Monsoon Winds Research Articles

Southward displacement of the glacial westerly jet over Asia driven by enhanced Arctic amplification after the Mid-Brunhes Event

The climate and paleoenvironmental evolution of the East Asian continent and adjacent Northwest Pacific Ocean is governed by the interplay of the region's dominant features in oceanic and atmospheric circulation, which control the redistribution of heat and moisture. In the atmospheric realm, the subtropical westerly jet stream and East Asian monsoon are crucial components of climate evolution over East Asia, an area that is inhabited by almost half of the world's population. Reconstruction of long-term changes in atmospheric circulation in this region is to date scarce, especially on timescales predating the last glacial-interglacial cycle. Here, we reconstruct dust fluxes, marine productivity and water temperatures in the Northwest Pacific Ocean using lipid biomarkers both from terrestrial and marine organisms and elemental scanning data. Land-plant derived wax lipids in the studied sediments were used as indicators for dust fluxes and hence are representative of past changes in wind strength and pathways. We evaluate changes both in the zonal westerlies and monsoonal winds over the past 1 Ma and across major climatic events. Prior to the Mid-Brunhes Event (MBE; ~ 430 ka ago), concentrations of these compounds showed a distinct glacial-interglacial pattern, which we relate to past changes in the position of the westerly jet stream. We demonstrate substantial changes in wind patterns across the MBE, resulting in reduced dust fluxes to the Northwest Pacific in ensuing glacials. We propose that the westerly jet was permanently located south of the Himalaya-Tibetan Plateau through peak glacials, fostered by amplified Arctic cooling.

Characterization of the 2012 and 2013 Metro Manila “Enhanced Habagat” Heavy Rainfall Events

The strong southwest monsoon episodes in August 2012 and 2013, locally referred to as the “Enhanced Habagat ” 2012 and 2013, respectively, resulted in rainfall that exceeded the monthly mean rainfall of the affected regions along western Luzon, including Metro Manila. The prolonged heavy rainfall events were the result of tropical cyclone enhancement of the monsoon winds. The synoptic environment in the two events was characterized by the deepening of the Asian monsoon trough depicted by the zonally-oriented and eastward-extended 1000 hPa isobar. The deep troughs were caused each year by a combination of tropical cyclones located to the northeast of the Philippines – Typhoon Haikui in 2012 and Severe Tropical Storm Trami in 2013, and remnant tropical cyclones in the northern South China Sea region that formed several days prior to the enhanced Habagat episodes. The monsoon trough induced a low-level westerly jet in the South China Sea toward the western Luzon region that transported a narrow stream of moisture-laden air mass to Metro Manila and surrounding areas. Consequently, heavy precipitation ensued. Analysis showed the remnant lows are as important as the enhancing tropical cyclones Haikui and Trami in inducing the westerly jets. Removal of the enhancing tropical cyclones in numerical model simulations still showed a relatively deep monsoon trough that led to heavy rainfall along western Luzon. In addition, the intrusion of low potential vorticity area to the eastern and northern flanks of the tropical cyclones facilitated the strengthening of the steering ridge that resulted in their westward and slow translational motion, making the events last for several days and exacerbating the impacts. Furthermore, the Madden-Julian Oscillation possibly serves as a precursor to heavy rainfall events. Compounded with a populous megacity, understanding the mechanisms that lead to these extreme hazards is vital to future forecasting and disaster risk management of similar events.

Wave climate characteristics and effects of tropical cyclones on high wave occurrences in Indonesian waters: Strengthening sea transportation safety management

Tropical cyclones can cause bad weather and high waves that can endanger maritime activities, especially in the waters of Indonesia, which is a maritime country. Understanding ocean wave climate characteristics and the effect of Tropical Cyclones (TCs) on high wave occurrences is important, particularly to ensure the safety of fisheries activities in Indonesian seas. We aim to do so by focusing on Indonesia's 11 Fisheries Management Areas (IFMAs) using descriptive and inferential statistics. Wind and wave data were taken from the European Center for Medium-Range Weather Forecast (ECMWF), namely ECMWF Reanalysis v5 (ERA5) within the range of 42 years (1979–2020), whereas the TC data were from the International Best Track Archive for Climate Stewardship (IBTrACS). We found that significant wave heights (SWHs) in the inner seas are strongly related to monsoonal wind fields. The maximum SWH occurred in northern Indonesian seas during December–February (DJF), while occurring in southern and inner seas between June–August (JJA). The highest extreme SWH and probability of exceedance (PE) for SWH >2 m were found in IFMAs facing the open ocean, such as Malacca Strait, Western Sumatra waters, Southern Java waters, Natuna Sea, Sulawesi Sea, and Northern Papua waters. We found that TCs activity in adjacent Indonesian waters could increase anomalous SWH occurrences. Positive SWH anomalies ranged from 0.1 to 0.4 m and varied depending on TC location and season. TC that forms in the following areas increase the PE for SWH >2 m: (1) Bay of Bengal: Western Sumatra waters (March–May, MAM) around 20%; (2) Western Pacific Ocean: Northern Papua waters (DJF) around 5%; (3) Northeastern Indian Ocean: Western Sumatra waters (DJF) about 3%; and (4) Western and Northern Australian waters: Southern Java waters (DJF) about 20%. The results of this study can serve as an early assessment for investigating wave climate characteristics and identifying the areas in Indonesian waters that are most susceptible to the impact of TCs, particularly in IFMAs. These findings hold significant value for managers and policy authorities, such as the Ministry of Transportation and the Ministry of Marine Affairs and Fisheries of the Republic of Indonesia. They can utilize this information to develop measures aimed at reducing vulnerabilities among marine resource users, specifically fishers, and improving fishing vessel safety. Additionally, these findings can be utilized to enhance advance warnings and forecasts, enabling marine managers to implement strategies that minimize the impact of extreme events and increase resilience in the face of ocean and coastal disasters.

EMD-based gray combined forecasting model - Application to long-term forecasting of wind power generation

Wind power is the most promising renewable energy source after hydropower because of its mature technology and low price, and has great potential for carbon emission reduction. Long-term forecasts of its power generation can help power companies to develop operational plans, grid configuration and power dispatch, and can also provide a basis for the government to formulate energy and environmental policies. However, due to the characteristics of China's monsoon climate and wind power industry development, wind power generation data are characterized by nonlinear cycles and small data volume, which makes accurate prediction more difficult. To this end, this paper develops a new prediction model and applies it to the long-term prediction of wind power generation in China, and proposes some targeted policy recommendations based on the prediction results to promote the development of China's wind power industry.

Estimation of chlorophyll-a contents on the sea surface by Remote Sensing Technology

Chlorophyll-a is a green pigment found in primary producers like phytoplankton and has always been used as an indicator of phytoplankton abundance in water sources. The objective of this study was to estimate the chlorophyll-a content at the upper Gulf of Thailand sea surface in 2021 using Aqua/MODIS satellite data, together with relevant factors: wind currents and sea surface temperatures. The chlorophyll-a content analysis was performed using NASA's Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Data Analysis System (SeaDAS). The analysis results showed that the chlorophyll-a content on the sea surface was highest during the southwest monsoon (May-October) and lowest during the northeast monsoon (November-April). The average chlorophyll-a content in 2021 was found to be the highest in October at 3.396 mg/m3and the lowest in August at 0.781 mg/m3. It was also found that the chlorophyll-a content on the sea surface was correlated with changes in wind currents caused by the influence of monsoon winds and sea surface temperatures.

A seasonal circulation index for the ocean and its application to the South China Sea

Ocean circulation is crucial in redistributing mass and energy on Earth. However, it varies significantly on a seasonal time scale due to external forcing. To quantify the seasonality of ocean circulation, we propose a seasonal circulation index (SCI). This index is defined as the normalized maximum deviation from the velocity vector, whose magnitude is the largest in one period. We have substantiated the efficiency of this index using the monsoon wind in the South China Sea (SCS). By utilizing this index, we have obtained the 3D structure of the seasonality of ocean circulation in the SCS. The SCI and the seasonal circulation amplitude (SCA) exhibit large values over 0.9 and 0.8 m s-1 in the western boundary current. Alternating southwest-northeastward bands of SCI with high and low values are distributed from the north shelf to the south, especially in the eastern basin. Although SCA decreases significantly with depth, SCI exhibits values higher than 0.7 in both the middle and deep layers, indicating a noteworthy seasonality and middle-layer enhancement in the abyssal basin of the SCS.

Possible Mechanisms of Interannual Variations in Surface Mixed Layer Temperatures off Somalia in Boreal Summer

Abstract The key processes responsible for the interannual variation of the surface mixed layer temperature off Somalia in the western Arabian Sea in boreal summer are investigated by the use of a regional ocean model. Our focus is on influences of remotely forced annual Rossby waves as well as local southwesterly monsoonal winds in the years with anomalously warm or cold mixed layer temperature conditions. Composite and heat budget analyses of the simulated results indicate that the interannual mixed layer temperature variations in the region off the coast of Somalia are generated by the combined effects of local upwelling, Rossby wave intrusion, and horizontal advection. In particular, interannual modulation of the annual Rossby wave before the onset of the southwest monsoon causes a subsurface temperature anomaly below the mixed layer along the coast of Somalia. It is also shown that this subsurface temperature anomaly is upwelled into the mixed layer by the upward flow associated with the seasonally evolving coastal upwelling and that the mixed layer temperature anomaly in the coastal region is advected into the offshore region by seasonal developments of the Somali Current. Results from sensitivity experiments with different wind forcing scenarios demonstrate that the contribution of this remotely forced Rossby wave to the interannual variations of the mixed layer temperature anomaly off Somalia is comparable to that of the local wind stress anomalies alone. Significance Statement The purpose of this study is to investigate the key processes responsible for the interannual variation of the temperature within the ocean surface layer off Somalia in boreal summer. Because this temperature variation is shown to be related to the Indian summer monsoon rainfall, this study can lead to improvement in the predictability of the Indian summer monsoon. Previous studies have demonstrated that interannual modulation of the local monsoonal winds along the coast of Somalia in spring and summer generate the temperature variation. We find for the first time that the large-scale ocean waves excited remotely in previous winter play an important role, and its contribution is comparable to that of the effect of the wind influences.

Reconstructing the Oxygen Depth Profile in the Arabian Sea During the Last Glacial Period

AbstractReconstructing the strength and depth boundary of oxygen minimum zones (OMZs) in the glacial ocean advances our understanding of how OMZs respond to climate changes. While many efforts have inferred better oxygenation of the glacial Arabian Sea OMZ from qualitative indices, oxygenation and vertical extent of the glacial OMZ is not well quantified. Here we present glacial‐Holocene oxygen reconstructions in a depth transect of Arabian Sea cores ranging from 600 to 3,650 m water depths. We estimate glacial oxygen concentrations using benthic foraminiferal surface porosity and benthic carbon isotope gradient reconstructions. Compared to the modern Arabian Sea, glacial oxygen concentrations were approximately 10–15 μmol/kg higher in the shallow OMZ (<1,000 m), and 5–80 μmol/kg lower at greater depths (1,500–3,650 m). Our results suggest that the OMZ in the glacial Arabian Sea was slightly better oxygenated but remained in the upper 1,000 m. We propose that the small increase in oxygenation of the Arabian Sea OMZ during the last glacial period was due to weaker upper ocean stratification induced by stronger winter monsoon winds coupled with an increase in oxygen solubility due to lower temperatures, counteracting the effects of more oxygen consumption resulting from higher primary productivity. Large‐scale changes in ocean circulation may have also contributed to better ventilation of the glacial Arabian Sea OMZ.

Shrinking of the Arabian Sea oxygen minimum zone with climate change projected with a downscaled model

In Arabian Sea (AS), land-locked northern boundary and strong seasonal productivity lead to the formation of one of the most intense open ocean Oxygen Minimum Zones (OMZs). Presence of this perennial OMZ has significant consequences on adjacent coastal fisheries and ecosystem. Simulations from CMIP5 suggest significant weakening of both monsoonal winds and productivity under high emission scenario. But the fate of AS OMZ in this scenario - whether it will expand or shrink - still remains elusive, mainly due to poor representation of extent and strength of AS OMZ in CMIP5 present-day simulations. To address this, we analyze the distribution of O2 in AS from a subset of three contrasted CMIP5 simulations, and complemented with a set of regional downscaled model experiments which we forced at surface and open boundaries using information from those three CMIP5 models. We tested two regional downscaling approaches - with and without correction of CMIP5 biases with respect to observations. Using a set of sensitivity experiments, we disentangle the contributions of local (atmospheric) forcing vs. remote (at the lateral boundaries) forcing in driving the future projected O2 changes. While CMIP5 projects either shrinking or expansion of the AS OMZ depending on the model, our downscaling experiments consistently project a shrinking of AS OMZ. We show that projected O2 changes in OMZ layer are affected by both local and remote processes. In the southern AS, the main response to climate change is oxygenation that originates from the boundaries, and hence downscalled and CMIP5 model responses are similar. In contrast, in northern AS, downscaling yields a substantial reduction in O2 projection discrepancies because of a minimal influence of remote forcing there leading to a stronger sensitivity to improved local physics and improved model representation of present-day conditions. We find that when corrected for present-day biases, projected deoxygenation in the northern AS is shallower. Our findings indicate the importance of downscaling of global models in regions where local forcing is dominant, and the need for correcting global model biases with respect to observations to reduce uncertainties in future O2 projections.

Identification of Surface Current Patterns in Small Pelagic Fishing Areas in the Western Season of the Spermonde Islands, Indonesia

Monsoonal wind commonly affects Indonesian waters, blowing in an adversative direction by turns in one year. These are well-known as west and east monsoonal winds. Spermonde Archipelago waters, located on the west coast of the southern part of South Sulawesi, is a water region comprising various islands with relatively shallow waters and situated in Makassar Strait. The study aimed to identify the pattern of current surface movement in each monsoon period, especially on the west monsoon on Small Pelagic Fish Catches Area. Data used in this study consisted of primary and secondary data. Primary data were obtained in the field for three months (April to Jun, second monsoonal transition monsoon into east monsoon). In December, the wind pattern was dominated from the northwest with a maximum speed of 8 knots. The surface current pattern offshore was from the south (0.16 m/s) to the north with decreasing speed (0.03 m/s). Meanwhile, in low tide, the current surface pattern offshore was from the north (speed may reach up to 0.04 m/s) to the south with an increasing speed of 0.20 m/s. The peak of the west monsoon occurs in January to February with high rainfall, and wind speed is dominated from south-west and west directions. Current pattern occurred in the offshore, either at high or low tide, showed similar pattern, which was divided into east and south directions.

Co-occurrence of a marine heatwave and a reported tomato jellyfish (<i>Crambione mastigophora</i> Maas, 1903) bloom in March 2020 at El Nido, Palawan, Philippines

Globally, observations on marine species during marine heatwaves (MHWs) help outline the scope of the MHW’s possible biological effects. In line with this effort, this paper presents a 2020 MHW that coincided with a reported ‘tomato jellyfish’ (Crambione mastigophora Maas, 1903) bloom on 23 March 2020 in the Corong-Corong Bay of Palawan, Philippines. Detecting a moderate MHW from 21 March to 04 April 2020, the analysis of sea surface temperatures revealed that most areas surrounding the bloom site attained their peak positive anomalies on the same day as the reported bloom. Certain physical mechanisms present in the first quarter of 2020 may have played a role in the occurrence of both events: the presence of cyclonic eddies and parallel monsoonal winds alongshore can induce upwelling which promotes biological productivity in surface waters, while the observed weakening of winds have been associated with anomalous warming of the sea surface. Further studies are still highly recommended to determine the exact causes of the jellyfish bloom and what conditions make it more likely to happen during MHWs. However, if the C. mastigophora is hypothetically able to continually bloom amidst warming temperatures, the increasing trend of MHW frequency and intensity in the West Philippine Sea (where the reported bloom site is situated) may consequently yield more future co-occurrences. This paper aims to hopefully contribute to the existing knowledge of possible biological impacts associated with extreme marine events, especially in the Philippine context where both jellyfish blooms and MHWs are understudied.

Anomalous widespread arid events in Asia over the past 550,000 years.

Records of element ratios obtained from the Maldives Inner Sea sediments provide a detailed view on how the Indian Monsoon System has varied at high-resolution time scales. Here, we present records from International Ocean Discovery Program (IODP) Site U1471 based on a refined chronology through the past 550,000 years. The record's high resolution and a proper approach to set the chronology allowed us to reconstruct changes in the Indian Monsoon System on a scale of anomalies and to verify their relationships with established records from the East Asian Monsoon System. On the basis of Fe/sum and Fe/Si records, it can be demonstrated that the Asia continental aridity tracks sea-level changes, while the intensity of winter monsoon winds responds to changes in Northern Hemisphere summer insolation. Furthermore, the anomalies of continental aridity and intensity of winter monsoon winds at millennial-scale events exhibit power in the precession band, nearly in antiphase with Northern Hemisphere summer insolation. These observations indicate that the insolation drove the anomalies in the Indian Summer Monsoon. The good correspondence between our record and the East Asian monsoon anomaly records suggests the occurrence of anomalous widespread arid events in Asia.

Nitrate and phosphate profiles in the Banda Sea during the northwest monsoon

The Banda Sea (BS) is subjected to monsoonal winds that affected upwelled rich nutrient waters and primary production. However, nutrient characteristic in the region is less constrained. Here, we examine nitrate and phosphate profiles in the Banda Sea from data collected during the northwest monsoon. Waters along the surface density (σθ ) < 22 were dominated by less saline originating from western Indonesia (i. e., Java Sea), accompanied by Indonesian throughflow water Banda (23.0-25.0σθ ) and Banda water (26.5-27.0σθ ), respectively. Surface water was accompanied by low nitrite+nitrate () and phosphate (), meanwhile, the average and concentrations in the upper 500 m were slightly higher in the western part than those in the eastern part suggesting additional sources from upwelled waters. Furthermore, the average nitrite+nitrate to phosphate ratio (N:P ratio) was 11.2:1, indicating nitrogen is a limiting factor for the growth of primary producers, and other sources may play a more dominant role. Two distinct layers in the euphotic zone within different sources and mechanisms namely the nutrient-depleted layer and nutrient-repleted layer were observed. Overall, the result of this study can only be seen as a starting point toward a comprehensive and holistic understanding of the nutrient biogeochemistry of the Indonesia Seas.

Temporal variability of a soundscape near a mid-oceanic atoll in the northern Indian ocean

Soundscape ecology in the context of physical oceanographic features is an emerging area of research revealing interactions between physically, biologically and anthropogenically driven sounds and their sources. Soundscapes can shape and reveal distributions of a range of species, from fish larvae to whales, within marine ecosystems. The northern Indian Ocean is a region of high environmental variability driven by seasonally reversing monsoonal winds. The mid-oceanic islands within these waters consist of steep slopes forming a crucial interface between shallow reef and deep oceanic habitats. Studies on soundscape are limited in these waters. The aim of this study was to characterize major sound sources off the southern and northern side of the Kavaratti atoll in Lakshadweep islands, India, located at the northern part of the Laccadive-Maldives-Chagos Ridge. A first look at shallow water soundscapes are provided here using passive acoustic monitoring, and how they correlate with satellite-derived oceanographic variables. Geophonic and biophonic sources across different frequency bands are identified with three major choruses – a dusk fish chorus, a midnight chorus that is speculated to be produced by myctophids, and a snapping shrimp night chorus. Low frequency biophonic choruses peaked in inter-monsoon months (January to March), while low frequency geophonic sound levels peaked during monsoon months (June to October) and increased with wind speed. The dusk fish chorus and the midnight chorus (at the south site) decreased with increasing sea surface salinity, while the snapping shrimp chorus (at the south site) increased with increasing sea surface salinity. Snapping shrimp chorus levels increased with decreasing wind speed. The dusk fish chorus peaked during full and waning moon, and the midnight and snapping shrimp choruses peaked during new moon periods. The sources and patterns described in this study will help compare with future soundscape and sound pressure level measurements within this region. This will be useful in the context of a changing climate and for planning future developmental projects on the islands. Reef choruses link with peak larval recruitment, spawning, or feeding activities, and further investigation into the peak calling times reported here will help uncover the function of choruses. Expanding the collection of passive acoustic monitoring data and oceanographic measurements over longer timescales will significantly advance ‘soundscape oceanography’.

The contrast in suspended particle dynamics at surface and near bottom on the river-dominated northern South China Sea shelf in summer: implication on physics and biogeochemistry coupling

To understand the process-response relations among physical forcing and biogeochemical properties of suspended particles (SPs) in the river-dominated northern South China Sea shelf, a 5-day shipboard observation was conducted at a fixed location on the dispersal pathway of the Zhujiang (Pearl) River plume (ZRP) in the summer of 2016. Instrumented moorings were deployed near the sampling site to record the flow and wave fields every 10 minutes. Hydrographic properties were measured hourly to identify different water masses. Water and SPs samples at the surface (3 m) and near the bottom (3 m above the bed) were taken every 3 h for the analyses of nutrients, chlorophyll-a (Chl-a), and particulate organic matter (POM including POC, PN, and δ13CPOC). Meanwhile, the grain-size composition of SPs and seafloor sediment were also analyzed. Results showed that monsoon winds drove cold upwelling and ZRP waters at the surface. Both the upwelling and ZRP regimes contained newly produced marine phytoplankton based on low POC/Chl-a ratio (PC ratio) and enriched δ13CPOC. However, SPs in the ZRP regime were smaller (&amp;lt;153 µm), having denser particle bulk density, and less enriched δ13CPOC, indicating different bio-communities from the upwelling regime. EOF analysis of the surface data suggested that mixing processes and the dispersal of the ZRP regime were mainly controlled by far-field storm winds, tidal modulation, and strength of mixing. On the other hand, a bottom nepheloid layer (BNL) was observed, mainly consisting of SPs&amp;lt;63 μm with higher bulk density than SPs at the surface. POM in the BNL was degraded and δ13CPOC-depleted according to the PC ratio and δ13CPOC. EOF analysis of the near-bottom data indicated that the dominant physical processes influencing the biogeochemical properties of SPs in the BNL were jointly the upwelling-associated lateral transport (first order) and tide-related resuspension (second order). Our study identified the contrast between the surface and near-bottom regimes with the coupling patterns among physical forcing and physiochemical properties of SPs using good constraints on particle dynamics and particle sources.

Understanding the Spatial–Temporal Patterns of Floating Islands Impacting the Major Dams of the White Nile

Floating islands in Lake Victoria, the world’s second-largest fresh water lake, disrupt transportation, fisheries, irrigation, and water quality. Despite their impact, the dynamics of these islands remain unexplored. This study investigates island dynamics within the Nalubaale, Kiira, and Bujagali dams in Uganda, exploring the causes of their formation and the subsequent impact on hydropower production. The study collects data of Landsat imagery from 2000 to 2020, CHIRPS precipitation, and Lake Victoria’s water level datasets from 2004, 2010, 2013, 2017, and 2020. The results reveal a strong correlation between precipitation, fluctuating water levels, and floating island formation, with nutrient-rich runoff from municipal waste and agriculture promoting island growth. In addition, rising water levels lead to the dislodging of rocks and soil, contributing to floating island formation, which may manifest with a lag time of up to one month. The analysis shows higher correlations between precipitation, water levels, and floating islands during the long (March–May) and short (September–November) rainy seasons as opposed to drier periods (June–August, December–February). The findings indicate that southeast monsoon winds, which transport floating vegetation, also are essential in influencing island dynamics. Consequently, the major drivers of floating islands in Lake Victoria are identified as precipitation, water level fluctuations and wind variations. Finally, a negative correlation between floating island eutrophication and power production at Kiira and Nalubaale stations suggests that the increased eutrophication caused by the presence of floating islands leads to reduced power output at both Kiira and Nalubaale power stations.

On the anomalous structure of the Southeast Vietnam Offshore Current during 1994 to 2015

The summer circulation in the South China Sea (SCS) often has a dipole structure associated with the eastward Southeast Vietnam Offshore Current (SVOC). The dipole has an anti-cyclone to the south and a cyclone to the north. A 22-year (1994–2015) HYbrid Coordinate Ocean Model (HYCOM) global reanalysis is used to study why the SVOC in the SCS is anomalous in summer of 1995, 1998, 2007, 2010, and 2015. The normal SVOC Sea Surface Height (SSH) pattern is defined based on previous observations of the dipole associated with it. An Empirical Orthogonal Function (EOF) analysis is performed on the monthly mean SSH and wind stress curl to seek the answer. SSH EOF1 and EOF2 explain 43.3% and 18.9% of the total SSH variance, respectively. Wind stress curl EOF1 and EOF2 explain 63.4% and 14.9% of the total variance, respectively. SSH EOF1 is a basin-scale gyre mode that represents the barotropic response to the basin-scale monsoon wind stress curl EOF1. SSH EOF2 is a dipole mode that represents a baroclinic response to both wind stress curl EOF1 and EOF2 (western North Pacific anticyclone mode) via forced baroclinic Rossby waves. SSH EOF2 explains 39.6% of the SSH variance in the SVOC dipole and is more important for the SVOC formation than SSH EOF1, which explains 28.2% of the SVOC dipole SSH variance. SSH EOF2 principal component time series indicate that the summer dipole mode in 1995, 1998, 2010, and 2015 is associated with an anti-cyclone to the north and a cyclone to the south, opposite to the normal SVOC dipole. In 2007, the SSH EOF2 is very weak with its principal component close to zero.

A 50 kyr record of eolian sedimentation in the Eastern Arabian Sea – Dust deposition changes synchronous with the Northern Hemisphere Climatic Oscillations

The Late Pleistocene Northern Hemisphere (NH) climate was extremely variable, owing to the abrupt warm Dansgaard–Oeschger (D/O) events and cold Heinrich events in the Greenland and North Atlantic. Although the close coupling between the Indian monsoon and the Northern hemisphere climatic fluctuations has been previously reported from several western and northern Arabian Sea records, these millennial-scale climatic oscillations are not clearly defined in the Eastern Arabian Sea (EAS) possibly because many of the past records are from the continental margin which are vulnerable to sediment slumps and slides. Here, we present a 50 kyr eolian sedimentation record from a bathymetric high off Goa in the EAS, reconstructed using the environmental magnetic parameter S-ratio (a measure of the relative proportions of ferromagnetic and canted antiferromagnetic minerals) and the mass accumulation rate of iron and magnesium (FeMAR and MgMAR). S-ratio record shows striking similarity with the δ18O record from the Greenland GISP2 ice core, indicating the control of the temperature fluctuations of high northern latitudes on the low-latitude climate variability. The cold Heinrich events are marked by lowered S-ratios indicating less eolian input while the D/O interstadials are marked by increased S-ratios illustrating the intensified summer monsoon wind strength and the increased eolian supply during these periods. The mass accumulation rate of Mg and Fe reveals high values during 29–18 kyr reflecting the increased source area aridity and dust transport during the last glacial period. The spectral analysis of the S-ratio record reveals significant periodicities centered at 24 kyr and 1.3 kyr establishing the orbital and northern hemisphere controls on the EAS climate.

Assessing the potential radiological impacts on Vietnam from a hypothetical accident at a nearby Chinese nuclear power plant

We assess the radiological impact on Vietnam from a hypothetical accident at the Fanchenggang nuclear power plant (F-NPP), 65 km from Vietnam’s Mongcai city. The accident was assumed to release, among other types of radionuclides, 1E + 16 Bq 131I in 24 h. The simulation of radioactive plumes using the FLEXPART model has revealed peak concentrations of radionuclides in the air and dry and wet depositions on the ground marking the passage of radioactive plumes over the receptor sites. The northeast monsoon wind drives the peak dry depositions in winter, while the peak wet depositions are associated mainly with the high monsoon rainfall in summer. The accident impact, reflected in the frequency of plume passage over the receptor site and the resultant radiation dose to people, decreases exponentially with the distance to F-NPP. The impact on Mongcai was most severe, implying people would be advised to stay indoors during plume passage. Meanwhile, at Danang, 630 km south of F-NPP, the impact was insignificant, as plumes rarely passed through, and the maximum dose was as low as the annual dose due to exposure from naturally occurring radionuclides in soils.

Sediment depositional pattern in the northern Japan Sea over the last 1200 ka and its linkages to orbital forcing

The semi‐enclosed marginal Japan Sea is sensitive to global changes and responds to orbital‐scale variability. Sediment core samples from Integrated Ocean Drilling Program Site U1423 were processed for detrital grain size and semi‐quantitative mineral analysis to assess the sediment characterization and depositional environment in the Japan Sea over the last 1200 ka. The mean grain data suggest the dominance of the silt size fraction over sand and clay in the whole period, while sand content increases dramatically between 600 and 150 ka. The end‐member energy modelling of grain size data suggests that sediment deposition took place under two energy conditions over the last 1200 ka. The low‐energy conditions observed during the middle Pleistocene transition (MPT) is mainly related to the wind deposition with the sediment characteristics being moderately to poorly sorted and coarse to nearly symmetrical skewed during global cooling and enhanced East Asian Winter Monsoon (EAWM) winds in the northern Japan Sea. Post MPT, periodic fluctuations between higher and lower energy conditions are observed, and the depositional environment is controlled by the EAWM wind, and precipitation intensity, glacio‐eustatic sea‐level changes and sea‐ice volumes. During the period, detrital sediments are poorly sorted and nearly symmetrically skewed, marked by the dominance of quartz, plagioclase and k‐feldspar. The spectral analysis grain size‐related data shows the presence of 228, 41 and 23 kyr orbital paced cycles, which are also observed in the Chinese Loess Plateau's normalized quartz mean grain size. This study is the first report of 228 kyr cycles from the Pleistocene Japan Sea sediments indicate that sediment deposition in the Japan Sea is associated with ~200 kyr eccentricity cycle as in the Chinese Loess Plateau.