Jet latitude regimes and the predictability of the North Atlantic Oscillation,Quarterly Journal of the Royal Meteorological Society

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Jet latitude regimes and the predictability of the North Atlantic Oscillation
Quarterly Journal of the Royal Meteorological Society ( IF 3.0 ) Pub Date : 2020-04-21 , DOI: 10.1002/qj.3796
Kristian Strommen ₁

Affiliation

In recent years, numerical weather prediction models have begun to show notable levels of skill at predicting the average winter North Atlantic Oscillation (NAO) when initialised one month ahead. At the same time, these model predictions exhibit unusually low signal‐to‐noise ratios, in what has been dubbed a ‘signal‐to‐noise paradox’. We analyse both the skill and signal‐to‐noise ratio of the Integrated Forecast System (IFS), the European Centre for Medium‐range Weather Forecasts (ECMWF) model, in an ensemble hindcast experiment. Specifically, we examine the contribution to both from the regime dynamics of the North Atlantic eddy‐driven jet. This is done by constructing a statistical model which captures the predictability inherent to the trimodal jet latitude system, and fitting its parameters to reanalysis and IFS data. Predictability in this regime system is driven by interannual variations in the persistence of the jet latitude regimes, which determine the preferred state of the jet. We show that the IFS has skill at predicting such variations in persistence: because the position of the jet strongly influences the NAO, this automatically generates skill at predicting the NAO. We show that all of the skill the IFS has at predicting the winter NAO over the period 1980–2010 can be attributed to its skill at predicting regime persistence in this way. Similarly, the tendency of the IFS to underestimate regime persistence can account for the low signal‐to‐noise ratio, giving a possible explanation for the signal‐to‐noise paradox. Finally, we examine how external forcing drives variability in jet persistence, and highlight the role played by transient baroclinic eddy feedbacks to modulate regime persistence.

中文翻译：

飞机的纬度状况和北大西洋涛动的可预测性

近年来，数值天气预报模型在提前一个月初始化时，已经开始显示出显着的水平，可以预测北大西洋涛动的平均冬天。同时，这些模型预测显示出异常低的信噪比，被称为“信噪比悖论”。在整体后验实验中，我们分析了欧洲中期天气预报中心（ECMWF）模型的综合预报系统（IFS）的技能和信噪比。具体来说，我们研究了北大西洋涡流驱动喷气机对动力系统的贡献。这是通过构建一个统计模型来完成的，该模型捕获了三峰喷射纬度系统固有的可预测性，并将其参数拟合到重新分析和IFS数据中。该方案系统的可预测性是由喷气纬度方案持续时间的年际变化所决定的，这决定了喷气机的优选状态。我们证明了IFS具有预测这种持久性变化的技能：由于射流的位置会强烈影响NAO，因此自动生成了预测NAO的技能。我们表明，IFS预测1980-2010年冬季NAO的所有技能都可以归因于其以这种方式预测政权持续性的技能。同样，IFS低估制度持续性的趋势可以解释低信噪比，从而为信噪悖论提供了可能的解释。最后，我们研究了外部强迫如何驱动射流持久性的变化，

更新日期：2020-04-21

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