Impact of Tropical Cyclones on Summertime Multiscale Perturbations in the Western North Pacific: A Focus on Barotropic and Baroclinic Processes

Abstract This study investigates the impact of tropical cyclones (TCs) on various scales of climate systems in the western North Pacific across 41 summer seasons (1979–2019). Updated TC-removed data are compared with reanalysis data to discern TC contributions to intraseasonal oscillations (ISOs), submonthly wave patterns, and synoptic waves. Upon TC removal, the monsoon trough retreats and the subtropical high extends westward, shifting ISO systems southwestward from east of Taiwan to the South China Sea with their intensity halved. Perturbation kinetic energy (PKE), a key measure of perturbation intensity, decreases considerably—by as much as 80% in the ISO westerly phase and 60% in the ISO easterly phase—at 850 hPa for both the submonthly and synoptic cases. Similar reduction ratios are noted in the barotropic and baroclinic conversion fields, with the former dominating PKE increasing rate in the lower troposphere and the latter in the upper troposphere. The higher frequency of TC occurrences in the westerly phase results in a more pronounced energy reduction following TC removal compared to the easterly phase. Moreover, synoptic PKE exceeds its submonthly counterpart, and the baroclinic conversion exhibits a north–south orientation, both due to the upstream recurving TCs that redirect their paths toward Japan. These findings enhance our understanding of climate variability, thereby advancing climate modeling accuracy.