IRTAM

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.

(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.

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.

IRI-2020 provides the updated electron density outputs.