Article ID: 2025-035
The Nonhydrostatic Icosahedral Atmospheric Model (NICAM)–Local Ensemble Transform Kalman Filter (LETKF) JAXA Research Analysis (NEXRA), a weather research and analysis system integrating NICAM with the LETKF, has been updated. NEXRA combines an atmospheric data assimilation system (NICAM–LETKF) and a five-day deterministic weather forecast model using NICAM. This study compares the previous system version, NEXRA2, with the updated version, NEXRA3. NEXRA3 features a higher-resolution NICAM–LETKF with a 56 km mesh for assimilation and an updated version of the 14 km mesh NICAM with improved physical schemes and optimized source code. We performed a statistical comparison by analyzing one year of data assimilation cycles and conducting five-day deterministic forecasts under both summer and winter conditions. The results demonstrate that NEXRA3 outperforms NEXRA2 in both the NICAM–LETKF analysis and five-day forecasting, particularly in terms of precipitation forecast accuracy. These findings show that the implementation of several model improvements, which have proven highly effective in previous developments, also improve both the data assimilation and forecasting cycles.
