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A comprehensive investigation was conducted to examine the variations in Chlorophyll-a (Chl-a) levels in the waters located to the south of Java Island throughout the past quarter-century. This study employs satellite data and reanalysis data gathered from multiple sources spanning the period between September 1997 and December 2022. The application of EOF analysis revealed that the most notable elevation in Chl-a contents took place during the seasons of SON (September, October, November) and DJF (December, January, February) in the years 1997/1998 and 2006/2007. It has been determined that this significant increase in Chl-a content in southern Java is contingent upon the fulfillment of a number of circumstances. These conditions are associated with climatic patterns in the Indian Ocean and Pacific Ocean. An elevation in Chl-a content was seen throughout the months of SON and DJF in instances where the Indian Ocean Dipole (IOD) had a positive phase. The concurrent occurrence of a powerful positive IOD and El Niño event in the Pacific Ocean is highly probable to result in a substantial elevation in Chl-a content in the southern region of Java. In addition, our findings indicate that the phenomenon of Kelvin wave upwelling significantly contributes to the elevation of Chl-a levels during the months of June, July, August (JJA), and SON. [ABSTRACT FROM AUTHOR]

Soil salinity plays an essential role in the growth of mangroves. Mangroves usually grow in intertidal zones. However, in Karimunjawa National Park (KNP), Indonesia, mangroves are also found in supratidal zones. Thus, this study aims to determine why mangroves can grow in this supratidal zone, even during the dry season. We analyze seasonal changes in groundwater flow and salinity dynamics using the hydraulic head, shallow groundwater salinity, and electrical resistivity imaging (ERI) data. The result shows that variation in groundwater salinity is caused by seawater intrusion, which is generated by a hydraulic gradient due to the sea level being higher than the water table in KNP. Rainfall and evapotranspiration, which change seasonally, likely affect the water table fluctuation and salt concentration. ERI images indicate this seawater intrusion in the top sediment up to the bedrock boundary. However, the resistivity difference in the wet and dry seasons shows that remarkable resistivity change occurs at the deeper layer (50–60 m below ground level (BGL)), likely due to freshwater recharge from rainwater on the land side. Groundwater in the KNP is shallow and saline; thus, mangroves in this zone, e.g., Ceriops tagal and Lumnitzera racemosa, can grow because their roots can reach this groundwater. These mangrove species can still grow in this zone even though the shallow groundwater is very saline (46–50 ppt). However, this condition might cause these mangroves to grow stunted. Thus, freshwater availability is crucial for mangrove growth in this supratidal zone to dilute this high groundwater salinity. [ABSTRACT FROM AUTHOR]

The short-lived events of high SST are called hot events (HEs) and can only be generated under the conditions of large daily heat gain due to strong solar radiation and weak wind. We investigated the thermal structure below HEs in the western equatorial Pacific by using in situ data obtained from TAO/TRITON buoys. We found that the occurrence of HEs can be identified by the typical vertical thermal structure within the isothermal layer. During the development stage of a HE, heat is accumulated in the surface layer due to strong solar radiation and weak wind, increasing temperature and creating strong stratification in the upper layer. During the decay stage, strong westerly winds induce current convergence which transports the heat from the upper layer to the deeper layer. Thus, temperature decreases at the surface and increases in the deeper layer. Furthermore, this mechanism indicates the important role of HEs in maintaining the warm isothermal layer in the western Pacific warm pool. The more HEs occur, the more heat in the surface layer gained from solar radiation is transported to the deeper layer. This process makes areas of frequent HE occurrences coincident with areas of warm pool. Since surface winds control the heat accumulation and heat transport in the isothermal layer by influencing current divergence and latent heat flux, surface winds become the key factor for the occurrence of HEs and the formation of the thermal structure in the Pacific warm pool. [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]