Composite analysis of Rossby wave train associated with tropical cyclones

Abstract:

Composite analysis was applied to the global-reanalysis data of ERA5 to detect the Rossby wave train that is generated by tropical cyclones. Total of about 4,400 global fields of 240 named tropical cyclones in the Northwestern Pacific ocean (Typhoons) for the period of 2000-2019 were analyzed. To select the disturbances relevant to the Rossby wave train, the disturbances of planetary scale and low-frequency component were eliminated from the reanalysis data, using a high-order spherical harmonics filter and a low-pass filter, respectively. Disturbance fields that contains the Rossby wave train were superimposed over the center of tropical cyclones to produce a composite map. The composite map showed the Rossby wave train which appeared to surround the tropical cyclone and have alignment in southeasterly direction, in agreement with the depiction by numerical simulations. Through the lag-composite analysis, it was revealed that the Rossby-wave train generated by tropical cyclones was found to rotate clockwise with time, implying that it continuously evolves with time without reaching a steady state. The structure of the Rossby wave train was found to depend on the translation direction as well as the size of tropical cyclones. Sensitivity analysis indicated that the Rossby-wave train is not sensitive to the criteria used to define the disturbances of planetary scale and low frequency.