Earth system models enable a broad range of climate interactions that physical climate models are unable to simulate. However, the extent to which adding Earth system components changes or improves the simulation of the physical climate is not well understood. Here we present a broad multivariate evaluation of the North Atlantic climate system in historical simulations of the UK Earth System Model (UKESM1) performed for CMIP6. In particular, we focus on the mean state and the decadal time scale evolution of important variables that span the North Atlantic climate system. In general, UKESM1 performs well and realistically simulates many aspects of the North Atlantic climate system. Like the physical version of the model, we find that changes in external forcing, and particularly aerosol forcing, are an important driver of multidecadal change in UKESM1, especially for Atlantic Multidecadal Variability and the Atlantic Meridional Overturning Circulation. However, many of the shortcomings identified are similar to common biases found in physical climate models, including the physical climate model that underpins UKESM1. For example, the summer jet is too weak and too far poleward; decadal variability in the winter jet is underestimated; intraseasonal stratospheric polar vortex variability is poorly represented; and Arctic sea ice is too thick. Forced shortwave changes may be also too strong in UKESM1, which, given the important role of historical aerosol forcing in shaping the evolution of the North Atlantic in UKESM1, motivates further investigation. Therefore, physical model development, alongside Earth system development, remains crucial in order to improve climate simulations.

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UKESM1 CMIP6历史模拟中对北大西洋气候系统的评估

地球系统模型可实现物理气候模型无法模拟的广泛的气候相互作用。但是，人们对增加地球系统组成部分在多大程度上改变或改善物理气候模拟的了解还不清楚。在这里，我们通过对CMIP6进行的英国地球系统模型（UKESM1）的历史模拟，对北大西洋气候系统进行了广泛的多元评估。特别是，我们关注跨越北大西洋气候系统的重要变量的平均状态和年代际尺度演变。总的来说，UKESM1表现良好，并且可以逼真的模拟北大西洋气候系统的许多方面。与模型的物理版本一样，我们发现外部强迫，尤其是气溶胶强迫的变化，是UKESM1多年代变化的重要推动力，尤其是对于大西洋多年代变率和大西洋子午向翻转环流。但是，发现的许多缺点与物理气候模型中发现的常见偏差相似，包括支持UKESM1的物理气候模型。例如，夏季喷气机太弱且向极点太远；冬季喷气机的年代际变化被低估了；季内平流层极地涡的可变性很难表示。北极海冰太厚。在UKESM1中，强迫的短波变化可能也太强，鉴于历史气溶胶强迫在塑造UKESM1中北大西洋的演变中的重要作用，这激发了进一步的研究。因此，物理模型开发与地球系统开发一起，