Tobias G.W. Verhulst

Tobias G.W. Verhulst
Koninklijk Meteorologisch Instituute van België | KMI · Section Ionospheric Research, Dept. Geophysics

PhD

About

58
Publications
13,319
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
283
Citations

Publications

Publications (58)
Article
Full-text available
This paper presents a review on the PECASUS service, which provides advisories on enhanced space weather activity for civil aviation. The advisories are tailored according to the Standards and Recommended Practices of the International Civil Aviation Organization (ICAO). Advisories are disseminated in three impact areas: radiation levels at flight...
Article
Full-text available
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...
Chapter
This chapter presents the development and use of the most reliable and widely used instrument for cosmic ray measurements from the ground, the neutron monitor, and the global database collecting data from the neutron monitors worldwide, the international Neutron Monitor Database (NMDB). NMDB collects data from about 50 stations worldwide, more than...
Poster
Full-text available
Travelling Ionospheric Disturbances (TIDs) are plasma density fuctuations that propagate as waves through the ionosphere. TIDs constitute a threat for operational systems using predictable ionospheric characteristics as they can impose signicant disturbances in the ambient electron density and Doppler frequency shift on HF signals. TIDs can have ef...
Poster
Full-text available
The warning system provides large-(LSTID) and medium-scale (MSTID) TID detection, TID activity indicators, and TID drivers to the user communities.
Conference Paper
Records of the standard ionospheric characteristics provided by ionosondes are analysed to detect distinct variations associated with the overpassing Large Scale Travelling Ionospheric Disturbances (LSTIDs). When observed in a sufficiently dense network of ionosondes, such as the one currently operating in the European region, coherency of the Four...
Presentation
Full-text available
Records of the standard ionospheric characteristics provided by ionosondes are analysed to detect distinct variations associated with the overpassing Large Scale Travelling Ionospheric Disturbances (LSTIDs). When observed in a sufficiently dense network of ionosondes, such as the one currently operating in the European region, coherency of the Four...
Conference Paper
Full-text available
A new technique for Travelling Ionospheric Disturbances (TID) identification in near-real time is presented, which is based on the analysis of oblique Digisonde-to-Digisonde (D2D) “skymap” observations for the direct identification of TIDs and the specification of the TID wave parameters. The technique is based on the measurement of angle-of-arriva...
Article
Full-text available
Travelling Ionospheric Disturbances (TIDs) are the ionospheric signatures of atmospheric gravity waves (AGWs). Their identification and tracking is important because the TIDs affect all services that rely on predictable ionospheric radio wave propagation. Although various techniques have been proposed to measure TID characteristics, their real-time...
Conference Paper
Full-text available
This presentation will address the issue of eclipse geometry effects on various ionospheric observations carried out during the total solar eclipse of August 21, 2017. In particular, GPS-based TEC and ionosonde measurements will be analysed and the eclipse effects on the ionosphere will be interpreted with respect to the actual eclipse geometry at...
Article
Full-text available
A total solar eclipse occurred on 20 March 2015, with a totality path passing mostly above the North Atlantic Ocean, which resulted in a partial solar eclipse over Belgium and large parts of Europe. In anticipation of this event, a dedicated observational campaign was set up at the Belgian Solar-Terrestrial Centre of Excellence (STCE). The objectiv...
Conference Paper
The presentation will report on our current and planned work related to monitoring and investigating various space weather effects and the services we offer to help mitigating these effects.
Conference Paper
Full-text available
The paper outlines the space-weather-related observations, instrumentation, research and service developments carried out at the Geophysical Centre of the Royal Meteorological Institute (RMI) in Dourbes, Belgium.
Article
Full-text available
A network of ionosondes in Europe has been established to monitor travelling ionospheric disturbances (TIDs) by simultaneously making vertical and oblique incidence HF sounding measurements. This network is the outcome of the Net-TIDE project, a collaboration between European Digisonde operators that have synchronized the sounding schedules of the...
Article
Full-text available
It is well established that the sunrise and sunset periods are of particular importance to ionospheric research and modelling because of the rapid changes in the ionospheric plasma density, temperature, and dynamics. In particular, the sharp increase in the ionisation following sunrise results in a quick increase in the ionospheric peak density, Nm...
Conference Paper
Full-text available
The K index is a quasi-logarithmic index characterizing the 3-hourly range in the transient geomagnetic field activity at a certain location relative to its regular "quiet-day" variation. It is a popular choice among researchers; however, the 3-hour time scale is much larger than the characteristic time of various phenomena associated with an eleva...
Conference Paper
Full-text available
In the framework of a new NATO Science for Peace and Security multi-year project (2014-2017) we are exploiting for the first time the European network of high precision ionospheric DPS4D sounders and the related software to directly identify TIDs over Europe and specify in real time the gravity wave parameters based on measuring the variations of t...
Conference Paper
Full-text available
A total solar eclipse occurred on 20 March 2015 over the North Atlantic. As a result, a partial solar eclipse was visible over Belgium, with a maximal eclipse of 81.5% happening at 9:34 UT. An eclipse will of course have an effect on the ionosphere and therefore also on the delay of the GNSS signals. Effects of previous solar eclipses on the ionosp...
Conference Paper
Full-text available
This paper presents preliminary results of a comparative study of the modeling capabilities of two ionospheric models, LIEDR (Local Ionospheric Electron Density profile Reconstruction) and NeQuick, by using ionospheric radio occultation (IRO) and vertical incidence sounding (VIS) measurements. LIEDR is based on a technique for constructing a vertic...
Article
The ionospheric behavior over Belgium during the partial solar eclipse of 20 March 2015 is analyzed based on high-resolution solar radio flux, vertical incidence sounding, and GPS TEC measurements. First results of ionosonde-based ionospheric plasma drift and tilt observations are presented and analyzed, including some traveling ionospheric disturb...
Conference Paper
Full-text available
The Total Electron Content (TEC) grid, provided by the International GNSS Service (IGS), offers a global coverage with an estimated accuracy of 2–8 TECU, time resolution of 2 hours, and spatial resolution of 5° in longitude and 2.5° in latitude. IGS TEC has been extensively used for developing empirical and assimilative TEC models needed for trans-...
Conference Paper
Full-text available
This presentation will outline the recent and future activities at the Royal Meteorological Institute (RMI) regarding space weather research, monitoring, and developing of related services, with focus on the modernisation and use of the cosmic ray observatory.
Conference Paper
Full-text available
Advanced models of the ionosphere, including the well-known International Reference Ionosphere (IRI) model, make use of various ionospheric characteristics, such as the critical frequency (f o F 2 ), peak density height (h m F 2 ), and total electron content (TEC), on which to base the construction of the vertical distribution profile of the ion an...
Article
In relation to the development of an operational ionospheric monitoring and imaging system, the most frequently used analytical ionospheric profilers (Chapman, Epstein, Exponential) were investigated in terms of suitability for topside ionosphere modelling. For the purpose, topside sounder measurements onboard Allouette and ISIS satellites have bee...
Conference Paper
Full-text available
A case study of the space weather events that took place in February 2014 will be presented. In particular, we investigate the influence of these events on the local ionospheric and magnetic conditions by using several collocated instruments – ionosonde, magnetometer, cosmic rays detector, and GNSS receivers – in operation at the RMI Geophysical Ce...
Article
Full-text available
The Earth’s magnetic field varies on a wide range of timescales, from long time trends caused by internal processes to rapid fluctuations caused primarily by solar events. Nowadays, the magnetic field is continually being monitored by worldwide networks of observatories. Different indices have been developed to characterise the magnetic activity, a...
Article
Full-text available
The Earth’s magnetic field creates a cavity in interplanetary space, called the magnetosphere. Physical processes in this region of space determine how mass and energy from the solar wind reach the ionosphere, the partially ionized upper atmosphere. Magnetosphere and ionosphere are strongly coupled. Together, they modulate the impacts of solar acti...
Article
An operational system for deducing and imaging the vertical distribution of the electron density in the local ionosphere has been recently developed. The electron density profile is deduced from combined ground-based measurements of the total electron content, ionospheric vertical incidence soundings, and empirically-obtained values of the O+/H+ io...
Article
The ionospheric topside sounder measurement database developed at the US National Space Science Data Center (NSSDC) is a valuable source of information when investigating the composition and complex dynamics of the upper ionosphere. The database is increasingly used by many scientists around the world for both research and development of empirical...
Conference Paper
Full-text available
Ground-based ionosonde measurements can be used to determine the electron density profile up to the ionospheric density peak, hmF2, only. In order to reconstruct a complete, full-height electron density profile, a model is usually needed for the shape of the topside ionospheric density. Different shapes have been used over the years, more frequentl...
Conference Paper
Full-text available
An operational system for deducing and imaging the vertical distribution of the electron density in the local ionosphere (LIEDR) has been recently developed at the RMI Geophysical Centre in Dourbes (50.1N, 4.6E). At a given location, the vertical electron density profile (EDP) is deduced from local ground-based measure¬ments of the total electron c...
Article
Full-text available
We introduce the notion of a generalised symmetry M of a hamiltonian H. It is a symmetry which has been broken in a very specific manner, involving ladder operators R and R†. In Theorem 1 these generalised symmetries are characterised in terms of repeated commutators of H with M. Breaking supersymmetry by adding a term linear in the supercharges is...
Article
Full-text available
We start from a Hamiltonian describing non-interacting fermions and add bosons to the model, with a Jaynes-Cummings-like interaction between the bosons and fermions. Because of the specific form of the interaction the model can be solved exactly. In the ground state, part of the electrons form bound pairs with opposite momentum and spin. The model...
Article
Full-text available
We consider a lattice model in which phonons scatter with pairs of electrons. All eigenvalues and eigenvectors can be obtained analytically. For a suitable choice of parameters the ground state consists of a Fermi sea of non-interacting electrons, with on top a layer of paired electrons. The binding energy of the electron pairs is partly cancelled...
Article
The first step in the counting operator analysis of the spectrum of any model Hamiltonian H is the choice of a Hermitean operator M in such a way that the third commutator with H is proportional to the first commutator. Next one calculates operators R and R^\dagger which share some of the properties of creation and annihilation operators, and such...
Article
We prove three theorems about the use of a counting operator to study the spectrum of model Hamiltonians. We analytically calculate the eigenvalues of the Hubbard ring with four lattice positions and apply our theorems to describe the observed level crossings.
Article
Full-text available
Recent results, extending the Schmidt decomposition theorem to wavefunctions of identical particles, are reviewed. They are used to give a definition of reduced density operators in the case of two identical particles. Next, a method is discussed to calculate time averaged entanglement. It is applied to a pair of identical electrons in an otherwise...
Article
Full-text available
We replace time-averaged entanglement by ensemble-averaged entanglement and derive a simple expression for the latter. We show how to calculate the ensemble average for a two-spin system and for the Jaynes-Cummings model. In both cases the time-dependent entanglement is known as well so that one can verify that the time average coincides with the e...

Network

Cited By

Projects

Projects (2)
Project
Warning and mitigation technologies for travelling ionospheric disturbances effects
Project
The project aims at setting up a system able to monitor the wave activity in the ionosphere, and using advanced modelling techniques to analyse the waves’ characteristics, understand their origin, predict their effects in different regions of the globe and assess their effects in operational systems.