Evaluation of reanalysis precipitable water vapor under typhoon conditions using multi-source observations

Abstract

Precipitable Water Vapor (PWV) exhibits rapid and complex variations during typhoons, and its evaluation under typhoon conditions remains challenging due to sparse observations over the oceans. This study systematically evaluates PWV estimates from three state-of-the-art reanalyses during 113 typhoons between 2020 and 2024 over the Northwest Pacific and East Asia. The fifth-generation European Centre for Medium-Range Weather Forecasts Reanalysis (ERA5), the Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2), and the Japanese Reanalysis for Three Quarters of a Century (JRA-3Q) are compared with ground-based Global Navigation Satellite System (GNSS), radiosonde, and Radio Occultation (RO) observations. Results based on ground-based GNSS, which serve as the primary reference in this study, show that ERA5 achieves the best overall accuracy, with a bias changing from -1.48 mm in non-typhoon periods to -0.18 mm during typhoons and root mean square error (RMSE) decreasing from 3.47 to 3.30 mm during typhoons. JRA-3Q also exhibits smaller errors during typhoons than during non-typhoon periods, although its bias and RMSE remain relatively large. Conversely, MERRA-2 shows higher error during typhoons, with the bias shifting from -0.63 mm in non-typhoon periods to 0.76 mm during typhoons, indicating a transition from modest underestimation to modest overestimation. Comparisons with radiosonde and RO observations show consistently high correlations for all three reanalyses, supporting their general reliability under typhoon conditions. Overall, the results provide an accuracy reference during typhoons and support the applicability of reanalysis PWV for typhoon-related studies, with ERA5 appearing the most robust among the datasets evaluated.