Comparison of Sporadic-E Characteristics from coincident COSMIC-2 Radio Occultation and Digisonde Observations

Abstract

Sporadic-E (Es) layers are thin, transient layers that influence radio propagation. Recently there has been growing interest in global Es occurrence modelling which is also relevant to the International Reference Ionosphere (IRI) model that is currently lacking a model component for Es occurrence. This study presents a comprehensive intercomparison of Es layer altitude and intensity from coincident COSMIC‑2 GNSS radio‑occultation (RO) and Digisonde observations during 2020‑2023. Using strict spatial (±2°) and temporal (±10 min) collocation, 4,367 quality‑controlled RO‑Digisonde profile pairs from 19 globally distributed stations were analysed. Es peak altitude (RO geometric height hRO vs Digisonde virtual height h′Es) shows weak‑to‑moderate station‑wise linear agreement (Pearson R ≈ 0.22‑0.66) and root‑mean‑square differences of ≈4.2‑7.8 km (multi‑station mean ≈6 km), indicating that COSMIC‑2 reproduces the broad statistical distribution of Es altitudes while instantaneous, site‑to‑site agreement varies. Intensity comparisons (RO L1 amplitude scintillation index S4 vs Digisonde blanketing frequency, fbEs), evaluated for RO‑detected Es events with S4 > 0.2, reveal a consistently positive but generally modest relationship (R up to ≈0.36), with statistically significant agreement at 14 of 19 stations and strongest correlations at equatorial and some low‑latitude sites. Even at the best locations, fbEs explains at most ∼13% of S4 variance, underscoring the influence of small‑scale structuring, differing physical sensitivities, sampling geometry, and collocation uncertainty on scintillation responses. These results quantify the complementarities and limitations of RO and ionosonde Es metrics and provide a benchmark assessment for their use in future monitoring systems and empirical modelling.

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