ANCHOR ionospheric model validation using Jason-2 and Jason-3 altimeter TEC via the open-source PyVALION tool

Abstract

This paper introduces the integration of Jason total electron content (TEC) data into PyVALION (Python VALidation for IONosphere), an open-source community tool for ionospheric model validation. PyVALION applies a novel data assimilation (DA)-based geometry matrix to improve validation adaptability, computational efficiency, and residual analysis. The updated version incorporates TEC measurements from the Jason-2 and Jason-3 satellite altimeter missions (2008–2026). It also automates data downloading, quality control, noise filtering, and bias correction, ensuring high-accuracy TEC for validation purposes. Jason missions provide vertical TEC (vTEC) measurements over the open ocean, where there are limited data from other ionospheric data sources, such as ground-based global navigation satellite system (GNSS) receivers, ionosondes, and incoherent scatter radars (ISRs). This addition delivers a valuable open-access validation source with consistent coverage in areas where many ionospheric models lack ionospheric observation data. New capabilities are demonstrated through validation of ANCHOR, an advanced parameterized ionospheric DA model developed at the U.S. Naval Research Laboratory. Using Jason TEC, the performance of ANCHOR in oceanic regions is assessed and compared with that of its climatological background model, the Python International Reference Ionosphere (PylRI). Results show ANCHOR reduces residual bias, spread, and skewness relative to PyIRI during moderate and high solar activity, with RMSE reductions in three of four events and improvements exceeding 50% in the high-activity case, primarily during daytime conditions. Overall, this work extends PyVALION's validation reach to the open ocean and offers the research community a standardized, flexible platform for model assessment.