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

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.