TEC variations during low solar activity period (2005–2007) near the Equatorial Ionospheric Anomaly Crest region in India

The dual frequency signals from the GPS satellites recorded at Rajkot (22.29° N, 70.74° E, Geographic, 14.03° N Geomagnetic) near the Equatorial ionization anomaly crest in India have been analyzed to study the ionospheric variations in terms of Total Electron Content (TEC) for the low solar activity period from April 2005 to December 2007. In this study, we describe the diurnal and seasonal variations of TEC, solar activity dependence of TEC and effects of a space weather related event, a geomagnetic storm on TEC. The diurnal variation of TEC shows pre-dawn minimum for a short period of time, followed by a steep early morning increase and then reaches maximum value between 14:00 LT and 16:00 LT. The mean diurnal variations during different seasons are brought out. It is found that TEC at Rajkot is at its maximum during Equinoctial months (March, April, September, October), and minimum during the Winter months (November, December, January, February), with intermediate values during Summer months (May, June, July, August), showing a semi annual variation. TEC values have been decreasing since 2005, onwards showing positive correlation with solar activity. TEC variations during the geomagnetic storm commencing 24 August 2005 with Dst=−216 nT are analysed. TEC shows a positive ionospheric storm effect on the first day of the storm and negative ionospheric storm effect on the next day. The equatorial Electrojet control on the development of the equatorial anomaly is also demonstrated

Ionospheric Signature Recorded on the Hawaii GPS Network of the Mw 6.9 Earthquake and Tsunami

International audienceOn 4 May 2018, a Mw 6.9 earthquake ruptured on the south flank of the Kilauea volcano, Hawaii. The rupture of this largest earthquake in the Hawaii region since 1975 extended offshore and a small tsunami was identified on regional tide gauges. Then we expect a significant shaking of the ionosphere, the ionized layer of the Earth's atmosphere located from 80 km to 2000 km of altitude. This ionization affects Global Positioning System (GPS) signals and these perturbations can be used to image the ionosphere response triggered by large (Mw > 6.5) and shallow earthquakes. Here, we analyze data collected by receivers of the permanent GPS network of Hawaii. While no clear disturbance was detected after the 1 May 2018 crater collapse, we observe clear disturbances in the Total Electron Content (TEC) directly above the rupture area. These fluctuations are consistent with an acoustic wave originating from the rupture area of the earthquake. We investigate the solid/ocean/atmosphere coupling efficiency using a spectral element modeling approach. We then conduct an acoustic ray tracing-based modeling to reconstruct the observed perturbations and relate them to the seafloor static deformation reconstructed using conventional data

Low-latitude ionospheric-thermospheric response to storm time electrodynamical coupling between high and low latitudes

Using multi-instrumental and multistation data, we present low-latitude ionospheric-thermospheric behavior during the geomagnetic storm of 15 May 2005. The diurnal pattern of total electron content (TEC) at a chain of equatorial to low-latitude stations shows strong positive ionospheric storm on 15 May. Latitudinal variation of TEC shows development of strong equatorial ionization anomaly (EIA) on the same day. Evidence, in terms of equatorial electrojet (EEJ) and magnetogram signatures, is presented for the prompt penetration of interplanetary electric field (IEF) as the cause of the positive ionospheric storm. Consequent to the storm time circulation resulting from the extra energy deposition via Joule heating over high latitudes, compositional changes occur in the global thermosphere. TEC enhancements on 16 May are attributed to enhancement of atomic oxygen at equatorial and low latitudes and the negative ionospheric storm on 17 May observed beyond certain low latitudes is explained in terms of enhancement of molecular species because of the storm time neutral composition changes. Strong ESF plume structures on range time intensity (RTI) map and L-band scintillation and TEC depletions in GPS measurements are observed in the longitude sectors where the local time of sudden storm commencement (SSC) falls after the post sunset hours. The ionospheric zonal electric fields are altered by the combined effects of eastward disturbance dynamo electric fields and direct prompt penetration of eastward electric fields associated with the northward turning of interplanetary magnetic field (IMF) B<SUB>z</SUB> leading to subsequent development of ESF after midnight