Solar Flares (SF) refer to sudden increases of electromagnetic radiation from the Sun lasting from minutes to hours. Irradiance in the Extremely Ultra-Violet (EUV) or X band is enhanced and it can produce a sudden over-ionization in the ionosphere, which can be tracked by several techniques. On the one hand, this over-ionization increases the ionospheric delays of GNSS signals in such a way as can be monitored using measurements collected by dual-frequency GNSS receivers. On the other hand, this over-ionization of the ionosphere is the origin of electrical currents which, in turn, induce magnetic fields which can be monitored with ground magnetometers. In this work we propose the use of a GNSS Solar Flare Monitor (GNSS-SF) for its utility to confirm the presence of ionospheric ionization which is able to produce Solar Flare Effects (Sfe) in geomagnetism. A period of 11 years (2008-2018) has been analyzed and contingency tables are shown. Although most of the GNSS-SF detections coincide with SF and most of the Sfe have a detected origin in the ionosphere, there are some paradoxes: sometimes small flares produce disturbances which are clearly detected by both methods while other disturbances, originated by powerful flares, go by virtually unnoticed. We analyzed some of these cases and proposed some explanations. We found that suddenness in the variation is a key factor for detection. Threshold values of the velocity of change to remove the background noise and the use of the acceleration of change instead of the velocity of change as the key performance detector are other topics we deal with in this paper. We conclude that the GNSS-SF detector could provide warnings of ionization disturbances from SF covering the time when the Sfe detectors are "blind", and can help to confirm Sfe events when Sfe detectors are not able to give a categorical answer.
The main objective of the TechTIDE project (Warning and mitigation Technologies for Travelling Ionospheric Disturbances Effects) is the development of an identification and tracking system for Travelling Ionospheric Disturbances (TIDs) which will issue warnings of electron density perturbations over large world regions. The TechTIDE project has put in operation a real-time warning system that provides the results of complementary TID detection methodologies and many potential drivers to help users assess the risks and develop mitigation techniques tailored to their applications. The TechTIDE methodologies are able to detect in real time activity caused by both large-scale and medium-scale TIDs and characterize background conditions and external drivers, as an additional information required by the users to assess the criticality of the ongoing disturbances in real time. TechTIDE methodologies are based on the exploitation of data collected in real time from Digisondes, Global Navigation Satellite System (GNSS) receivers and Continuous Doppler Sounding System (CDSS) networks. The results are obtained and provided to users in real time. The paper presents the achievements of the project and discusses the challenges faced in the development of the final TechTIDE warning system.
Medium-scale traveling ionospheric disturbances (MSTIDs) are fluctuations in the plasma density that propagate through the upper layer of the atmosphere at velocities of approximately 100 m/s and periods reaching some tens of minutes. Due to their wavelengths, MSTIDs can degrade the performance of differential positioning techniques, such as real-time kinematics (RTK) or network-RTK (NRTK). This paper defines a novel methodology as a tool for relating the errors in NRTK positioning based on an MSTIDs indicator using the second difference in time of the slant total electron content (STEC). The proposed methodology performs integer ambiguity resolution (IAR) on the undifferenced measurements instead of using double-differenced carrier-phase measurements, as it is usual in RTK and NRTK. Statistical tests are applied to evaluate the degradation in the position errors caused by the impacts of MSTIDs on RTK and NRTK positioning over a data set spanning one year gathered from the CATNET network; a dual-frequency network of fixed permanent GNSS receivers located at the mid-latitudes of northeastern Spain. With the development of the proposed methodology for measuring the position degradation, another results of the present research are the establishment of thresholds for the proposed MSTIDs index, which can be used to monitor the positioning solution and to warn users when the measurements are affected by MSTIDs events, relating the position error to MSTIDs that affect not only the user receivers but also of the reference receivers within the network.
The Galileo High Accuracy Service (HAS) is a new capability of the European Global Navigation Satellite System that is currently under development. The Galileo HAS will start providing satellite orbit and clock corrections (i.e. non-dispersive effects) and soon it will also correct dispersive effects such as inter-frequency biases and, in its full capability, ionospheric delay. We analyse here an ionospheric correction system based on the fast precise point positioning (Fast-PPP) and its potential application to the Galileo HAS. The aim of this contribution is to present some recent upgrades to the Fast-PPP model, with the emphasis on the model geometry and the data used. The results show the benefits of integer ambiguity resolution to obtain unambiguous carrier phase measurements as input to compute the Fast-PPP model. Seven permanent stations are used to assess the errors of the Fast-PPP ionospheric corrections, with baseline distances ranging from 100 to 1000 km from the reference receivers used to compute the Fast-PPP corrections. The 99% of the GPS and Galileo errors in well-sounded areas and in mid-latitude stations are below one total electron content unit. In addition, large errors are bounded by the error prediction of the Fast-PPP model, in the form of the variance of the estimation of the ionospheric corrections. Therefore, we conclude that Fast-PPP is able to provide ionospheric corrections with the required ionospheric accuracy, and realistic confidence bounds, for the Galileo HAS.
Hernández-Pajares and García-Rigo have written a document criticizing our paper “Confirming geomagnetic Sfe by means of a solar flare detector based on GNSS. J Space Weather Space Clim 9: A42. https://doi.org/10.1051/swsc/2019040” (Curto et al., 2019). The main goal of our paper was to define a methodology based on GNSS measurements that is able to detect solar flares (SF) in an automatic way. This methodology was used to confirm Sfe (SF effects) detected by geomagnetism in an unsupervised manner. In their document, Hernández-Pajares and García-Rigo posed two objections related to the correctness and the novelty of the methodology used in our paper. This document is a reply to these objections and concludes that they are not relevant.
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