Assimilation of KOMPSAT-5 bending angle in GSI 4D-En Var assimilation system

Bending Angle from Korea Multi-Purpose Satellite-5 (KOMPSAT-5) Global Navigation Satellite System-Radio Occultation (GNSS-RO) data is assimilated in the Global Data Assimilation and Forecast System. The observations are incorporated using the Grid-point Statistical Interpolation (GSI) 4 Dimensional-Ensemble Variational (4D-EnVAR) analysis scheme. Before assimilation, the data is processed and undergoes quality control by the COSMIC Data Analysis and Archive Center (CDAAC), University Corporation for Atmospheric Research (UCAR). In this study, the evaluation & assessment procedure goes through four phases: (i) diagnostics through assimilation in cold start mode; cyclic assimilation for (ii) summer and (iii) winter months and (iv) a case study for investigating its impact on severe weather events. Two separate NWP forecast experiments, a control (named CTRL) and the experiment (called KOMPSAT5), are run simultaneously. The only difference between the two is the presence (in KOMPSAT 5) and absence (in CTRL) of the KOMPSAT-5 GNSS-RO. Summer cycle statistics show better, significant, and consistent improvement compared to the winter cycle.