A global model of the occurrence probability of sporadic E for the International Reference Ionosphere

This paper presents ESPROB, a new global model describing the occurrence probability of sporadic E (Es) layers, designed for integration into the International Reference Ionosphere (IRI) model. The model is constructed from an extensive database comprising more than 20 million globally distributed Es occurrence data points. The database was compiled by analyzing a large number of radio occultation (RO) profiles from 12 Global Navigation Satellite System (GNSS) RO missions including CHAMP, GRACE, COSMIC 1 and 2, TerraSAR-X, PAZ, and TanDEM-X among others. The model describes the latitudinal and local time variations of Es occurrence probability by employing spherical harmonics up to 16 th order in invdip latitude and magnetic local time (MLT), separately for 24 magnetic-longitude sectors and four seasons. An interpolation scheme provides a continuous representation of the model output as a function of longitude and day of year. Variations related to solar and geomagnetic activity are parametrized using additive terms linear in the solar and geomagnetic indices. The model captures the principal climatological pattern of global Es occurrence probability and has now been embedded in IRI.