A new mathematical framework for atmospheric blocking events
A new mathematical framework for atmospheric blocking events
复制标题
大气阻塞事件的新数学框架
作者：
V. Lucarini;A. Gritsun
我们使用一个简单的，但地球一样的半球大气模型，提出了一个新的框架阻塞事件的数学性质。使用有限时间的李雅普诺夫指数，我们表明，阻塞的发生与条件具有极大的高不稳定性。较长时间的阻塞非常罕见，通常具有较高的不稳定性。在大西洋阻塞的情况下，可预测性特别是在阻塞事件的发生和衰减减少，而相对增加的可预测性被发现在成熟阶段。太平洋板块的情况正好相反，成熟阶段的可预测性最低。当系统的轨迹处于特定的不稳定周期轨道（UPO）的附近时，就会发生阻塞，这些不稳定周期轨道是覆盖系统吸引子的自然变化模式。与阻塞相对应的UPO确实比与纬向流相关联的UPO具有更高程度的不稳定性。我们的研究结果提供了一个严格的理由，经典的马尔可夫链为基础的分析天气制度之间的转换。UPO的分析阐明，该模型具有非常严重的违反双曲性，由于不稳定的维度的数量存在很大的变化，这解释了为什么大气状态可以在其可预测性方面有很大的不同。此外，这样的可变性解释了需要进行数据同化的状态空间，不仅包括不稳定和中性的子空间，但也有一些稳定的modes.The缺乏鲁棒性与违反双曲性可能是一个基本的原因，导致难以表示阻塞的数值模式，并在预测他们的统计数据将如何改变气候变化的结果。这对应的基本问题，限制了我们的能力，建立非常准确的数值模型的大气，在可预测性的第一和第二种意义上的洛伦兹。
We use a simple yet Earth-like hemispheric atmospheric model to propose a new framework for the mathematical properties of blocking events. Using finite-time Lyapunov exponents, we show that the occurrence of blockings is associated with conditions featuring anomalously high instability. Longer-lived blockings are very rare and have typically higher instability. In the case of Atlantic blockings, predictability is especially reduced at the onset and decay of the blocking event, while a relative increase of predictability is found in the mature phase. The opposite holds for Pacific blockings, for which predictability is lowest in the mature phase. Blockings are realised when the trajectory of the system is in the neighbourhood of a specific class of unstable periodic orbits (UPOs), natural modes of variability that cover the attractor the system. UPOs corresponding to blockings have, indeed, a higher degree of instability compared to UPOs associated with zonal flow. Our results provide a rigorous justification for the classical Markov chains-based analysis of transitions between weather regimes. The analysis of UPOs elucidates that the model features a very severe violation of hyperbolicity, due to the presence of a substantial variability in the number of unstable dimensions, which explains why atmospheric states can differ a lot in term of their predictability. Additionally, such a variability explains the need for performing data assimilation in a state space that includes not only the unstable and neutral subspaces, but also some stable modes. The lack of robustness associated with the violation of hyperbolicity might be a basic cause contributing to the difficulty in representing blockings in numerical models and in predicting how their statistics will change as a result of climate change. This corresponds to fundamental issues limiting our ability to construct very accurate numerical models of the atmosphere, in term of predictability of the both the first and of the second kind in the sense of Lorenz.
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DOI：
10.1016/j.physd.2017.02.015
发表时间：
2016-04
期刊：
Physica D: Nonlinear Phenomena
影响因子：
--
作者：
A. Gritsun;V. Lucarini
通讯作者：
A. Gritsun;V. Lucarini
影响因子：
3.1
作者：
Franzke, Christian;Woollings, Tim;Martius, Olivia
通讯作者：
Martius, Olivia
影响因子：
4.9
作者：
G. Masato;B. Hoskins;T. Woollings
通讯作者：
G. Masato;B. Hoskins;T. Woollings
影响因子：
3.7
作者：
Chandler, Gary J.;Kerswell, Rich R.
通讯作者：
Kerswell, Rich R.