Effect of Tropical Cyclones on the Northward Propagation of Boreal Summer Intraseasonal Oscillation over the Western North Pacific

It has been reported that although individual tropical cyclones (TCs) have a short existence period, their intense convective activity affects the expression of seasonal mean and intraseasonal variance (Hsu et al. 2008; Arakane and Hsu 2020, 2021). It has also been reported that many TCs occur during the active phase of the Boreal Summer Intraseasonal Oscillation (BSISO, Kikuchi 2021). Therefore, the TC signal may influence the expression and characteristics of BSISO. In this presentation, we report the effect of TC signals on the northward propagation of BSISO over the western North Pacific.
We use the potential vorticity inversion technique (Davis and Emanuel 1991) to remove the TC vortex that existed from 1958 to 2019 represented in the reanalysis data. By comparing the BSISO represented in the TC-removal data with the BSISO represented in the original data, we estimate the effect of the intrinsic TC signal in the BSISO.
Compared to the BSISO northward propagation represented in the original data, the phase speed of the northward propagation in the TC-removed data is almost unchanged, but its amplitude is reduced. This amplitude difference is considered to be an effect of TCs on the northward propagation of BSISO. This indicates that the TC signals are related to the northward propagation of BSISO, and also suggests that the TCs may promote the northward propagation.