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The seas of Southern Java are located at the eastern equatorial Indian Ocean and therefore, they are strongly influenced by the Indian Ocean Dipole (IOD). Strong negative IOD occurred in 2016. However, none of the previous studies investigated its effect on the seas of Southern Java. This study aims to reveal the influence of the strong negative IOD in 2016 on the upwelling intensity along the seas of Southern Java as represented by surface temperature and chlorophyll-a. This research was conducted using satellite-based data and the analysis was based on climatology, and anomaly for 15 years (2007-2021). The data used includes sea surface temperature (OISST), wind (ASCAT), IOD index (DMI), chlorophyll-a (OC-CCI), and sea level anomaly (altimetry). The findings show that the strong negative IOD in 2016 had a significant impact on sea surface temperatures which made these waters warmer. The most visible impact is through the sea surface temperature anomaly map where in 2016 throughout the year it experienced a positive anomaly with a value of 2°C higher than the climatological average. The value of chlorophyll-a in these waters has also dropped drastically which, when viewed from the anomaly map, has a value of 0.2 mg/m³ lower than the climatological average, especially during the upwelling month. This means that, strong negative IOD in 2016 reduced the upwelling intensity along the seas of Southern Java. We also found the propagation of downwelling Kelvin waves from the Indian Ocean to the Southern Java waters which bring warm temperatures and cause downwelling events during the strong negative IOD in 2016 that hampers coastal upwelling along the seas of Southern Java. [ABSTRACT FROM AUTHOR]

Indonesia as a region located in the tropics gets a greater heat distribution than the other hemisphere and has an important role in the phenomenon of atmospheric and ocean interactions in the Indo-Pacific region. The heat exchange between the ocean and the atmosphere affects the dynamics of both. The southern coast of Java is known as the upwelling area which is driven by the variability of Ekman transport and Ekman pumping. The present study aims to investigate the effect of heat flux variability on sea surface temperature variability and chlorophyll-a in surface upwelling areas along the Southern coast of Java which was less observed in the previous study. The study was conducted with a quantitative descriptive approach through climatological spatial and temporal data processing for 10 years from 2007 - 2016. The data used are Shortwave Radiation, Longwave Radiation, Latent Heat Flux, Sensible Heat Flux, Sea Surface Temperature, Chlorophyll-a, Surface Wind, and Mixed Layer Depth. The results show that the Southern coast of Java receives an average heat of 547.8 W/m2 per year. Net Heat Flux fluctuations are dominated by heat intake by Shortwave Radiation and heat release by Latent Heat Flux. Net Heat Flux has a very strong relationship with sea surface temperature with the best correlation of 0.84 and 0.83 at lag+2 and lag+3 months indicating that Net Heat Flux plays an important role in modulating changes in sea surface temperature in the next 2-3 months. A significant increase in chlorophyll-a occurred after the Net Heat Flux was positive or there was ocean heating which caused the shoaling of Mixed Layer Depth, resulting in primary productivity in the east monsoon along with nutrient rich entrainment to the surface by EMT and EPV. [ABSTRACT FROM AUTHOR]

The precision of sea surface temperature (SST) from remote sensing data is essential to recognize SST fluctuations prompted by extreme weather conditions due to global climate warming, such as tropical cyclones (TCs). Since 1981 the active remote sensing of satellite-based SST measurements has been around and proliferating to date in Indonesia. However, there has not been much research on the validation of several remote sensing datasets in Indonesia’s seas that has limited coverage of buoy observations. Moreover, no studies correspond to which data are the most precise in describing SST fluctuations in tropical storms. In this study, six remote sensing/satellite (Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA), Regional Australian Multi-Sensor SST Analysis (RAMSSA), Global Australian Multi-Sensor SST Analysis (GAMSA), Microwave Infrared Optimally Interpolated (MWIROI), Multi-scale Ultra-high Resolution (MUR), and K10) data are validated and compared to analyze SST fluctuations in TC as a case study. The validation method uses the Haversine distance formula to reach the highest quality iQuam data with satellite data. The comparison analysis is performed by plotting the SST and wind slop in a TC area. Based on the validation, The OSTIA, RAMSSA, GAMSSA, and MWIROI datasets ranked in the top 4 of the smallest RMSEs with values < 0.5. Moreover, in the SST and wind slop in a TC area, TC affects SST cooling as detected in the MUR and K10 datasets where there is a decrease of > 2 ºC. In the MWIROI, the decline is more noticeable significant > 3 ºC. [ABSTRACT FROM AUTHOR]

Marine heatwave (MHW) is an extreme phenomenon of warm sea surface temperature anomaly that has a destructive impact on the marine ecosystem and organisms. This phenomenon increases every year in duration, frequency, and area due to the global warming. Almost all of the world's oceans have experienced MHW, including in the seas of the southern Java-Nusa Tenggara. The lack of detailed research in this area motivated us to analyze MHW drivers. MHW was identified with the 99th percentile method and duration of = 5 days as a threshold by using blended product of SST data. In 2013, an MHW event was identified in the seas of the southern Java-Nusa Tenggara. This MHW lasts for 37 days, from 8 June to 14 July. The maximum (mean) intensity of sea surface temperature anomaly reaches 2.60°C (1.83°C) above climatology with an average area of 36.53 × 104 km². Locally, we found that probably the positive downward shortwave radiation affected this anomaly. Furthermore, a remote process of the propagation of downwelling Kelvin wave during negative Indian Ocean Dipole may also affect this anomaly. The strong westerly wind along the equatorial Indian ocean forms downwelling Kelvin wave that propagates to the southern Java-Nusa Tenggara increasing SST in this area. [ABSTRACT FROM AUTHOR]

The previous studies of upwelling within the Indonesian seas only focused on the Southeast Monsoon (SEM) season. The western coast of Sumatra Island; the southern coast of Java Island, Sunda Islands, and Sulawesi Island; the Banda Sea, the Maluku Sea, and the Arafura Sea are well-known SEM upwelling areas. However, the upwelling events during Northwest monsoon (NWM) have never been investigated. The investigation of NWM upwelling is challenging due to the broad cloud coverage, limiting the observation of infrared and visible sensors of the satellites. This study used the blended products of the satellite-based sea surface temperature (SST), chlorophyll-a (chl-a), sea level anomaly (SLA), surface wind, and rainfall to identify the NWM upwelling occurrences. Remote sensing reflectances 443 nm and 555 nm were also used to examine the influence of suspended sediment and organic matter which may bias the chl-a concentration. Along the northern coast of the Lesser Sunda Islands, the north coast of Papua Island and the Malacca Strait are the areas of NWM upwelling as denoted by the positive anomaly of chl-a, the negative anomaly of SST, and the negative anomaly of SLA. Focusing on the area along the northern coast of the Lesser Sunda Islands, the NWM upwelling is generated by offshore Ekman Mass Transport that reduces SST and increases chl-a. From 2010 onwards, El Niňo Southern Oscillation has a more consistent effect on the NWM upwelling than Indian Ocean Dipole. El Niňo (La Niňa) tends to weaken (strengthen) upwelling. The magnitude of NWM upwelling is weaker than SEM upwelling. [ABSTRACT FROM AUTHOR]

It has been widely known that the coastal upwelling along the southern coast of Java is generated by southeasterly wind which induces offshore Ekman Mass Transport (EMT) during southeast monsoon. However, the variability of EMT has not been fully described in previous studies. The present study investigated the variability of Ekman dynamics which consist of EMT and Ekman Pumping Velocity (EPV) along the southern coast of Java, based on remotely sensed data. We demonstrated the incongruity between the distribution of southeasterly wind speed and sea surface temperature (SST) during southeast monsoon which is related to the distribution of Ekman dynamics. Offshore EMT at the western region of the southern coast of Java is stronger than offshore EMT at the eastern region. However, stronger offshore EMT at the western part is inhibited by downwelling EPV while weaker offshore EMT at the eastern part is accelerated by upwelling EPV. Consequently, SSTs at the eastern parts are lower than those at the western parts. Thus, the changes of offshore EMT intensity from eastern to western parts are balanced by their EPV distributions which explain the incongruity between the distribution of wind speed and SST during southeast monsoon. On an interannual timescale, the combination of La Niña and negative Indian Ocean Dipole (IOD) events tends to weaken offshore EMT and EPV which reduce the intensity of Chl-a bloom and SST cooling during southeast monsoon season. Furthermore, ENSO has a less significant impact on the Ekman dynamics variability than IOD. [ABSTRACT FROM AUTHOR]

Novel and long-term satellite data (2003–2017) are analyzed to investigate the variability of ocean surface chlorophyll-a (Chl-a) concentration off the Western Lesser Sunda Islands (WLSI) under the influence of the Indonesian Australian monsoon, the El Niño-Southern Oscillation, and the Indian Ocean Dipole (IOD). In this article, we first analyzed the seasonal variability of Chl-a, and then describe the relationship among the sea surface Chl-a, sea surface temperature (SST), and sea surface wind stress in the region. Our results demonstrate that prevailing southeasterly wind stress plays a pivotal role in generating the Chl-a maxima off the WLSI. Particularly on seasonal time scale, the strengthening of southeasterly wind stress (up to ∼0.01 N·m−2) during the southeast monsoon season produces enhanced Chl-a concentrations (0.59 mg·m−3) associated with sea surface cooling (∼28.8 °C) in the area of study. In contrast, the Chl-a maxima completely vanished during the northwest monsoon season. On interannual time scale, the largest positive Chl-a and wind stress anomalies and the coolest SST anomaly are observed in 2006 when El Niño and positive IOD events occur at the same time. Meanwhile, the greatest negative Chl-a anomaly is prevailed during the 2016 negative IOD event. This article demonstrates that wind variability is the essential factor in determining the magnitude of the Chl-a maxima off the WLSI. [ABSTRACT FROM AUTHOR]

The Sulawesi Sea and the northern part of the Maluku Sea belong to the western equatorial Pacific that is influenced by the Mindanao Current. During the southeast (SE) monsoon, contrasting sea surface temperature (SST) distributions occur between these two seas. The purpose of this research is to investigate the mechanisms of contrasting SST distribution in the Sulawesi Sea and the northern part of the Maluku Sea under the condition of strong southerly wind during the SE monsoon season. Our analysis was based on satellite observations. Warmer (colder) SSTs are identified in the Sulawesi Sea (northern part of the Maluku Sea), which correspond to the weaker (stronger) southerly wind speed. Strong southerly winds in the northern part of the Maluku Sea generate eastward Ekman mass transport (EMT) that carries the water mass away from the coast, inducing upwelling. In contrast, the southerly winds from the Maluku Sea are blocked by the Gorontalo and North Sulawesi Mountains, creating low-wind areas in the Sulawesi Sea that are located on the lee side of those mountains. Furthermore, the existence of a valley between those mountains acts as a wind gap that channels the southerly wind to the Sulawesi Sea. Since the seaward EMT is weak and the latent heat release is not dominant, SSTs in front of the wind gap are only slightly reduced, possibly through the mechanisms of oceanic mixing. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the variation of diurnal SST amplitude (∆SST) in the seas west of the Tsugaru Strait, Japan, which exhibit complex topography that affects the wind pattern during "Yamase" season, when cold easterly winds blow around northeastern Japan. We used infrared based satellite SSTs to obtain strong ∆SST signals. The objective analysis data on surface wind, air temperature and relative humidity patterns was used to explain possible mechanisms responsible for the observed phenomena. Although easterly winds are frequently accompanied by clouds that hinder frequent observation of SSTs from space, four cases of high ∆SST were obtained under clear sky conditions. The results show that high resolution satellite data can capture ∆SSTs of more than 5 °C. Further, the ∆SST variation was strongly influenced by topography. The existence of mountains near the study area have the effect of blocking the easterly winds, creating a low wind speed area on the lee side of the mountain range, which is responsible for the generation of high ∆SST, especially in the offshore area. In addition to the topographic effect, the ∆SST values measured in the in-shore area were influenced by the sea breeze. The warm-dry air mass is advected to the coastal seas by the anti-sea breeze which heats the in-shore area and keeps the ∆SST at the same level as that of the offshore area. This finding highlights the importance of understanding air, sea and land interactions in terms of the variation observed in ∆SST in the study area. [ABSTRACT FROM AUTHOR]

We investigated the climatology of hot events (HEs) in the western equatorial Pacific. HEs are characterized by well-organized high sea surface temperatures (SSTs). We proposed a method for identifying HEs using a space-time-dependent threshold with a minimum areal size of 2 × 10 km, and with a duration (period) of >6 days. We thus identified 71 HEs from the optimally interpolated SST dataset during 2003-2011. Their mean duration, areal size, and amplitude were 18.14 days, 6.30 × 10 km, and 0.33 °C, respectively. On average, the HEs developed more slowly than they decayed. They were distributed within the equatorial band to the subtropical Pacific (20°S-30°N), with an eastward extension to 150°W. In particular, the HEs occurred most frequently along the northern coasts of New Guinea and the Solomon Islands to 180°E. Seasonal variation in the HE distribution was observed: a northward shift during boreal summer and a southward shift during boreal winter. The distribution of HE occurrences corresponded to the climatological SST of the western Pacific warm pool. HEs occurred under conditions of low wind speeds (~2.56 m/s) and high levels of solar radiation (~225 W/m). However, since the high levels of solar radiation occurred over the entire area of the western equatorial Pacific during HE periods, the low wind speed distribution became a key factor in the occurrence of HEs in the western equatorial Pacific. Seasonal shifts in wind speed and solar radiation were found to influence the seasonal shift in HE distribution. [ABSTRACT FROM AUTHOR]

The southern coast of South Sulawesi-Indonesia is known as an upwelling area occurring during dry season, which peaks in August. This upwelling area is indicated by high chlorophyll-a (Chl-a) concentrations due to a strong easterly wind-induced upwelling. However, the investigation of Chl-a variability is less studied along the western coast of South Sulawesi. By taking advantages of remote sensing data of Chl-a, sea surface temperature, surface wind, and precipitation, the present study firstly shows that along the western coast of South Sulawesi, there are two areas, which have high primary productivity occurring during the rainy season. The first area is at 119.0° E–119.5° E; 3.5° S–4.0° S, while the second area is at 119.0° E–119.5° E; 3.5° S–4.0° S. The maximum primary productivity in the first (second) area occurs in April (January). The generating mechanism of the high primary productivity along the western coast of South Sulawesi is different from its southern coast. The presence of river runoff in these two areas may bring anthropogenic organic compounds during the peak of rainy season, resulting in increased Chl-a concentration. [ABSTRACT FROM AUTHOR]

Near-surface diurnal warming is an important process in the climate system, driving exchanges of water vapor and heat between the ocean and the atmosphere. The occurrence of the hot event (HE) is associated with the high diurnal sea surface temperature amplitude (δSST), which is defined as the difference between daily maximum and minimum sea surface temperature (SST). However, previous studies still show some inconsistency for the area of HE occurrence and high δSST. The present study produces global δSST data based on the SST, sea surface wind data derived from microwave radiometers, and solar radiation data obtained from visible/infrared radiometers. The value of δSSTs are estimated and validated over tropical oceans and then used for investigating HE in the western equatorial Pacific. A three-way error analysis was conducted using in situ mooring buoy arrays and geostationary SST measurements by the Himawari-8 and Geostationary Operational Environmental Satellite (GOES). The standard deviation error of daily and 10-day validation is around 0.3 °C and 0.14–0.19 °C, respectively. Our case study in the western Pacific (from 110°E to 150°W) shows that the area of HE occurrence coincided well with the area of high δSST. Climatological analysis shows that the collocated area between high occurrence rate of HE and high δSST, which coincides with the western Pacific warm pool region in all seasons. Thus, this study provides more persuasive evidence of the relation between HE occurrence and high δSST. [ABSTRACT FROM AUTHOR]

A rare event known as Fujiwhara effect occurred in the southeastern tropical Indian Ocean when tropical cyclones (TCs) Seroja and Odette were co-existed, interacted each other, and merged into one TC in April 2021. Here, remotely sensed data (surface winds, sea surface temperature, chlorophyll-a concentration, and surface currents) were analyzed to determine the impact of Fujiwhara effect on the ocean biophysical variables in the region. Ekman pumping velocity were computed to determine the upwelling/downwelling process. During the entire development of the TCs to the merging, the TCs induced sea surface temperature (SST) cooling and raising sea surface chlorophyll-a. Ekman pumping and inertial pumping may serve as the primary driving force for the observed negative SST anomaly and positive anomaly in chl-a concentration associated with TCs. This rare event adds the complexity of ocean and climate dynamics of the region as an exit gate of the Indonesian throughflow to the Indian Ocean and may have implications to circulation and climate in the Indian Ocean and beyond. The present research likely represents the first scientific documentation of oceanic responses to a Fujiwhara effect in the region. • TC Odette and TC Seroja merged in the southeastern tropical Indian Ocean. • The Fujiwhara effect influences the ocean biophysical parameters. • The Ekman and inertial pumping partly affect the ocean biophysical parameters. [ABSTRACT FROM AUTHOR]