Quantification of Precipitation Asymmetries of Tropical Cyclones at Different Landfall Stages: An Emphasis on the Over-Land Precipitation Structure

This study analyzes the rainfall asymmetries of tropical cyclones (TCs) before, during, and after landfall from an observational perspective, with a special emphasis on the over-land precipitation distribution. Our analyses of TC rainfall are based on quantifying the asymmetries relative to the directions of storm motion and vertical wind shear using the Fourier decomposition method for both low and higher wavenumbers. The primary source of information is the final run of the Global Precipitation Measurement (GPM) rainfall product, Integrated Multi-satellitE Retrievals for GPM (IMERG), applied to both data eras of the Tropical Rainfall Measuring Mission (TRMM) and GPM mission. The satellite dataset enabled the analysis of the total extent of TC rainfall through a consistent spatial-temporal series of more than two decades over all the TC-prone global basins.

Once quantified, the resulting asymmetries were categorized by different landfall categories as a function of the percentage of the TC precipitating area over the land-ocean ratio, along with the location of the TC centers within distance intervals from the coast. Preliminary results show that the maximum precipitation asymmetry is preserved as down-motion-right in most landfall stages except for the down-motion pattern at the category before to the exact landfall time. Something similar occurs to the classic down-shear-left maxima across the proposed landfall stages, showing a transient weakening and down-shear pattern when falling under the same landfall category. We also found that storm motion is a more important factor than the vertical wind shear in producing precipitation asymmetry, especially for the wavenumber-1 across all the over-land landfall categories. Finally, the influence of TC intensity, TC motion speed, magnitudes of upper-level trough, and selected environmental parameters is also analyzed and presented.