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The offshore China (OC) region is a significant sea area in the Western Pacific and many researchers have been interested in the distribution of sea surface temperature (SST) fronts in this area. In this study, the Cayula and Cornillon single image edge detection algorithm was used to detect SST fronts using the Daily Optimum Interpolation Sea Surface Temperature data from 1982 to 2021. The results revealed that there are eighteen SST fronts in OC— three in the Bohai Sea, seven in the Yellow Sea, two in the East China Sea, five in the South China Sea, one in the Pacific Ocean east of Taiwan province, China—and among them a new front was detected in the Yellow Sea and named the Yellow Sea Ring Front. The frequency of most fronts showed a tendency of initially increasing and then decreasing from January to September, followed by a trend of growing steadily from October to December. The frequency of a few fronts showed a decreasing tendency from January to September and an increasing tendency from October to December. The frequency of most fronts is highest in winter and lowest in summer. In spring and autumn, the frequency of most fronts is lower than that in winter and higher than that in summer. The annual average frontal probability of five-ninths of the fronts showed an upward trend, and the annual average frontal probability value of one-third of the fronts showed a downward trend. The rest of the fronts showed a stable trend. The results of this paper also showed that the Liaodong Bay Front and the Bohai-Laizhou Bay Front did not form a complete front, as previously reported. In addition, the frontal probability of the Bohai Front to the north of 39° N was in the tendency of decreasing. [ABSTRACT FROM AUTHOR]

The Shantou-Taiwan shoal fishing ground in southeastern China supports a significant population of pelagic fish, which play a key role in the marine ecosystem. An acoustic survey was carried out using a digital scientific echosounder in June 2019. In this paper, the spatial distribution of pelagic fish is analyzed based on acoustic data using geostatistical analysis tools. Meanwhile, the relationship between fish density from acoustic data and sea surface environment factors were evaluated by using generalized additive models (GAMs) based on the satellite-based oceanographic data of sea surface temperature, sea surface chlorophyll-a concentration, sea surface height and sea surface wind. The results showed the following: (1) Fish density and acoustic biomass have strong spatial correlation; the optimal model for acoustic biomass is exponential and the optimal model for fish density is gaussian; based on optimal model, spatial interpolation analysis of fish density and acoustic biomass was performed using the ordinary kriging method, and the higher values of density and acoustic biomass were located in the central and eastern parts of the study area. The total fish density and acoustic biomass is 2.56 × 1010 ind. and 1908.99 m2/m, respectively. (2) In vertical distribution, fish gradually move to the middle and lower layers of water during daytime, and gather in the middle and upper layers of water at night. (3) The variance explanation rate of GAM was 88.2% which indicates that the model has an excellent fitting degree, and the results of GAM showed that longitude, sea surface temperature (SST), sea surface wind (SSW), and sea surface height (SSH) had significant effects on fish density. Results of this study were meaningful for understanding the distribution of fishery resources, and as a guide for fish management in the Shantou offshore water. [ABSTRACT FROM AUTHOR]

Satellite measurements are becoming popular among the scientific community to identify earthquake precursors since its spatial coverage is more and round the clock measurements are possible. In this paper, we analyzed Total Electron Content (TEC), Outgoing Longwave Radiation (OLR), Sea Level Pressure (SLP), Surface Latent Heat flux (SLHF) and Sea Surface Temperature(SST) to identify any abnormal anomalies before Taiwan earthquakes which occurred on 4th February 2018 (M = 6.1, depth = 12 km) and 6th February 2018 (M = 6.4, depth = 17 km). The GPS data of International GNSS Service(IGS) stations (TWTF and CKSV) which operated 90 and 200 km away from the epicenter of the earthquake on 6th February 2018 respectively, were used for calculation of VTEC. The locations of these stations are within the preparatory zone of these earthquakes. The global parameters such as Dst, Kp, and IMF are also analyzed for the corresponding period of VTEC. We noticed the raise of temporal variations of 5–8 TECU before few days of the present earthquakes. The VTEC and other parameters such as SLP, SST, SLHF, and OLR were analyzed using the "Sliding Interquartile range method" during the period of 09th Jan to 10th Feb 2018 (33 days) to identify the abnormal signal due to these earthquakes. Strong positive anomalies occurred one day before the earthquake of 4th February and 1st, 3rd and 5th day before the Taiwan earthquake of 6th February 2018 with strong anomalous nature with an absolute amplitude of 5–8 TECU.The Cross wavelet analysis between Kp and TEC is carried out to study the impact of global geomagnetic activity on TEC during the seismic event and we found a negligible influence of global geomagnetic activity. The good raise of SLP on the day of the earthquake on 6th February 2018 have been noticed with the raise of 300 mb, the SLHF anomalies are observed at the interface of the earth's surface and atmosphere. Moreover, anomalous variations in air temperature and OLR were observed 2 days before the occurrence of the earthquake on 6th February 2018. Well co-ordinated scrutiny of various parameters such as TEC, SLHF, and OLR indicates that they can be used as promising precursors to the impending devastating earthquakes with reasonable accuracy. [ABSTRACT FROM AUTHOR]

From 2001 to 2020, three typhoons with similar moving paths and intensities were found to trigger markedly different cooling off northeastern Taiwan. They were typhoons Utor (2001), Nuri (2008), and Hagupit (2008), which led to maximum sea surface temperature (SST) cooling temperatures of 8.8, 2.7, and 1.4 °C, respectively. The drastic cooling discrepancy implies that the existing understanding of the key mechanism leading to the cooling off northeastern Taiwan could be insufficient. For further exploring the key reason(s) contributing to the marked discrepancy, a regional oceanic modeling system (ROMS) was used to reconstruct the background oceanic environment corresponding to three typhoon passages. Results show that the wide radius of maximum winds of typhoon Utor contributes to the strongest SST cooling by enhancing the Kuroshio intrusion (KI) onto the shelf northeast of Taiwan. Heat budget diagnostics explain why including tidal forcing can substantially promote SST cooling. The process was associated mainly with a stronger vertical advection tied to the influence of de-stratification by tidal mixing. Finally, warmer Taiwan Strait currents, driven by wind forcing the typhoons to pass zonally through the north South China Sea, intruded clockwise into the Longdong coast and accelerated the recovery of sea surface cooling around Longdong. [ABSTRACT FROM AUTHOR]

Convective afternoon rainfall (CAR) is a significant summer rainfall feature in Taiwan. This study investigates the projected uncertainties in summer CAR in Taiwan, using a dynamical downscaling approach with the Weather Research and Forecasting Model (WRF) and the High-Resolution Atmospheric Model (HiRAM). The projections were driven by four different sea surface temperature (SST) categories derived from CMIP5 model simulations under the RCP8.5 scenario. All projections indicate a reduced frequency but increased intensity of CAR over Taiwan by the end of the 21st century. However, notable differences in the degree of CAR changes were observed among simulations with varying degrees of Pacific SST warming. These variations in potential future changes in CAR frequency and intensity can be attributed to the variations in daytime thermal instability, local inland wind convergence, and moisture flux convergence over Taiwan. Furthermore, this study explored the linkage between local thermodynamic conditions and projected large-scale circulation patterns. [ABSTRACT FROM AUTHOR]

Water vapor transport from the South China Sea (SCS) by the marine boundary layer jet (MBLJ) can be an important moisture source for heavy rainfall events in Taiwan during the mei‐yu season. However, the variability in the MBLJ due to sea surface temperature (SST) changes and its impact on extreme rainfall events have yet to be well understood. This study investigates how varying the SST over SCS modifies the structure of MBLJ and further impacts an extreme mei‐yu rainfall in Taiwan during 1–4 June 2017. Results show that SST over the SCS can affect rainfall in Taiwan through its modulation of the MBLJ. Increasing SST leads to a southward shift of the mei‐yu rainfall. This is attributed to the weakening of the MBLJ and the enhanced convection at the leading edge of the mei‐yu front. The opposite effect is observed when the SST is decreased but with a smaller impact. Plain Language Summary: The marine boundary layer jet (MBLJ) is a strong airflow in the lower atmosphere that can transport moisture to Taiwan and lead to heavy rainfall during the mei‐yu season. This study conducts numerical simulations to investigate the impact of varying sea surface temperature (SST) over the South China Sea (SCS) on the MBLJ and how it affects rainfall in Taiwan. Based on the simulation results of an extreme mei‐yu rainfall in Taiwan during 1–4 June 2017, we found that when SST over the SCS increased, the MBLJ weakened. Hence, the mei‐yu front can move forth south and lead to a southward shift in rainfall location. On the other hand, decreasing the SST has the opposite effect but with a relatively smaller impact. Key Points: Varying sea surface temperature (SST) over the South China Sea (SCS) can modulate the marine boundary layer jet (MBLJ) and affect an extreme rainfall event in Taiwan (2017)SST modulates MBLJ by adjusting vertical mixing in the boundary layerThe warm (cold) SST perturbation leads to a weak (strong) MBLJ, and the mei‐yu rainband over Taiwan is shifted southward (northward) [ABSTRACT FROM AUTHOR]

The flathead gray mullet (Mugil cephalus L.) is a cosmopolitan fish that lives in warm and temperate zones over 42°N-42°S. It is a key fish species for industrial fishing off coastal Taiwan. Gray mullets enter the coastal waters of the southeastern Taiwan Strait (22°N-25°N) to spawn in winter and feed in the coastal and tidal waters of China (25°N-30°N). From 1986 to 2010, the annual catch of gray mullet decreased substantially and remained low. Although the Pacific Decadal Oscillation and El Niño-Southern Oscillation are recognized to affect gray mullet migration, the increase in sea surface temperature may be the main cause of the aforementioned decrease. We explored how weather changes affect fishing conditions and patterns at the gray mullet fishing grounds in Taiwan's coastal areas. Because of the decrease in gray mullet catches, the most common method for catching gray mullet in Taiwan's coastal areas between 1990 and 2010 was the use of drift or trawl nets instead of two-boat purse-seiner fleets. Since 2012, purse-seiner fleets have become the most common method for catching gray mullet. This trend indicates that the local fishing industry is adapting to changing environmental conditions. [ABSTRACT FROM AUTHOR]

We carry out the Lagrangian diurnal warm layer (DWL) observations, supplemented by satellite products, along the strong Kuroshio east of Taiwan, where the boundary terrain modifies the winds and the advection effect is significant. The synoptic easterly wind bifurcates as it encounters Taiwan's coast, forming the southward‐blowing and the northward‐blowing branches in the southern and northern regions of the bifurcation, respectively. The two branches produce areas with enhanced and weakened apparent wind speed relative to the northeastward flowing Kuroshio. The DWL can reach 5 m in the south of the bifurcation due to the shear instability‐induced mixing. Sea surface temperature (SST) enhancement occurs around and in the north of the wind bifurcation, where the solar heat is only trapped in the upper 2 m due to the absence of instability, forming inhomogeneous SST along the Kuroshio. The synoptic wind variations and Kuroshio advection further modulate the location of SST enhancement. Plain Language Summary: Sea surface temperature could change in a day due to solar heating over the top few meters, where a thin surface warm layer is created. This layer's thickness and mean temperature are related to solar heating and wind speed. The wind blowing works like a stick stirring the surface water to spread the surface heat from the sun to the deeper ocean and, therefore, affect the thickness of the upper ocean's warm layer. However, the warm layer and its associated surface temperature variation exist only in the weak to moderate wind (0–4 m s−1). In the region of a strong current, such as the western boundary current, the moving speed of surface water (1–2 m s−1) is comparable to the wind speed suitable for warm layer formation. It is essential to use the wind speed that the surface waters "feel" as they move to evaluate the warm layer. We found that the above effect has resulted in the asymmetric sea surface warming along the Kuroshio in response to the daily solar heating. Key Points: Lagrangian observations and satellite remote sensing reveal inhomogeneous diurnal surface temperature warming along the Kuroshio pathInhomogeneous diurnal surface warming is due to terrain‐induced bifurcated wind and the strong Kuroshio flow speedThe critical wind speed of ∼2 m s−1 relative to the current determines whether the solar heat could transfer deeper via shear instability [ABSTRACT FROM AUTHOR]

Aim: Reef fishes are commonly recognized as sentinels of the ongoing tropicalization in biogeographic transition zones between temperate and tropical areas. Despite the reliance of these marine ectotherms on the benthos, the importance of benthic habitat has rarely been considered as a factor constraining fish distribution. Therefore, our study aims at examining the consequences of both temperature and benthic variations on the fish fauna and diagnosing potential sentinels of these environmental changes. Location: Taiwan, West Pacific. Taxon: Teleostei (184 species). Methods: We examined how the partitioning of habitats can influence the specialization of fish fauna along a latitudinal gradient. We diagnosed 'specialist' and 'generalist' fishes in this partitioning. For each specialist, we further evaluated whether its distribution is constrained by temperature, benthic habitat or both factors combined. The change in sea surface temperature over the last three decades was also monitored. Results: Fish fauna showed the highest specialization when tropical and subtropical partitions of habitat were considered. Fifty‐one tropical specialists, 7 subtropical specialists and 21 possible generalists were identified. Among specialists, 13 species were associated with temperature, 19 with habitat and 26 with both factors. Steady warming occurred across latitudes, but was accentuated in the winter of subtropical habitat. Main Conclusions: Our results suggested that the distribution of some specialist fishes was constrained only by temperature while the distribution of some others also depended on the availability of benthic habitats. Consequently, under global warming, the distribution of some specialists might shift in a manner that follows the movement of isotherms, while the distribution of others might also be conditioned by the poleward shifts of benthos. A temporal mismatch between the emergence of suitable thermal environments and the arrival of some specialists may exist. Therefore, the tropicalization of high‐latitude areas may be characterized by different waves of colonization. [ABSTRACT FROM AUTHOR]

Satellite remote sensing sea surface temperature (SST) data are lost due to cloud cover. Missing data often cause inconvenience in subsequent applications and thus need to be reconstructed. In this study, the Data Interpolating Empirical Orthogonal Function (DINEOF) method was used to reconstruct the hourly SST data missing from the Himawari-8 satellite in the waters near Taiwan. The SST characteristics in the waters around Taiwan are quite complex, with high SST at Kuroshio in the east of Taiwan and great variation in the SST west of Taiwan due to the influence of tides. Therefore, the analysis with DINEOF was conducted using 25-h data to match the tidal cycle. The influence of SST characteristics on the accuracy of SST reconstruction is also discussed. The results show that in the western sea area where the variation of SST is large, the average root-mean-square error of SST between the original SST and the reconstructed SST is the lowest and the average coefficient of determination is the highest. The accuracy of the reconstructed SST is positively correlated with the SST variation. Furthermore, the statistical results also show that the DINEOF method can effectively reconstruct the SST regardless of the missing data rate. [ABSTRACT FROM AUTHOR]

In massive bleaching events (losing symbiotic algae from corals), more sensitive corals are bleached earlier than other corals. To perform a comparison of bleaching susceptibility within and across coral species, a simple quantitative method is required. Accordingly, we present a laboratory-based method for comparing the bleaching susceptibility of various coral species by using a standardized image analysis protocol. Coral fragments were sampled from the colonies of five species selected from Kenting, southern Taiwan, and maintained in the same aquarium tank with circulating seawater; 2 seawater temperature regimes were used (i.e., fast-heating program (FHP), with a heating rate of 1 °C per day; and slow-heating program (SHP), with a heating rate of 1 °C per 3 days). Each coral fragment was photographed periodically, and the colored images were subsequently converted to grayscale images and then digitally analyzed to determine the standardized grayscale values (G0) by comparing with that of standard color strip. The G0 of a sample at each time of photographing during bleaching was divided by the difference of G0 between the acclimating and the same but completely bleached fragment to derive the relative grayscale (RG%) at a particular stage of bleaching; this is done for each coral fragment of a colony. The smaller the RG% of a coral fragment the closer it is approaching completely bleached condition. The level of decrease in RG% within a time series of images in each heating regime was used to establish a bleaching time index (BTI). The lower the BTI, the sooner to reach a defined bleaching level (e.g., 30%), this indicates the coral is more sensitive to thermal bleaching. In the experiment, we compared the bleaching susceptibility of the five species. Based on the proposed BTI, the five species were ranked in terms of bleaching susceptibility, and the rankings were identical between the two temperature regimes; three species in Pocilloporidae had lower BTI, whereas the hydrocoral Millepora species had the highest BTI. Within each heating regime, the BTI of different species were ranked and used to indicate susceptibility. In the FHP, the three Pocilloporidae species could be divided into two groups in terms of bleaching susceptibility. FHP not only displayed a higher differentiating capability on coal bleaching susceptibility than SHP, but also had a faster completion time, thus reducing the likelihood of unforeseen complications during the tank experiments. Our color-based method is easier and less effort-intensive than methods involving the assessment of zooxanthellae densities. Moreover, it requires much fewer replicates and all samples in one large tank (e.g., 300 L) for the studies considering multiple species comparisons. This method opens opportunities for studying the effects of species types, acclimatization (e.g., seasons), and environmental factors other than temperature on coral bleaching. [ABSTRACT FROM AUTHOR]

The El Niño–Southern Oscillation (ENSO) changes the air flow in the tropics, causing global droughts, floods, typhoons, and other natural disasters. Therefore, monitoring and forecasting of ENSO events effectively play an important role in disaster prevention and mitigation. This paper proposes a novel ENSO monitoring index using GNSS-derived zenith tropospheric delay (ZTD) and temperature (T), which is called the standardized ENSO monitoring index (SEMI), and validated its performance by introducing the standardized precipitation evapotranspiration index (SPEI). Multichannel singular spectral analysis (MSSA) and Lomb-Scargle periodogram are first applied to determine the periodic signals of ZTD and T. Empirical Orthogonal Function (EOF) is then used to analyze the spatio-temporal characteristics of ZTD and T. Finally, the response thresholds of ZTD and T to ENSO events are determined using the moving window correlation analysis (MWCA) method, and the SEMI is established based on the relationship between abnormal changes of sea surface temperature anomaly (SSTa) and ZTD/T. ZTD and T of 97 GNSS stations and the corresponding SPEI over the period of 2006–2016 in Taiwan province has been obtained to validate the capacity of the proposed SEMI for ENSO monitoring. Experimental results reveal that (1) annual and semi-annual periods existed in ZTD and T with the values of 365.25 and 182.625 days, respectively. (2) ZTD and T have good correlations with SSTa, and the coefficients are 0.64 and 0.70, respectively. (3) The response thresholds of ZTD and T to ENSO events in Taiwan province are [−1.13 °C, 0.84 °C] and [−1.09 °C, 0.69 °C], respectively. (4) The proposed SEMI has a good relationship with SSTa with a correlation coefficient of 0.77 and has been proven to have good ENSO monitoring capacity by comparing with SPEI with a correlation coefficient of 0.83. This result is of great significance for drought and flood disaster monitoring by the GNSS technique. • A standardized ENSO monitoring index (SEMI) is proposed. • SEMI only considers the parameters of GNSS-derived ZTD and temperature. • Response thresholds of ZTD and T to ENSO events are determined. • The performance of SEMI is validated by drought monitoring index (SPEI). [ABSTRACT FROM AUTHOR]

Based on National Oceanic and Atmospheric Administration/Advanced Very High-Resolution Radiometer (NOAA/AVHRR) remote sensing and Cross-Calibrated Multi-Platform (CCMP) wind field data from 2007 to 2019, oceanographic conditions are analysed, respectively, in the Source Area (SA) and Typical Bloom Area (TBA) of Ulva prolifera (U. prolifera) in the west of the Southern Yellow Sea (SYS) using Sea Surface Temperature (SST), Suspended Sediment Concentration (SSC) and Wind Speed over the years. The results indicate that the annual maximum SST Difference (SSTD) between U. prolifera SA and TBA is strongly consistent with the intensity of U. prolifera, and a high SST Warming Rate (WR) from May to July may constrain the U. prolifera blooms. The Taiwan Warm Current (TWC), crossing Yangtze River Estuary northward from March to April, leads to SST increasing in the SA and becomes a key trigger for the growth of U. prolifera in the early period. The amount of U. prolifera may decrease in the early period because of the lower light intensity with high SSC and turbidity in SA. The summer monsoon is one of determinants for the spread of U. prolifera, and the distribution of U. prolifera reaches its highest point with a higher mean wind speed in the TBA. [ABSTRACT FROM AUTHOR]

The global mean surface temperature does not increase monotonously over the past decades, with accelerated warming from the late 1970s to 1998 and followed by the warming slowdown during 1998–2013 (the so‐called warming hiatus). This study assessed and compared the temporal evolutions of sea surface temperature (SST) trends in the East China Seas (ECS, including Bohai, Yellow and East China Sea) and other key ocean regions. The results revealed an amplified response of ECS SST to both global warming acceleration and hiatus. This amplification was manifested as remarkably enhanced winter warming rates in the ECS of over 1.1 and 0.8°C⋅decade–1 for the 1980–1989 and 1990–1999, respectively, and as an obvious cooling trend of nearly −0.5°C⋅decade‑1 during 1998–2013. The enhanced response can be explained well by the combined effects of the Kuroshio Current (KC) and East Asian Winter Monsoon (EAWM). The weakened EAWM during the 1980s, accompanied by lower wind speeds and higher air temperatures, impeded the releases of latent and sensible heat fluxes from the ocean to the atmosphere, resulting in rapid ECS warming. During 1998–2013, the strengthened EAWM led to the enhanced cooling trend in the ECS. In addition, the volume transport of the KC east of Taiwan strengthened (weakened) during the 1990s (2000s), which might also have contributed to the enhanced warming (cooling) in the ECS. Our research suggests their sensitivity makes the ECS potentially vulnerable to the effects of global climate change, which has important implications regarding regional impact assessments. [ABSTRACT FROM AUTHOR]

The diurnal fluctuation of acoustic propagation in a cold dome region was studied by using the output of the high-resolution Finite Volume Coastal Ocean Model. The 3-D acoustic propagation in this region was studied first, and the results suggest that the diurnal fluctuation of the ocean environment results in the fluctuation of acoustic propagation. However, the variation pattern cannot be determined with only few outputs, and comprehensive analysis was needed. Then, a feature model for the thermal front on the edge of the cold dome was proposed. By analyzing the output of the ocean model, fluctuations were found to mainly occur in the two aspects of the feature model: first, horizontal excursion of the thermal front and second, vertical motion of the isothermal lines in the cold dome. The variation pattern of acoustic propagation over the two kinds of fluctuations was quantified. Results suggest that both kinds of fluctuations of model parameters result in great transmission loss (TL) variation in some cases. Typically, acoustic propagation with high frequency and deep source experience great influence from the fluctuations. The TL versus range usually experience influence from the fluctuations of the first kind from an approximately 40-km range and from the start for the second kind. The reason is that the vertical motion of the isothermal lines of the cold dome induces variation over the temperature profile from the start until the end, whereas the horizontal excursion of the thermal front brings influence mainly over the temperature profiles near the thermal front. [ABSTRACT FROM AUTHOR]

Temporal variation in seawater temperature plays a crucial role in coral reef ecology. Nanwan Bay, Southern Taiwan is home to well-developed coral reefs, which frequently experience cold-water intrusions caused by internal wave-induced upwelling, that manifest in distinct daily temperature minima. These temperature minima and their associated sources were studied by recording in situ bottom temperatures and sea levels observed at depths of 5 and 30 m from May 2007 to September 2008. These data were then compared to the East Asian Seas Nowcast/Forecast System, and it was found that daily temperature minima presented large variations with magnitudes of 2–3 °C over periods from days to months. It was further demonstrated that the cold-water intrusions may have originated from depths of ~100 m and were strongly affected by westward propagating mesoscale eddies from the Pacific basin. An impinging warm anticyclonic eddy in July 2007 may have combined with the El Niño, resulting in temperatures surpassing 29 °C and degree heating days >4.0 °C-days at both depths, which were coincidental with a mass coral bleaching event. This eddy's impact was additionally evident in high correlations between daily temperature minima and residual sea levels, suggesting that mesoscale eddies alter stratification, substantially influence temperature variation, and play important roles in understanding ecological processes on coral reefs. [ABSTRACT FROM AUTHOR]

Reconstructions of key climate parameters prior to anthropogenic influences serve to constrain decadal to multicentury natural climate variability. In the western Pacific region, relatively few reconstructions exist north of the Western Pacific Warm Pool (WPWP), a region critical to global climate. In this study, we collected a coral core from Houbihu, southern Taiwan, and generated a 225‐year reconstruction of annual and wintertime sea surface temperature, dry season sea surface salinity, and wet season rainfall records derived from paired Porites Sr/Ca and δ18O profiles extending back to the end of the Little Ice Age (1850 CE). Multidecadal sea surface temperature trends generally track regional surface temperature reconstructions, indicating the dominant influence of solar and volcanic radiative forcings. Reconstructed dry season sea surface salinity reflects an advection signal linked to the East Asian Winter Monsoon and the Pacific Decadal Oscillation, both influencing variations in the Kuroshio Intrusion across the Luzon Strait. Reconstructed wet season rainfall, on the other hand, reveals influence of the Pacific Decadal Oscillation on the decadal variability of local and regional rainfall patterns. Relative to the late 1900s, our climate reconstructions document cooler and drier (high salinity and low rainfall) conditions during the end of the Little Ice Age, supporting other lines of evidence of a retracted WPWP region during this period. In the late 20th to early 21st century, our climate reconstructions record warming and freshening (low salinity and high rainfall) trends, highlighting the potential impact of anthropogenic forcing in the extension of the WPWP. Key Points: Robust calibrations of sea surface temperature, salinity, and rainfall allow for climate reconstructions at different seasons in Houbihu, southern TaiwanENSO, PDO, and the EAM drive climatic and oceanographic variability at the northern edge of the Western Pacific Warm PoolTwo centuries of climate reconstructions record cool/dry conditions at the end of the Little Ice Age and warm/fresh conditions in the late twentieth century to the present [ABSTRACT FROM AUTHOR]

This study examines inter‐decadal and inter‐annual variability of meridional tropical cyclone (TC) activity during September–October (SO) in the northwestern North Pacific (NWNP) around Taiwan after 1998. From inter‐decadal period 1 (1980–1997) to period 2 (1998–2017), the Pacific Decadal Oscillation (PDO) changes its phase from positive to negative, characterizing cold sea surface temperature (SST) anomalies in the tropical eastern Pacific and warm SST anomalies in the tropical western Pacific. An induced low‐level convergent centre around the Maritime Continent evokes a cyclonic anomaly on its northwestern side overlying Taiwan that facilitates TC formation in the region north of 20°N. These TCs later move northwards/northwestwards in association with a westwards extension of the western Pacific subtropical high, leading to inter‐decadal increase of northwards TC movements in the 120°–130°E region. For inter‐annual variability, TC passage frequency in the NWNP tends to decrease during El Niño events but to increase or decrease in La Niña‐related events. In La Niña‐related conditions, the low‐level anomalous convergent centre situating to the west of 130°E (east of 135°E) tends to increase (decrease) TC passage frequency in the NWNP around Taiwan. This region is influenced by an anomalous anticyclone (cyclone) on its eastern side that induces anomalous southeasterly (northeasterly) steering flows to facilitate (hinder) TC movement from the tropical western Pacific into this region. Inter‐annual and inter‐decadal variability of TC passage frequency in the NWNP is highly and positively connected with TC passage frequency and TC counts affecting Taiwan. More (less) TC passage frequency in the NWNP thus tends to relate to increased (decreased) TC rainfall in Taiwan. [ABSTRACT FROM AUTHOR]

This study quantifies large‐scale indices associated with variations in the western Pacific subtropical high (WPSH) and tropical sea surface temperature (SST) to assess typhoon activity around Taiwan. A WPSH index is constructed for both summer and early autumn as the meridional difference of areal means between the northern (120°–130°E, 25°–30°N) and southern (120°–130°E, 20°–25°N) regions (north minus south) of the 500 hPa height. These are regions north and south of Taiwan. In the high index years, typhoons forming in the tropical western North Pacific tend to be steered by easterly/southeasterly flows at the southwestern boundary of a northwards‐shifted WPSH to move northwestwards towards Taiwan, leading to increased typhoon activity around Taiwan. In the low index years, a southwards‐shifted, eastwards‐retreated WPSH steers typhoons along its western periphery to move northwards away from Taiwan. The northwards shift of the WPSH and consequent enhanced typhoon activity around Taiwan associate with a meridional wave train induced by a zonal SST gradient in summer, but link with a Matsuno‐Gill‐type response induced by tropical SSTs in early autumn. As so, the summer SST index is defined as a zonal gradient of areal‐mean SSTs between the tropical western Pacific (150°–175°E, 10°–20°N) and the Bay of Bengal–South China Sea–Philippine Sea region (80°–130°E, 5°–20°N) (former minus latter). In early autumn, the SST index is averaged from the tropical western Pacific over 130°–165°E, 5°S–5°N. All WPSH and SST indices in summer and early autumn are significantly correlated (at the 99% level) with the number of typhoons affecting Taiwan. (a) The domain of typhoon impact zone surrounding Taiwan. (b) Seasonal cycle of the typhoon count per decade affecting Taiwan averaged over the period 1979–2016. The 5‐day running mean of the typhoon count represents the seasonal cycle. The vertical dashed lines from left to right indicate the dates: June 15, September 1, and October 15, respectively. (c) Monthly climatology of 500 hPa, 5,870 gpm contour for June, July, August, September, and October, respectively. The JJASO‐mean contour is shaded. The rectangular box denotes the areas: 120°–130°E, 25°–30°N and 120°–130°E, 20°–25°N. [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) variability affects marine ecosystems, fisheries, ocean primary productivity and human activities and is the primary influence on typhoon intensity. SST drops of a few degrees in the open ocean after typhoon passages have been widely documented; however, few studies have focused on coastal SST variability. The purpose of this study is to determine typhoon-induced SST drops in the near-coastal area (within 1 km of the coast) and understand the possible mechanism. The results of this study were based on extensive field data analysis. Significant SST drop phenomena were observed at the Longdong Buoy in northeastern Taiwan during 43 typhoons over the past 20 years (1998–2017). The mean SST drop (Δ SST) after a typhoon passage was 6.1 ∘ C, and the maximum drop was 12.5 ∘ C (Typhoon Fungwong in 2008). The magnitude of the SST drop was larger than most of the observations in the open ocean. The mean duration of the SST drop was 24 h, and on average, 26.1 h were required for the SST to recover to the original temperature. The coastal SST drops at Longdong were correlated with the moving tracks of typhoons. When a typhoon passes south of Longdong, the strong and persistent longshore winds induce coastal upwelling and pump cold water up to the surface, which is the dominant cause of the SST drops along the coast. In this study, it was determined that cold water mainly intruded from the Kuroshio subsurface into the Okinawa Trough, which is approximately 50 km from the observation site. The magnitude of coastal SST drops depends on the area of overlap between typhoons generating strong winds and the Kuroshio. The dataset used in this study can be accessed from 10.1594/PANGAEA.895002. [ABSTRACT FROM AUTHOR]

A 110-year precipitation record in Taiwan, located at the western edge of the subtropical North Pacific, depicts a pronounced quasi-decadal oscillation (QDO). The QDO in Taiwan exhibits a fluctuating relationship with the similar decadal variations of sea surface temperature (SST) anomalies in the central equatorial Pacific, known as the Pacific QDO. A regime change was observed around 1960, such that the decadal variation of Taiwan’s precipitation became more synchronized with the Pacific QDO’s coupled evolutions of SST and atmospheric circulation than before, while the underlying pattern of the Pacific QOD did not change. Using long-term reanalysis data and CMIP5 single-forcing experiments, the presented analysis suggests that increased SST in the subtropical western Pacific and the strengthened western extension of the North Pacific subtropical anticyclone may have collectively enhanced the relationship between the Taiwan precipitation and the Pacific QDO. This finding provides possible clues to similar regime changes in quasi-decadal variability observed around the western Pacific rim. [ABSTRACT FROM AUTHOR]

ABSTRACT: Winter crop losses from extreme weather in Taiwan have increased in the recent decade, with those losses associated with pronounced wet‐and‐cold events (temperature < 10 °C and precipitation >5 mm day−1). The regional and global patterns of atmospheric circulation and the sea surface temperature (SST) related to the extreme cold that damages fruits, vegetables, and paddy rice in northwest Taiwan were investigated. Cool SST anomalies in the western North Pacific (WNP) and warm SST in the central‐eastern Pacific associated with the Pacific meridional mode (PMM) shared a significant role in the occurrence of wet‐and‐cold events in northwest Taiwan. The interactions of the WNP/PMM with the North Pacific Oscillation (NPO) and the Central Pacific type of El Niño led to a pronounced lead–lag relationship with the occurrence of wet‐and‐cold events. An empirical model was subsequently developed to predict the wet‐and‐cold event frequency using observed values of WNP, Niño‐3.4, and Arctic Oscillation from year‐1 and predicted indices of WNP and PMM derived from the Climate Forecast System Version 2 (CFSv2) outputs. The predictive skill of this hybrid empirical–dynamical model was statistically significant throughout the 6 months leading up to the occurrence of wet‐and‐cold events. [ABSTRACT FROM AUTHOR]

Northern hemisphere anguillid eel populations declined after continental habitat losses and ocean-atmosphere regime shifts occurred, but the exact causes of declines or recruitment fluctuations remain uncertain. Recruitment variations have been hypothesized to result from variable early larval survival, which could be related to phytoplankton blooms caused by typhoons, because leptocephali feed on productivity-related marine snow. We investigated typhoon occurrences in the Japanese eel early larval growth zone in the western North Pacific relative to Taiwan and Japan glass eel recruitment, sea surface temperature (SST), and Chl-a (2003–2017). Recruitment to the 2 areas was significantly correlated, but was not correlated with general typhoon parameters (wind speed, duration, storm radius) or the number of typhoons each year. The highest (2005, 13 typhoons) and lowest (2012, 14 typhoons) recruitment years had very different storm tracks, and SST and Chl-a anomalies were higher in 2005. Larval transport modelling showed regions where larvae were transported in 2005 in relation to typhoon tracks, and 2005 was unique for having 6 April–August typhoons/storms that affected areas with larvae compared to all other study years (194 total typhoons). Storm-induced phytoplankton blooms and species composition shifts (e.g. , diatom increases) are temporary and likely need to occur just before new moon to affect the most vulnerable first-feeding larvae (spawning only occurs near new moons). Typhoon Nesat passed near the spawning area ∼6 days before new moon in June 2005, just before the first-ever caught Japanese eel preleptocephali were collected, and there were 2 well-timed-placed August typhoons. The largest-ever eruption of the Anatahan Volcano north of Guam (eruptions 2003–2008) appeared to deposit potentially iron-rich ash (can cause blooms) into the region before new moon in April 2005, which might have increased April-spawned larval survival. Increased early larval survival could have occurred in 3-of-5 new moon spawning periods in 2005, and ash could also have increased productivity, which might have increased recruitment. Further research is needed to examine if marine snow composition and early larval survival may influence anguillid eel recruitment. • Typhoons, ocean productivity, Japanese eel larval survival/recruitment were studied. • Unique typhoon timing-locations occurred in high-recruitment year of 2005. • The Anatahan Volcano also likely deposited nutritive ash in the spawning area in 2005. • Chl-a anomalies suggest higher 2005 productivity in spawning/larval transport areas. • Observations support that productivity influences first-feeding larval survival. [ABSTRACT FROM AUTHOR]

The distribution and the structure of benthic assemblages vary with latitude. However, few studies have described benthic communities along large latitudinal gradients, and patterns of variation are not fully understood. Taiwan, lying between 21.90°N and 25.30°N, is located at the center of the Philippine-Japan arc and lies at the northern margin of coral reef development. A wide range of habitats is distributed along this latitudinal gradient, from extensive fringing coral reefs at the southern coast to non-reefal communities at the north. In this study, we examined the structure of benthic communities around Taiwan, by comparing its assemblages in four regions, analyzing the effects of the latitudinal gradient, and highlighting regional characteristics. A total of 25 sites, 125 transects, and 2,625 photographs were used to analyze the benthic communities. Scleractinian corals present an obvious gradient of increasing diversity from north to south, whereas macro-algae diversity is higher on the north-eastern coast. At the country scale, Taiwanese coral communities were dominated by turf algae (49%). At the regional scale, we observed an important heterogeneity that may be caused by local disturbances and habitat degradation that smooths out regional differences. In this context, our observations highlight the importance of managing local stressors responsible for reef degradation. Overall, this study provides an important baseline upon which future changes in benthic assemblages around Taiwan can be assessed. [ABSTRACT FROM AUTHOR]

Typhoons can cause substantial sea surface cooling (typically 2-4 °C), which is usually biased to the right side of the storm track. Under influence of the complex bathymetry of the southern Taiwan Strait (TS), two types of sea surface temperature (SST) response, cooling and warming, each associated with a different type of typhoon track were identified using satellite and mooring observations. When a typhoon moved westward (or northwestward) and passed through the TS (track A), the SST cooling in the TS was biased toward the left of the storm track. Numerical model results indicated that in track A, strong wind stress accelerates the flow east of the Taiwan Banks and drove the bottom flow to uplift due to the topography. Moreover, both wind stress and wind stress curl enhanced the Luzon loop. After the typhoon passed, the mean circulation was modified around strong cooling in the southern TS, causing more South China Sea surface water to be distributed to the Kuroshio region. However, when a typhoon moved westward (or northwestward) and passed south of the TS, SST warming was induced in the southern TS (track B). The model results indicated that when the typhoon passed to the south of the TS, the typhoon-induced horizontal divergent flow travelled to the north, where it encountered the shallower shelf of the TS that was confined to the water, causing warm water transported into this area to accumulate and downwelling to occur. This can be regarded as redistributing the heat content in the shelf area. After the typhoon, the thickened mixed layer resulting from downwelling prevented the formation of near-inertial waves and reduced the vertical mixing. [ABSTRACT FROM AUTHOR]

This research investigates the applicability of combining spatial filter's algorithm to extract surface ocean current. Accordingly, the raster filters were tested on 80–13,505 daily images to detect Kuroshio Current (KC) on weekly, seasonal, and climatological scales. The selected raster filters are convolution, Laplacian, north gradient, sharpening, min/max, histogram equalization, standard deviation, and natural break. In addition, conventional data set of sea surface currents, sea surface temperature (SST), sea surface height (SSH), and non-conventional data such as total heat flux, surface density (SSD), and salinity (SSS) were employed. Moreover, controversial data on ocean color are included because very few studies revealed that chlorophyll- α is a proxy to SST in the summer to extract KC. Interestingly, the performance of filters is uniform and thriving for seasonal and on a climatological scale only by combining the algorithms. In contrast, the typical scenario of identifying Kuroshio signatures using an individual filter and by designating a value spectrum is inapplicable for specific seasons and data set. Furthermore, the KC's centerlines computed from SST, SSH, total heat flux, SSS, SSD, and chlorophyll- α correlate with sea surface currents. Deviations are observed in the various segments of Kuroshio's centerline extracted from heat flux, chlorophyll- α , and SSS flowing across Tokara Strait from northeast Taiwan to the south of Japan. [ABSTRACT FROM AUTHOR]

The Kuroshio Current has its origin in the northwestern Pacific, flowing northward to the east of Taiwan and the northern part of Luzon Island. As the Kuroshio Current flows northward, it quasi-periodically intrudes (hereafter referred to as Kuroshio intrusion (KI)) into the northern South China Sea (SCS) basin through the Luzon Strait. Despite the complex generation mechanisms of KI, the purpose of this study is to improve our understanding of the effects of KI through the Luzon Strait on the regional atmospheric and weather variations. Long-term multiple satellite observations, including absolute dynamic topography, absolute geostrophic currents, sea surface winds by ASCAT, multi-scale ultra-high resolution sea surface temperature (MURSST) level-four analysis, and research-quality three-hourly TRMM multi-satellite precipitation analysis (TMPA), was used to systematically examine the aforementioned scientific problem. Analysis indicates that the KI is interlinked with the consequential anomalous precipitation off southwestern Taiwan. This anomalous precipitation would lead to ~560 million tons of freshwater influx during each KI event. Subsequently, independent moisture budget analysis suggests that moisture, mainly from vertical advection, is the possible source of the precipitation anomaly. Additionally, a bulk formula analysis was applied to understand how KI can trigger the precipitation anomaly through vertical advection of moisture without causing an evident change in the low-level flows. These new research findings might reconcile the divisiveness on why winds are not showing a synchronous response during the KI and consequential anomalous precipitation events. [ABSTRACT FROM AUTHOR]

Typhoon-induced cooling in the cold dome region off northeastern Taiwan has a major influence on ocean biogeochemistry. It has previously been studied using numerical models and hydrographic observations. Strong cooling is related to upwelling of the Kuroshio subsurface water accompanied by the westward intrusion of the continental shelf by Kuroshio water. By employing satellite observations, local measurements, and a reanalysis of model data, this study compared 18 typhoon-induced sea surface temperature (SST) responses in the cold dome region and determined that SST responses can differ dramatically depending on the relative location of a typhoon path, the Kuroshio Current, and the topography off northeastern Taiwan. The results indicated that local westward and northward wind stress is positively correlated with upwelling intensity. Decreased northward transport in the Taiwan Strait created a condition that favored the Kuroshio intrusion, thus, the typhoon-induced change in Taiwan Strait transport was also positively correlated with the intensity of cooling. However, the strength of Ekman pumping was weakly correlated with the intensity of SST cooling. Nevertheless, Ekman pumping helped reduce the cover of warm water, facilitating the intrusion of the Kuroshio Current. [ABSTRACT FROM AUTHOR]

Dynamics of ocean current-induced island wake has been an important issue in global oceanography. Green Island, a small island located off southeast of Taiwan on the Kuroshio path was selected as the study area to more understand the spatial structure and temporal variation of well-organized vortices formed by the interaction between the Kuroshio and the island. Sea surface temperature (SST) and chlorophyll-a (Chl-a) concentration data derived from the Himawari-8 satellite and the second generation global imager (SGLI) of global change observation mission (GCOM-C) were used in this study. The spatial SST and Chl-a variations in designed observation lines and the cooling zone transitions on the left and right sides of the vortices were investigated using 250 m spatial resolution GCOM-C data. The Massachusetts Institute of Technology general circulation model (MITgcm) simulation confirmed that the positive and negative vortices were sequentially detached from each other in a few hours. In addition, totals of 101 vortexes from July 2015 to December 2019 were calculated from the 1-h temporal resolution Himawari-8 imagery. The average vortex propagation speed was 0.95 m/s. Totals of 38 cases of two continuous vortices suggested that the average vortex shedding period is 14.8 h with 1.15 m/s of the average incoming surface current speed of Green Island, and the results agreed to the ideal Strouhal-Reynolds number fitting curve relation. Combined with the satellite observation and numerical model simulation, this study demonstrates the structure of the wake area could change quickly, and the water may mix in different vorticity states for each observation station. [ABSTRACT FROM AUTHOR]

The seasonal warming over the southwestern Yellow Sea (YS) in the spring is of vital importance to the local ecologic environment, especially to the massive green algae blooms of the YS in late spring and early summer. Based on daily optimum interpolation sea surface temperature (SST) data consisting of satellite derived SST from Advanced Very High Resolution Radiometer (AVHRR) and in situ measurements, this study analyzed the spring SST variation over the southwestern YS (SWYS) from 1982 to 2018. The results show that the recent warming trend of spring SST over the SWYS is four-to-six times that of the global average, and as a result, sea water over the Subei Shoal (SBS) shifts about 10–13 days earlier to reach 10 °C in early April. This implies that, accordingly, the micro-propagules of green algae over the SBS may have the chance to germinate earlier. SST variability in early April significantly correlates with northerly wind and exhibits a general warming over the SWYS with an intensified warming anchored along the axis of the submarine canyon off the Yangtze estuary. The Moderate Resolution Imaging Spectroradiometer (MODIS) red–green–blue composite images captured the intrusion of the Taiwan Warm Current (TWC) into the SWYS through the submarine canyon during northerly wind relaxation in early April. Ocean remote sensing provides important clues for understanding the regional SST variability in the SWYS. Following this clue, this study finds that the weakening of winter monsoon in the spring leads to northward migration of the TWC and results in enhanced spring warming over the SWYS. The attendant advanced warming in spring, resulting in a favorable temperature condition for early development of green alga, may have contributed to the green tide blooms in the Yellow Sea in the recent decade. [ABSTRACT FROM AUTHOR]