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ABSTRACT
An algorithm for identifying extratropical cyclones (ECs) on the basis of gridded data is proposed in this study. The algorithm, which is named the eight-section slope detecting (ESSD) method, has five key procedures to identify an EC by using the mean sea level pressure (MSLP) or geopotential height. They are: (i) finding the location of every minimum of the MSLP/geopotential-height; (ii) establishing a targeted box for each minimum; (iii) dividing the targeted box into eight sub-regions; (iv) calculating eight relative slopes within the eight sub-regions; (v) confirming an EC only if all eight relative slopes are above an appropriate threshold. Based on the 0.75° × 0.75° ERA-Interim reanalysis field, comparisons show that the ESSD method performs better in identifying ECs than the other three previous EC detection algorithms, as it can lower the error caused by mistaking a trough for an EC. Moreover, a test of detecting ECs in the Northern Hemisphere using the ESSD method repeated 500 times (randomly distributed across 40 years) shows that the accuracy of this method varies from 79% to 91%, with an annual mean accuracy of ~85%. This means that the ESSD method can provide credible results with respect to EC identification.
Graphical abstract
摘要
本文提出了一种用于格点数据识别气旋 (EC) 的算法—八区域斜率法 (ESSD) 。该方法基于平均海平面气压 (MSLP)/位势高度场, 主要步骤如下: (1) 搜索MSLP/位势高度场极小值的位置; (2) 在极小值位置周围建立一个矩形关键区; (3) 将关键区划分成八个子区; (4) 计算各子区变量的相对斜率; (5) 如果所有子区的斜率均超过给定阈值, 则识别为气旋。基于0.75° × 0.75° ERA-Interim资料与其他三种方法的比较显示, ESSD方法可以减少将槽误识别成气旋的情况。此外, 在北半球区域, 在40年间随机选取500个时次, 对该方法进行测试, 结果显示准确率在79%到91%之间波动, 其中平均准确率约为85%。这表明ESSD方法对气旋进行的识别效果是可信的。
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Disclosure statement
No potential conflict of interest was reported by the authors.