温帯及び熱帯低気圧に関する成長モードの比較

Abstract

We constructed a regional ensemble prediction system using the NCEP regional spectral model (RSM) to investigate forecast uncertainty of disturbances around Japan. The breeding method is applied to the generation of ensemble perturbations in NCEP RSM. Using this system, ensemble forecast experiments were conducted for a case in late August 2022, when a synoptic extratropical cyclone and a tropical cyclone existed simultaneously around Japan, to demonstrate the ability to identify the characteristic growing modes for each disturbance. The uncertainty of the tropical cyclone in terms of kinetic energy is found to be large near the center. Although all members underestimate the strength of the tropical cyclone, its growing modes yield a meridional spread of tracks. On the other hand, the specific humidity has a large variance around a dry air mass entering the extratropical cyclone. The perturbations in moisture are found to affect the development of the cyclone by modulating water vapor flux from the tropical cyclone and the lower tropospheric stability below the dry air mass through the ensemble sensitivity analysis.