一个使用传输算子的大气阻塞事件预警指标
An early warning indicator for atmospheric blocking events using transfer operators
摘要：
中纬度大气流动状况持续存在，时间尺度大于5-10天，并有迹象表明它们之间存在优先过渡，这促使人们为这种状况过渡制定预警指标。在本文中，我们使用一个半球正压模式与估计的传输运营商在一个约化的相空间开发一个预警指标的纬向阻塞流过渡在这个模型中。结果表明，转移算子的谱可以用来研究流动的慢动力学以及约化的非马尔可夫性质。最慢的运动，从而发现有三至六个星期的时间尺度，并与亚稳定制度（及其过渡），可以检测到几乎不变的转移算子集。从模型的能量收支，我们能够解释的制度的亚稳定性和优先过渡路径的存在。尽管该模型是高度简化的，但预警指标的技能是有希望的，这表明转移算子方法可以与业务确定性模型并行使用，用于随机预测或评估预测的不确定性。
英文摘要：
The existence of persistent midlatitude atmospheric flow regimes with time-scales larger than 5-10 days and indications of preferred transitions between them motivates to develop early warning indicators for such regime transitions. In this paper, we use a hemispheric barotropic model together with estimates of transfer operators on a reduced phase space to develop an early warning indicator of the zonal to blocked flow transition in this model. It is shown that, the spectrum of the transfer operators can be used to study the slow dynamics of the flow as well as the non-Markovian character of the reduction. The slowest motions are thereby found to have time scales of three to six weeks and to be associated with meta-stable regimes (and their transitions) which can be detected as almost-invariant sets of the transfer operator. From the energy budget of the model, we are able to explain the meta-stability of the regimes and the existence of preferred transition paths. Even though the model is highly simplified, the skill of the early warning indicator is promising, suggesting that the transfer operator approach can be used in parallel to an operational deterministic model for stochastic prediction or to assess forecast uncertainty.
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