strength of the CZE broadcasting station. On March 26, 1998 a strong earthquake (M=5.5) occurred in the same zone, starting the final phase of the Umbria-Marche seismic sequence. The seismic sequence was shallow with focal depths ranging from 1 km to a maximum of 10 km; on the contrary the March 1998 earthquake was unusual because of its great focal depth (∼ 50 km). The path from the CZE station to the receiver crosses the epicentral zone so it is possible that the increase in signal strength detected could be a precursor of the March 1998 earthquake, possibly related to an ionospheric effect. On the basis of a single observation, however, one can only tentatively suggest this as a precursor.

The ionosphere is the main error source in GNSS measurements and in extreme cases can degrade the positioning significantly, with errors exceeding 100 m; therefore, modelling and predicting of this type of error is crucial and critical. The ionospheric effect can be reduced using different techniques, such as dual-frequency receiver or suitable augmentation system (DGPS, SBAS); the aforesaid approaches involve the use of expensive devices and/or complex architectures. Single frequency stand-alone receivers are the cheapest and most widespread GNSS devices; they can estimate and partially correct the error due to the ionosphere, through adequate algorithms, which use parameters broadcasted by the navigation message. The aim of this paper is performance assessment of the ionospheric model NeQuick, adopted by the European GNSS Galileo for single frequency receivers. The analysis is performed in measurements domain and the data are collected in different geographical locations and in various geomagnetic conditions.

Many GPS networks which were initially surveyed with Texas Instruments TI-4100 receivers have now been resurveyed with mixtures of TI-4100 and Trimble 4000 receivers or exclusively with Trimble receivers. In order to make confident tectonic interpretation of displacements observed between such surveys, it is necessary to understand any biases which may be introduced by using different receiver types or by mixing receivers within a network. Therefore, one of the primary objectives of the Ecuador 1990 GPS campaign (February 1990) was to provide a direct long baseline comparison between the TI-4100 and Trimble 4000SDT GPS receivers. p ]During this campaign, TI and Trimble receivers were co-located at each end of a 1323 kilometer baseline (Jerusalen to Baltra). Solutions for this baseline show no variation with receiver type. Zero-length baseline solutions showed no evidence for any intrinsic bias caused by mixing the two receiver types. Short baseline solutions indicate a bias of -34±10 mm in the baseline vertical component; the sign of the bias indicates that either the assumed phase center location for the TI is too low or the assumed location for the Trimble is too high. The bias is explainable if the phase centers of the Trimble SDT and SST antennas are similarly located. p ]Solutions for baselines measured with codeless receivers (such as the Trimble) should be as precise as those for baselines measured with P-code receivers (such as the TI) as long as it is possible to resolve ambiguities. Resolution of the widelane ambiguity is the limiting factor in ambiguity resolution with any codeless receiver, and in the February 1990 campaigns it was not successful fore baselines longer than 100 km. Without explicit modeling of the ionospheric effect on the widelane, ambiguity resolution with codeless receivers will not be successful for baselines longer than about 100 km, depending on the local ionospheric conditions.

The Mean Solar Magnetic Field (MSMF) measured daily by ground based observations at the Standford Observatory shows similar structures like the Interplanetary Magnetic Field (IMF) near the Earth about 5 to 7 days later. The ionospheric effect in the mid-latitude F2-region due to such MSMF changes is most marked for strong MSMF changes from anti to pro sectors. The mean ionospheric response is very similar to the results obtained earlier with IMF sector structure data derived from Svalgaard (1976) and Wilcox (1982, private communication). Therefore, the MSMF data can successfully be used to predict the mean IMF sector structure and the mean ionospheric response 5 to 7 days in advance.

In an earlier paper ( Green and Hamilton , J. atmos. terr. Phys. 40 , 1223, 1978), we reported on a preliminary analysis of six months' magnetic data from the conjugate stations St. Anthony and Halley Bay, which showed indications of a seasonal variation in the phase differences between Pi2 magnetic pulsations recorded simultaneously at the two stations. We tentatively attributed this behaviour to the different seasonal variation of the ionospheres above the two stations. In this present paper we are able to extend our analysis using 21 months magnetic data, and simultaneous ionospheric data from the Halley Bay station. We confirm the seasonal variation, and from further analysis suggest that it results from an asymmetric damping of the Pi2 signals when the ionospheric boundary conditions at the conjugate stations are not the same.

The effects of geomagnetic activity on F -region ionization are investigated by calculating correlations between F -region parameters and the Kp -index, including delays of up to 33 hours. At Kingston, Jamaica, total electron content values are used, while at Ottawa, Churchill and Resolute Bay tabulated values of foF 2 are subjected to correlation. The correlations are evaluated for each hour of the day in groups of two months so that seasonal variations can also be detected. Results indicate that it may be possible to separate geomagnetic effects according to whether the lag between Kp and the ionospheric effect is short (0–6 h), medium (9–18 h), or long (21–30 h). The various processes which might correspond to these categories are discussed and applied to the results from the four stations mentioned above.

In this paper, the author has used the superposed-epoch method to study the geomagnetic effect caused by the large sunspots with areas greater than 1000 millionths of the sun's disc. The results show that the geomagnetic activity caused by the large sunspots on the northern hemisphere is larger than that caused by those on the southern one: i.e. asymmetrical geomagnetic effects caused respectively by the northern and the southern sunspots exist. The same method was used to study the ionospheric effect of the large sunspots. The results show that the ƒ 0 F2 corresponding to the sunspots which appeared on the northern hemisphere is, contrary to the case of the geomagnetic activity, smaller than that corresponding to the sunspots which appeared on the southern hemisphere. Reasons for such an asymmetry were not well known; however, one of the possible reasons for the smaller value of ƒ 0 F2 for the northern sunspots than that for the southern ones seems to be explainable as the result that the geomagnetic activity caused by the northern sunspots is larger than that caused by the southern ones.