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IRTAM (NECTAR v0.2A_D3/1)

IRI-based Real-Time Assimilative Model

Model Description

IRI-based Real-Time Assimilative Model (IRTAM) is a collection of global 3D ionospheric electron density (Ne) computations produced every 15 minutes to follow the timeline of the ionospheric weather dynamics. IRTAM 3D belongs to a class of "assimilative IRI" models that replace the internal coefficients of International Reference Ionosphere (IRI), an empirical quiet-time model of ionospheric climate, with updated coefficients. Updated coefficients are obtained by smoothly transforming ("morphing") IRI into agreement with available measurements. The morphing algorithm is called NECTAR (Non-linear Error Correction Technique with Associative Restoration); the version 0.2A computations for CCMC assimilate near-real-time measurements by the Global Ionosphere Radio Observatory (GIRO) ionosondes. NECTAR is a 4D-Var assimilative model whose single computation best fits a sliding window of the 24-hour history of GIRO observations prior to the analysis time. IRTAM’s underlying formalism of representing Ne distributions is the same as in IRI: a set of 2D surface maps are computed to obtain the "anchor" points of the 1D vertical extent of Ne at any location and time.

Model Figure(s) :

Model Inputs Description

Single run of IRI-2020 requires 4 sets of IRTAM weather coefficients for foF2, hmF2, B0, and B1. Replacing the default IRI climatology coefficients/formulas with IRTAM coefficients makes it a weather model.

Model Outputs Description

IRI-2020 provides the updated electron density outputs.

Model Caveats

(1) IRTAM shows little advantage in the temporal forecast mode, gradually losing its advantage over IRI at the forecast horizon above 4 hours. 

(2) The spatial coverage of GIRO ionosondes is fragmentary; data gaps are especially wide over the ocean and at high latitudes. Where observations are missing, IRTAM smoothly returns to the quiet-time climatology. A better version of IRTAM is in the early stage of development that uses radio occultation data to fill the data gaps.

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Curator: Chiu Wiegand | NASA Official: Dr. Masha Kuznetsova | Privacy and Security Notices | Accessibility | CCMC Data Collection Consent Agreement