子計畫：尺度交互作用對超高解析度全球模式模擬颱風氣候變遷之影響(II）

The heavy rainfall associated with typhoon has strong impact on the total precipitation (drought and flood) over the East Asia and Taiwan region. Thus, the impact of large-scale circulation on the tropical cyclones activity has received considerable attention. However, two-way interaction may exist between tropical cyclones and the large-scale circulation. The effect of this two-way interaction on the simulation tropical cyclones (TC) activity in the climate models has less been investigated. In this study, the effect of scale-interaction on the simulation of TC in two high resolution models: HiRAM at 25 km and MRI at 20 km horizontal resolution was investigate. A newly developed three-dimensional SSE kinetic energy equation was adopted to quantitatively estimate the relative contribution of synoptic-mean and synoptic-intraseasonal oscillation (ISO) interactions to the growth of synoptic-scale eddy (SSE) kinetic energy at different ISO phases. Results showed that TC genesis frequency increase (decrease) during ISO westerly (easterly) phase in the western North Pacific. This feature was well simulated in two high resolution models. Ensemble mean from two individual models reduced bias from each individual model and performed the best. TC genesis frequency increase (decrease) during ISO westerly (easterly) phase not only contributed by the enhancement (reduction) of CKS-M (barotropic energy conversion between SSE and mean flow) but also modulated by CKS-ISO (barotropic energy conversion between SSE and ISO). The mean circulation provided more (less) energy to SSE due to the enhancement (weakening) of the monsoon trough and SSE during ISO westerly (easterly) phase. The observed and simulated ISO cyclonic circulation enhanced CKS-ISO which are coincided with the mean monsoon trough and favorable for the TC genesis at ISO westerly phase. On the other hand, upscale energy conversion from SSEs to ISO anti-cyclonic flow (CKS-ISO < 0) was observed and simulated during the ISO easterly phase. The weaker SSE activity during the ISO easterly phase occurred not only because the mean circulation provides less energy to SSEs but also owing to SSEs upscale transferring energy to ISO during the ISO easterly phase. The two-way interaction between the ISO and SSEs can be captured by the high resolution models. However, models at 20 km horizontal resolution underestimate the upscale energy conversion from SSE to ISO. Indirectly, the simulated ISO anticyclonic circulation associated subtropical high (monsoon trough) was too weak (strong). High resolution model may improve the simulation of two-way interaction between the ISO and SSEs and improve the simulation of TC over the WNP.