大气环流简化模式中热浪和寒潮的大偏差理论分析
A Large Deviation Theory-based Analysis of Heat Waves and Cold Spells in a Simplified Model of the General Circulation of the Atmosphere
摘要：
本文利用大偏差理论研究了时间上持续和空间上扩展的极端温度异常事件，即热浪和寒潮。为此，我们考虑了一个简化的大气环流模式，并数值估计中纬度地区近地表温度的大偏差率函数。我们发现，重新归一化后的综合自相关的基础上，率函数在给定的纬度，通过寻找，在当地的空间，在长时间的平均值与所获得的一致，而不是通过寻找，在当地的时间，在大的空间平均值沿纬度。这是时空湍流尺度对称性和平流主要是纬向的结果。这种一致性暗示了温度场大偏差的普遍性。此外，我们发现，所获得的速率函数是能够描述空间上扩展和时间上持续的热浪或寒潮，如果我们考虑在中间空间尺度的空间平均值的时间平均值。最后，我们发现，大的偏差是相对更容易发生时，在这些空间平均在中间尺度上进行，从而指向与大气的低频变化的天气模式的存在。极值理论是用来衡量我们的结果。
英文摘要：
We study temporally persistent and spatially extended extreme events of temperature anomalies, i.e. heat waves and cold spells, using large deviation theory. To this end, we consider a simplified yet Earth-like general circulation model of the atmosphere and numerically estimate large deviation rate functions of near-surface temperature in the mid-latitudes. We find that, after a re-normalisation based on the integrated auto-correlation, the rate function one obtains at a given latitude by looking, locally in space, at long time averages agrees with what is obtained, instead, by looking, locally in time, at large spatial averages along the latitude. This is a result of scale symmetry in the spatial-temporal turbulence and of the fact that advection is primarily zonal. This agreement hints at the universality of large deviations of the temperature field. Furthermore, we discover that the obtained rate function is able to describe spatially extended and temporally persistent heat waves or cold spells, if we consider temporal averages of spatial averages over intermediate spatial scales. Finally, we find out that large deviations are relatively more likely to occur when looking at these spatial averages performed over intermediate scales, thus pointing to the existence of weather patterns associated to the low-frequency variability of the atmosphere. Extreme value theory is used to benchmark our results.
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