Impact of global warming on summertime submonthly wave patterns and tropical cyclone activity in the western North Pacific

This study analyzes the re-analysis and model simulations to determine changes in circulation features for submonthly (6 - 20 days) wave patterns and tropical cyclones (TCs) in the western North Pacific (WNP) under global warming. The High Resolution Atmospheric Model (HiRAM) that can produce tropical cyclones is adopted to perform present (1979 - 2008) and future (2075 - 2100) simulations under the Representative Concentration Pathway (RCP) 8.5 scenarios. In the present simulation, the wave pattern is effectively simulated in the WNP. However, in the future simulation, the monsoon trough is weakened and fewer cases are detected. The intraseasonal oscillation (ISO) mostly exhibits a westward propagation tendency in the present simulation but northward movement tendency in the future simulation. Although the background seasonal fields are weakened in the future, the growth rate of the submonthly wave pattern in the westerly phase of the ISO is enhanced in the future simulation. A kinetic energy analysis reveals that the barotropic conversion will supply more kinetic energy from the background flow to the wave pattern in the future westerly phase. This enhancement from barotropic conversion is attributable to the northward displacement of the monsoon trough caused by the northward propagating ISO; this northward monsoon trough displacement and the northwest - southeast-oriented submonthly perturbations and TCs are more strongly coupled. Therefore, the submonthly cases in the westerly phase of the future simulation are unique because of the higher efficiency of kinetic energy transfer from the background flow to submonthly perturbations which provides a more favorable environment for stronger cases in the future westerly phase.

Automated summary

The study reveals changes in circulation features and tropical cyclones in the western North Pacific under global warming, showing weakened monsoon trough, enhanced growth rate of submonthly wave patterns, and alterations in background seasonal fields and kinetic energy transfer.