Project Overview

The TAGMOS-F project aims to advance the understanding of ionospheric Spread F (SF) by developing a global statistical and climatological framework based on long-term ground-based observations. SF is a manifestation of ionospheric plasma irregularities in the F region that can severely affect radio wave propagation, satellite-based navigation, and communication systems (see Figure 1). Its occurrence exhibits strong variability with latitude, local time, season, solar activity, and geomagnetic conditions.

Scientific Background and Motivation

Over the past decades, significant progress has been made in modelling and characterising SF at regional scales. Regional and latitude-specific SF models—particularly for equatorial and low-latitude regions—have demonstrated good performance within their respective domains. However, these models are typically optimized for specific geophysical environments and cannot be directly extended to other latitude regions where the physical drivers of SF differ substantially.

At present, no observation-based global SF model exists that consistently describes SF occurrence across equatorial, midlatitude, and high-latitude ionospheres. Existing global ionospheric models, such as the International Reference Ionosphere (IRI), include a climatological prediction model of SF; however, this model is primarily confined to equatorial regions and does not adequately reproduce SF variability even there under many conditions. As a result, midlatitude and high-latitude SF occurrence remains largely unaccounted for in global modelling frameworks.

TAGMOS-F is designed to address this long-standing limitation by constructing a global statistical description of SF occurrence directly from long-term ground-based observations, rather than extrapolating regional behaviour beyond its valid domain.

Why TAGMOS-F Is Well Positioned

The TAGMOS-F project builds upon extensive prior experience of the project team in the investigation of SF and related ionospheric irregularities. Over more than a decade, the team has carried out systematic studies of SF occurrence, ionogram signatures, and associated ionospheric variability across different latitude regions and solar activity conditions.

This prior work has provided an in-depth understanding of:

• long-term and solar-cycle-dependent SF behaviour,
• Ionogram signatures and parameter variations associated with SF occurrence,
• Differences in SF characteristics between equatorial, midlatitude, and high-latitude ionospheres,
• The role of ionospheric disturbances and background conditions in modulating SF occurrence.

This accumulated expertise ensures that TAGMOS-F is grounded in validated methodologies and realistic physical interpretation, making it well-suited to tackle the complexity of global SF modelling.

PROJECT STRUCTURE

The TAGMOS-F project is organised into six interlinked Work Packages (WPs), each addressing a specific stage in the development of a global SF climatological framework.

1. WP1 – Project Management

This Work Package ensures effective coordination, administrative oversight, financial monitoring, and quality control throughout the project lifecycle. It maintains alignment with the project timeline and contractual objectives.

Outcome: Smooth project execution, timely reporting, and delivery of high-quality scientific outputs.

2. WP2 – Dissemination and Exploitation Activities

WP2 promotes the scientific results of TAGMOS-F through peer-reviewed publications, conference presentations, scientific networking, and outreach activities. It ensures that project outcomes are visible, accessible, and integrated into the broader ionospheric and space weather community.

Outcome: Enhanced international visibility, knowledge exchange, and long-term scientific impact.

3. WP3 – Global Ionospheric Parameter Database

WP3 focuses on compiling, organising, and quality-controlling long-term ionospheric parameters derived from the global Digisonde network. Particular emphasis is placed on parameters that indicate SF occurrence or reflect ionospheric conditions conducive to its development.

Outcome: A comprehensive, quality-controlled global ionospheric database forming the observational foundation of the project.

4. WP4 – Statistical Analysis of Global SF Events

This Work Package analyses the compiled database to identify and statistically characterise SF occurrence across equatorial, midlatitude, and high-latitude regions. The analysis examines diurnal, seasonal, and solar activity dependencies.

Outcome: An observation-based global statistical description of SF variability.

5. WP5 – Development of the Global SF Climatological Model

WP5 synthesises the statistical findings into a structured climatological framework suitable for global representation of SF. The work bridges observational analysis and model-oriented formulation.

Outcome: A prototype global SF climatological model based on long-term observations.

6. WP6 – Model Evaluation and Future Forecasting Framework

WP6 evaluates the robustness and applicability of the developed framework and explores pathways for future integration into operational ionospheric modelling and forecasting systems.

Outcome: A validated modelling framework and a roadmap toward future global SF forecasting capabilities.

GENERAL PROJECT OBJECTIVES

The TAGMOS-F project aims to develop the first observation-driven global climatological framework for ionospheric SF. While regional studies of SF exist, a comprehensive and physically consistent global representation remains lacking. TAGMOS-F addresses this gap by systematically analysing long-term ionospheric observations from the worldwide Digisonde network.

The primary objectives of the project are to:

• compile a comprehensive global database of long-term ionospheric parameters derived from Digisonde observations;
• identify and characterise SF occurrence across equatorial, midlatitude, and high-latitude regions;
• investigate the diurnal, seasonal, and solar activity dependence of SF occurrence;
• establish a global climatological description of SF variability based on observations;
• provide the scientific foundation for the development of future global and short-term SF forecasting capabilities.

To achieve these goals, TAGMOS-F follows a structured and stepwise methodology. Long-term autoscaled ionospheric parameters extracted from ionograms are systematically collected, quality-controlled, and organised into a unified global database. Particular emphasis is placed on parameters that act as indicators of SF occurrence or reflect ionospheric conditions conducive to its development.

A regional-to-global analysis strategy is adopted. Statistical investigations are first conducted within well-observed latitude regions, such as the midlatitudes, to establish robust detection criteria and validate the methodological framework. These validated approaches are then progressively extended to other latitude sectors, ensuring methodological consistency and reliability at the global scale.

SF occurrence is analysed as a function of local time, season, latitude, and solar activity, enabling the construction of an observation-based global climatological description. The resulting statistical patterns are synthesised into a framework suitable for integration with global ionospheric modelling efforts, laying the groundwork for future inclusion of SF representation in global ionospheric models.

The development of a global SF model presents significant challenges. Digisonde stations are unevenly distributed geographically, data availability varies across regions and time periods, and SF itself is highly intermittent and variable. TAGMOS-F addresses these challenges through rigorous quality-control procedures, a statistically robust and observation-driven approach, and careful consideration of regional differences and data limitations. By explicitly confronting these constraints, the project aims to deliver a realistic and scientifically defensible global description of SF variability.

RESEARCHERS

Krishnendu Sekhar Paul/ Frederick Research Center

Haris Haralambous / Frederick Research Center

Christina Oikonomou / Frederick Research Center

Dieter Bilitza /Space Physics Data Facility (SPDF), NASA’s Goddard Space Flight Center/ George Mason University (GMU)