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The stratospheric version of LMDz: dynamical climatologies, arctic oscillation, and impact on the surface climate

机译：LMDz的平流层版本：动态气候，北极振荡以及对地表气候的影响

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A climatology of the stratosphere is determined from a 20-year integration with the stratospheric version of the Atmospheric General Circulation Model LMDz. The model has an upper boundary at near 65 km, uses a Doppler spread non-orographic gravity waves drag parameterization and a subgrid-scale orography parameterization. It also has a Rayleigh damping layer for resolved waves only (not the zonal mean flow) over the top 5 km. This paper describes the basic features of the model and some aspects of its radiative-dynamical climatology. Standard first order diagnostics are presented but some emphasis is given to the model's ability to reproduce the low frequency variability of the stratosphere in the winter northern hemisphere. In this model, the stratospheric variability is dominated at each altitudes by patterns which have some similarities with the arctic oscillation (AO). For those patterns, the signal sometimes descends from the stratosphere to the troposphere. In an experiment where the parameterized orographic gravity waves that reach the stratosphere are exaggerated, the model stratosphere in the NH presents much less variability. Although the stratospheric variability is still dominated by patterns that resemble to the AO, the downward influence of the stratosphere along these patterns is near entirely lost. In the same time, the persistence of the surface AO decreases, which is consistent with the picture that this persistence is linked to the descent of the AO signal from the stratosphere to the troposphere. A comparison between the stratospheric version of the model, and its routinely used tropospheric version is also done. It shows that the introduction of the stratosphere in a model that already has a realistic AO persistence can lead to overestimate the actual influence of the stratospheric dynamics onto the surface AO. Although this result is certainly model dependent, it suggests that the introduction of the stratosphere in a GCM also call for a new adjustment of the model parameters that affect the tropospheric variability.
机译：平流层的气候学是通过与大气总环流模型LMDz的平流层版本进行20年整合而确定的。该模型的上限位于65 km附近，使用多普勒扩展非地形重力波拖曳参数化和次网格规模地形参数化。它还具有瑞利阻尼层，仅用于顶部5 km的已分解波（不是区域平均流量）。本文介绍了该模型的基本特征及其辐射动力气候学的某些方面。提出了标准的一阶诊断方法，但对模型在冬季北半球平流层低频变化的再现能力也有所强调。在这个模型中，平流层的变化性在每个海拔高度上都由与北极振荡（AO）有一些相似性的模式所决定。对于这些模式，信号有时会从平流层下降到对流层。在夸大到达平流层的参数化地形重力波的实验中，新罕布什尔州的模型平流层呈现出的可变性要小得多。尽管平流层的变化性仍由类似于AO的模式所控制，但平流层沿这些模式的向下影响几乎完全消失了。同时，表面AO的余辉减小，这与该余辉与AO信号从平流层到对流层的下降有关的图片一致。还对模型的平流层版本与其常规使用的对流层版本进行了比较。它表明将平流层引入已经具有实际AO持久性的模型中可能导致高估平流层动力学对表面AO的实际影响。尽管此结果当然取决于模型，但它表明在GCM中引入平流层也需要对影响对流层变化性的模型参数进行新的调整。

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