AMIP Simulations of a Global Model for Unified Weather‐Climate Forecast: Understanding Precipitation Characteristics and Sensitivity Over East Asia

Abstract

A global model formulation for unified weather‐climate forecast is evaluated, with emphasis on the climate simulations at typical hydrostatic resolutions. The internal sensitivity is explored by considering different dynamical configurations (resolution, solver type, transport scheme). After a basic assessment of the global mean climate, a detailed analysis of precipitation characteristics is extended to East Asia. The model shows a reasonable mean state, seasonal variation, frequency–intensity structure, and diurnal phase time. The artificial rainfall around the steep slopes of the Tibetan Plateau can be improved through choices in the dynamical configuration. The regional features characterized by “afternoon versus nocturnal‐to‐early‐morning peaks” are properly distinguished. The hourly climatic features are comparable to super‐parameterized CAM5. Different dynamical configurations demonstrate unique sensitivities related to underling physical mechanisms, which are studied from the perspective of the diurnal cycle for three representative regions. Over South China, the higher‐resolution models decrease the weak‐precipitation while increase intense rainfall, thus reducing the dry biases. This is contributed by enhanced grid and sub‐grid scale motions associated with daytime convection progression. Over central western China, the variable‐resolution model better simulates the eastward propagating episodes characterized by a transition from convective to stratiform rainfall along the eastern slope of the Plateau. This reduces the positive biases at the high topography of the Plateau and alleviates the negative biases at the lower foot. Over central eastern China, the model replicates the dominant role of large‐scale governing factors in regulating the early morning rainfall peaks, and produces stratiform heating patterns.

Improved Climate Simulation by Using a Double‐Plume Convection Scheme in a Global Model

“…Park et al, 2014). In addition, the positive biases around the great mountain areas have a close relationship with the advection scheme in the dynamical core (Zhang et al, 2021). Precipitation simulations from DP show smaller RMSE (1.12) and larger pattern correlation (0.91) than those from ZM-UW (RMSE = 1.26, r = 0.87).…”

“…Park et al., 2014). In addition, the positive biases around the great mountain areas have a close relationship with the advection scheme in the dynamical core (Zhang et al., 2021).…”

“…The simulated wind magnitude at midlatitudes is slightly stronger than observed, especially in the upper troposphere, the maximum of which shows a northward shift in December–January–February (DJF). This may be related to the absence of parameterized orographic gravity wave drag (cf., Zhang et al., 2021). The zonal‐mean temperature and zonal wind simulated by ZM‐UW are very similar to those of DP (not shown).…”

“…The model physics time step is 1,800 s. Except the physics suite and its coupling strategy to dynamics (including time step), other model configurations (dynamics, initial and boundary datasets) are identical to those in Zhang et al. (2021). Thus, though not a particular focus of this study, our work loosely gives an intercomparison (e.g., mean climate and precipitation) of different physics suites within a unified modeling system.…”

“…The horizontal discretization uses the "hexagonal" Arakawa-C grid approach (Ringler et al, 2010;Skamarock & Gassmann, 2011;Thuburn et al, 2009), 10.1029/2021JD036069 3 of 23 behaving like a high-order anticipated potential vorticity method (Zhang, 2018). The dynamical solver has been assessed in various configurations (e.g., Wang et al, 2019;Zhang et al, 2021;Zhou et al, 2020), and demonstrates reliable physical and computational performance. In this study, we restrict our efforts to the hydrostatic dynamical core and a uniform-resolution (120 km, 30 vertical levels) configuration, both of which are typical of today's GCMs.…”