Application of the Cyclone Phase Space to Extratropical Transition in a Global Climate Model
Application of the Cyclone Phase Space to Extratropical Transition in a Global Climate Model
复制标题
气旋相空间在全球气候模型中温带转变中的应用
DOI：
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发表时间：
2020
影响因子：
6.8
通讯作者：
G. Vecchi
中科院分区：
文献类型：
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作者：
M. Bieli;A. Sobel;S. Camargo;H. Murakami;G. Vecchi
分析了全球热带气旋温带转换(ET)的全球统计资料，采用通量调整模式(FLOR-FA)预报了CM2.5的低海洋分辨率版本。气旋相空间(CPS)用于诊断ET。分析了近期历史气候的模拟，并与日本55年再分析(JRA-55)资料进行了比较，然后将代表集中路径4.5下的21世纪末气候模拟与历史模拟进行了比较。当将CPS应用于历史模拟中的FLOR-FA输出时，由于高层位势中存在强烈的局地极大值，结果与从JRA-55获得的结果不同，因为在低纬地区有不现实的ET个例数量。这些特征会误导CP探测到没有冷核的冷核。通过将CPS所需的最大值替换为第95个百分位值，或及时平滑CPS轨迹，或两者兼而有之，可在很大程度上纠正误诊。其他气候模型可能包含类似于FLOR-FA中的网格尺度结构，当用于CPS分析时，需要这里讨论的解决方案。预测未来气候中的ET与历史气候的比较显示，许多变化与ET诊断的细节是稳健的，尽管根据标准测试，很少有统计上显著的变化。其中包括ET含量的增加和出现在西北太平洋的ET的平均纬度的降低。
The authors analyze the global statistics of tropical cyclones undergoing extratropical transition (ET) in the Forecast‐oriented Low Ocean Resolution version of CM2.5 with Flux Adjustment (FLOR‐FA). The cyclone phase space (CPS) is used to diagnose ET. A simulation of the recent historical climate is analyzed and compared with data from the Japanese 55‐year Reanalysis (JRA‐55), and then a simulation of late 21st century climate under Representative Concentration Pathway 4.5 is compared to the historical simulation. When CPS is applied to the FLOR‐FA output in the historical simulation, the results diverge from those obtained from JRA‐55 by having an unrealistic number of ET cases at low latitudes, due to the presence of strong local maxima in the upper‐level geopotential. These features mislead CPS into detecting a cold core where one is not present. The misdiagnosis is largely corrected by replacing the maxima required by CPS with the 95th percentile values, smoothing the CPS trajectories in time, or both. Other climate models may contain grid‐scale structures akin to those in FLOR‐FA and, when used for CPS analysis, require solutions such as those discussed here. Comparisons of ET in the projected future climate with the historical climate show a number of changes that are robust to the details of the ET diagnosis, though few are statistically significant according to standard tests. Among them are an increase in the ET fraction and a reduction in the mean latitude at which ET occurs in the western North Pacific.