Characterisation of ionospheric TEC variations over the equatorial and polar regions during solar cycle 24

The TEC variations in the equatorial and polar region are known to be high compared to the mid latitude region. Investigation on ionospheric TEC at individual regions has been carried out by many studies but the investigation between these regions simultaneously is still lacking. TEC values from Libreville (NKLG), Gabon (0.4162°N, 9.4673°E), and Ny-Alesund (NYA1), Norway (78.9235°N, 11.9099°E), each representing equatorial and polar station, respectively, are obtained for the year 2009, 2011, and 2013 to observe their TEC behaviors. The diurnal and seasonal variations of TEC and geomagnetic effects on TEC variations are analyzed for both stations. Besides, the rate of TEC change, K, is obtained to relate the TEC variations between these locations simultaneously. The pseudo-TEC measurement measured by dual frequency GPS which can be obtained from IGS server, is used to calculate vertical TEC. The ranges of maximum diurnal TEC at NKLG and NYA1 station is 23-114 TECU and 8-55 TECU, respectively. The seasonal TEC peak at both stations encountered the highest TEC at equinoctial months and the lowest value at solstitial months. However, in 2009, the seasonal TEC showed the highest and lowest TEC peak, both at equinoctial months at NYA1 station. During geomagnetic days, the enhancement percentages of TEC are found on 22 July 2009 and 17 March 2013 at NKLG station, and 22 July 2009 and 25 October 2011 at NYA1 station. The decrement percentage of TEC observed on 25 October 2011 and 17 March 2013 at NKLG and NYA1 station, respectively. The rate of TEC change shows a same definite pattern over all the years. It can be concluded that the hourly maximum TEC values at NKLG station fell within 0.4-1.9 times larger than that NYA1 station. This study helps to have more understanding of the unique characteristics at the equatorial and polar ionosphere

Real-time detection of tsunami ionospheric disturbances with a stand-alone GNSS receiver. A preliminary feasibility demonstration

It is well known that tsunamis can produce gravity waves that propagate up to the ionosphere generating disturbed electron densities in the E and F regions. These ionospheric disturbances can be studied in detail using ionospheric total electron content (TEC) measurements collected by continuously operating ground-based receivers from the Global Navigation Satellite Systems (GNSS). Here, we present results using a new approach, named VARION (Variometric Approach for Real-Time Ionosphere Observation), and estimate slant TEC (sTEC) variations in a real-time scenario. Using the VARION algorithm we compute TEC variations at 56 GPS receivers in Hawaii as induced by the 2012 Haida Gwaii tsunami event. We observe TEC perturbations with amplitudes of up to 0.25 TEC units and traveling ionospheric perturbations (TIDs) moving away from the earthquake epicenter at an approximate speed of 316 m/s. We perform a wavelet analysis to analyze localized variations of power in the TEC time series and we find perturbation periods consistent with a tsunami typical deep ocean period. Finally, we present comparisons with the real-time tsunami MOST (Method of Splitting Tsunami) model produced by the NOAA Center for Tsunami Research and we observe variations in TEC that correlate in time and space with the tsunami waves

Ionospheric effects of the solar flares of September 23, 1998 and July 29, 1999 as deduced from global GPS network data

This paper presents data from first GPS measurements of global response of the ionosphere to solar flares of September 23, 1998 and July 29, 1999. The analysis used novel technology of a global detection of ionospheric effects from solar flares (GLOBDET) as developed by one of the authors (Afraimovich E. L.). The essence of the method is that use is made of appropriate filtering and a coherent processing of variations in total electron content (TEC) in the ionosphere which is determined from GPS data, simultaneously for the entire set of visible (over a given time interval) GPS satellites at all stations used in the analysis. It was found that fluctuations of TEC, obtained by removing the linear trend of TEC with a time window of about 5 min, are coherent for all stations and beams to the GPS satellites on the dayside of the Earth. The time profile of TEC responses is similar to the time behavior of hard X-ray emission variations during flares in the energy range 25-35 keV if the relaxation time of electron density disturbances in the ionosphere of order 50-100 s is introduced. No such effect on the nightside of the Earth has been detected yet.Comment: EmTeX-386, 13 pages, 5 figure

Effects of Ionospheric Asymmetry on Electron Density Standard Inversion Algorithm Applicable to Radio Occultation (RO) Data Using Best-suited Ionospheric Model

The "Onion-peeling" algorithm is a very common technique used to invert Radio Occultation (RO) data in the ionosphere. Because of the implicit assumption of spherical symmetry for the electron density (Ne) distribution in the ionosphere, the standard Onion-peeling algorithm could give erroneous concentration values in the retrieved electron density vertical profile Ne(h). In particular, this happens when strong horizontal ionospheric electron density gradients are present, like for example in the Equatorial Ionization Anomaly (EIA) region during high solar activity periods. Using simulated RO Total Electron Content (TEC) data computed by means of the best-suited ionospheric model and ideal RO geometries, we evaluated the asymmetry level index for quasi-horizontal TEC observations. This asymmetry index is based on the Ne variations that a signal may experience along its ray-path (satellite to satellite link) during a RO event. The index is strictly dependent on RO geometry and azimuth of the occultation plane and is able to provide us indication of the errors (in particular those concerning the peak electron density NmF2 and the vertical TEC) expected in the retrieval of Ne(h) using standard Onion-peeling algorithm. On the basis of the outcomes of our work, and using best-suited ionospheric model, we will try to investigate the possibility to predict the ionospheric asymmetry expected for the particular RO geometry considered. We could also try to evaluate, in advance, its impact on the inverted electron density profile, providing an indication of the product qualit