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Ionospheric TEC (Total Electron Content) variations prior to the deep (≈600 km) earthquake doublet close to magnetic equator in Peru ( M = 7.6) and to the intermediate (≈200 km) earthquake in Afghanistan ( M = 7.5) during 2015 were investigated using measurements from Global Navigation Satellite System (GNSS) network with the aim to detect possible ionospheric precursors of these events. For this we applied both statistical and spectral analysis. Ionospheric anomalies related to both earthquakes were observed few hours and few days prior to the earthquakes during daytime localized mainly near the epicenter. These were large-scale positive TEC anomalies and small-scale TEC oscillations with periods of 20 min and duration around 2–4 h appearing at the same local time each day. Several days prior to the earthquake in Peru a significant phenomenon was observed during afternoon time related to the modification of the Equatorial Ionization Anomaly (EIA) structure. During nighttime, however, it was not possible to identify any ionospheric earthquake precursor due to the concurrence of various phenomena, such as Equatorial Plasma Bubbles and pre- and post-midnight TEC peaks prior to Peru earthquake, and solar terminator transition prior to both earthquakes which could induce resembling ionospheric anomalies. [ABSTRACT FROM AUTHOR]

Abstract: Electric fields have been determined at three longitudes corresponding to Peru, India, and the Philippines. We compare these fields to applying a frequency-dependent linear transfer function (TF) to the dawn-to-dusk component of the interplanetary electric field (IEF). The TF is based on four years of simultaneous observations of the IEF and equatorial data. The model gives good results for the prompt penetrating electric field (PPE) in the case of an oscillatory IEF with a period in the 1–2h range, when the interplanetary magnetic field remains southward for a long period and, to a lesser extent, when the IEF can be described as a square wave. There is evidence that a disturbance dynamo (DD) effect contributes on the dayside, where it leads to suppression of the normal quiet time pattern. A very strong counter-electrojet was seen at two locations during a time of persistent south and was not predicted by the model or a linear scaling of the IEF. This suggests that suppression (and even reversal) of the E-region dynamo can occur in a large storm. Both the data and the model yielded a long-lived response to a sustained southward interplanetary magnetic field. Previously suggested effects on equatorial electric fields are confirmed by a sequence of three distinct spikes in the component of the IMF, one of which had no associated change and yet was reproduced by two independent ground magnetometer-based electric field determinations. The sometimes remarkable agreement of a linear relationship between the equatorial and interplanetary electric fields shown here and elsewhere remains somewhat mysterious for such an apparently complex system. [Copyright &y& Elsevier]

Abstract: During the main phase of large magnetic storms significant energy can be deposited in the ionosphere but produce no commensurate magnetic perturbations on the ground. Consequently, models designed to predict and specify thermospheric energy budgets based on ground magnetic data are negatively impacted. To quantify these effects we compare thermospheric densities predicted by the MSIS model with those inferred from accelerometer measurements by the Gravity Recovery and Climate Experiment (GRACE) satellites during two magnetic storm periods in 2004. Although predictions and measurements are in substantial agreement during quiet times, the model significantly underpredicts densities during storms. Also, the model''s maxima occur several hours after observed stormtime peaks. We show that polar cap potentials and magnetospheric electric fields derived from interplanetary parameters measured by the Advanced Composition Explorer satellite are roughly proportional to neutral densities observed by GRACE with lead times of ∼4h. Finally, ion drift meter data from Defense Meteorological Satellite Program spacecraft suggest that unpredicted positive and negative spikes found in high latitude accelerometer data reflect encounters with strong head and tail thermospheric winds driven by anti-sunward convecting plasma. [Copyright &y& Elsevier]