Composite Analysis of the Beta-gyre and Rossby Wave Induced by Tropical Cyclones

Beta gyre and Rossby wave train induced by tropical cyclones were identified from the ERA5 global-reanalysis data of the recent 30 years using a composite method. To pick up the disturbances relevant to the beta gyre and Rossby wave train surrounding tropical cyclones, the disturbances were decomposed into three distinct horizontal scales including small, intermediate, and planetary-scale. Composite map of the disturbances containing small- and intermediate-scale showed a well-organized Rossby wave train. The orientation of wave train was found to depend on the translation direction of tropical cyclones, and also appeared to split into two orientations except for those translating in the west-northwestward direction. The wave energy of the wave train was shown to propagate along the wave train axis, which was inferred from the amplitude change with time within the wave train. The wave train shows a weak upward-westward tilt and increasing amplitude with height, implying the wave energy propagating upward. A dipole circulation cell, bearing a close resemblance to the beta gyre depicted in the theories and numerical models, was found from the Rossby wave train. The strength and orientation of the beta gyres were revealed to vary with the translation direction of the tropical cyclones, with the weakest and strongest amplitudes being found for the westward- and northward-translation cases, respectively. It was shown that the orientation of the beta gyre obtained by a lag-composite method rotates clockwise with time regardless of the translation direction of tropical cyclones.