Observational evidence of overlooked downwelling induced by tropical cyclones in the open ocean.

Tropical cyclones (TCs) cause severe natural hazards and drive intense upper ocean cooling through a series of oceanic and atmospheric physical processes, including vertical mixing and upwelling. Among these processes, TC-induced warming of near-surface waters in the open ocean has rarely been noted. This study provides a detailed analysis of upper ocean responses to 30 TC events observed by two buoys in the western North Pacific between 2016 and 2021. Supplemented with numerical experiments, we suggest that downwelling frequently occurs at the periphery of upwelling regions (around the radius of the 34 knot wind speed) following the passage of a TC. Downwelling is identified via pronounced warm anomalies under a shallow mixed layer depth, and its dynamics are attributed to negative wind stress curl and current-induced convergence. These findings highlight the important role played by TC-induced downwelling and offer insights for reconsidering the influence of TCs on biogeochemical processes.

Mooring observed intraseasonal oscillations in the central South China Sea during summer monsoon season.

The South China Sea (SCS) is a high biodiversity region in the world ocean, supports abundant marine resources to the peripheral nations, and affects weather/climate in southeast Asia. A better understanding of its circulation is important to better prediction and management of the SCS. Here we reveal sizable intraseasonal oscillations at period ~ 50 days between May and November 2017 in the acoustic Doppler current profiler observed velocity in the central SCS. Satellite observed wind and sea level data together with a process-oriented numerical experiment suggest that the oscillations were caused by locally-generated and remotely-penetrated westward-propagating Rossby waves. The summer southwesterly monsoon strengthening/weakening and the resultant Ekman pumping velocity and shoreward Ekman transport increase/decrease and consequent coastal sea level rise/fall off the west coast of Palawan create westward-propagating Rossby waves causing velocity oscillations in the central SCS. Besides the local generation, Rossby waves with sea level anomaly > 0.2 m propagating from the Pacific through the Sulu Sea into the SCS could contribute to the intraseasonal velocity oscillations in the central SCS.

Glider observations of interleaving layers beneath the Kuroshio primary velocity core east of Taiwan and analyses of underlying dynamics.

Submesoscale interleaving layers are caused by lateral intrusions of dissimilar water masses in frontal zones, which are significant processes in shaping physical, biogeochemical, and ecological parameters in the ocean. Possible interleaving layers were sometimes observed by ship-based conductivity-temperature-depth (CTD) surveys with coarse spacing between adjacent stations in the Kuroshio region east of Taiwan but have never been examined dynamically. Here we show the characteristics of interleaving layers observed by a Seaglider with two repeated hydrographic surveys along a triangle track east of Taiwan from December 2016 to March 2017. Salinity profiles indicate that prominent interleaving layers appeared in the intermediate layer (approximately 500-800 m) with vertical and horizontal length scales of O(50) m and O(10-100) km, respectively, during our observations. A dipole eddy pair and a relatively large anticyclonic eddy impinged on the Kuroshio during the first and second surveys, respectively, which brought certain impacts on the interleaving motion as the eddy potentially altered the density slope across the Kuroshio. The associated instability analysis and the Turner angle suggest that the double diffusive instability is the primary driving mechanism for the development of interleaving layers.

The role of enhanced velocity shears in rapid ocean cooling during Super Typhoon Nepartak 2016.

Typhoon is a major cause of multiple disasters in coastal regions of East Asia. To advance our understanding of typhoon-ocean interactions and thus to improve the typhoon forecast for the disaster mitigation, two data buoys were deployed in the western North Pacific, which captured Super Typhoon Nepartak (equivalent to Category 5) in July 2016 at distances <20 km from the typhoon's eye center. Here we demonstrate that the unprecedented dataset combined with the modeling results provide new insights into the rapid temperature drop (~1.5 °C in 4 h) and the dramatic strengthening of velocity shear in the mixed layer and below as the driving mechanism for this rapid cooling during the direct influence period of extremely strong winds. The shear instability and associated strong turbulence mixing further deepened the mixed layer to ~120 m. Our buoys also observed that inertial oscillations appeared before the direct wind influence period.

The formation and fate of internal waves in the South China Sea.

Internal gravity waves, the subsurface analogue of the familiar surface gravity waves that break on beaches, are ubiquitous in the ocean. Because of their strong vertical and horizontal currents, and the turbulent mixing caused by their breaking, they affect a panoply of ocean processes, such as the supply of nutrients for photosynthesis, sediment and pollutant transport and acoustic transmission; they also pose hazards for man-made structures in the ocean. Generated primarily by the wind and the tides, internal waves can travel thousands of kilometres from their sources before breaking, making it challenging to observe them and to include them in numerical climate models, which are sensitive to their effects. For over a decade, studies have targeted the South China Sea, where the oceans' most powerful known internal waves are generated in the Luzon Strait and steepen dramatically as they propagate west. Confusion has persisted regarding their mechanism of generation, variability and energy budget, however, owing to the lack of in situ data from the Luzon Strait, where extreme flow conditions make measurements difficult. Here we use new observations and numerical models to (1) show that the waves begin as sinusoidal disturbances rather than arising from sharp hydraulic phenomena, (2) reveal the existence of >200-metre-high breaking internal waves in the region of generation that give rise to turbulence levels >10,000 times that in the open ocean, (3) determine that the Kuroshio western boundary current noticeably refracts the internal wave field emanating from the Luzon Strait, and (4) demonstrate a factor-of-two agreement between modelled and observed energy fluxes, which allows us to produce an observationally supported energy budget of the region. Together, these findings give a cradle-to-grave picture of internal waves on a basin scale, which will support further improvements of their representation in numerical climate predictions.

Clinical correlation of nonalcoholic fatty liver disease in a Chinese taxi drivers population in Taiwan: Experience at a teaching hospital.

BACKGROUND: To explore any gender-related differences in the prevalence of conditions-associated with non-alcoholic fatty liver disease (NAFLD) among Taiwanese taxi drivers in Taipei, Taiwan. METHODS: We studied 1635 healthy taxi drivers (1541 males and 94 females) who volunteered for physical check-ups in 2006. Blood samples and ultrasound fatty liver sonography results were collected. RESULTS: The prevalence of NAFLD was 66.4% and revealed no statistically significant decrease with increasing age (p = 0.58). Males exhibited a greater prevalence of NAFLD than did females (67.5% vs 47.9%, p < 0.0001). Gender-related differences for associated factors were found. For males, hypertension, hyperuricemia, higher AST, higher ALT, hypertriglyceridemia, and higher fasting plasma glucose were significantly related to NAFLD. These conditions were not sigfinicantly related to NAFLD in females. CONCLUSION: Several gender-related differences were noted for NAFLD among Taiwanese taxi drivers.