GIM-TEC Data Research Articles

The correlation study between EIA north crest in the south Asia region and strong earthquakes

Paying attention to the relationship between EIA signatures and earthquakes can be useful to further understand the earthquake anomalies and seismo-ionospheric coupling mechanism. Based on the GIM TEC data, the EIA north crest signature in the south Asia region was investigated for 92 M ≥ 6.0 earthquakes from 1999 to 2022. A running mean method was utilized to extract the anomalies potentially associated with earthquakes. It was found that before the strong earthquakes, the EIA north crest significantly moves equatorward, and the formation time of the crest appears earlier than that in normal days. The TEC strength of EIA north crest can both increase or decrease prior to earthquakes. The results in this study further imply that the abnormal electric field formed around the epicenter is potential the main channel of Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) mechanisms during the earthquake preparation period.

Investigation of GIM-TEC disturbances before M\u2009\u2265\u20096.0 inland earthquakes during 2003\u20132017

With the rapid development of the Global Navigation Satellite System (GNSS) and its wide applications to atmospheric science research, the global ionosphere map (GIM) total electron content (TEC) data are extensively used as a potential tool to detect ionospheric disturbances related to seismic activity and they are frequently used to statistically study the relation between the ionosphere and earthquakes (EQs). Indeed, due to the distribution of ground based GPS receivers is very sparse or absent in large areas of ocean, the GIM-TEC data over oceans are results of interpolation between stations and extrapolation in both space and time, and therefore, they are not suitable for studying the marine EQs. In this paper, based on the GIM-TEC data, a statistical investigation of ionospheric TEC variations of 15 days before and after the 276 M ≥ 6.0 inland EQs is undertaken. After eliminating the interference of geomagnetic activities, the spatial and temporal distributions of the ionospheric TEC disturbances before and after the EQs are investigated and compared. There are no particularly distinct features in the time distribution of the ionospheric TEC disturbances before the inland EQs. However, there are some differences in the spatial distribution, and the biggest difference is precisely in the epicenter area. On the other hand, the occurrence rates of ionospheric TEC disturbances within 5 days before the EQs are overall higher than those after EQs, in addition both of them slightly increase with the earthquake magnitude. These results suggest that the anomalous variations of the GIM-TEC before the EQs might be related to the seismic activities.

The performance of the IRI-Plas model as compared with Alouette II and GIM-TEC data over the midlatitude station Alma-Ata

Climatic ionospheric models present an important medium for both investigation of physical structure and correction of detrimental effects of ionospheric variability on space based communication, navigation and positioning systems. International Reference Ionosphere Extended to Plasmasphere (IRI-Plas) is one of the empirical models that can provide ionospheric layer parameters and electron density profiles up to GPS satellite orbital height of 20,200 km. IRI-Plas can input not only F2 layer critical parameters, foF2 and hmF2, but also the Total Electron Content (TEC) values. In this study, Ne(h)-profiles and TEC values obtained from the IRI-Plas model are compared with topside Alouette II satellite profiles and Global Ionospheric Map (GIM) TEC values, respectively. The satellite Ne(h) profiles are averaged over a midlatitude region for various seasons of 1966 and 1969. It is observed that IRI-Plas is in good agreement with Alouette profiles between 300 km and 500 km. After 500 km up to 2000 km, the profiles seem to differ where IRI-Plas Ne(h) usually overestimates the Alouette profile. When IRI-Plas TEC is compared with GIM-TEC, it is observed that model TEC generally overestimates the GIM-TEC values during daytime hours. The lowest ΔTEC values (10–20%) are observed in March and September, and the highest values are observed in the months of January (around 30%) and July (up to 67%). During nighttime, the IRI-Plas model results mainly underestimate the observational ones, up to 30% in equinoctial months, and with ±10% discrepancies in January and July. Since the IRI-Plas model can scale foF2 and hmF2 values using an external TEC input by equating instantaneous and median slab thickness (TEC/NmF2 ratio), the correlation between GIM-TEC and ionosonde NmF2 values measured at the midlatitude station Alma-Ata located at [43.25°N, 76.92°E] is obtained for various seasons during 1999, 2000, 2008, 2009 and 2012. The study showed a positive correlation for all seasons and levels of solar activity. The correlation coefficients between the data sets were very high (greater than or equal to 0.79) for hourly data and (greater than or equal to 0.91) for monthly-medians at a significance level of 5%. Thus, for the practical applications, the correlation results can be used to update slab thickness model of IRI-Plas which will lead to better scaling of foF2 and hmF2 values and plasmaspheric Ne(h)-profile with external instantaneous TEC input.

Study of ionospheric precursors using GPS and GIM-TEC data related to earthquakes occurred on 16 April and 24 September, 2013 in Pakistan region

In this paper, we have examined the diurnal variations of GPS-TEC observed at two Indian stations of Agra (27.2°N, 78°E) and Surat (21.16°N, 72.78°E) and global ionospheric maps data (GIM-TEC) for the months of April and September 2013 in search of ionospheric precursors of three major earthquakes (M>6.5) that occurred in these months. The well-established quartile based statistical technique is adopted for the analysis of TEC data. The results show two kinds of anomalies, one in which simultaneous enhancements in TEC occurred in the three sets of data, 1–9days and 3days before the main shock in the two months respectively, and another in which anomalies occurred 15days before in April, and 21days before in September at Surat respectively. The depletions have also been found in three data sets but they are not significant. These anomalies are unlikely be influenced by geomagnetic parameters due to quiet magnetic conditions. The effect of also solar activity have also been considered and examined very precisely. The results are interpreted in terms of Lithosphere-Atmosphere-Ionosphere coupling (LAIC) mechanisms available in the literature.

Ionospheric anomalies possibly associated with M ⩾ 6.0 earthquakes in the Japan area during 1998–2010: Case studies and statistical study

In this paper, we examine pre-earthquake ionospheric anomalies in time series and perform a statistical test by using total electron content (TEC) derived from global ionosphere maps (GIM) around the Japan area for the first time. The normalized GIM-TEC (GIM-TEC *), which is computed based on 15 days backward running mean of GIM-TEC, have been investigated for minimizing possible confounding effects of consecutive earthquakes and identify the abnormal signals. Meanwhile, to reduce the effect of strong geomagnetic activities such as geomagnetic storms, the criterion for removing the GIM-TEC data have been adapted; that is when Dst index exceeds −60 nT. Temporal variations of GIM-TEC * for large and destructive earthquakes in Japan have been studied; which are the 2004 mid-Niigata Prefecture Earthquake (M6.8), its aftershock (M6.1), the 2007 offshore mid-Niigata Earthquake (M6.8), and the 2008 Iwate–Miyagi Nairiku Earthquake (M7.2). Although there are some positive and negative TEC anomalies before and after the four earthquakes, there is a tendency that positive TEC anomalies appear 1–5 days before all the above earthquakes even during the quiet geomagnetic condition. Superposed epoch analyses have been performed for the statistical analysis of TEC anomalies associated with M ⩾ 6.0 earthquakes during the 12-year period of May 1998–May 2010. The statistical result indicates the significance of the positive TEC anomalies 1–5 days before earthquakes within 1000 km from the epicenter around Japan.

GPS-based ionospheric corrections for single frequency radar altimetry

The global ionospheric total electron content maps (GIMs) provide integrated electron densities between the ground and the GPS satellite altitude (20,200 km). Satellite altimeter ionospheric delay corrections require integrated electron densities between the ground and altimeter satellite altitude. In the case of the Geosat Follow-On (GFO) spacecraft, flying at 800 km, we estimated that using GIM TEC data alone, up to a 2 cm path delay can be introduced into the GFO measurements for high solar activity period by not taking into account the electron content above this altitude. Furthermore, the GIMs can have errors of 20–30 TECU in low latitudes for high solar activity in areas where there is little GPS data (such as over the oceans). In this paper, we describe the results of ingesting GIM TEC data into the International Reference Ionosphere model (IRI-95) to mitigate these two effects.