Examining the Rainfall Asymmetries during the Landfalling Process of Tropical Cyclones Using 20-Year NASA IMERG Satellite Data

Rainfall-induced flooding from tropical cyclones (TCs) remains a significant cause of damage along coastal areas. Therefore, a better understanding of the precipitation patterns at different landfalling stages is an extremely important task. Recent studies using remote sensing information have shown that rainfall distribution in a landfalling TC can be decomposed into wavenumbers that reveal the azimuthal behavior and asymmetries of the TC precipitation field. Our current understating is that over the open ocean, TCs experience asymmetries often controlled by storm motion and environmental wind shear, but as the landfall process begins, little is known about the changes or evolution of the TC rainfall patterns.

This study analyzes the rainfall anisotropies of TCs before, during, and after landfall from an observational perspective. The primary source of information is the use of more than two decades of satellite rainfall information obtained from the Tropical Rainfall Measuring Mission (TRMM) and the Global Precipitation Measurement (GPM) mission, particularly from the Integrated Multi-satellitE Rainfall (IMERG) product. Our analyses of TC rainfall are based on quantifying the asymmetries relative to storm motion and wind shear using the Fourier decomposition method. Once obtained, the resulting asymmetries are categorized by landfall stage, TC intensity, TC motion speed, magnitudes of upper-level trough, and selected environmental parameters. All the global TC-prone basins are considered in our study: Northern Atlantic (ATL), East-central Pacific (EPA), Western North Pacific (WNP), North Indian Ocean (NIO), South Indian Ocean (SIO), and South Pacific (SPA).