Quasi‐Periodic Intensification of Convective Asymmetries in the Outer Eyewall of Typhoon Lekima (2019)

• Published in: Geophysical research letters 2021-03, Vol.48 (5), p.n/a
• Main Authors: Dai, Huaning, Zhao, Kun, Li, Qingqing, Lee, Wen‐Chau, Ming, Jie, Zhou, Ang, Fan, Xueqi, Yang, Zhengwei, Zheng, Feng, Duan, Yihong
• Format: Article
• Language: English
• Subjects: asymmetric convection; concentric eyewall; vortex Rossby wave
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL091633

Typhoon Lekima (2019) possessed a double‐eyewall structure before making landfall in eastern China, with its outer eyewall showing quasi‐periodic convective intensification. Several physical mechanisms that may cause eyewall convection asymmetries were examined. The upshear occurrence of the strongest convection could not be explained by either the typhoon's motion or the effect of descending inflow from outer rainbands. Radar reflectivity analysis showed that phase locking occurred between the wavenumber‐2 vortex Rossby waves (VRWs) propagating radially outward from the inner eyewall and the azimuthally propagating wavenumber‐1 VRWs on the inner edge of the outer eyewall. Additional phase locking further arose between the aforementioned wavenumber‐1 VRWs and the azimuthally propagating wavenumber‐2 VRWs on the outer edge of the outer eyewall. These two phase‐locking processes led to the pronounced quasi‐periodic intensification of the convective asymmetry in the western semicircle of Lekima's outer eyewall. Plain Language Summary Tropical cyclone eyewalls are commonly accompanied by torrential rainfall that tends to cause flooding and devastation. In particular, precipitation prediction becomes more challenging when the eyewall convective activity exhibits a markedly asymmetric structure. This work focuses on the repeated occurrence of strong convection in the outer eyewall of Typhoon Lekima (2019) before it made landfall in China. The coastal ground‐based radar observations show that phase locking between waves associated with the double eyewalls serves as a plausible mechanism for the presence of the repeated strong precipitation in Lekima's outer eyewall. The findings in this study highlight the merit of coastal ground‐based radar observations in examining physical processes of tropical cyclone structure evolution, particularly in regions without aircraft reconnaissance. Key Points Radar observations revealed quasi‐periodic intensification of convective asymmetries in the outer eyewall of Typhoon Lekima The strongest convection in the outer eyewall occurred upshear Phase locking between vortex Rossby waves in the concentric eyewalls led to the occurrence of quasi‐periodic asymmetric convection