Observations on the Typhoon-ocean interaction using surface drifters in the western North Pacific

Abstract

Typhoons moving north towards the South Korea are known to rapidly intensify due to oceanatmosphere interactions in the Northwest Pacific Warm Pool region. To examine the oceanic physical factors that affect this rapid intensification, it is important to observe surface sea temperatures and winds before, during, and after the typhoon passage. In this study, we present observations of surface sea temperature, sea level pressure, wind direction, and wind speed collected from 41 MiniMet drifters deployed in the northwestern Pacific region (10-24 °N, 125-135 °E) over the past several years (2017- 2023). Most drifters were deployed in September, and the average surface sea temperature observed in the Northwestern Pacific from September to November was approximately 28.8 °C. For the observation period, ancillary data on ocean conditions were obtained from geostrophic currents calculated from satellite altimeters and surface sea temperatures from the reanalysis. The wind data from the drifters were cross-validated with reanalysis datasets (ERA5, MERRA2, NCEP1 and NCEP2). In addition, we used the best track data (typhoon track, intensity and maximum wind radius) provided by the Joint Typhoon Warning Center (JTWC) to determine the proximity of the drifter to the typhoon before and after its passage. For example, during Typhoon Chanthu in 2021, a drifter located approximately 50 km from the center of the typhoon after passage was observed the surface sea temperature cooling (~approximately 1.5°C). To improving our understanding of ocean-atmosphere interactions, the multi-year dataset from these drifters is expected to contribute to several fields, including the validation of satellite-observed surface sea temperatures and winds.