Footprints of Tropical Cyclones in the Global Climate. Part I: Improved Potential Vorticity Inversion for Tropical Cyclone Vortex Removal

Abstract

While tropical cyclones (TCs) are short-lived, they are known to have upscale effects. Isolating TC-vortex contributions embedded in climate fields is difficult because the observed atmosphere always includes TC activity. This study develops a framework to diagnostically separate TC-vortex-induced components from global reanalysis data. TC vortices are diagnostically removed to isolate their instantaneous contribution to the analyzed fields. An improved potential vorticity inversion technique incorporates previously neglected dynamical effects, enabling a faithful representation of the three-dimensional circulation structure of TCs. The method is applied to the JRA-3Q reanalysis, and TC components and TC-vortex-filtered datasets are constructed at 6-hourly resolution. Case studies demonstrate that the method successfully isolates TC-induced circulation features, including low-level cyclonic vorticity and upper-tropospheric warm cores, without introducing dynamical inconsistencies. The results show that TC vortices constitute part of the large-scale climatological atmospheric circulation over the North Pacific. Compared with the original field, the Pacific subtropical high extends farther westward and the monsoon trough extends less far eastward in the TC-removed field. We demonstrate TCs’ contribution to more than 50% of the intraseasonal (20–80-day) variability of low-level relative vorticity over broad regions, with contributions exceeding 90% at some grid points during peak seasons. The dataset enables comparisons between the original and TC-vortex-filtered fields at identical analysis times. The TC-removed data represent atmospheres in which TC vortices are diagnostically removed at each analysis time, rather than hypothetical climates in which TCs never occur. This framework provides a foundation for quantifying TC-vortex contributions to climate variability across scales in TC-prone basins and opens up new opportunities for studying TC-climate interaction.