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 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.