Inputs received from Ionospheric research groups on activities related with RT global electron content determination

Peer ReviewedPostprint (author’s final draft

Solar flare detection system based on global positioning system data: first results

A solar flare detector has been developed using the Global Positioning System (GPS) capabilities to monitor the ionospheric Total Electron Content (TEC). It is based on obtaining the variation of the vertical TEC data with respect to the previous sidereal day and then, on performing a second order time difference to obtain the information of the instantaneous TEC changes. The detector can be applied looking for solar flares backwards or in real time as well. To make a first assessment of the solar flare detector, several specific days, when there is the certainty that a solar flare had occurred, have been analyzed. The results, which are presented in this work, have been obtained from the X17.2 flare on 28th October, 2003, the X5.7 flare on 14th July, 2000 and the X7.1 flare on 20th January, 2005, using the GPS data of the International GNSS Service (IGS) network with a sampling rate of 30 s. The results obtained are compatible with the results presented previously by different authors, and with the flare records included in the Geostationary Operational Environmental Satellite (GOES) database. In addition, several receivers, located in the southern hemisphere and far from the geomagnetic equator, detect a lower overionization amplitude than other receivers with similar mean solar zenith angle. Moreover, minor disturbances in the TEC enhancement can also be observable and studied.Peer Reviewe

The self organizing map of neighbour stars and its kinematical interpretation

The Self-Organizing Map (SOM) is a neural network algorithm that has the special property ofcreating spatially organized tepresetüatioes of various features of input signals. The resulting maps resemble realneural structures found in the cortices of developed animal brains.: Also, the SOM. has been successful in various pattern recognition tasks involving noisy signals, as for instance, speech recognition and for this reason we are studying its application to some astronomical problems. In this paper w~ present the 2-D mapping and subsequerít study of one local sample of 12000 stars using SOM. The available attributes are 14: 3-D position and velocitiesvphotometric indexes, spectral type and luminosity class. The possible location of halo, thick disk and thin disk stars is discussed. Their kinematical properties are also compared using the velocity distribution moments up to order four.Peer ReviewedPostprint (published version

Global distribution of ionospheric scintillations from the Real-Time GPS ROTI

A global real-time monitoring system has been implemented in the frame of ESA-ESTEC/EGNOS-POfunded project MONITOR. It is based on world-wide GNSS datastreams distributed by means of NTRIP and provides multiple ionospheric indices and products to the scientific community and industry. In particular, the Rate Of Total Electron Content Index (ROTI) proxy, which is correlated with scintillation activity and has been running for several years for real-time detection and monitoring. It shall also be pointed out that the multiple products, also aiming at the identification of Travelling Ionospheric Disturbances (TIDs), Solar Flares overionization, among other ionospheric perturbations, are useful to properly characterize scenarios where these could occur simultaneously to scintillations. In addition, there is also a new proxy suitable for radio-occultation GNSS measurements, named OSPI. In this context, a climatological ionospheric scintillation study has been conducted in different latitudinal regions from the UPC-IonSAT database of global ROTI. For this purpose, we have obtained results from several receivers in 30-degree latitudinal strips and distinguishing between North- and South-Hemisphere locations.Postprint (published version

Models for atmospheric propagation delays

Techniques operated for the realization of the IERS reference systems make use of electromagnetic signals received on the surface of the Earth. During their transit of the atmosphere, the signals experience delays which must be modeled in the analysis software. This chapter presents models for the propagation of optical signals in the troposphere (9.1), for radio signals in the troposphere (9.2) and for radio signals in the ionosphere (9.4). For Doppler techniques which use time- di erenced phases as observables, the models presented in this chapter should be time-di erenced as well.Peer ReviewedPostprint (published version

Teorema astronómico de resistencia y unicidad

Peer Reviewe

Real-time detection, location, and measurement of geoeffective stellar flares from Global Navigation Satellite System Data: new technique and case studies

An alternative approach to detect solar flares and quantify the associated extreme ultraviolet (EUV) solar flux rate was introduced in this journal by the authors: Global Navigation Satellite Systems Solar FLAre Indicator (GSFLAI) was founded on the dependence of the sudden electron content increase of the Earth ionosphere versus the angle regarding the flare source, the Sun, given by a simple but accurate first-principles-based model. Such overionization is directly measured from the dual-frequency phase measurements gathered from hundreds of worldwide permanent receivers of the Global Navigation Satellite Systems, GNSS (like the Global Positioning System GPS), working many of them in real time. In this work we generalize GSFLAI for the very challenging scenario of stellar superflares, with a much weaker expected geoeffectiveness on the Earth ionosphere, making it difficult to distinguish its potential footprint regarding conventional ionospheric variability sources. Indeed, we will show that, unlike GSFLAI for solar flares, the new algorithm presented here (Blind GNSS search of Extraterrestrial EUV Sources [BGEES]) is able to detect EUV flares without the previous knowledge of the position of the source, which is also simultaneously estimated, providing an additional quality check of the detection. It will be first assessed with several case studies of solar flares of different intensities analyzed previously with GSFLAI. Finally, by focusing on the night hemisphere to avoid the Sun's larger effect on the ionosphere, the detection and location with BGEES of two recent stellar superflares, Proxima Centauri (18 March 2016, 08:32UT) and NGTS J121939.5-355557 (1 February 2016, 04:00UT), are presented, strongly suggesting the extension and applicability of the new technique, also in real time.Peer ReviewedPostprint (published version

Electron density retrieval from truncated Radio Occultation GNSS data

This paper summarizes the definition and validation of two complementary new strategies, to invert incomplete Global Navigation Satellite System Radio-Occultation (RO) ionospheric measurements, such as the ones to be provided by the future EUMETSAT Polar System Second Generation. It will provide RO measurements with impact parameter much below the Low Earth Orbiters' height (817 km): from 500 km down approximately. The first presented method to invert truncated RO data is denoted as Abel-VaryChap Hybrid modeling from topside Incomplete Global Navigation Satellite System RO data, based on simple First Principles, very precise, and well suited for postprocessing. And the second method is denoted as Simple Estimation of Electron density profiles from topside Incomplete RO data, is less precise, but yields very fast estimations, suitable for Near Real-Time determination. Both techniques will be described and assessed with a set of 546 representative COSMIC/FORMOSAT-3 ROs, with relative errors of 7% and 11% for Abel-VaryChap Hybrid modeling from topside Incomplete Global Navigation Satellite System RO data and Simple Estimation of Electron density profiles from topside Incomplete RO data, respectively, with 20 min and 15 s, respectively, of computational time per occultation in our Intel I7 PC.Peer ReviewedPostprint (published version

Pulsar-based Navigation

Preprin

ADDTID: An alternative tool for studying earthquake/tsunami signatures in the ionosphere. Case of the 2011 Tohoku earthquake

Traveling Ionospheric Disturbances (ADDTID) algorithm. This algorithm automatically detects and characterizes Traveling Ionospheric Disturbances (TIDs) from Global Navigation Satellite System (GNSS) measurements. Applying the high-precision estimates of ADDTID, the propagation parameters would make it easier to distinguish TIDs from different origins, in particular the characteristics conforming the acoustic gravity waves driven by the earthquake/tsunami. This method does not assume that disturbances follow a circular pattern of propagation, and can estimate the location by the propagation pattern of tsunami wavefronts and related TIDs. In this work, we present in a single framework a description of phenomena observed by different researchers. By means of the ADDTID algorithm, we detect: (a) simultaneous TIDs of different characteristics, where the detection was robust against the curvature of the wave fronts of the perturbations and the accuracy of the estimated parameters. The results were double-checked by visual inspection from detrended Vertical Total Electron Content (VTEC) maps and keogram plots, and the parameters of the slow-speed TIDs were consistent with the tsunami waveform measurements; (b) different wavefronts between the west and east TIDs around the epicenter, consistent in time and space with the post-earthquake tsunami; (c) complete evolution of the circular TIDs driven by the tsunami during the GNSS observable area; (d) fast and short circular TIDs related to the acoustic waves of earthquake; (e) the pre-seismic activity consisting of a set of fast westward TIDs, and the comparison with neighboring days; (f) the location estimation of the tsunami wavefront along the coast and the possible use as early warning. Finally, we report disturbances that had not been previously published with a possible application to local and real-time detection of tsunamis.Peer ReviewedPostprint (published version