BUOY Seaglider VMP

Scientific Topic: Development of Typhoons and Their Interaction with Upper Ocean Layers / Enhancing Typhoon Numerical Forecast Accuracy - Development of Marine Meteorological Observation Buoys and Northwest Pacific Buoy Array Network. (Yang Ying-jian, Ma Yu-fang, Zheng Xin-ya, Xie Xiang-zhi, Hong Wei-ting)

The development of Taiwan's buoy technology and observation techniques began in the 1990s. At that time, Taiwan participated in international collaborative programs such as TOGA and SCSMEX, and cooperated with the U.S. PMEL/NOAA, jointly deploying ATLAS buoys in the equatorial Pacific and South China Sea. With the emphasis and support of the Ministry of Science and Technology / National Science Council, the research team started developing the second-generation marine meteorological buoys in 2015. This five-year project builds on the past buoy development foundation, continuously improving related detection technologies, and adapting designs based on different scientific purposes and available resources. For example, the first three years of the project focus on the interaction between typhoons and the ocean, and in the following years, in addition to studying the impact of typhoons, probes are densely deployed at the near-surface depth of coastal areas to observe the diurnal warm layer.

The NTU1 and NTU2 buoys are deployed annually after June and recovered before November of the same year. For example, the 2022 marine meteorological buoy observation mission was conducted from late May to early October of 2022, and the 2023 summer marine meteorological buoy observation was carried out from June to October.

Since the summer of 2015, marine meteorological buoys have been deployed to observe typhoons, with a total of 23 typhoons observed so far, including Soudelor, Swan, Nepartak, Meranti, Malakas, Megi, Nisha, Haima, Mangkhut, Doksuri, Lekima, Bailu, Lingling, Mitag, Sinlaku, Canshu, Round, Hinnamnor, Meihwa, Doksuri, Surigae, Haiyan, and others, as shown in Table 2.1. During this period, buoy design has gradually improved, and success rates have increased. The team has recently compiled accumulated technologies into scientific papers, submitting them to relevant SCI journals. For example, the 2023 edition marine meteorological buoy includes equipment to observe turbulence mixing caused by typhoons and changes in the diurnal warm layer, such as: propeller-type anemometers, ultrasonic anemometers, thermohygrometers, barometers, shortwave radiometers, net radiometers, rain gauges, wave gauges, sea surface temperature gauges, control and communication modules, meteorological data collection modules, solar navigation warning lights, Iridium satellite communication antennas, International Maritime Satellite communication antennas, UHF radio communication antennas, Iridium satellite GPS transmitters, radar reflectors, and time-lapse cameras.

The anchoring design includes SBE37 temperature-salinity-depth sensors, SBE39 temperature-pressure sensors, SBE56 thermometers, RBR temperature-pressure sensors, Aquadopp single-point ocean current meters, Aquadopp Profiler Doppler current profilers, acoustic recorders, acoustic release devices, and others. These instruments come from the Valuable Instrumentation Usage Center, Central Weather Bureau, and Professor Yang Ying-jian.

Additionally, the sea surface passing through a typhoon can cause upper ocean temperature cooling due to vertical mixing, upwelling, and heat flux changes, known as cold wake. However, research team analysis of observation data from NTU1 and NTU2 buoys between 2016 and 2021 shows that there were 30 cases where typhoons passed near the two buoys (with the closest distance less than 1.5 times the 34-knot wind radius), 8 of which showed warming in the upper ocean. Research indicates that the warming of the upper ocean is related to the subsurface flow caused by the typhoon, and there are two mechanisms for the subsurface flow: downward wind stress vorticity outside the maximum wind radius and surface flow field divergence. The warming is related not only to the typhoon's intensity, movement speed, and relative position but also to the background sea temperature vertical structure before the typhoon's arrival, as shown in Figure 2.8. These results from observations of typhoons beneath the buoys have been published in several internationally renowned journals.

Table 2.1: Typhoons observed by NTU1 buoy over the years (with closest distance less than 34-knot windstorm radius). From left to right, the typhoon name, closest distance (km), time of closest approach (UTC), typhoon intensity, Central Weather Bureau 7-level storm radius (km), buoy's relative position to the typhoon center, JTWC 34-knot storm radius (nautical miles).

Figure 2.2: 2023 edition NTU1 marine meteorological buoy anchoring design and underwater instruments. SBE37 is a temperature-salinity-depth sensor, Aquadopp is a single-point ocean current meter, Aquadopp Profiler is a Doppler current profiler, SBE39 and RBR are temperature-pressure sensors.

Figure 2.8: Diagram of ocean changes caused by typhoon dynamics. This figure is excerpted from Yang et al. (2024a).

3. Scientific Topic: Boundary Ocean Observing Network Global Ocean Boundary Current Observing Network's Kuroshio Observation (Using Underwater Autonomous Vehicles Seaglider Fleet). (Zhang Ming-hui, Zhan Sen, Yang Kai-xie, Wang Shi-hong, Xie Xiang-zhi)

The institute currently has five underwater autonomous observation vehicles, Seagliders, to perform Taiwan's marine physical observation tasks. Compared to other underwater unmanned vehicles, Seagliders can overcome Taiwan's surrounding complex and strong Kuroshio currents, increasing their importance. The Seaglider is manufactured, developed, and sold by the University of Washington's Applied Physics Laboratory. In this five-year project, at least one Seaglider performs a mission lasting over one month annually, with the longest reaching three and a half months. Among these observation missions, the most notable experiments were the 111th year observations in the Kuroshio area on Taiwan's east side and the 112th year's international cooperative observations in the Northwest Pacific.

In the 111th year's observation mission, we tested Seaglider's ability to observe small-scale turbulence. Two sea tests were conducted that year, with the second test performed in July 111th. The Seaglider crossed the Kuroshio from Taiwan's southern end and entered an anti-cyclonic eddy east of the Kuroshio. Deployment and recovery were performed by the Xinhai 3 and Xinhai 2 voyages, completing a total of 124 dives. Despite the SG682's uncontrolled movement before recovery, the observation data was preserved well. SG682 was deployed in Taiwan's southern waters, passing through the Kuroshio and the anti-cyclonic eddy's western side, eventually being caught in the eddy's core (at which point the glider had lost control). Encouragingly, we successfully estimated the turbulence dissipation rate along the Kuroshio using the Large Eddy Method (LEM) (Figure 1-3.2 right), showing close agreement with the results measured directly with a turbulence probe (Figure 1-3.2 left). The strong turbulence dissipation rate (~10⁻⁷–10⁻⁵ W kg⁻¹) in the Luzon Strait is likely related to flow-topography interactions or internal tide generation, while the intense turbulence dissipation between the eddy and Kuroshio may be related to front instability. The T-S diagram shows two main water types (omitted here): South China Sea Tropical Water (SCSTW) found in the western Kuroshio and the anti-cyclonic eddy's east side, and West Philippine Sea Tropical Water (WPSTW) found in the Kuroshio's eastern side, with further analysis required on the relationship between water types and turbulence mixing. Regardless, the hydrological and turbulence data obtained by SG682 is reliable. The aforementioned LEM turbulence estimation method uses hydrological data to "estimate" turbulence intensity, and the preliminary results are similar to direct observations. With calibration, this method can be applied to future Seaglider observations without turbulence probes.

112th year Seaglider observation mission: In the 112th year's observation experiment, SG687 participated in the large international ARCTERX experiment between Taiwan and the U.S., highlighting Taiwan's advances in automated underwater observation technology. On May 31, SG687 was deployed in the Northwest Pacific (West Philippine Sea) in coordination with the R/V Thomas G. Thompson TN-417C voyage, collaborating with 10 other underwater gliders from U.S. research teams for a mesoscale vortex joint observation mission. The glider was recovered on September 12 after 104 days, covering a total distance of 2,352 kilometers (1,270 nautical miles) and completing 707 continuous profiles. Data collected included temperature, conductivity (salinity), pressure, dissolved oxygen, chlorophyll fluorescence, and backscatter intensity. The experimental data is extremely valuable, and the research teams are currently analyzing the data.

Figure Nine: Seaglider (SG682) purchased in the first year of the project with turbulence probe.

Figure 1-3.2: Comparison of turbulence dissipation rate observed directly using a shear probe (left) and estimated using the LEM method (right).

4. Scientific Topic: Deployment of Ocean Bottom Seismometers in the Eastern and Western Offshore Taiwan to Understand Seismic and Crustal Deformation Mechanisms. (Chen Jin-cai, Tsai Ing-wen, Lü Xue-ru, Deng Jing-hui, Zhou Yong-ming)

To better understand seismic activities and crustal deformations in Taiwan's surrounding seas, the research team continues to deploy ocean bottom seismometers (OBS) in the eastern and western offshore regions of Taiwan. These devices can monitor small seismic activities and crustal deformations on the ocean floor over long periods, playing a key role in understanding plate boundary activities and potential earthquake zones.

During the project period, multiple OBS units have been successfully deployed in the waters off Hualien-Taitung and the Penghu Islands, combined with seismic data analysis techniques to create a more complete seismic activity map and crustal structure model. Through these data, the team discovered significant earthquake clusters and active fault systems off Taiwan's eastern coast, while the western offshore region showed signs of subtle crustal deformation.

Ship-based Air-sea Flux & Exchange System (SAFE)

Figure 1-4.1: Distribution Diagram of Surface Meteorological Instruments in the SAFE System.

Figure 12: Schematic Diagram of the Second Version of the SAFE T-bar System Structure, Meteorological Instruments, Anemometer, GPS, Temperature Sensor Array, and Doppler Flow Profiler Combination (Left). The SAFE T-bar was released and tested during the Xinhai Research 1 cruise from December 2 to 4, 2021, in the southwestern waters of Taiwan (Right).