[A-AS03] Advances in Tropical Cyclone Research: Past, Present, and Future

[AAS03-07] Three-Dimensional Aspects of the Fujiwara Effect

Jae-Deok Lee¹, *Kosuke Ito², Johnny C. L. Chan³ (1.Kyungpook National University, 2.University of the Ryukyus, 3.City University of Hong Kong)

Keywords:tropical cyclone, Fujiwhara effect

A set of f-plane idealized numerical simulations at 15° N was conducted to understand the fundamental three-dimensional characteristics of the binary interaction of tropical cyclones (TCs). When the vortices are zonally separated by more than or equal to (less than) 10° of longitude, they tend to repel (rotate or merge). Binary interacting TCs have two maximum diabatic heating regions: one in the boundary layer and the other in the mid-troposphere. The maximum diabatic heating in the boundary layer is related to the supergradient wind with large radial inflows. As the vortex intensifies, the upper-anticyclonic circulation is also strengthened. These two upper-anticyclonic circulations form an extensive single anticyclonic circulation. In the absence of a background flow, this single anticyclonic circulation results in a vertical wind shear that contributes to a substantial asymmetry in diabatic heating, subsequently modifying TC motion. This shear-induced diabatic heating results in repelling storm trajectories. In contrast, experiments without microphysical heating show distinctly approaching trajectories. These two different experiments demonstrate the importance of diabatic heating in storm movement. The time series of the potential vorticity (PV) budget shows a well-balanced feature between the local change term and the sum of other PV diagnostic terms. Above the boundary layer, the PV budget is balanced between the diabatic and advective terms. The local change in PV shows that the subsequent TC motion coincides with the positive PV area. In addition, the positive PV explained by the PV advection term accounts for the same scenario. Meanwhile, When two vortices interact in closer proximity, vortex Rossby waves form inward of the vortex. Since the horizontal shear could generate these vortex Rossby waves, this result may account for an increase in the horizontal shear as a result of the direct binary interaction of TCs.