Information Length as a Useful Index to Understand Variability in the Global Circulation
Information Length as a Useful Index to Understand Variability in the Global Circulation
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DOI：
10.3390/math8020299
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发表时间：
2020-02-01
期刊：
影响因子：
2.4
通讯作者：
Liu, Hanli
中科院分区：
文献类型：
--
作者：
Kim, Eun-jin;Heseltine, James;Liu, Hanli
随着测量和建模技术的改进，可变性已成为非平衡过程的一个基本特征。虽然传统上，均值和方差被大量使用，但它们不适合描述经常发生显著偏离均值的极端事件。此外，稳态概率密度函数（PDF）错过了与可变性相关的动态的关键信息。因此，关键是要超越传统的方法，处理时间依赖的PDF。在这里，我们考虑来自全大气社区气候模式（WACCM）的大气数据，并计算随时间变化的PDF和来自这些PDF的信息长度，这是一个系统在时间上演变的统计上不同的状态的总数。具体而言，我们考虑了三种情况下的抽样数据，以调查信息（信息预算）沿海拔和经度的分布沿着，以获得一个新的视角来理解变异性，不同变量和地区之间的相关性。随时间变化的PDF被证明是非高斯一般的信息长度往往会增加的高度，虽然在一个复杂的形式，这种趋势是更强大的流量/剪切比温度。与温度相比，流动和剪切在信息长度上也有很大的相似性。这意味着流动/剪切之间的强相关性，因为它们在这个特定的WACCM模型中通过重力波耦合。我们还发现，随着纬度和有趣的半球不对称的流量/剪切/温度的信息长度的增加，与反相关（相关）的趋势之间的流量/剪切和温度在高（低）纬度。这些结果表明高纬度/高度在地球大气层信息预算中的重要性，信息长度的空间梯度是信息流的一个有用的代理。
With improved measurement and modelling technology, variability has emerged as an essential feature in non-equilibrium processes. While traditionally, mean values and variance have been heavily used, they are not appropriate in describing extreme events where a significant deviation from mean values often occurs. Furthermore, stationary Probability Density Functions (PDFs) miss crucial information about the dynamics associated with variability. It is thus critical to go beyond a traditional approach and deal with time-dependent PDFs. Here, we consider atmospheric data from the Whole Atmosphere Community Climate Model (WACCM) and calculate time-dependent PDFs and the information length from these PDFs, which is the total number of statistically different states that a system evolves through in time. Specifically, we consider the three cases of sampling data to investigate the distribution of information (information budget) along the altitude and longitude to gain a new perspective of understanding variabilities, correlation among different variables and regions. Time-dependent PDFs are shown to be non-Gaussian in general; the information length tends to increase with the altitude albeit in a complex form; this tendency is more robust for flows/shears than temperature. Much similarity among flows and shears in the information length is also found in comparison with the temperature. This means a strong correlation among flows/shears because of their coupling through gravity waves in this particular WACCM model. We also find the increase of the information length with the latitude and interesting hemispheric asymmetry for flows/shears/temperature, with the tendency of anti-correlation (correlation) between flows/shears and temperature at high (low) latitude. These results suggest the importance of high latitude/altitude in the information budget in the Earth's atmosphere, the spatial gradient of the information length being a useful proxy for information flow.