Vertical Structure of Global Oceanic Summer Precipitation Identified from GPM GMI EOF Analysis

Abstract

This study extends an Empirical Orthogonal Function (EOF)-based diagnostic framework to a global scale to characterize oceanic precipitation systems during hemispheric summer, applied to multi-channel Polarization Corrected Temperature (PCT) observations from the Global Precipitation Measurement (GPM) Microwave Imager (GMI). The EOF framework condenses multi-channel microwave variability into a two-dimensional coordinate space defined by the first two principal components (PC1 and PC2), providing a physically interpretable structural representation of precipitation systems. PC1 represents bulk hydrometeor loading; its global distribution is characterized by elevated values in the ITCZ, Asian monsoon regions, and major midlatitude storm-track belts. PC2 modulates the relative contributions of upper-level ice scattering and lower-level liquid emission, characterizing vertical phase partitioning within the column. Collocated GPM Dual-frequency Precipitation Radar (DPR) observations demonstrate that the PC coordinates correspond systematically to three-dimensional reflectivity structures across both convective and stratiform regimes. This partitioning exhibits a systematic meridional contrast, shifting toward greater ice-phase contribution in the tropics and greater liquid-phase contribution across the midlatitudes—consistent with DPR-observed reflectivity profiles, storm-top height, and the Ice-to-Rain Path Ratio (IRPR). The EOF framework provides an observation-based reference for evaluating microphysical representations in numerical models and satellite precipitation retrieval algorithms.