The NeQuick model utilizes three empirical parameters (H0,g, andr) to define the effective scale height in the topside ionosphere and plasmasphere, which drives vertical electron density variations. However, previous studies have identified weaknesses in the NeQuick topside model, particularly the underestimation of the plasmaspheric contribution to the total electron content (TEC). To address these shortcomings, the study aims to improve the NeQuick model’s empirical representation of electron density distribution in the topside ionosphere and plasmasphere. Radio occultation (RO) electron density profiles from COSMIC/FORMOSAT-3 satellites are integrated with TEC measurements from the same mission derived from precise orbit determination (POD) antennas. A novel two-step optimization procedure is developed for therparameter, which is critical for describing the plasmaspheric electron density. This process initially derivesH0,g, andrfrom RO observations and subsequently refines therparameter by incorporating POD-derived TEC data, yielding a more robust representation of the plasmasphere. The optimizedrparameter, derived from a dataset spanning from 2006 to 2018, demonstrates improved consistency with effective scale height observations from the Van Allen Probes. The results reveal that the improved parametrization ofrbetter captures the spatial, temporal, and solar activity-dependent variations in the topside ionosphere and plasmasphere compared to the fixed value traditionally used in the NeQuick model. The proposed updates to the NeQuick topside model provide a more accurate framework for modeling the electron density in the topside ionosphere and plasmasphere, reducing errors in TEC estimates and advancing the NeQuick model use in space weather and trans-ionospheric propagation applications. Results derived in this study are the basis for the future development of a revised version of the NeQuick topside model.

The objective of this study is to perform a comparison between bottomside electron density measurements from the Global Navigation Satellite System (GNSS) radio occultation (RO) FORMOSAT3/COSMIC (F3/C) constellation mission along with collocated (in space and time) plasma frequency measurements from bottomside electron density profiles from manually scaled ionograms from Nicosia. This comparison demonstrates that there is a systematic underestimation of Digisonde plasma frequency (as compared to F3/C plasma frequency) in the bottomside and that the relative difference between F3/C and Digisonde plasma frequency increases with decreasing altitude (below the F-layer peak).

This paper presents co-seismic earthquake-related ionospheric signatures observed by remote sensing instrumentation situated in the eastern Mediterranean and Middle-East and in particular in Cyprus, Iraq and UAE by exploiting Total Electron Content measurements from calibrated 1-30 sec RINEX files NICO and ISBA IGS stations and ionograms from Nicosia and Sharjah ionosonde stations. Based on the analysis of measurements from these instruments we observe daytime acoustic ionospheric waves after the second (10:24 UTC) 7.6 (Mw) earthquake shock of the 6 February 2023 Turkey earthquake. Although the GNSS ionospheric signatures are only detectable in the near-field, multiple-cusp ionogram signatures generated by Rayleigh surface waves, generating acoustic waves propagating up to the ionosphere, appear as far as Sharjah.

This study aims to describe the main objectives and activities of the research project "Cyprus GNSS (Global Navigation Satellite System) Meteorology Enhancement" (CYGMEN) funded (€1.500.000) by the Cyprus Research Innovation Foundation (RIF) in the frames of "Strategic Research Infrastructures" Call for Proposals. CYGMEN was initiated at January 2024 with the aim to establish a Meteorological cluster (CyMETEO) in Cyprus that will strategically augment existing Frederick Research Center (FRC) and Department of Meteorology (DoM) infrastructure, through the introduction of: a) a Lighting detection network, b) a dense GNSS network for atmospheric water vapor estimation (supported by Cloudwater Ltd (CW) and Nicosia Development Agency (ANEL), c) a Radar Wind Profiler (RWP) and d) a Microwave Radiometer (MWR). Within this framework, the evaluation of the CyMETEO GNSS tropospheric analysis component prior to its deployment at Nicosia district is pursued in this study. Furthermore, CyMETEO will enrich severe weather forecasting, through the assimilation of relevant datasets into WRF Numerical Weather Prediction model (NWP), in the context of a near real-time local weather service, that will be realized through the key collaboration with the Meteo Unit of the National Observatory of Athens.

Solar flares are violent eruptions on the Sun that affect the Earth’s sunlit ionosphere almost instantly. Understanding how corresponding ionospheric characteristics vary is crucial for evaluating such effects. This study aims to highlight the importance of ionosondes in monitoring such effects by utilising foF2, fminF and hmF2 data from nine Digisonde stations to demonstrate their response to the X-2.8 class flare that occurred on December 14, 2023. According to this event the solar flare is shown to cause a decrease in the foF2 profile and an increase in fminF and hmF2. We suggest that these digisonde data, along with high-resolution observations of solar EUV flux emissions and ionospheric models, might help us gain a better understanding of the ionospheric dynamics and photochemistry that support the capacity to evaluate these effects on relevant communication systems such as HF.

The present article describes the principal objectives, the methodology and the main activities of the research project BeRTISS (Balkan-Mediterranean Real Time Severe weather Service) which is funded by the European Territorial Cooperation Programme "Interreg V-B Balkan-Mediterranean 2014-2020". Electron density of the ionosphere and water vapor in the troposphere affect the propagation speed of the GNSS signals transmitted from satellites to the ground reference stations, causing signal propagation delay. Ionospheric delay can be easily removed whereas tropospheric delay, which comprises one of the most significant error sources in satellite signal transmission, should be calculated using surface pressure and temperature variables. Tropospheric delay allows the assessment of Precipitable Water Vapour (PWV). For the first time, BeRTISS real-time service will offer perpetual information for forecasting of PWV over Greece, Bulgaria and Cyprus to the interested public by employing the GNSS derived tropospheric products.

Sporadic E layer is an ionospheric phenomenon which has been classified as an E region (90-150 km) irregularity described by thin layers of extremely dense ionization patches which can significantly affect radio wave propagation. Especially in the case of Cyprus complete blocking of HF signals emanating from short and long-distance HF signals has been observed around noon during the summer. Sporadic E layer can occur during daytime or night-time, and its characteristics vary with latitude. The generating mechanism of the phenomenon has been explained within the general concept of neutral atmosphere-ionosphere coupling and in accordance to windshear theory where long-lived metal ions in the lower thermosphere move vertically to converge into dense plasma layers under the combined action of ion-neutral collisional coupling and geomagnetic Lorentz forcing driven by vertical shears in the horizontal wind. Sporadic E layer formation has been correlated in literature with solar activity, geomagnetic activity and associated to thunderstorms and meteor showers.

The determination of the ionospheric electron density profile below the electron density peak (bottomside) has been traditionally conducted by ground-based ionosondes, which probe the ionosphere up to the maximum electron density and define the profile above the peak (topside) using functions which extrapolate the profile above the peak. An alternative modern technique for measuring electron density profiles is the GPS Radio Occultation, conducted by means of signals transmitted by GPS satellites and received by LEO satellites. The FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) is such a system operating since 2006. In this paper a comparison of the topside electron density profiles over Cyprus is investigated in terms of these two different measurement techniques, within a period of four years. The ability of the International Reference Ionosphere model (IRI-2012) to represent the topside electron density profile is also examined.

This paper addresses the problem of reliably predicting an important HF communication systems parameter, the critical frequency of the F2 ionospheric layer, with the use of a new machine learning technique, called Conformal Prediction (CP). CP accompanies the predictions of traditional machine learning algorithms with measures of confidence. The proposed approach is based on the wellknown Ridge Regression technique, but instead of the point predictions produced by the original method, it produces predictive intervals that satisfy a given confidence level. Our experimental results on an extended critical frequency dataset show that the obtained intervals are well-calibrated and narrow enough to be useful in practice.

This paper presents examples of a multi-instrument approach in ionospheric disturbance detection over the Eastern Mediterranean region. The results presented are based on a scientific initiative to establish an ionospheric monitoring network over Cyprus and Egypt by linking the corresponding instruments in operation in the two countries: a group of three Coherent Ionospheric Doppler Receiver (CIDR) systems being deployed in a roughly north-south chain in Egypt and a modern digital DPS-4D digisonde and a dual-frequency GNSS receiver in Cyprus. The CIDR and DPS-4D instruments considered in this paper have been recently installed in an effort to initiate ionospheric research in the two countries. The cooperation in the frames of this project is considered very beneficial especially taking into account the fact that both countries lack important infrastructure and a tradition of ionospheric observations.