Characterizing ionospheric disturbances caused by the North Korean rocket (Hwasung-15) using a four-dimensional variational (4D-VAR) data-assimilation model

Abstract

The four-dimensional variational (4D-VAR) technique, originally developed for weather forecasting applications, has been utilized in a data-assimilated model to estimate rocket exhaust emission from observed ionospheric disturbances. In this study, we improved the 4D-VAR method by utilizing a more realistic chemical model in the ionosphere and applied it to characterize ionosphere disturbances caused by the Hwasung-15 (H-15) rocket exhaust chemicals. The H-15 rocket was launched southeastward from North Korea at 18:17 UT on 28 November 2017. During the first hours of the launch, the total electron content (TEC) derived from the Korean ground-based GNSS receiver network exhibited ionospheric disturbances along the Rocket’s trajectory. The disturbances were most distinct along the GLONASS (Global Orbiting Navigational Satellite System) line of site. By assimilating the measured TEC data into the 4D-VAR model, we were able to characterize the ionospheric depletion and recovery with respect to the standard ionospheric model, IRI-2016. In addition, the rocket exhaust emissions were estimated to be ~ 1.5 × 10²⁷ molecules per sec, with a number ratio of 2:1 for water to hydrogen in the rocket’s exhaust gas.