Upper-tropospheric potential vorticity anomaly before the rapid intensification of Typhoon Mujigae (2015) and its response to reduced SST

ABSTRACT

As the strongest typhoon in 2015, the rapid intensification (RI) process of Typhoon Mujigae is simulated at the cloud-resolving scale by utilizing the Weather Research and Forecasting model, coupled with observed sea surface temperature (SST) and reduced SST as the control and sensitivity experiments, respectively. The spatiotemporal distribution characteristics of upper-tropospheric potential vorticity (PV) and its response to SST changes are analyzed simultaneously. The results show a significant upper-tropospheric PV anomaly 6 h before RI, which indicates the approaching RI of Typhoon Mujigae. Deep convection overlies the strong signals of upper-tropospheric PV anomalies. More insight into the PV budget analysis verifies that the diabatic heating effect and vertical advection terms associated with deep convection dominate the upper-tropospheric PV anomaly, inferring that deep convection plays a crucial role in the upper-tropospheric PV anomaly. As SST decreases, diabatic heating and vertical advection effects are weakened due to reduced deep convection; therefore, the PV anomaly in the model run is not stronger than that in the control run, and the RI process of Mujigae disappears. Therefore, from the viewpoint of upper and lower-level interactions, how SST impacts upper-tropospheric PV anomalies and their interactions with RI are clarified. Thus, in addition to SST, the upper-tropospheric PV anomaly might be a significant factor in differentiating between RI and non-RI tropical cyclones.

GRAPHICAL ABSTRACT

摘要利用数值模拟, 研究了台风‘彩虹’快速增强 (RI) 前的高层位涡异常及其对海温改变的响应。发现 RI前6小时高对流层位涡异常显著, 伴随深对流的发展, 对RI有一定预示作用。位涡收支分析表明, 与深对流相关的非绝热加热项和垂直输送项是高层位涡异常的主要原因; 降低海温的数值模拟进一步验证了深对流对高层位涡异常的关键作用。本文从高低层相互作用的视角, 阐明除了海温, 高层位涡异常也成为区分RI与非RI热带气旋的重要因素之一。

KEYWORDS:

• Upper-tropospheric
• potential vorticity
• typhoon
• rapid intensification

关键词:

• 高层位涡
• 台风
• 快速增强

Acknowledgments

The valuable comments of the two anonymous reviewers, which helped considerably in improving the original manuscript, are greatly appreciated.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the National Key Research and Development Program of China [Grant Nos. 2018YFF0300102 and 2018YFC1506801]; and the National Natural Science Foundation of China [Grant Nos. 41405059, 41575064, 41875079, 41875077, 41875056, and 41630532].