IRTAM 3D global real-time assimilative model of ionospheric electron density

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 that are obtained by smoothly transforming ("morphing") IRI into agreement with available observations. The observations are provided provided in near-real-time by Global Ionosphere Radio Observatory (GIRO) ionosondes. IRTAM 3D is a 4DVAR assimilative model whose single computation provides the best fit of the model to 24-hour history window of observations prior to analysis time. Its 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.