Journal Article

Increased Vertical Resolution of Initial Field in TRAMS Model Leads to Spurious Convection Over Sea Surface in Simulating a Typical Warm Sector Rainfall Event in the Southern China

Liu, Zijing, Jian, Yuntao, Lin, Xiaoxia, Zhang, Banglin, Gao, Cuicui, Xu, Daosheng, Zhou, Lingkang, Feng, Yerong, Liang, Jiahao, Li, Yi

2025

Overview

In order to investigate the impact of increasing the vertical resolution of the initial field on the 12–24 h forecasts of the TRAMS (Tropical Regional Atmosphere Model System) model, this study conducted numerical experiments focusing on a typical coastal warm sector rainfall event that occurred in the South China. The findings indicate that increasing the vertical resolution of the initial field led to improved simulation of coastal convection during the 0–12 h period. However, spurious convection was observed over the sea surface and continued to intensify in the 12–24 h period. Subsequent analysis revealed that the spurious convection is primarily associated with the hydrostatic adjustment of initial potential temperature in the TRAMS model. The hydrostatic adjustment leads to a reduction in the stability of the initial temperature stratification in the lower layers of the model, particularly when the number of vertical layers in the initial field increased from 17 to 32. A noticeable spurious unstable layer emerged between 0–200 m over the sea surface, triggering false convection. Further investigation revealed that the area where this unstable stratification occurs over the sea is situated below the height of the lowest level of the input analysis field (1000 hPa), indicating that the spurious disturbances are caused by an unreasonable vertical extrapolation process. Therefore, the findings of this study indicate that the extrapolation calculations using cubic splines in the initialization module of the TRAMS model introduce significant errors. Moreover, these errors increase with the enhancement of the vertical resolution of the initial field, which limits the improvement in model forecasting that could be achieved by increasing the vertical resolution of the initial field. We found that increasing the vertical resolution of the initial field in the TRAMS model led to spurious convection. This spurious convection is triggered by a false unstable layer near the surface. The computational errors during the hydrostatic adjustment of the initial perturbed potential temperature resulted in this false unstable layer.

• Publisher: John Wiley & Sons, Ltd,John Wiley & Sons, Inc,Wiley
• Subject: Atmospheric models / Boundary conditions / Convection / Errors / Extrapolation / Forecasting / hydrostatic adjustment / Numerical experiments / Potential temperature / Precipitation / Rain / Rainfall / Sea surface / Simulation / Splines / spurious convection / Stratification / Trams / Tropical atmosphere / vertical resolution / Weather