Effects of a Dry-Mass Conserving Dynamical Core on the Simulation of Tropical Cyclones

Abstract

The accurate forecasting of tropical cyclones (TCs) is a challenging task. The purpose of this study was to investigate the effects of a dry-mass conserving (DMC) hydrostatic global spectral dynamical core on TC simulation. Experiments were conducted with DMC and total (moist) mass conserving (TMC) dynamical cores. The TC forecast performance was first evaluated considering 20 TCs in the West Pacific region observed during the 2020 typhoon season. The impacts of the DMC dynamical core on forecasts of individual TCs were then estimated. The DMC dynamical core improved both the track and intensity forecasts, and the TC intensity forecast improvement was much greater than the TC track forecast improvement. Sensitivity simulations indicated that the DMC dynamical core-simulated TC intensity was stronger regardless of the forecast lead time. In the DMC dynamical core experiments, three-dimensional winds and warm and moist cores were consistently enhanced with the TC intensity. Drier air in the boundary inflow layer was found in the DMC dynamical core experiments at the early simulation times. Water vapor mixing ratio budget analysis indicated that this mainly depended on the simulated vertical velocity. Higher updraft above the boundary layer yielded a drier boundary layer, resulting in surface latent heat flux (SLHF) enhancement, the major energy source of TC intensification. The higher DMC dynamical core-simulated updraft in the inner core caused a higher net surface rain rate, producing higher net internal atmospheric diabatic heating and increasing the TC intensity. These results indicate that the stronger DMC dynamical core-simulated TCs are mainly related to the higher DMC vertical velocity.

摘 要

准确预测热带气旋(TC)是一项具有挑战性的工作, 本文研究了干空气质量守恒 (DMC)全球谱动力核心对热带气旋模拟的影响. 为了有效评估DMC对热带气旋模拟的影响, 本文将 DMC 和总 (湿) 空气质量守恒 (TMC) 动力核心进行了对比试验, 针对 2020 年台风季观测到的西太平洋地区 20 个 热带气旋 s 进行统计评估, 并选择了一个典型热带气旋进行系统评估. 结果显示: DMC 动力核心对路径和强度预报都有改进, 其中对热带气旋强度预测的改进要远大于对热带气旋路径预测的改进; 不同起报时间的敏感性试验表明, 无论预测起报时间, DMC 动力核心模拟的热带气旋强度都更强; 在 DMC 试验中, 三维风场和暖湿核随着热带气旋强度的增加而持续增强; 在模拟早期, 发现 DMC 动力核心试验边界入流层中的空气较干燥, 通过水汽混合比收支分析可知这主要取决于模拟的垂直速度; DMC 试验边界层上方较高的上升气流使得 DMC 试验的边界层较 TMC 干, 这也导致热带气旋增强的主要能源[表面潜热通量 (SLHF)]增强; DMC 动力核心模拟的内核中上升气流较高, 导致净地表降雨率较高, 从而产生较高的内部净大气非绝热加热, 最终使得热带气旋 强度更强. 所有结果表明, DMC 动力核心模拟的热带气旋更强主要与 DMC 模拟的垂直速度更高有关.