Application of quality-controlled sea level height observation at the central East China Sea: Assessment of sea level rise

Abstract

This study presents a state-of-the-art quality control (QC) process for the sea level height (SLH) time series observed at the Ieodo Ocean Research Station (I-ORS) in the central East China Sea, a unique in situ measurement taken in the open sea for over 2 decades at a 10 min interval. The newly developed QC procedure, named Temporally And Locally Optimized Detection (TALOD), has two notable differences in characteristics from the typical ones: (1) spatiotemporally optimized local range check based on the high-resolution tidal prediction model TPXO9 and (2) consideration of the occurrence rate of a stuck value over a specific period. In addition, the TALOD adopts an extreme event flag (EEF) system to provide SLH characteristics during extreme weather. A comparison with the typical QC process, satellite altimetry, and reanalysis products demonstrated that the TALOD method could provide reliable SLH time series with few misclassifications. A budget analysis suggested that the sea level rise at the I-ORS was primarily caused by the barystatic effect, and the trend differences between observations, satellite, and physical processes were related to vertical land motion. It was confirmed that ground subsidence of −0.89 ± 0.47 mm yr−1 is occurring at I-ORS. As a representative of the East China Sea, this qualified SLH time series makes dynamics research possible spanning from a few hours of nonlinear waves to a decadal trend, along with simultaneously observed environmental variables from the air–sea monitoring system at the research station. This TALOD QC method is designed to process SLH observations in the open ocean, but it can be generally applied to SLH data from tidal gauge stations in the coastal regions.