Observations of Temperature and Salinity Mesoscale Variability off the East Coast of Korea using an Underwater Glider: Comparison with Ship CTD Survey Data

Abstract

An underwater glider is an autonomous underwater vehicle that observes oceanographic data while following way points. Underwater gliders can be operated remotely, regardless of dangerous sea states such as typhoons, and have the advantage of acquiring high-resolution three-dimensional oceanographic data over large areas and long time periods. Here, we present water temperature and salinity data observed by an underwater glider following the ship conductivity, temperature, and depth (CTD) survey line 105 off the east coast of Korea for a period of 30 days (20 August-20 September 2018). In total, the underwater glider traveled 450 km horizontally in two round trips along the survey line at depths of approximately 200 m. The CTD profile data from the underwater glider and the ship were compared at three sites on the survey line. The root mean square error of the water temperature and salinity measured by the underwater glider and the ship at site 105-8 were 0.08-0.10 degrees C, and 0.02-0.17 psu, respectively. Overall, the distribution, range, and variability of the data collected by the underwater glider and the ship were similar at this site. The underwater glider was able to continuously observe changes in water temperature and salinity between the sites during Typhoon Soulik. Following the passage of the typhoon, the surface water temperature at site 105-7 decreased by 2.68 degrees C and salinity increased by 0.87 psu; at site 105-9, temperature decreased by 3.54 degrees C and salinity increased by 0.44 psu. These changes were caused by vertical mixing of surface water with sub-surface water during the typhoon. The mesoscale vertical mixing effect of the typhoon was examined using zonal hydrographic section measurements of temperature and salinity data. Our findings demonstrate the suitability of using underwater gliders off the east coast of Korea for long-term observations of mesoscale variability in water temperature and salinity.