Energetics characteristics accounting for the low-level wind’s rapid enhancement associated with an extreme explosive extratropical cyclone over the western North Pacific Ocean

ABSTRACT

During mid-January 2011, a rarely seen twin-extratropical-cyclone event appeared over the western North Pacific Ocean. One of the twin cyclones developed into an extreme explosive extratropical cyclone (EEC), which was comparable to the intensity of a typhoon. Rotational and divergent wind kinetic energy (KE) analyses were applied to understand the low-level wind’s rapid enhancement associated with the cyclone. It was found that: (i) the total wind KE associated with the EEC showed a remarkable enhancement in the lower troposphere during the cyclone’s maximum development stage, with the maximum/minimum wind acceleration appearing in the southeastern/northwestern quadrant of the EEC; (ii) the rotational wind KE experienced an obvious increase, which corresponded to the total wind KE enhancement, whereas the divergent wind KE, which was much smaller than the rotational wind, mainly featured a decreasing trend; (iii) the rotational wind KE enhancement showed variational features consistent with the horizontal enlargement and upward stretching of the EEC; (iv) the nonorthogonal wind KE enhanced the total wind KE in regions with strong rotational wind, which resulted in the maximum lower-tropospheric maximum wind, whereas in regions with strong divergent wind it mainly reduced the total wind KE; (v) the northward transport of total wind KE and the rotational wind KE production due to the work done by pressure gradient force were dominant factors for the enhancement of winds associated with the EEC, particularly in its southeastern section. In contrast, an overall conversion from rotational wind KE to divergent wind KE decelerated the rotational wind enhancement.

Graphical abstract

摘要

2011年一月中旬, 西北太平洋上发生了一次罕见的双子气旋事件。该双子气旋中的一个气旋 (简称气旋A) 迅速发展成为一个强度堪比台风的极端强度爆发气旋。本文采用旋转风, 辐散风动能收支分析来研究造成该极端强度爆发气旋风速迅速增强的原因。研究发现, 在气旋A的最快发展期, 对流层低层, 气旋的总动能迅速增大, 风速增大最迅速的象限是气旋的东南象限, 而西北象限的增速最慢。旋转风动能的增长显著, 对应了总动能的增大, 而辐散风的动能显著小于旋转风动能并且主要表现出减少的趋势。旋转风动能的增大与气旋A在水平和垂直方向上的伸展过程相一致, 非正交风动能在旋转风动能大值区增强总动能, 这促使了对流层低层最大风速的形成, 然而, 在辐散风动能较强的区域, 非正交风动能主要减弱总动能。向北的总动能输送以及气压梯度力对旋转风动能的做功是气旋A风速迅速增大的主导因子, 尤其是在其东南象限。然而, 从旋转风向辐散风动能的转换在一定程度上延缓了气旋风速的增强过程。

KEYWORDS:

• Explosive extratropical cyclone
• rotational wind
• divergent wind
• kinetic energy
• twin cyclones

关键词:

• 爆发气旋
• 旋转风
• 辐散风
• 动能
• 双子气旋

Acknowledgments

The authors thank the National Centers for Environmental Prediction and the China Meteorological Administration for providing the data.

Disclosure statement

No potential conflict of interest was reported by the authors.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This research was supported by the National Key R&D Program of China [grant number 2018YFC0809400]; the National Natural Science Foundation of China [grant numbers 41775046 and 91637211]; and the Youth Innovation Promotion Association, Chinese Academy of Sciences.