Ig-Chan Pang

On physical factors that controlled the massive green tide occurrence along the southern coast of the Shandong Peninsula in 2008: A numerical study using a particle‐tracking experiment

Received 22 August 2011; revised 15 October 2011; accepted 18 October 2011; published 23 December 2011. [1] A Lagrangian-particle-tracking experiment has been conducted using Regional Ocean Modeling System to determine physical factors that controlled the occurrence of the record-breaking massive green tide along the southern coast of the Shandong Peninsula (SP) in 2008. The numerical results reveal that the southerly wind in May is responsible for the offshore movement of the green tide from the Jiangsu Province and the easterly wind in June is responsible for its extension up to the coast of the SP. From the analysis of 30 year wind fields, it was also found that the wind patterns in 2008, which were very unique and rare, provided the most favorable conditions for the migration of the bloom to the SP. Through analyzing the pathway of particles, a recurrent upwelling region due to tides was found between the Jiangsu coast and the western Yellow Sea where the massive green tide bloomed. This area seems to provide nutrients for the green tide blooms. In particular, it is estimated that the nutrient supply in 2008 was large because the upwelling occurred during a spring tide. These results suggest that the massive green tide along the SP in 2008 occurred due to the combination of a recent rapid expansion of seaweed aquaculture, unique wind patterns, and nutrient supplies due to strong tidal forcing in blooming regions. This implies that the massive green tides in the SP could occur again as a very rare event if all conditions become favorable for the blooming and migration in the future. Citation: Lee, J. H., I.-C. Pang, I.-J. Moon, and J.-H. Ryu (2011), On physical factors that controlled the massive green tide occurrence along the southern coast of the Shandong Peninsula in 2008: A numerical study using a particle-tracking experiment, J. Geophys. Res., 116, C12036, doi:10.1029/2011JC007512.

Intrusion of low-salinity water into the Yellow Sea Interior in 2012

Abnormally low-salinity water was detected in the surface layer of the central region of the Yellow Sea in August 2012. The presence of such low-salinity water in the Yellow Sea interior has never been reported previously. To understand the origin of this low-salinity water, oceanographic and wind data were analyzed, and the circulation of the surface layer was also examined in the Yellow and East China Seas using a numerical ocean model. The results confirmed that typhoons caused the low-salinity water. Two consecutive typhoons passed from east to west across the East China Sea, around the Changjiang Bank in early August 2012. Strong easterly and southeasterly winds created by the typhoons in the Yellow and East China Seas drove the low-salinity water to the north along the coast of China and northeastward toward the central region of the Yellow Sea, respectively. Usually, the northward drifting of Changjiang Diluted Water along the coast of China ends around the Jiangsu coast, where the drifting is blocked and is turned by the offshore Eulerian residual current. Therefore, the Changjiang Diluted Water does not intrude more into the Yellow Sea interior. However, in 2012, the low-salinity water drifted up to the Shandong Peninsula along the coast of China, and formed massive low-salinity water in the Yellow Sea interior combining with the other low-salinity water extended toward the central region of the Yellow Sea directly from the Changjiang Bank. Thus, the typhoons play a key role in the appearance of abnormally low-salinity water in the Yellow Sea interior and it means that the Yellow Sea ecosystem could be significantly influenced by the Changjiang Diluted Water.

Contribution of the Yellow Sea bottom cold water to the abnormal cooling of sea surface temperature in the summer of 2011

Satellite-based sea surface temperature (SST) measurements revealed an abnormal cooling anomaly over the Yellow Sea (YS) in the summer of 2011. Using in situ hydrographic profiles, meteorological fields, and an ocean circulation model with a passive tracer experiment, we identified the cold SST anomaly and its connection with the YS Bottom Cold Water (YSBCW), which occupies the central part of the YS below the thermocline in the summer. The summer SST anomalies in the YS showed three cold peaks in 1993, 2003, and 2011 over the past 20 years, but the reasons for the cooling events were different, as one was due to weakened surface heating and the other was attributed to mixing with the YSBCW. In 1993 and 2003, relatively weak surface heating made the surface water cooler compared with that during the other years, whereas in 2011, a strong vertical mixing of water was induced by a typhoon that passed through the central YS, causing the surface water to cool by ∼8°C and the bottom water to warm up by ∼4°C. A tracer experiment further confirmed that the vertical heat transfers between the warm surface and the cold bottom water masses when the typhoon passed through the YS interior.

Modeling temperature inversion in southeastern Yellow Sea during winter 2016

A significant temperature inversion with temperature differences larger than 3°C was observed in the southeastern Yellow Sea (YS) during February 2016. By analyzing in situ hydrographic profiles and results from a regional ocean model for the YS, this study examines the spatiotemporal evolution of the temperature inversion and its connection with wind-induced currents in winter. Observations reveal that in winter, when the northwesterly wind prevails over the YS, the temperature inversion occurs largely at the frontal zone southwest of Korea where warm/saline water of a Kuroshio origin meets cold/fresh coastal water. Our model successfully captures the temperature inversion observed in the winter of 2016 and suggests a close relation between northwesterly wind bursts and the occurrence of the large inversion. In this respect, the strong northwesterly wind drove cold coastal water southward in the upper layer via Ekman transport, which pushed the water mass southward and increased the sea level slope in the frontal zone in southeastern YS. The intensified sea level slope propagated northward away from the frontal zone as a shelf wave, causing a northward upwind flow response along the YS trough in the lower layer, thereby resulting in the large temperature inversion. Diagnostic analysis of the momentum balance shows that the westward pressure gradient, which developed with shelf wave propagation along the YS trough, was balanced with the Coriolis force in accordance with the northward upwind current in and around the inversion area.

Modeling the largest inflow of Changjiang freshwater into the Yellow Sea in 2012 with particle-tracking experiment

Abnormally low-salinity water originating from the Changjiang River (CR) was observed at the central Yellow Sea (YS) in 2012, which was quite unique compared to other years. In this study, the intrusion process of the Changjiang Diluted Water (CDW) into the YS interior was examined using a hindcast simulation (2003–2012) with particle-tracking experiments. The particles representing the behavior of the CDW were released at the CR mouth from May to August, and then tracked. The simulated salinity patterns coincide fairly well with those derived from observations, particularly showing a large low-salinity structure around the central YS in 2012. A substantial intrusion of freshwater into the YS occurred in 2012, and this accounted for approximately 16% of all the released particles in 2012 which is twice as high as the mean average covering the 10 years. According to the trajectories in 2012, the particles took less than 50 days to travel from the mouth to the YS interior and followed mainly two paths toward the YS. One pathway traveled northward to the central entrance of the YS and then reached the western coast of Korea. This pathway was attributed to the strong easterly winds in late June and early August when three consecutive typhoons passed through the YS, which was a unique pattern that is rarely found in other years. The other pathway involved particles trapped along the Jiangsu coast drifting farther to the north up to the Shandon Peninsula against the anticyclonic tidal residual circulations during the passage of typhoons.

4DVAR Data Assimilation with the Regional Ocean Modeling System (ROMS): Impact on the Water Mass Distributions in the Yellow Sea

In this study, we evaluate the performance of the recently developed incremental strong constraint 4-dimensional variational (4DVAR) data assimilation applied to the Yellow Sea (YS) using the Regional Ocean Modeling System (ROMS). Two assimilation experiments are compared: assimilating remote-sensed sea surface temperature (SST) and both the SST and in-situ profiles measured by shipboard CTD casts into a regional ocean modeling from January to December of 2011. By comparing the two assimilation experiments against a free-run without data assimilation, we investigate how the assimilation affects the hydrographic structures in the YS. Results indicate that the SST assimilation notably improves the model behavior at the surface when compared to the non-assimilative free-run. The SST assimilation also has an impact on the subsurface water structure in the eastern YS; however, the improvement is seasonally dependent, that is, the correction becomes more effective in winter than in summer. This is due to a strong stratification in summer that prevents the assimilation of SST from affecting the subsurface temperature. A significant improvement to the subsurface temperature is made when the in-situ profiles of temperature and salinity are assimilated, forming a tongue-shaped YS bottom cold water from the YS toward the southwestern seas of Jeju Island.

Climate-change driven range shifts of anchovy biomass projected by bio-physical coupling individual based model in the marginal seas of East Asia

Recent studies in the western North Pacific reported a declining standing stock biomass of anchovy (Engraulis japonicus) in the Yellow Sea and a climate-driven southward shift of anchovy catch in Korean waters. We investigated the effects of a warming ocean on the latitudinal shift of anchovy catch by developing and applying individual-based models (IBMs) based on a regional ocean circulation model and an IPCC climate change scenario. Despite the greater uncertainty, our two IBMs projected that, by the 2030s, the strengthened Tsushima warm current in the Korea Strait and the East Sea, driven by global warming, and the subsequent confinement of the relatively cold water masses within the Yellow Sea will decrease larval anchovy biomass in the Yellow Sea, but will increase it in the Korea Strait and the East Sea. The decreasing trend of anchovy biomass in the Yellow Sea was reproduced by our models, but further validation and enhancement of the models is required together with extended ichthyoplankton surveys to understand and reliably project range shifts of anchovy and the impacts such range shifts will have on the marine ecosystems and fisheries in the region.