Early Warning of ionospheric disturbances for GNSS users

Temporal and spatial gradients in the ionosphere can cause major threats on communication and navigation satellite systems, because the propagation of transionospheric radio signals is influenced by the ionospheric electron content. Space weather events are often the source of strong ionospheric disturbances. Forecasting ionospheric perturbations related to space weather events is therefore a crucial task being of special interest for GNSS users. The climatology of ionospheric storms seen in the Total Electron Content (TEC) over Europe as a response of the ionosphere towards Earth oriented space weather events is well known. It depends on season, elapsed time from event arrival, location and local time. However, the deviation of a single storm to the mean behavior can be large. A good correlation between strength of the ionospheric storm, i.e. the maximum deviation of the TEC to 27 day median, to solar wind or geomagnetic activity indices is hard to define. Hence forecasting TEC for disturbed conditions is a challenging task. However, the storm climatology and comprehensive correlation studies allow forecasting of the most probable TEC perturbation amplitude for the European region. GNSS users are in need of information about arriving threads due to space weather events as early as possible. Therefore, an Early Warning message for GNSS users has been developed at the DLR within the FP7-Project AFFECTS. It provides information about Earth endangering space weather events to interested GNSS users up to two days before their arrival. Additional information are now added by a second warning message distributed thirty minutes before arrival at Earth giving more specific information like exact arrival time, forecasts of geomagnetic indices, approximate TEC perturbation and range error for the European region. An overview on the Early Warning for GNSS user service provided by DLR is presented in this paper

Forecast of Total Electron Content over Europe for disturbed ionospheric Conditions

A general picture of the occurrence of ionospheric storms as function of local time, season and location is known from numerous studies over the past 50 years. Nevertheless, it is not yet possible to say how the ionosphere will actually respond to a given space weather event because the measurements of the onset time, location of maximum perturbation, amplitude and type of storm (positive or negative) deviate much from the climatology. However, statistical analyses of numerous storm events observed in the Total Electron Content (TEC) since 1995 enable to estimate and predict a most probable upcoming perturbed TEC over Europe based on forecasts of geomagnetic activity. A first approach will be presented here. The forecast of perturbed TEC is part of the Forecast System Ionosphere build under the umbrella of the FP7 project AFFECTS∗ (Advanced Forecast For Ensuring Communication Through Space). It aims to help users mitigating the impact on communication system

Polar tongue of ionisation during geomagnetic superstorm

During the main phase of geomagnetic storms, large positive ionospheric plasma density anomalies arise at middle and polar latitudes. A prominent example is the tongue of ionisation (TOI), which extends poleward from the dayside storm-enhanced density (SED) anomaly, often crossing the polar cap and streaming with the plasma convection flow into the nightside ionosphere. A fragmentation of the TOI anomaly contributes to the formation of polar plasma patches partially responsible for the scintillations of satellite positioning signals at high latitudes. To investigate this intense plasma anomaly, numerical simulations of plasma and neutral dynamics during the geomagnetic superstorm of 20 November 2003 are performed using the Thermosphere Ionosphere Electrodynamics Global Circulation Model (TIE-GCM) coupled with the statistical parameterisation of high-latitude plasma convection. The simulation results reproduce the TOI features consistently with observations of total electron content and with the results of ionospheric tomography, published previously by the authors. It is demonstrated that the fast plasma uplift, due to the electric plasma convection expanded to subauroral mid-latitudes, serves as a primary feeding mechanism for the TOI anomaly, while a complex interplay between electrodynamic and neutral wind transports is shown to contribute to the formation of a mid-latitude SED anomaly. This contrasts with published simulations of relatively smaller geomagnetic storms, where the impact of neutral dynamics on the TOI formation appears more pronounced. It is suggested that better representation of the high-latitude plasma convection during superstorms is needed. The results are discussed in the context of space weather modelling.</p

Polar cap plasma transport during geomagnetic superstorm

Positive plasma anomalies appear during the main phase of geomagnetic storms at (sub)auroral latitudes, extending across the polar cap as tongue of ionisation (TOI). Physical mechanisms of TOI, including electrodynamic plasma transport and neutral wind forcing, are simulated with TIE-GCM during the superstorm of Nov. 2003. The simulations are compared with TEC observations and GNSS tomography. The electrodynamic transport (vertical ExB component in particular) is identified as the main mechanism controlling TOI anomaly during great storms (Dst < -300 nT). This makes the choice of high-latitude convection model critical for simulations

Report on recent and planned activies of the International Space Weather Action Team (ISWAT) on Ionospheric Indices and Scales

Ionospheric indices have a high potential to operate user requirements in ground and space-based radio system applications such as HF communication, GNSS based safe navigation and precise positioning. Considering the fact that the current NOAA space weather scales consider ionospheric impact on radio systems only for HF propagation (Radio blackout scale) there is a need to extend the SW scales for trans-ionospheric radio systems such as GNSS, intersatellite telecommunication and remote sensing radars. Following the discussions at previous COSPAR assemblies, the International Space Weather Activity Team (ISWAT) G2B-04 [1], established in 2021, encourage studies and test runs to specify the effectiveness of different types of ionospheric indices and scales to fill the gap in the SW scales in particular for trans-ionospheric radio system applications. Regularly organized online meetings enable intensive discussion on selected topics concerning ionospheric indices and scales and their use. Considering the growing capabilities of ionospheric measurements onboard satellites, the development of new indices and scales covering the entire globe without regional restrictions, typically for ground-based observations, are expected. To review the specification of current indices and scales to characterize the perturbation degree of the ionosphere for different applications, the team has started the elaboration and discussion of compact fact sheets for numerous indices currently used. The initiative intends to provide a quick orientation for young scientists and customers. Recently, the team has initiated a Coordinated Ionospheric Study on Scales and Indices (CISSI) to enable a comparison of the outcome of different index approaches based on identical data sets. Participants may contribute with studies on index approaches and/or related applications on their own choice on a best efforts basis. Participants may also contribute ground and/or space based GNSS data sets for creating a common database useable in the collaborative work. Besides the discussion at ISWAT meetings, the team members are encouraged to collaborate and present their results at international meetings and in journal publications. The present CISSI activity focuses on two periods from16-19 March 2015 (St. Patrick storm) and from 22-25 May 2015 (quiet reference). Predefined regions cover Europe, North- and South-America and Asia. The current data sets stored and hosted by data centers and research institutions in different countries contain ground based GNSS and vertical sounding data. This and further campaigns shall help to consolidate ionospheric space weather scales used in space weather services

Identification of potential precursors for the occurrence of Large-Scale Traveling Ionospheric Disturbances in a case study during September 2017

Traveling Ionospheric Disturbances (TIDs) reflect changes in the ionospheric electron density which are caused by atmospheric gravity waves. These changes in the electron density impact the functionality of different applications such as precise navigation and high-frequency geolocation. The Horizon 2020 project TechTIDE establishes a warning system for the occurrence of TIDs with the motivation to mitigate their impact on communication and navigation applications. This requires the identification of appropriate indicators for the generation of TIDs and for this purpose we investigate potential precursors for the TID occurrence. This paper presents a case study of the double main phase geomagnetic storm, starting from the night of 7th September and lasting until the end of 8th September 2017. Detrended Total Electron Content (TEC) derived from Global Navigation Satellite System (GNSS) measurements from more than 880 ground stations in Europe was used to identify the occurrence of different types of large scale traveling ionospheric disturbances (LSTIDs) propagating over the European sector. In this case study, LSTIDs were observed more frequently and with higher amplitude during periods of enhanced auroral activity, as indicated by increased electrojet index (IE) from the International Monitor for Auroral Geomagnetic Effects (IMAGE). Our investigation suggests that Joule heating due to the dissipation of Pedersen currents is the main contributor to the excitation of the observed LSTIDs. We observe that the LSTIDs are excited predominantly after strong ionospheric perturbations at high-latitudes. Ionospheric parameters including TEC gradients, the Along Arc TEC Rate (AATR) index and the Rate Of change of TEC index (ROTI) have been analysed for their suitability to serve as a precursor for LSTID occurrence in mid-latitude Europe, aiming for near real-time indication and warning of LSTID activity. The results of the presented case study suggest that the AATR index and TEC gradients are promising candidates for near real-time indication and warning of the LSTIDs occurrence in mid-latitude Europe since they have a close relation to the source mechanisms of LSTIDs during periods of increased auroral activity

Statistical analysis and predictability of large scale travelling ionospheric disturbances over Europe

Since the ionosphere electron density has an effect on radiowave propagation, it is essential to characterize and predict the occurrence of ionosphere perturbations. Ionosphere perturbations are particularly strong during storm conditions, when the solar wind and interplanetary magnetic field transfer significant amounts of energy into the Earth’s magnetosphere-ionosphere-thermosphere system. One ionosphere perturbation phenomenon, which can be frequently observed during storm conditions, are Large Scale Travelling Ionospheric Disturbances (LSTIDs). They are the signature of atmospheric gravity waves, which are generated in the Auroral region due to sudden and intense Joule heating and expansion of the thermosphere. In past, many case studies analysed the occurrence of LSTIDs, and discussed the generation and propagation mechanisms. Total Electron Content (TEC) estimates, derived from Global Navigation Satellite System (GNSS) observations, are a well-suited parameter to study LSTIDs. They have been used to generate statistical studies on the LSTID characteristics and revealed a correlation of LSTID amplitudes with Joule heating, indicated by the Auroral Electrojet index (AE). The prediction of LSTIDs is a challenging task because of their transient nature. So far, no reliable LSTID forecast is available. In this study, we present a modified approach for assessing the LSTID occurrence and propagation. Statistical analyses for the European region show the correlation of LSTID occurrence with solar wind perturbations. The predictability of LSTIDs will be discussed and an initial approach for a prediction model based on artificial intelligence methods will be presented

Improving estimates of the ionosphere during geomagnetic storm conditions through assimilation of thermospheric mass density

Dynamical changes in the ionosphere and thermosphere during geomagnetic storm times can have a significant impact on our communication and navigation applications, as well as satellite orbit determination and prediction activities. Because of the complex electrodynamics coupling processes during storms, which cannot be fully described with the sparse set of thermosphere–ionosphere (TI) observations, it is crucial to accurately model the state of the TI system. The approximation closest to the true state can be obtained by assimilating relevant measurements into physics-based models. Thermospheric mass density (TMD) derived from satellite measurements is ideal to improve the thermosphere through data assimilation. Given the coupled nature of the TI system, the changes in the thermosphere will also influence the ionosphere state. This study presents a quantification of the changes and improvement of the model state produced by assimilating TMD not only for the thermosphere density but also for the ionosphere electron density under storm conditions. TMD estimates derived from a single Swarm satellite and the Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) physics-based model are used for the data assimilation. The results are presented for a case study during the St. Patricks Day storm 2015. It is shown that the TMD data assimilation generates an improvement of the model’s thermosphere density of up to 40% (measured along the orbit of the non-assimilated Swarm satellites). The model’s electron density during the course of the storm has been improved by approximately 8 and 22% relative to Swarm-A and GRACE, respectively. The comparison of the model’s global electron density against a high-quality 3D electron density model, generated through assimilation of total electron content, shows that TMD assimilation modifies the model’s ionosphere state positively and negatively during storm time. The major improvement areas are the mid-low latitudes during the storm’s recovery phase