Evaluation of calibrated salinity from profiling floats with high resolution conductivity‐temperature‐depth data in the East/Japan Sea

Abstract

The East/Japan Sea is an ideal region for the assessment of the quality of calibrated profiling float salinity data due to the availability of recent shipboard conductivity‐temperature‐depth (CTD) observations, dense spatial occupation by profiling floats, and its unique water mass structure. More than 5000 salinity profiles obtained from the profiling floats have been corrected with respect to two calibration methods, and their qualities have been evaluated using 787 high‐resolution CTD profiles. In this paper, we suggest not only a method for the real‐ and non‐real‐time quality control of the float salinity data acquired in the East/Japan Sea (EJS) but also the uncertainty in the quality‐controlled salinity estimated from a statistical comparison with independent high‐resolution measurements. After applying the scientific quality control (Wong et al., 2003, hereafter referred to as WJO), the salinity data exhibit 1 standard deviation uncertainty of 0.003 psu which is comparable to the manufacturer's accuracy. However, the scientific calibration in the EJS provides a significant bias error of about 0.002 psu in the float salinity profiles adjusted to historical CTD data over the last 7 years. The WJO method could produce a bias error in the calibrated salinity for an open ocean where recent hydrographic data are insufficient and if significant salinity trends exist. Since the deep salinity change in the North Atlantic is two times larger than that in the EJS, the bias problem of the calibrated float salinity could be more serious in the North Atlantic.