Statistical analysis and modeling of the local ionospheric critical frequency: a mid-latitude single-station model for use in forecasting

The hourly values of the F-layer critical frequency from the ionospheric sounder in Dourbes (50.1°N, 4.6°E) during the time interval from 1957 to 2010, comprising five solar cycles, were analyzed for the effects of the solar activity. The hourly time series were reduced to hourly monthly medians which in turn were used for fitting a single station foF2 monthly median model. Two functional approaches have been investigated: a statistical approach and a spectral approach. The solar flux F10.7 is used to model the dependence of foF2 on the solar activity and is incorporated into both models by a polynomial expression. The statistical model employs polynomial functions to fit the F-layer critical frequency while the spectral model is based on spectral decomposition of the measured data and offers a better physical interpretation of the fitting parameters. The daytime and nighttime foF2 values calculated by both approaches are compared during high and low solar activity. In general, the statistical model has a slightly lower uncertainty at the expense of the larger number of fitting parameters. However, the spectral approach is superior for modeling the periodic effects and performs better when comparing the results for high and low solar activity. Comparison with the International Reference Ionosphere (IRI 2012) shows that both local models are better at describing the local values of the F-layer critical frequency

Nowcasting, forecasting and warning for ionospheric propagation: tools and methods

The paper reviews the work done in the course of the COST 271 Action concerned with the development of tools and methods for forecasting, nowcasting and warning of ionospheric propagation conditions. Three broad categories of work are covered. First, the maintenance and enhancement of existing operational services that provide forecast or nowcast data products to end users; brief descriptions of RWC Warsaw and the STIF service are given. Second, the development of prototype or experimental services; descriptions are given of a multi-datasource system for reconstruction of electron density profiles, and a new technique using real-time IMF data to forecast ionospheric storms. The third category is the most wide-ranging, and deals with work that has presented new or improved tools or methods that future operational forecasting or nowcasting system will rely on. This work covers two areas - methods for updating models with prompt data, and improvements in modelling or our understanding of various ionospheric-magnetospheric features - and ranges over updating models of ionospheric characteristics and electron density, modelling geomagnetic storms, describing the spatial evolution of the mid-latitude trough, and validating a recently-proposed technique for deriving TEC from ionosonde observations

pilot ionosonde network for identification of traveling ionospheric disturbances

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 implementation still has several difficulties. In this contribution, we present a new technique, based on the analysis of oblique Digisonde-to-Digisonde (D2D) "skymap" observations, to directly identify TIDs and specify the TID wave parameters based on the measurement of angle-of-arrival, Doppler frequency, and time-of-flight of ionospherically reflected high-frequency (HF) radio pulses. The technique has been implemented for the first time for the Net-TIDE project with data streaming from the network of European Digisonde DPS4D observatories. The performance is demonstrated during a period of moderate auroral activity, assessing its consistency with independent measurements such as data from auroral magnetometers and electron density perturbations from Digisondes and GNSS stations. Given that the different types of measurements used for this assessment were not made at exactly the same time and location, and that there was insufficient coverage in the area between the AGW sources and the measurement lo cations, we can only consider our interpretation as plausible and indicative for the reliability of the extracted TID characteristics. In the framework of the new TechTIDE project (European Commission H2020), a retrospective analysis of the Net-TIDE results in comparison with those extracted from GNSS TEC-based methodologies is currently being attempted, and the results will be the objective of a follow up paper

A real-time operational procedure for GPS TEC based reconstruction of the electron profile at a single ionosonde location

The propagation delays in GNSS, introduced by the ionosphere, can be estimated and corrected much easier if the (vertical) electron density profile is available at a given location on a real-time basis. As the theoretical ionospheric models are not sufficiently good for the purpose, actual on-line measurements immediately available should be considered. Presented is a robust procedure for real-time reconstruction of the electron density profile from concurrent GPS TEC and ionosonde measurements. On the one hand, the on-line ionosonde measurements are used primarily for the reconstruction of the bottom-side profile. On the other hand, the ionosonde data together with simultaneously-measured TEC and upper transition level information, are required and used for determination of the topside electron profile. It is important that the method provides variable topside scale height, and the crucial information for this variability comes from measurements of the oxygen-hydrogen ion transition height, where the largest change in the electron density gradient occur. The procedure is demonstrated and tested on actual GPS TEC and digital ionosonde data obtained at the Dourbes Geophysics Centre of the Royal Meteorological Institute of Belgium. At this center, a GPS receiver is collocated with a digital ionosonde, capable of producing TEC values every 15 minutes. Measurements have been conducted since 1994 and a large TEC database created for the best part of the current solar activity cycle