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The Makassar Strait (MS) is characterized by water mass from the Pacific Ocean and is one of the ITF (Indonesia Throughflow) branches. It carries warm water masses from the Pacific Ocean to the Indian Ocean. This research aims to analyze the relationship between CPUE of Eastern Little Tuna (Euthynnus affinis) and oceanographic variables, likewise predict the fishing area using the Generalized Additive Model (GAM). The research method used is spatial and temporal analysis. The data was used from 2015 to 2020. The data processed were sea surface temperature, chlorophyll-a, salinity, currents, sea level as predictor variables, and Eastern Little Tuna production as a response. Eastern Little Tuna catch data were normalized into Catch per Unit Effort, while the oceanographic data were extracted using ArcGIS. Based on the results of the GAM model, it was found that the model with five variables is the most suitable predictive model, with 16.4% CDE. Salinity is the most influential parameter on the catch of Eastern Little Tuna with a significance value of <2.00 × 10−16 ***. The optimum value for SST is 30–31 °C, chlorophyll-a is 1–2 mg/m3, salinity is 29–30 ppt, current velocity is 0.3–0.5 m/s and sea level is between 0.6–0.7 m. Based on the GAM prediction results, a high CPUE value will be obtained in the southwest monsoon (March to May). Fishing activity carried out in the best season will implement the adoption of harvest control measures. [ABSTRACT FROM AUTHOR]

This study investigates the coherency of volume transport between Halmahera throughflow and current major system in the western equatorial Pacific Ocean (Mindanao Current – MC, New Guinea Coastal/Under Current – NGCC/NGCUC, and North Equatorial Counter Current – NECC). The validated daily ocean general circulation model datasets of INDESO (2010-2014) were used in this study. The results showed that the estimated average transport volume was 25.6 Sv flowing southward through MC, 34.5 Sv flowing eastward through NECC, 18.3 Sv flowing northwestward through NGCC/NGCUC, and 2.5 Sv flowing southward through the Halmahera Sea. The variability of volume transport was dominated by intraseasonal, semiannual, and annual time-scales. The increased transport of NECC corresponded to the intensification of MC and NGCC/NGCUC transports. NGCC/ NGCUC significantly controlled the South Pacific water inflow into the Halmahera Sea because of the positively high correlation between NGCC/NGCUC transport and Halmahera throughflow transport. [ABSTRACT FROM AUTHOR]

Turbulent mixing enhanced in the Indonesian Archipelago (IA) is thought to influence the coupled ocean‐climate system through sea surface temperature cooling and water‐mass transformation. The present study describes the first extensive microstructure measurements conducted in the IA in 2019. A total of 120 profiles of turbulent energy dissipation rates showed that strong turbulent mixing was extremely localized in a few narrow tidal straits, where large density overturns and high vertical diffusivity associated with downslope jets were found. Far away from mixing hotspots, in contrast, observed vertical diffusivities were similar to typical open ocean values. Microstructure measurements together with a high‐resolution numerical simulation suggest that significant water‐mass transformation occurred within very short distances, O (10 km), in these narrow tidal straits through not only vertical mixing but also horizontal mixing enhanced by submesoscale topographic eddies. Plain Language Summary: Turbulent mixing enhanced in the Indonesian Archipelago (IA) is thought to play an important role in global climate, since it strongly cools the sea surface temperature and also alters the water‐mass properties. However, until now, only a limited number of direct microstructure measurements have been carried out in the Indonesian Seas. To describe the spatial distribution of turbulent mixing intensity in the IA, we carried out the first extensive direct microstructure measurements in this region during February, March, and August 2019. Observed results showed that, in the narrow straits, turbulent mixing was significantly enhanced due to the interaction between strong tidal currents and steep bottom topography. Furthermore, it is suggested that lateral diffusion enhanced by small‐scale (<10 km) eddies can rapidly modify the water‐mass properties in the IA. Key Points: To describe the spatial distribution of turbulent diffusivity in the Indonesian Seas, extensive microstructure measurements were conductedMixing hotspots are confined in narrow tidal straits, where large density overturns associated with downslope jets take placeNot only vertical but also horizontal mixing caused by submesoscale topographic eddies might play a key role in water‐mass transformation [ABSTRACT FROM AUTHOR]

Real-time offshore coastal acoustic tomography (CAT) with mirror-transpond functionality is the most recent feature added to CAT to transfer travel-time data obtained in an offshore subsurface station to a shore station in real time, forming a round-trip travel time by original transmission and subsequent mirror transmission. The minimum unit, composed of one land and one offshore system, was operated to validate the performance of CAT with mirror-transpond functionality (MCAT) in the feasibility experiment, which was carried out in April 2017 in the Nekoseto Strait of the Seto Inland Sea, Japan. The root-mean-square error (RMSE) of the hourly mean range-average currents calculated from the original–original and original–mirror reciprocal travel-time pairs was 0.05 ms–1, significantly smaller than the variation range of the semidiurnal tidal current (0.2–0.3 ms–1) dominant at the experimental site. The RMSE for the residual current was also significantly smaller than its variation range. This study suggests the feasibility of using a compact MCAT array composed of one land and three offshore stations. [ABSTRACT FROM AUTHOR]

We investigated ocean variability at intermediate depths (300–750 m) in the western equatorial Pacific (WEP) using data from underwater sensors of the Triangle Trans-Ocean Buoy Network (TRITON) buoys. The data were specially processed because high accuracy is necessary for such an application, and we confirmed that sufficient accuracy was achieved. Variability of the temperature and salinity was large in the western boundary regions of the WEP. Seasonal variability is generally dominant at intermediate depths in the WEP; however, intraseasonal variability with period of 30–80 days is not negligible, particularly at 2°N, 138°E, where the New Guinea Coastal Undercurrent retroflects to the east as the Equatorial Undercurrent and/or Northern Subsurface Countercurrent. High correlation is seen between 12-month running means of the Niño 3.4 index anomaly and temperature at 300 and 750 dbar. In other words, the influence of El Niño/Southern Oscillation phenomena reaches to at least a depth of 750 dbar. We found a decreasing trend in salinity at intermediate depths in the WEP: − 0.0032 Practical Salinity Unit (PSU) year−1 at 300 dbar and − 0.00053 PSU year−1 at 750 dbar. This trend is likely associated with the freshening of the North Pacific Intermediate Water and Antarctic Intermediate Water. [ABSTRACT FROM AUTHOR]

The subsurface structures of internal solitary waves were observed over two days from 27 to 29 February 2019, by two bottom‐moored coastal acoustic tomography systems over a path length of 18.286 km in the Lombok Strait, Indonesia. One‐way travel times along the transmission path between the acoustic stations were determined for the first three arrival peaks. The resulting three travel times were used to execute a four‐layer (0–50, 150–300, 300–450, and 400–603 m) temperature inversion, constructing an underdetermined problem. The inverted four‐layer temperatures show three positive peaks and two negative peaks during the observation period, implying the sequential passage of internal solitary waves with depressed and elevated interfaces. The generation of these temperature peaks is synchronized with the diurnal tides, and the peak heights decrease with depth. The inverted four‐layer temperatures are in excellent agreement with conductivity‐temperature‐depth data obtained near the acoustic stations. Plain Language Summary: Internal solitary waves (ISWs) are generated around continental shelf edges, the subsurface slopes of islands and seamounts, and sills in straits by an interaction between the permanent thermocline and strong barotropic tidal currents. ISWs induce sudden changes in the water temperature and severe hydrodynamic forces acting on structures such as oil platforms during their propagation to adjacent regions. Furthermore, water is strongly mixed by the breaking of large ISWs, enhancing the level of turbulence and influencing biological environments in the surrounding regions. Unlike the generation and propagation of ISWs detectable at the surface by synthetic aperture radar satellites, the subsurface structures of ISWs are beyond the spatial resolution limits of synthetic aperture radar satellites. Bottom‐moored coastal acoustic tomography is a new cost‐efficient and innovative technology for measuring the subsurface structures of ISWs propagating from a source region to surrounding regions. Key Points: Internal solitary waves generated in the Lombok Strait are measured by two bottom‐moored coastal acoustic tomography systemsFour‐layer temperatures are reconstructed by a vertical‐slice inversion using one‐way travel times for the first three arrival peaksThe inverted temperatures show five peaks with heights ranging from 3 to 6°C, implying the sequential passage of internal solitary waves [ABSTRACT FROM AUTHOR]

The diurnal cycle over tropical coastal waters is characterized by offshore migration of precipitation area during nighttime. This study analyzes in situ observational data collected during the YMC-Sumatra 2017 field campaign around the western coast of Sumatra Island, Indonesia, to examine the offshore migration phenomenon during 5–31 December 2017, when the Research Vessel Mirai was deployed about 90 km off the coast to perform observation. The offshore migration is observed in only less than a half of the 27 days. A comparison of radiosonde data at the vessel between days with and without the offshore migration reveals that vertical wind shear in the lower troposphere is a key environmental condition. In late afternoon of the days with the offshore migration, offshore (northeasterly) wind shear with height with considerable magnitude is observed, which is due to weaker daily mean southwesterly wind in the lower free troposphere, stronger southwesterly wind in the boundary layer, and sea breeze. As this condition is considered favorable for regeneration of convective cells to the offshore side of old ones, these results support an idea that the regeneration process is critical for the offshore migration. The Madden–Julian oscillation and cold surges play some roles in the weakening of the free-tropospheric wind. The migration speed is estimated at 2–3 m s−1, which is lower than that observed in another field campaign conducted in 2015 (Pre-YMC 2015). This difference is partly due to the difference in the environmental wind in the lower to midtroposphere. [ABSTRACT FROM AUTHOR]

The land-sea surface temperature contrast on the western coast of Sumatra Island was examined using observation data obtained from the pre-Years of the Maritime Continent (YMC) field campaign from November to December 2015. Surface observations showed that, on most days, strong daytime solar radiation caused a pronounced diurnal cycle in surface air temperatures on the island, even during the local active phase of the Madden-Julian Oscillation (MJO). Sudden drops in surface air temperature occurred frequently on the island in the late afternoon and over the sea at nighttime, accompanied by precipitation. Temperatures on the island were higher than those over the sea during the daytime and lower in the night and early morning. Prior to the local active phase of the MJO, dual maxima in the land-sea surface air temperature contrast occurred in the evening and early morning. During the local active phase of the MJO, in spite of cloudy conditions, there were still large land-sea temperature contrasts during the daytime and in the early morning. In addition to the nighttime radiative cooling of the land surface, decreases in air temperature over the land due to precipitation cooling and the lower solar insolation in the MJO active phase caused the larger temperature differences in the morning. These results suggest that the decrease in air temperature caused by precipitation cooling had a substantial effect on the land-sea surface air temperature contrast on the western coast of Sumatra Island, particularly during an active phase of the MJO. [ABSTRACT FROM AUTHOR]

Videosonde observations were conducted at the southwestern coastal region of Sumatra Island, Indonesia, as part of a pilot field campaign of the Years of the Maritime Continent project (Pre- YMC), to investigate the role of solid hydrometeor for precipitation processes in clouds. Videosondes were launched into three types of clouds: convective and stratiform clouds, and a thick upper stratiform cloud with shallow convection at lower level. A quantitative evaluation of the graupel shape data obtained from the videosondes showed different graupel formations in different rain systems. For the typical stratiform cloud, almost no graupel was observed. In contrasts, for the thick upper stratiform clouds with shallow convection, large numbers of ice crystals in the upper layer suggested to act as embryos and form a lot of graupel with the riming of the supercooled droplets that was supposed to be provided from the shallow convection. On the other hand, for the convection case, the videosonde observed spherical graupel just above the freezing level. This suggested that frozen drops acting as embryos formed spherical graupel, which were uplifted by the strong updraft in the convective cloud, and were different from the generally irregular-shaped graupel in the thick upper stratiform cloud. [ABSTRACT FROM AUTHOR]

This study analyzes data obtained by intensive observation during a pilot field campaign of the Years of the Maritime Continent Project (Pre-YMC) to investigate the diurnal cycle of precipitation in the western coastal area of Sumatra Island. The diurnal cycle during the campaign period (November-December 2015) is found to have a number of similarities with statistical behavior of the diurnal cycle as revealed by previous studies, such as afternoon precipitation over land, nighttime offshore migration of the precipitation zone, and dependency on Madden-Julian oscillation (MJO) phase. Composite analyses of radiosonde soundings from the Research Vessel (R/V) Mirai, deployed about 50 km off the coast, demonstrate that the lower free troposphere starts cooling in late afternoon (a couple of hours earlier than the cooling in the boundary layer), making the lower troposphere more unstable just before precipitation starts to increase. As the nighttime offshore precipitation tends to be more vigorous on days when the cooling in the lower free troposphere is larger, it is possible that the destabilization due to the cooling contributes to the offshore migration of the precipitation zone via enhancement of convective activity. Comparison of potential temperature and water vapor mixing ratio tendencies suggests that this cooling is substantially due to vertical advection by an ascent motion, which is possibly a component of shallow gravity waves. These results support the idea that gravity waves emanating from convective systems over land play a significant role in the offshore migration of the precipitation zone. [ABSTRACT FROM AUTHOR]

This study examined the relationship between El Niño-Southern Oscillation (ENSO) and atmospheric water isotopes during the wet season over the Maritime Continent. The model data used were obtained by incorporating stable isotopes into atmospheric general circulation and analytical moisture transport models. These models were used to analyze the climatological variables and rainout processes from various water sources that control isotopic variation. The correlation between the simulated stable isotope ratios and ENSO varied between -0.31 and 0.75 with stronger correlation over most of the Maritime Continent (|r|> 0.36, corresponding to the 95 % significance level) except Java. In general, during La Niña years, the isotopic ratio in water vapor and precipitation is smaller than that during El Niño years by approximately 2 ‰. It was suggested that anomalous water vapor flux, precipitable water, and precipitation, but not evaporation, are responsible for isotopic variation. Furthermore, it was revealed that water vapor flux is convergent (divergent) during La Niña (El Niño) years, which suggests that the strengthened (weakened) Walker Circulation increases (reduces) precipitation, resulting in lighter (heavier) atmospheric water isotopes. The relationship between isotopes and precipitation, or the so-called "amount effect", is evident over most of the Maritime Continent. Analysis of moisture transport suggested that rainout processes control isotopic variation. An increase in the quantity of water source, expressed in precipitable water, transported from the north and south Maritime Continent during El Niño years, does not result in isotopic depletion attributable to the lack of condensation processes. Moreover, a decrease in the quantity of both water source during La Niña years does not result in isotopic enrichment attributable to intensive rainout. An asymmetric ENSO feature was found in this study, evidenced by the similar contributions of water source from the northern Maritime Continent and the Pacific Ocean during both ENSO phases. [ABSTRACT FROM AUTHOR]

Remotely derived environmental variables, including sea surface height anomaly (SSHA), sea surface temperature (SST), chlorophyll-a (chl-a), eddy kinetic energy (EKE), mixed layer data set of argo float (MLD), Niño 3.4 index, and bigeye tuna catch data for the period 1997-2008, were used to analyse ocean climate variability and how they relate to the hotspots of bigeye tuna catch in the eastern Indian Ocean off Java. The empirical orthogonal function (EOF) was performed to obtain a more detailed structure of the spatio-temporal ocean variability in the region. The results showed that the first EOF modes of chl-a, SSHA, and SST accounted for 42.8%, 36.5%, and 27.4% of total variance, respectively, and these corresponded to the interannual signal. The maps of spatial patterns of the first EOF modes of SSHA, SST, and chl-a gave very typical values for cold-water SSHA, low SST, and high chl-a concentration along the southern coast of the Indonesian archipelago; and warm-water SSHA, high SST, and low chl-a concentration in the offshore region to make frontal areas along the latitudinal line around 10-12° S. The EOF analysis further revealed a strong relationship between the El Niño event and favourable oceanographic conditions, resulting in a significant increase in bigeye tuna catch. The average hook rate of 0.71 (0.43) was recorded during El Niño (La Niña). Major hotspots were located away from the confluence region and frontal areas around 11-16° S and 110-118° E and were thus demonstrated as the most favourable oceanographic conditions for bigeye tuna fishing in the eastern Indian Ocean off Java. [ABSTRACT FROM AUTHOR]

The heat island (HI) effect in metropolitan Jakarta was studied using air temperature measurements at 9 meteorological stations in Jakarta, Tanjung Priok, Serang, Halim, Cengkareng, Pondok Betung, Curug, Bogor, Citeko during 1986-2008 and Serpong during 2008-2011 and 2013; land use for forest, industry, water, settlement, open/cleared land in 1997, 2004, 2009, 2012; and total number of industries and total number of vehicles during 1986-2011. Harmonic analysis was used to remove the seasonal component from the temperature time series data, which was filtered with the 30-day moving average technique to capture trends whose significance was tested with the Mann- Kendall method. The results show that industry was a major factor in land use change over Jakarta with an increasing growth/year of 502 ha (9.76%) concentrated in the eastern part of Jakarta from 1997 to 2012. Industry had a spatial cover change similar to deforestation and open/cleared land expansion, especially in Jakarta from 2009 to 2012: 38.8%/year (industry), 8.3%/year (deforestation), and 13.8%/year (open/cleared land). The HI effect increased the temperature trend rate/year in Jakarta, Tanjung Priok, Serang, Halim, Pondok Betung, Cengkareng, Curug, and Bogor about 0.051°C, 0.021°C, 0.018°C, 0.012°C, 0.006°C, 0.006°C, 0.005°C, and 0.004°C from 1986 to 2008, respectively, equivalent to average warming in the city, suburban, and mountainous areas of around 2.5°C, 0.6°C, and 0.4°C, respectively within 100 years from 2009. [ABSTRACT FROM AUTHOR]

Abstract: ADCP measurements in the southern Banda Sea, obtained with the bulk carrier “MS First Jupiter” from 1997 until 2000, have been analysed. The observations reveal the presence of an eastward flowing southern boundary current, bringing water from the Indonesian throughflow towards the connections with the Indian Ocean in Ombai Strait and the Timor Sea. The mean transport in the upper 300m is estimated to be about 5Sv, over 50% of the outflow towards the Indian Ocean in this layer through the eastern passages near Timor. The velocity in the boundary current shows a clear annual variation, more or less in phase with the annually varying inflow through Makassar Strait and the outflow near Timor. The phase of the annual variation cannot be explained by the monsoonal variation of the local winds. Therefore this annual variation of the throughflow is probably generated by large-scale forcing. A considerable reduction of the strength of the boundary current was observed in 1998, following the 1997–1998 El Niño with a delay of about half a year. On shorter time scales, Kelvin waves, entering the Banda Sea from the Indian Ocean, cause flow reversals of the boundary current. [Copyright &y& Elsevier]

Spatial and temporal information on oceanic flow is fundamental to oceanography and crucial for marine-related social activities. This study attempts to describe the short-term surface flow variation in the area south of the Lombok Strait in the northern summer using the hourly Himawari-8 sea surface temperature (SST). Although the uncertainty of this temperature is relatively high (about 0.6 ∘ C), it could be used to discuss the flow variation with high spatial resolution because sufficient SST differences are found between the areas north and south of the strait. The maximum cross-correlation (MCC) method is used to estimate the surface velocity. The Himawari-8 SST clearly shows Flores Sea water intruding into the Indian Ocean with the high-SST water forming a warm thermal plume on a tidal cycle. This thermal plume flows southward at a speed of about 2 m / s . The Himawari-8 SST indicates a southward flow from the Lombok Strait to the Indian Ocean, which blocks the South Java Current flowing eastward along the southern coast of Nusa Tenggara. Although the satellite data is limited to the surface, we found it useful for understanding the spatial and temporal variations in the surface flow field. [ABSTRACT FROM AUTHOR]