Ionosphere Disturbances Preceding Earthquakes according to the Data of Ground Based Station of the Vertical Ionospheric Sounding Wakkanai

The paper analyzes the data of manual ionograms processing of hourly measurements of the critical frequency foF2 of the F2 ionospheric layer at the Wakkanai ionospheric vertical sounding station (Japan) in a geomagnetically quiet environment before a series of earthquakes with magnitude M > 6.0, for which the station entered the earthquake preparation zone, in order to detect possible Ionospheric Disturbances Preceding Earthquakes (IDPE), and to determine their quantitative characteristics. Detected IDPE, in the opinion of the authors, can be related to the processes of preparation of the corresponding earthquakes, i.e., to be Ionospheric Precursors of Earthquakes (IPE).     

Estimation of the Ionospheric Effects of Geomagnetic Disturbances Based on Data from Wakkanai Station

Geomagnetism and Aeronomy - Ionosonde measurements of the critical frequency of the ionospheric F2 layer (foF2) at Wakkanai station (Japan) are analyzed with the method of superposed epochs. The...     

Anomalous increase in the foF2 critical frequency prior to the Spanish earthquake of May 11, 2011

A study of variations in the critical frequency of the F2 layer (foF2) prior to a shallow-focus eartquake with a magnitude M = 5.1 which occurred in Spain on May 11, 2011, is carried out. The obtained results show that a positive disturbance in the foF2 value was observed at the ionospheric Del’ebre station, which is the closest to the earthquake epicenter. At the same time, no disturbances in foF2 are revealed at ionospheric stations located at a greater distance from the epicenter. This fact makes it possible to conclude that the positive disturbance in the F2 layer observed at the Del’ebre station could have a sesmogenic nature.     

Variations of the critical frequency <Emphasis Type="Italic">foF</Emphasis>2 at middle latitudes during strong disturbance in the electric field observed in the <Emphasis Type="Italic">F</Emphasis> region over saint-santin

Morphological analysis of variations of the critical frequency foF2 in the midlatitude ionosphere at various sectors of local time is carried out on the basis of data from ground-based stations of vertical sounding of the ionosphere in the period when during use of the incoherent scatter radar at Saint-Santin an anomalously strong increase in the electric field was observed at heights of the ionospheric F region in the period of enhanced geomagnetic activity (4+ < Kp < 6−). The obtained picture of the space-time distribution of disturbances in foF2 makes it possible to assume that they could be caused by penetration to middle latitudes of the large-scale electric field of the magnetospheric convection directed westward in the nighttime and morning hours and eastward in the noon and evening sectors.     

Comparative analysis of disturbances in the midlatitude ionospheric F 2 layer during strong and extreme magnetic storms in March 2001 according to the data from magnetically conjugate ground ionospheric stations

Ionospheric disturbances at heights of the F ₂ layer maximum during the strong magnetic storm (the minimum value of the Dst index was ?149 nT) and the magnetic superstorm (the minimum value of the Dst index was ?387 nT) have been compared based on the data from two pairs of magnetically conjugate midlatitude ground stations for ionospheric vertical sounding. The storms began on March 19, 2001, and March 31, 2001, respectively. It has been obtained that almost only negative ionospheric disturbances were observed in the Northern and Southern hemispheres in both cases. The maximum effect in changes in the layer critical frequency (foF2) in both hemispheres has a time delay relative to the moment of the maximum disturbance in the Dst index on the order of 3–4 h for the strong storm and about 1 h for the superstorm. The disturbed variations in the foF2 critical frequency in different hemispheres correlate well with each other in the plane of one magnetic meridian, but the correlation substantially weakens at different magnetic longitudes. An assumption is made that the revealed features of the behavior of the disturbed midlatitude ionospheric F ₂ layer are caused by the complex character of the thermospheric response to the energy release in the auroral zone during the considered magnetic storms.     

Ionospheric precursor of a destructive earthquake that occurred on April 6, 2009 at L’Aquila (Italy)

On the basis of the 15-min data from a series of ground-based vertical ionospheric sounding stations, a study of variations of the foF2 critical frequency before the strong earthquake (M = 6.3) that occurred on April 6, 2009 at L’Aquila (Italy) was carried out. The earthquake epicenter was located 85 km north-eastward from Rome. Approximately 20 h prior to the earthquake, a well-pronounced statistically significant effect of foF2 increase relative to the average background for magnetically quiet days was observed for almost 1.5 h at the Rome ionospheric station. In this case, at control stations distanced from the earthquake epicenter, no statistically significant deviations of foF2 from the background values were detected during the same observations period. This fact provides grounds for consideration of the foF2 increase observed at Rome station as a possible ionospheric precursor of this earthquake.     

New Parameter for Analysis of Ionospheric Disturbances and the Search for Ionospheric Precursors of Earthquakes Based on Barbier’s Formula

Geomagnetism and Aeronomy - A new relative parameter (δBarbier) is proposed for the analysis of ionospheric disturbances and the search for ionospheric precursors of earthquakes. The parameter...     

Estimation of a Tropospheric Electric Field Associated with the African Zone of Thunderstorm Activity that Penetrates the Ionosphere

Geomagnetism and Aeronomy - The penetration of the nighttime ionosphere by electric fields in the African zone of thunderstorm activity is studied based on calculations. These fields are caused by...     

Comparison of variations in the <Emphasis Type="Italic">F</Emphasis>2 layer critical frequency before the strong Italian earthquakes and during the magnetic storm: Data of the stations for ground-based vertical sounding of the ionosphere

The possible seismic ionospheric effects before two strong earthquakes in Italy, which took place near Rome station (January 7, 1962, M = 6.0; April 5, 1998, M = 5.3), have been studied using the data of several European stations for ground-based vertical sounding of the ionosphere. An analysis of the behavior of the foF2 critical frequencies for the earthquake that occurred on January 7, 1962, made it possible to simultaneously consider the effects, originating during earthquake preparation under quiet geomagnetic conditions and caused by the magnetic strom that began on January 10, 1962, using a unified technique. It has been indicated that the distinguished precursor effects of two considered earthquakes with magnitudes not more than 6.0 are localized in the region with an epicentral distance of about 400 km, whereas the disturbances caused by the magnetic storm are of a planetary character. The amplitude of foF2 seismic ionospheric disturbances is much smaller than the maximal variations caused by the magnetic storm; however, the absolute value of this amplitude is a factor of 1.5 as large as the standard deivation from the monthly median.     

Anomalous variations in the foF2 critical frequency above Japan prior to the earthquake of March 9, 2011

Based on data from the Japanese Kokubunji and Wakkanai stations of vertical sounding of the ionosphere, the variations in the foF2 critical frequency prior to the strong earthquakes of March 9 and 11, 2011 (M 7.2 and 9.0, respectively), are analyzed. It is found that significant positive disturbances of foF2 had been recorded approximately one day before the first earthquake. Notably, at the Irkutsk reference station, which is located about 3300 km from the earthquake epicenters, there were no significant disturbances of foF2. This suggests that the effects of increased foF2, observed at the Kokubunji and Wakkanai stations, were probably caused by the earthquake preparation processes. The seismo-ionospheric manifestations of the stronger earthquake on March 11, 2011, even if they took place, were hidden by the geomagnetic storm’s effects.