This study assesses a Continuous Data Assimilation (CDA) dynamical-downscaling algorithm for enhancing the simulation of the Indian summer monsoon (ISM) system. CDA is a mathematically rigorous technique that has been recently introduced to constrain the large-scale features of high-resolution atmospheric models with coarse spatial scale data. It is similar to spectral nudging but does not require any spectral decomposition for scales separation. This is expected to be particularly relevant for ISM, which involves various interactions between large-scale circulations and regional physical processes. Along with a control simulation, several downscaling simulations were conducted with the Weather Research and Forecasting (WRF) model using CDA, spectral (retaining different wavenumbers) and grid nudging for three ISM seasons: normal (2016), excess (2013), and drought (2009). The simulations are nested within the NCEP Final Analysis and the model outputs are evaluated against the observations. Compared to grid and spectral nudging, the simulations using CDA produce enhanced ISM features over the Indian subcontinent including the low-level jet, tropical easterly jet, easterly wind shear, and rainfall distributions for all investigated ISM seasons. The major ISM processes, in particular the monsoon inversion over the Arabian Sea, tropospheric temperature gradients and moist static energy over central India, and zonal wind shear over the monsoon region, are all better simulated with CDA. Spectral nudging outputs are found to be sensitive to the choice of the wavenumber, requiring careful tuning to provide robust simulations of the ISM system. In contrast, control and grid nudging generally fail to well reproduce some of the main ISM features.
翻译:本研究评估了持续数据同化(CDA)动态降缩算法,用于加强印度夏季季风系统模拟。CDA是一种数学上严格的技术,最近采用了这一技术来限制高分辨率大气模型的大规模特征,其空间尺度数据粗糙。这与光谱裸化相似,但不需要光谱分解来进行比例分离。这对ISM特别相关,它涉及大型循环流和区域敏感物理进程之间的各种互动。在进行控制模拟的同时,与天气研究和预报(WRF)模型一起进行了几次降缩缩缩缩缩模拟,使用的是CDA、光谱(保持不同的波数)和电网,以限制高分辨率大气模型模型的三个季节:正常(2016年)、超升和干旱(2009年)。模拟在NCEPEB最后分析中嵌入,模型输出根据观测结果进行评估。与大型循环的网络和光谱内层内,利用CDA的模拟在印度次大陆次中发现了强化的IMM特征,包括需要低级的轨道、热带的轨道 Slove Streal Syal Serverial 和整个海流流流流流流中,一般的流流流流流流流流流流流的S。