Southern Taiwan Strait Research Articles

Interannual variability of remotely sensed chlorophyll a during an autumn monsoon transitional period in the Taiwan Strait

973 Program Grant of China [2009CB421201]; National Natural Science Foundation of China [171305231, 40706041]; Natural Science Foundation of Fujian Province [2011J01278]; Foundation of Key Laboratory of Marine Integrated Monitoring and Applied Technologies for Harmful Algal Blooms, State Oceanic Administration [MATHAB20100313]

Effects of an Unusual Cold-Water Intrusion in 2008 on the Catch of Coastal Fishing Methods around Penghu Islands, Taiwan

Based upon long-term observations (1993-2010) of satellite-derived winter sea surface temperature (SST) data, an exceptional cold-water intrusion into the southern Taiwan Strait (TS) was noted in February 2008. In the winter of 2008, La Nina caused a strong and continuous northeasterly wind that drove the cold ocean current, the China Coastal Current, more southward to penetrate the southern TS north of the Chang-Yuen Ridge. A portion of this current turned eastward to the south of Penghu Islands (PHI). The low-SST event significantly impeded local marine aquaculture and wild fish, causing the death of more than 73 tons of fish around PHI. Comparing variations of the first quarterly catches in 2008 with the long-term averages from 1993 to 2010 (excluding 2008), we noted a 50 to 80% decrease in catches from pole-and-line, long-line, and gill-net fishery. Non-migratory species dominated the composition of the catches. We also noted a greater than 230% increase in the catches from set-net fishery, with the majority being migratory species. These results illustrate the positive and negative effects of cold-water intrusion on several fish communities and species.

Sand wave deposition in the Taiwan Shoal of China

The Taiwan Shoal is the convex terrain in the southern Taiwan Strait, the largest strait in China. In 2006 and 2007, 21 samples and more than 200-km sub-bottom data as well as 80-km near shore side-scan sonar data were gotten, which gave an initial image of the boundaries of the Taiwan Shoal and revealed the internal structure of the sand waves in this area. The results showed that the major component of the sediment samples was sand, and sand waves occurred everywhere in this area, which closely followed the range of the Taiwan Shoal as we know. The western boundary of the Taiwan Shoal thus reaches the 30 m isobaths near the shore, and as a result, its area potentially covers approximately 12 800–14 770 km2. The sand waves have different shapes under the complex ocean dynamics, and the height of sand waves in the near shore is usually smaller than that in the Taiwan Shoal. The number of sand waves ranged from1–5 per kilometer, with more waves in the isobath-intensive area, suggesting the importance of topography for the formation of sand waves. The stratigraphic structure under the seabed has parallel bedding or cross bedding, and large dipping groove bedding can be seen locally in different parts, which may be the result of terrestrial deposition since the Late Pleistocene.

Seasonal and interannual variations of surface current in the southern Taiwan Strait to the west of Taiwan Shoals

Seasonal and interannual variations of surface currents in the southern Taiwan Strait to the west of Taiwan Shoals were investigated by using measurements of high frequency (HF) ground wave radars from January 2006 to April 2009. The results demonstrate that surface currents in the water channel to the west of Taiwan Shoals are composed of a significant, seasonally fluctuating component and a relatively stable northward component. Forced by the East Asia monsoon, the annual variation of the surface longshore current is linearly correlated with the longshore wind. Behind the seasonal signal is a stable northward flow with speeds of O (10 cm/s). The observations also show that surface currents in the area are subject to distinct interannual variation, and the southward surface flow was more profound in winter 2007/2008 than in other winters. Observations from bottom-mounted ADCP also indicated that, in that winter, longshore currents in the west side of the Taiwan Strait are very different from the previous winter. The northward flow appeared much weaker, the currents were southward in most layers, and the interannual differences were observed throughout the water column. Hydrographic observations in the same period suggest that the large-scale southward intrusion of the Zhe-Min coastal water is the direct cause of the interannual difference. The enhancement of the East Asian monsoon during the 2007/2008 La Nina event is considered as the main reason for the winter current anomalies in the study area.

Observations of High-Frequency Internal Waves in the Southern Taiwan Strait

ABSTRACT Bai, X.; Liu, Z.; Li, X.; Chen, Z.; Hu, J.; Sun, Z.; and Zhu, J., 2013. Observations of high-frequency internal waves in the southern Taiwan Strait. Based on in situ hydrographic measurements at a station at about 60 m depth near the local shelf break in July 2011 and a satellite image of the sea-surface roughness, we present the evidence of existence and characteristics of high-frequency internal waves (HIWs) in the southern Taiwan Strait. Variations of the thermohaline structure at the observational site were revealed by repeating conductivity-temperature-depth (CTD) profiling measurements of every 2 hours, while fluctuations of the isothermals due to the passage of HIWs were recorded by continuous CTD measurements with a probe positioned approximately in the middle of the pycnocline. A fast sampling frequency of 8 Hz allows the structure of the HIWs to be captured in great detail. The waves were depression waves, with a period of about 6.2 min and an amplitude of about 25 m. The propagation sp...

Adaptation of fisheries and mariculture management to extreme oceanic environmental changes and climate variability in Taiwan

Abstract This study presents the response of fisheries management to the extreme climatic events that affect marine capture fisheries and mariculture in Taiwan. Two regional approaches that can be applied universally to help capture fisheries and mariculture adapt to extreme weather events are also proposed. In the winter of 2008, an anomalously strong and continuous northeasterly wind caused by a La Nina event drove the cold China Coastal Current southward to penetrate the southern Taiwan Strait, and a portion of this current intruded eastward to the southern Penghu Archipelago. The cold current intrusion appreciably damaged marine aquaculture and the wild fish population, causing the death of more than 73 t of wild fish and 80% of cage aquaculture fish at the Penghu Islands. This extremely cold seawater event occurred between late January and the beginning of February 2008. To recover fishery resources around the waters of Penghu, fishery-related agencies adapted recovery measures over 3 years starting in April 2008 that included hatchery juvenile release, environmental monitoring, fishery subsidies, and ecological field investigations. This study suggests that responding to extreme climatic influences on fisheries and mariculture should include (1) establishing an early warning system by connecting fisheries agencies and marine research institutions to assist decision makers in performing time-adaptive measures, (2) temporarily suspending fishing activities after the occurrence of a natural disaster to help recover fishery resources and ecosystems, (3) altering the governance of farming fishing right so that fish farmers can temporarily transfer their aquaculture cages from high-risk areas to waters outside the influence of extreme weather events, and (4) continually filing surveys to understand the recovery status of marine ecosystems.

Larval fish assemblages in the Taiwan Strait, western North Pacific: linking with monsoon‐driven mesoscale current system

AbstractThis study, based on samples taken in seven cruises from February 2003 to November 2004, linked larval fish assemblages with mesoscale oceanographic features dominated by the monsoon‐driven current system in the Taiwan Strait. A total of 7753 specimens of larval fish were identified from our samples, belonging to 467 taxa in 112 families and 230 genera. Engraulidae, Myctophidae, Scombridae, Carangidae, and Gobiidae were the five most abundant families. Three larval fish assemblages were distinguished by association respectively with the China Coastal Current, Kuroshio Branch Current, and South China Sea Surface Current, and accordingly designated as the cold‐period northern Taiwan Strait (CNTS), southern Taiwan Strait (STS), and warm‐period northern Taiwan Strait (WNTS) assemblages. The composition of larval fish differed significantly between assemblages, with the CNTS being the most dissimilar assemblage, probably due to the presence of neritic/oceanic taxa in the STS and WNTS and primarily neritic‐associated taxa in the CNTS. The alternate intrusions of currents in the Taiwan Strait driven by seasonal monsoons play a pivotal role in the dispersal and community structure of larval fish. In addition, winter front turbulence and local topographic upwelling contributed to the increase in biological production; consequently resulting in high chlorophyll a concentrations and zooplankton biomass to provide abundant food for the survival of larval fish. The high correlation between the environmental variables and the larval fish assemblages offers the possibility to use the assemblages as indicators of the surface circulation in the Taiwan Strait and thereby improve our understanding of the ecosystems.

Characteristics and mechanisms of the upwelling in the southern Taiwan Strait: a three-dimensional numerical model study

Using a nested circulation model based on the Princeton Ocean Model, we investigate the characteristics and mechanisms of two main upwellings in the southern Taiwan Strait: the Southwest upwelling and the Taiwan Bank upwelling. The Southwest upwelling exists in summer when the southwesterly monsoon dominates, and the Taiwan Bank upwelling occurs over a longer period from May to September. The upslope current over a distinctly widened shelf transports the cold water on-shoreward at the lower layer and the southwesterly monsoon wind drives the cold water to the surface layer, forming the Southwest upwelling, while tidal residual current weakens the upslope advection. For the Taiwan Bank upwelling, the upward transport of the South China Sea water due to the Bank topography carries the cold water from the subsurface layer to the depth of approximately 25 m near the Taiwan Bank, then the strong tidal mixing forces this upwelled water further upward to the surface layer.

Remote Trigger of Deep Convection by Cold Outflow over the Taiwan Strait in the Mei-Yu Season: A Modeling Study of the 8 June 2007 Case

In this study, the heavy-rainfall event over central Taiwan during the mei-yu season on 8 June 2007 is investigated, with an emphasis on the triggering mechanism for the deep convection that produced the rain. Observations indicate that there existed two lines of forcing with convection prior to the rain: one over the northern Taiwan Strait along the mei-yu front and the other over the southern Taiwan Strait. Yet, the convection in question developed over the central strait between these two lines, in an unstable environment with strong westerly vertical wind shear. This motivated the authors to carry out the present study.The Cloud-Resolving Storm Simulation (CReSS) of Nagoya University was used and the event was reproduced at a horizontal grid size of 2 km, including the initiation of new convection over the central strait at the correct location and time. The model results suggest a crucial role played by the series of active, persistent, and propagating storms in the southern strait (along the aforementioned second forcing line). On their back (northern) side, these storms repeatedly produced pulses of cold outflow that traveled toward the north-northeast with positive pressure perturbation. With characteristics of gravity waves, the perturbation propagated faster than the cold air and the associated increase in forward-directed (horizontal) pressure gradient force led to northward acceleration of near-surface flow (by up to 4–5 m s−1h−1). The stronger southerly flow in turn enhanced downstream convergence, and the deep convection was triggered in the central strait near the arrival of the gravity wave ahead of the cold air. When the convection moved eastward over Taiwan, heavy rainfall resulted. The mechanism presented here for remote triggering of convection over the ocean has not been documented near Taiwan during the mei-yu season. With a better understanding about the behavior of convection, these results can contribute to the improvement of quantitative precipitation forecasts and hazard prevention and reduction.

Source water of two-pronged northward flow in the southern Taiwan Strait in summer

It is generally accepted that the flow is northward in the Taiwan Strait during summer and that the strongest current is detected in the Penghu Channel between the Penghu Islands and the Taiwan Island. This current, the eastern prong flow, is made up of waters from the South China Sea (SCS) and the Kuroshio. North of the Penghu Islands, the current veers to the west before turning northward again because of the shallow Chang-Yuen Ridge, and extends westward off the coast of Taiwan. There is a second prong of northward flow existing between the Taiwan Bank and the China mainland coast. Here, we show with observational data as well as results from a numerical model that this water receives little influence from the Kuroshio and is distinctively cooler, fresher, less oxygenated and more acidic, and contains more dissolved inorganic carbon than waters at the same density level of the eastern prong. Evidence is provided to show that the source water of the western prong should be the subsurface water from the strong upslope advection flowing northward from the SCS to the southern Taiwan Strait and upwelling along the coast during the favorable southwesterly wind. Subsequently, the upwelled water flows over the saddle west of the Taiwan Bank and joins the main flow northwest of the Penghu Islands.

Currents in the Taiwan Strait as observed by surface drifters

The trajectories of 110 satellite-tracked surface drifters from 1989 to 2007 were analyzed to elucidate near-surface circulation in the Taiwan Strait. Although the summer circulation observed generally agrees with previous studies, several aspects of the winter circulation were revealed by the analyses. Unlike many earlier studies, which have suggested that a northward (southward) current prevails in the eastern (western) part of the Taiwan Strait during the northeast monsoon season, this study shows that almost all winter drifters that entered the Taiwan Strait eventually moved southward. Inside the Taiwan Strait, northward moving tracks can only be found in the Penghu Channel. After passing the Penghu Channel, the drifters were blocked by the northeast monsoon wind and the Yun-Chang Rise, and turned southward. None of the drifters flowed persistently northward through the Taiwan Strait in winter. In the southern Taiwan Strait, three typical patterns of circulation were observed for the winter trajectories—the “throughflow” pattern that enters the South China Sea flowing westward along the slope; the loop current pattern that circulates anticyclonically and returns to the Kuroshio; and the blocked intrusion pattern that penetrates into the Taiwan Strait through the Penghu Channel.

MODIS observed phytoplankton dynamics in the Taiwan Strait: an absorption-based analysis

Abstract. This study used MODIS observed phytoplankton absorption coefficient at 443 nm (Aph) as a preferable index to characterize phytoplankton variability in optically complex waters. Aph derived from remote sensing reflectance (Rrs, both in situ and MODIS measured) with the Quasi-Analytical Algorithm (QAA) were evaluated by comparing them with match-up in situ measurements, collected in both oceanic and nearshore waters in the Taiwan Strait (TWS). For the data with matching spatial and temporal window, it was found that the average percentage error (ε) between MODIS derived Aph and field measured Aph was 33.8% (N=30, Aph ranges from 0.012 to 0.537 m−1), with a root mean square error in log space (RMSE_log) of 0.226. By comparison, ε was 28.0% (N=88, RMSE_log = 0.150) between Aph derived from ship-borne Rrs and Aph measured from water samples. However, values of ε as large as 135.6% (N=30, RMSE_log = 0.383) were found between MODIS derived chlorophyll-a (Chl, OC3M algorithm) and field measured Chl. Based on these evaluation results, we applied QAA to MODIS Rrs data in the period of 2003–2009 to derive climatological monthly mean Aph for the TWS. Three distinct features of phytoplankton dynamics were identified. First, Aph is low and the least variable in the Penghu Channel, where the South China Sea water enters the TWS. This region maintains slightly higher values in winter (~17% higher than that in the other seasons) due to surface nutrient entrainment under winter wind-driven vertical mixing. Second, Aph is high and varies the most in the mainland nearshore water, with values peaking in summer (June–August) when river plumes and coastal upwelling enhance surface nutrient loads. Interannual variation of bloom intensity in Hanjiang River estuary in June is highly correlated with alongshore wind stress anomalies, as observed by QuikSCAT. The year of minimum and maximum bloom intensity is in the midst of an El Niño and a La Niña event, respectively. Third, a high Aph patch appears between April and September in the middle of the southern TWS, corresponding to high thermal frontal probabilities, as observed by MODIS. Our results support the use of satellite derived Aph for time series analyses of phytoplankton dynamics in coastal ocean regions, whereas satellite Chl products derived empirically using spectral ratio of Rrs suffer from artifacts associated with non-biotic optically active materials.

Response of phytoplankton to nitrogen addition in the Taiwan strait upwelling region: Nitrate reductase and glutamine synthetase activities

This study investigated the activities of two nitrogen assimilation enzymes, nitrate reductase (NR) and glutamine synthetase (GS) in phytoplankton in relation to sample, as well as the nutrient levels and phytoplankton biomass (Chl- a concentrations) during an upwelling event in the southern Taiwan Strait during an upwelling period from 6 to 12 July, 2005. The results showed that high NR activity (NRA) was always found with low nitrate and high Chl- a concentrations, while GS activity (GSA) exhibited positive correlations with ammonium and Chl- a concentration. Both NRA and GSA varied with the time and stage of upwelling: high NRA and GSA were observed initially at the subsurface layers in the early stage of upwelling, accompanied by the consumption of nutrients and the increase of Chl- a concentration; and then at the surface with high Chl- a concentrations in the middle and late stages of upwelling. Results from in situ enzyme bioassays on water samples along the tracing of upwelling track and on board mesocosm experiments on board the ship showed that there was a time-lag between nitrate addition and NRA and GSA, but. However, no time-lag was found between ammonium addition and GSA. The present results indicated that both NRA and GSA reflect the status of ambient nitrogen levels and the assimilation process of the phytoplankton, and could be used as effective parameters for the analysis of the physiological response of the phytoplankton to nitrogen variations during upwelling periods. Measurements of NRA and GSA in the phytoplankton in newly upwelled water appeared to provide ecophysiological indicators of phytoplankton, which will make it possible to trace during the sequence of upwelling events (such as nutrient supplementation) leading to enhanced productivity.

Phytoplankton growth and microzooplankton grazing in a subtropical coastal upwelling system in the Taiwan Strait

Phytoplankton growth and microzooplankton grazing were measured in a coastal upwelling system in the southern Taiwan Strait during the summers of 2004–2007, with emphasis on a comparison between upwelling and non-upwelling areas. Diatoms significantly dominated the phytoplankton community (49–92%, by pigment content) in the coastal upwelling area, while the prevailing groups varied, with Cyanophyceae, Chlorophyceae and diatoms, in the different stations of the non-upwelling area. Aloricate ciliates and tintinnids dominated the microzooplankton community, and there was a higher abundance of microzooplankton in the coastal upwelling area (1869 ind L −1), while there was lower abundance in the non-upwelling area (544 ind L −1). The phytoplankton growth rate in the upwelling area (1.02±0.27 d −1) was significantly higher than that in the non-upwelling area (0.51±0.05 d −1) ( p<0.05), while the microzooplankton grazing rate in the upwelling area (0.85±0.37 d −1) was only a little higher than that in the non-upwelling area (0.50±0.17 d −1). Growth (synthesis) rates were similar among the four representative pigments, while grazing (destruction) rates were higher for 19′-hexanoyloxyfucoxanthin than those for fucoxanthin, zeaxanthin and divinyl chlorophyll a. In addition, there was almost a balance between phytoplankton growth and microzooplankton grazing in the non-upwelling area, while phytoplankton growth was higher than grazing in most cases in the upwelling area.

The coupling of temporal and spatial variations of chlorophyll a concentration and the East Asian monsoons in the southern Taiwan Strait

The impact of monsoon on the temporal and spatial variations of phytoplankton standing stock (Chl a) in the southern Taiwan Strait was studied based on long-term satellite data (1997–2008) and field observations (during 1987–1988 and 2006–2007). During the NorthEast (NE) monsoon, the high Chl a was induced by vertical mixing, the Zhejiang–Fujian Coastal Current and upwelling. However, for most of the area, the vertical mixing was the dominant process that enhanced phytoplankton growth. During the SouthWest (SW) monsoon, two low temperature and high Chl a areas were observed: one near the Dongshan Island and the other in the southeast edge of the Taiwan Bank. Both of them were identified as the upwelling areas a half century ago. The Dongshan upwelling is mainly caused by the cold waters, which is derived from the famous “East Guangdong upwelling” induced by the SW monsoon. And the latter upwelling is mainly induced by a shallowing of the topography and the Kuroshio intrusion. In the last decades, most of the studies suggested that the Chl a during the SW monsoon is higher than that during the NE monsoon, due to the upwelling and cold temperature, respectively. However, some recent studies made contrary conclusion. Using the satellite seasonal climatological Chl a data (SeaWiFS and MODIS), we acquired more extensive and long-term records and found a significant difference in the temporal variation patterns of Chl a concentrations in the three sub-areas of southern Taiwan Strait. In the coastal area, two Chl a peaks were observed, which were due to upwelling during the SW monsoon and Zhejiang–Fujian Coastal Current during the NE monsoon. On the Taiwan Bank, the high Chl a occurred throughout the year due to the topographical upwelling all year round. For the shelf break area, a higher Chl a was observed during the NE monsoon, which was induced by vertical mixing. For the whole study area, a significant coupling occurred between Chl a and wind speed ( r 2=0.23, p<0.05) during the NE monsoon, while it was very weak during the SW monsoon. On the other hand, the mean surface Chl a was significantly higher in the NE monsoon (0.69 mg m −3) than in the SW monsoon (0.53 mg m −3). All these results demonstrated that the temporal and spatial variations of phytoplankton standing stock were affected by the East Asia monsoon system in the southern Taiwan Strait.

Planktonic copepod compositions and their relationships with water masses in the southern Taiwan Strait during the summer upwelling period

The species composition and distribution of planktonic copepods in relation to hydrographical characteristics in the southern Taiwan Strait were investigated during the summers of 1988, 1994, 2005 and 2006. Two station groups (I and II) and two copepod assemblages (nearshore and offshore) based on sea surface temperature, salinity, chlorophyll a and copepod abundance were revealed through cluster and detrended correspondence analysis. Station-group I was found in nearshore regions including the upwelling areas, and primarily consisted of coastal/neritic species; while station-group II was found in offshore regions and primarily consisted of oceanic species. Indicator analysis identified the coastal/neritic species Temora turbinata and Acrocalanus gibber are good indicators of the nearshore assemblage. The oceanic species Paraeuchaeta russelli and 6 additional species are indicators of the offshore assemblage. The results showed that Acartia pacifica is an indicator species of coastal waters with freshwater runoff, and Calanus sinicus is an indicator species of hypothermic upwelled waters in the southern Taiwan Strait during summer.

Evolution of a coastal upwelling event during summer 2004 in the southern Taiwan Strait

A coastal upwelling event in the southern Taiwan Strait (STWS) was investigated using intensive cruise surveys (four repeated transects in a month) and satellite data in July and early August 2004. The extensive upwelling-associated surface cold water was first observed in early July (∼2.0×104 km2) along the STWS coast. Then, the cold surface water reduced in size by ∼50% with decreased chlorophyll concentrations after 15 days, indicating the weakening of the upwelling event. At the end of July, the cold surface water disappeared. The temporal variations of the surface cold water and the 3-D hydrography around Dongshan Island are thought to be mainly attributed to the weakened upwelling-favorable southwestern wind, the asymmetric spatial structure of the wind field and the intrusion of warm water from the northern South China Sea.

A Subtropical Oceanic Mesoscale Convective Vortex Observed during SoWMEX/TiMREX

AbstractThis study examines a subtropical oceanic mesoscale convective vortex (MCV) that occurred from 1800 UTC 4 June to 1200 UTC 6 June 2008 during intensive observing period (IOP) 6 of the Southwest Monsoon Experiment (SoWMEX) and the Terrain-influenced Monsoon Rainfall Experiment (TiMREX). A dissipating mesoscale convective system reorganized within a nearly barotropic vorticity strip, which formed as a southwesterly low-level jet developed to the south of subsiding easterly flow over the southern Taiwan Strait. A cyclonic circulation was revealed on the northern edge of the mesoscale rainband with a horizontal scale of 200 km. An inner subvortex, on a scale of 25–30 km with maximum shear vorticity of 3 × 10−3 s−1, was embedded in the stronger convection. The vortex-relative southerly flow helped create local potential instability favorable for downshear convection enhancement. Strong low-level convergence suggests that stretching occurred within the MCV. Higher θe air, associated with significant potential and conditional instability, and high reflectivity signatures near the vortex center suggest that deep moist convection was responsible for the vortex stretching. Dry rear inflow penetrated into the MCV and suppressed convection in the upshear direction. A mesolow was also roughly observed within the larger vortex. The presence of intense vertical wind shear in the higher troposphere limited the vortex vertical extent to about 6 km.

Spring of no Kuroshio intrusion in the southern Taiwan Strait

The Taiwan Strait connects the East China Sea (ECS) to the South China Sea (SCS). Typically, in spring, the water in the SCS and a branch of the Kuroshio occupy the eastern part of the strait while the China coastal waters, including a large contribution from the Changjiang (Yangtze River), occupy the western part. During spring 2008, when the Taiwan Strait was under the influence of La Niña, and according to field observations, the Kuroshio branch did not contribute much to the waters in the southern Taiwan Strait. A numerical model verifies this observation. The China coastal waters also seem to have had less effect than in typical years. Since the SCS waters contain more nutrients than the Kuroshio branch, more nutrients may be transported from the SCS to the ECS in a La Niña spring than at other times.

Investigation of a heavy rainfall event over southwestern Taiwan associated with a subsynoptic cyclone during the 2003 Mei-Yu season

The objective of this study is to perform observational data analyses, including European Centre for Medium-Range Weather Forecasts (ECMWF) data, satellite imagery, radar reflectivity, and rainfall data, and numerical simulations with the Weather Research and Forecast (WRF) model to investigate both the synoptic and mesoscale processes responsible for causing the heavy rainfall event which produced up to 379.5 mm over southwestern Taiwan on 7 June 2003. We found that an 850 hPa subsynoptic cyclone, composed of both a low-pressure center and a vortex, formed over the eastern Tibetan Plateau and moved with a 500 hPa shortwave trough toward a wind shear zone over southeastern China in the early morning of 7 June. The wind shear zone was generated by a southwesterly monsoonal flow and a northeasterly flow associated with a high pressure in eastern China. The intensifying 850 hPa subsynoptic cyclone served as a precursor of the heavy rainfall episode in Taiwan. The 850 hPa subsynoptic cyclone extended downward to form a surface subsynoptic cyclone over the southeastern coast of China by coupling the ascending motions associated with the 500 hPa shortwave trough and the 850 hPa subsynoptic cyclone. The mesoscale convective system associated with this surface subsynoptic cyclone migrated from southeastern China to the southwestern Taiwan Strait and then toward southwestern Taiwan. Meanwhile, the speed of the 850 hPa low-level jet on the southern side of the subsynoptic cyclone exceeded 20 m s − 1 over the southern Taiwan Strait. This jet then served as a conveyor belt of the moist airstream and enhanced the inland-moving convection over the mountain slopes. In addition, the low-level convergence resulted from the confluence of flow due to flow deflection over southern Taiwan topography also facilitated rainfall there.