Characteristics of tropical-extratropical cloud bands over tropical and subtropical South America simulated by BAM-1.2 and HadGEM3-GC3.1
Characteristics of tropical-extratropical cloud bands over tropical and subtropical South America simulated by BAM-1.2 and HadGEM3-GC3.1
复制标题
BAM-1.2和HadGEM3-GC3.1模拟的南美洲热带和副热带云带特征
DOI：
10.1002/qj.4470
复制
发表时间：
2023
影响因子：
8.9
通讯作者：
Zilli M
中科院分区：
文献类型：
--
作者：
Zilli M
热带-温带云带在南美洲很常见，对雨季总降水量有很大贡献。因此，至关重要的是，气候和天气预报模型正确地反映了它们及其相关的动态方面。采用基于事件的框架，我们评估了两个全球模型在模拟SAm上观测到的云带方面的性能：巴西全球大气模型版本1.2（BAM‐1.2）和全球耦合配置3.1中的Hadley中心全球环境模型（HadGEM 3 ‐ GC 3.1）。这两个模式再现云带的主要特征和动力学方面导致其发展和持续性。尽管如此，在模拟云带降水的偏差贡献了50%以上的偏差，在一些地区的总降水。BAM-1.2模拟的云带比观测到的少，但更持久; HadGEM-3-GC 3.1模拟的云带活动在初夏较弱，1月后比观测到的更持久。在所有模式中，云带事件的偏差来自基本状态偏差和天气尺度区域环流之间的相互作用。在基本状态下，中纬度南太平洋上空较强的高层西风支持较长和较慢的Rossby波向副热带SAm的传播，增加了云带事件的持续时间。这种偏差与副热带南半球上空高层西风带的负偏差相互作用，增加了风切变，阻碍了天气尺度罗斯贝波向低纬度地区的传播，并导致云带位置、强度和季节性的偏差。在本研究中应用基于事件的框架，对模型分辨率和复杂性的差异具有鲁棒性，能够识别循环中微小但关键的偏倚。这些偏差与天气尺度降雨系统偏差有关，有助于解释季节总降雨量模型偏差。
Tropical–extratropical cloud bands are common in South America (SAm), contributing significantly to the total rainy season precipitation. Thus, it is fundamental that climate and weather forecast models correctly represent them and their associated dynamic aspects. Adopting an event‐based framework, we evaluate the performance of two global models in simulating the observed cloud bands over SAm: the Brazilian Global Atmospheric Model version 1.2 (BAM‐1.2) and the Hadley Centre Global Environment Model in the Global Coupled configuration 3.1 (HadGEM3‐GC3.1). Both models reproduce the main characteristics of cloud bands and the dynamical aspects leading to their development and persistence. Nonetheless, the biases in precipitation during simulated cloud bands contribute more than 50% of the bias in total precipitation in some regions. BAM‐1.2 simulates fewer but more persistent cloud bands than observed; HadGEM3‐GC3.1 simulates weaker cloud band activity during early summer and more persistent events after January than observed. In all models, the biases in cloud band events arise from the interaction between biases in the basic state and the synoptic‐scale regional circulation. In the basic state, stronger upper level westerlies over the midlatitude South Pacific support the propagation of longer and slower Rossby waves towards subtropical SAm, increasing the duration of the cloud band events. This bias interacts with negative biases in the upper level westerlies over subtropical SAm, increasing the wind shear, hindering the propagation of synoptic‐scale Rossby waves into lower latitudes, and resulting in biases in the cloud band location, intensity, and seasonality. The application in this study of an event‐based framework robust to differences in model resolution and complexity enables the identification of small but critical biases in circulation. These biases are linked to synoptic‐scale rainfall system biases and help to explain the season total rainfall model biases.