Features of the Ionospheric Total Electronic Content Response to the Annular Solar Eclipse of June 21, 2020

Geomagnetism and Aeronomy - The features of the annular solar eclipse of June 21, 2020, in variations of the ionospheric total electron content (TEC) were analyzed using GPS observations of the IGS...     

Approaches to studying the multiscale ionospheric structure using nanosatellites

Permanent variation in parameters affecting the key characteristics of the auroral ionosphere hinders the creation of a sufficiently accurate model for practical application within classical approaches describing quasi-stationary phenomena. The fractal approach for describing the properties of plasma in the auroral region has the following advantages: the results are versatile and the emergence of self-similar structures is nature-independent. Due to the self-similarity and fractality of ionospheric structures, it will suffice to have a few measurements within a characteristic scale; therefore, it is necessary to obtain a series of simultaneous measurements at intervals of tens of meters to tens of kilometers to describe the spatial and temporal distribution of inhomogeneities in the ionospheric plasma. Small and relatively low-cost satellites (the socalled cubesats) are supposed to be used to check whether the fractal approach can be applied to study the inhomogeneous structure of the ionosphere, including with artificial heating. The satellites should be located at different distances from each other to span the scales ranging from the inertial length of electrons to the inertial length of O⁺ ions. For each satellite, it is supposed to measure the variations in plasma density and electric and magnetic fields.     

Ionospheric electron density observed by FORMOSAT-3/COSMIC over the European region and validated by ionosonde data

This research is motivated by the recent IGS Ionosphere Working Group recommendation issued at the IGS 2010 Workshop held in Newcastle, UK. This recommendation encourages studies on the evaluation of the application of COSMIC radio occultation profiles for additional IGS global ionosphere map (GIM) validation. This is because the reliability of GIMs is crucial to many geodetic applications. On the other hand, radio occultation using GPS signals has been proven to be a promising technique to retrieve accurate profiles of the ionospheric electron density with high vertical resolution on a global scale. However, systematic validation work is still needed before using this powerful technique for sounding the ionosphere on a routine basis. In this paper, we analyze the properties of the ionospheric electron density profiling retrieved from COSMIC radio occultation measurements. A comparison of radio occultation data with ground-based measurements indicates that COSMIC profiles are usually in good agreement with ionosonde profiles, both in the F2 layer peak electron density and the bottom side of the profiles. For this comparison, ionograms recorded by European ionospheric stations (DIAS network) in 2008 were used.     

Response of the ionosphere to the Baltic Sea earthquake of 21 September 2004

GPS observations of the European permanent network were used to identify seismo-ionospheric precursors of Baltic Sea earthquake of 21 September 2004. It is a very rare event for this region of Europe (magnitude of about 5.0). This value is the threshold for the occurrence of seismic effects in the ionosphere. In total electron content (TEC) data over the region of the earthquake, a specific ionospheric anomaly appeared one day before the earthquake was detected. The ionospheric variability had a positive sign with an enhancement of about 4–5 TECU (1 TECU = 10¹⁶ electrons/m²) relative to the non-disturbed state of the ionosphere. The anomaly had a duration of 4–5 hours in the day time. The special size of this anomaly was about 1000 km. The characteristic parameters of the anomaly show that it can be associated with ionospheric precursors of an earthquake.     

Features of the ionosphere behavior before the Kythira 2006 earthquake

In this paper we present specific features of TEC (total electron content of the ionosphere) behavior as possible precursors of Kythira (Southern Greece) earthquake of January 8, 2006 (M6.8). For this purpose, we used both the TEC data of GPS-IGS stations nearest to the epicenter, and TEC maps over Europe. The favorable circumstance for this analysis was the quiet geomagnetic situation during the period prior to the earthquake. One day before the earthquake, a characteristic anomaly was found out as the day-time significant increase of TEC at the nearest stations, up to the value of 50% relative to the background condition. To estimate the spatial dimensions of seismo-ionospheric anomaly, the differential mapping method was used. The ionosphere modification as a cloud-like increase of electron concentration situated in the immediate vicinity of the forthcoming earthquake epicenter has been revealed. The amplitude of modification reached the value of 50% relative to the non-disturbed condition and was in existence from 10:00 till 22:00 UT. The area of significant TEC enhancement had a size of about 4000 km in longitude and 1500 km in latitude.     

Physical mechanism and mathematical modeling of earthquake ionospheric precursors registered in total electron content

The physical mechanism by which the regions with increased or decreased total electron content, registered by measuring delays of GPS satellite signals before strong earthquakes, originate in the ionosphere has been proposed. Vertical plasma transfer in the ionospheric F ₂ region under the action of the zonal electric field is the main disturbance formation factor. This field should be eastward, generating the upward component of plasma electromagnetic drift, in the cases of increased total electron content at midlatitudes and deepened minimum of the F ₂ layer equatorial anomaly. Upward plasma drift increases electron density due to a decrease in the O⁺ ion loss rate at midlatitudes and decreases this density above the equator due to an enhancement of the fountain effect (plasma discharge into the equatorial anomaly crests). The pattern of the spatial distribution of the seismogenic electric field potential has been proposed. The eastward electric field can exist in the epicentral region only if positive and negative electric charges are located at the western and eastern boundaries of this region, respectively. The effectiveness of the proposed mechanism was studied by modeling the ionospheric response to the action of the electric field generated by such a charge configuration. The results of the numerical computations indicated that the total electron content before strong earthquakes at middle and low latitudes is in good agreement with the observations.     

Physical interpretation and mathematical simulation of ionospheric precursors of earthquakes at midlatitudes

The paper presents the results of studying anomalous variations in the total electron content (TEC) of the ionosphere as probable precursors of strong seismic events. The vertical drift of the F2 layer’s ionospheric plasma under the effect of seismically generated zonal electric field is considered as a likely reason for the observed variations in the TEC. An estimation of this drift effects is made by mathematical simulation utilizing the global numerical model of the Earth’s upper atmosphere (UAM). Midlatitude ionospheric effects were simulated. Two types of seismogenerated electric fields (dipole and monopole) were used with various magnitudes and spatial configurations. The derived results were compared with the TEC data of GPS observations from the IGS for the Kitira earthquake in southern Greece (January 8, 2006; M 6.8). It was shown that variations generated by additional sources of the dipole type are consistent with the observed data; monopole-type sources did not reproduce some typical peculiarities of these observations and systematically underestimated the deviation value.     

Features of High-Latitude Ionospheric Irregularities Development as Revealed by Ground-Based GPS Observations,Satellite-Borne GPS Observations and Satellite In Situ Measurements over the Territory of Russia during the Geomagnetic Storm on March 17–18, 2015

The dynamic picture of the response of the high- and mid-latitude ionosphere to the strong geomagnetic disturbances on March 17–18, 2015, has been studied with ground-based and satellite observations, mainly, by transionospheric measurements of delays of GPS (Global Positioning System) signals. The advantages of the joint use of ground-based GPS measurements and GPS measurements on board of the Swarm Low-Earth-Orbit satellite mission for monitoring of the appearance of ionospheric irregularities over the territory of Russia are shown for the first time. The results of analysis of ground-based and space-borne GPS observations, as well as satellite, in situ measurements, revealed large-scale ionospheric plasma irregularities observed over the territory of Russia in the latitude range of 50°–85° N during the main phase of the geomagnetic storm. The most intense ionospheric irregularities were detected in the auroral zone and in the region of the main ionospheric trough (MIT). It has been found that sharp changes in the phase of the carrier frequency of the navigation signal from all tracked satellites were recorded at all GPS stations located to the North from 55° MLAT. The development of a deep MIT was related to dynamic processes in the subauroral ionosphere, in particular, with electric fields of the intense subauroral polarization stream. Analysis of the electron and ion density values obtained by instruments on board of the Swarm and DMSP satellites showed that the zone of highly structured auroral ionosphere extended at least to heights of 850–900 km.     

Ionospheric Effects of Solar Flares in September 2017 and an Evaluation of Their Influence on Errors in Navigation Measurements

Geomagnetism and Aeronomy - The manifestation of the most powerful flares of class X9.3 and X8.2 recorded on September 6 and 10, 2017, respectively, in the total electronic content (TEC) of the...