Dynamical feedback between synoptic eddy and low-frequency flow as simulated by BCC_CSM1.1(m)

Abstract

Since the interaction between atmospheric synoptic eddy (SE) (2–8 days) activity and low-frequency (LF) (monthly) flow (referred to as SELF) plays an essential role in generating and maintaining dominant climate modes, an evaluation of the performance of BCC_CSM1.1(m) in simulating the SE feedback onto the LF flow is given in this paper. The model captures well the major spatial features of climatological eddy vorticity forcing, eddy-induced growth rate, and patterns of SELF feedback for the climate modes with large magnitudes in cold seasons and small magnitudes in warm seasons for both the Northern and Southern Hemisphere. As in observations, the eddy-induced growth rate and SELF feedback patterns in the model also show positive SE feedback. Overall, the relationships between SE and LF flow show that BCC_CSM1.1(m) satisfactorily captures the basic features of positive SE feedback, which demonstrates the simulation skill of the model for LF variability. Specifically, such an evaluation can help to find model biases of BCC_CSM1.1(m) in simulating SE feedback, which will provide a reference for the model’s application.

摘 要

由于中高纬大气中天气尺度涡旋(2–8天尺度)与低频流(月尺度)的相互作用对于气候主模态的产生和维持起着重要的作用, 本文就 BCC_CSM1.1(m)模式中大气低频流与天气涡旋反馈的模拟能力进行了检验评估. 结果表明, 模式能够很好的抓住气候平均的涡旋涡度强迫, 涡旋增长率, 以及涡旋对大气主模态的动力反馈的空间特征. 气候平均的涡旋涡度强迫的量级在北半球和南半球均在冷季节大于暖季节. 模式中的涡旋增长率以及涡旋对大气低频主模态的反馈特征均表明涡旋反馈为正反馈作用, 这些结果与观测相一致. 总体来说, 天气尺度涡旋与大气低频流的关系显示 BCC_CSM1.1(m)模式能够抓住涡旋反馈的基本特征, 表明该模式对于低频变率具有一定的模拟技巧. 此外, 该评估工作可以找到模式模拟涡旋反馈的偏差, 这对于模式的应用具有重要的参考依据.