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Dynamical properties and extremes of Northern Hemisphere climate fields over the past 60 years

机译：过去60年中北半球气候场的动力学性质和极端

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Atmospheric dynamics are described by a set of partial differential equations yielding an infinite-dimensional phase space. However, the actual trajectories followed by the system appear to be constrained to a finite-dimensional phase space, i.e. a strange attractor. The dynamical properties of this attractor are difficult to determine due to the complex nature of atmospheric motions. A first step to simplify the problem is to focus on observables which affect – or are linked to phenomena which affect – human welfare and activities, such as sea-level pressure, 2?m temperature, and precipitation frequency. We make use of recent advances in dynamical systems theory to estimate two instantaneous dynamical properties of the above fields for the Northern Hemisphere: local dimension and persistence. We then use these metrics to characterize the seasonality of the different fields and their interplay. We further analyse the large-scale anomaly patterns corresponding to phase-space extremes – namely time steps at which the fields display extremes in their instantaneous dynamical properties. The analysis is based on the NCEP/NCAR reanalysis data, over the period 1948–2013. The results show that (i) despite the high dimensionality of atmospheric dynamics, the Northern Hemisphere sea-level pressure and temperature fields can on average be described by roughly 20 degrees of freedom; (ii) the precipitation field has a higher dimensionality; and (iii) the seasonal forcing modulates the variability of the dynamical indicators and affects the occurrence of phase-space extremes. We further identify a number of robust correlations between the dynamical properties of the different variables.
机译：大气动力学由一组产生无穷维相空间的偏微分方程描述。但是，系统所遵循的实际轨迹似乎被限制在一个有限维的相空间中，即一个奇怪的吸引子。由于大气运动的复杂性，很难确定该吸引子的动力学特性。简化问题的第一步是关注可观察到的事物，这些可观察到的事物会影响人类的福利和活动，或者与这些现象相关联，例如海平面压力，2？m温度和降水频率。我们利用动力学系统理论的最新进展来估计北半球上述场的两个瞬时动力学性质：局部维和持久性。然后，我们使用这些指标来描述不同字段的季节性及其相互作用。我们进一步分析与相空间极端相对应的大规模异常模式，即相变场在其瞬时动态特性中显示极端的时间步长。该分析基于1948–2013年期间的NCEP / NCAR再分析数据。结果表明：（i）尽管大气动力学的维数很高，但平均而言，北半球的海平面压力和温度场可以用大约20个自由度来描述; （ii）降水场具有更高的维数; （iii）季节性强迫调节了动力指标的可变性，并影响了相空间极端的发生。我们进一步确定了不同变量的动力学特性之间的一些稳健的相关性。

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