Monsoon Winds Research Articles

Seasonal variation in diel vertical migration of zooplankton and micronekton in the Andaman Sea observed by a moored ADCP

The diel vertical migration (DVM) behaviors of zooplankton and micronekton vary among species in response to diverse ambient conditions. Based on the observed mean volumes of backscattering strength (MVBS), we studied the mean features and seasonal variations of DVM in the Andaman Sea. Nocturnal-ascent DVM pattern prevailed throughout the observation period, with a mean downward (upward) migratory speed of 3.85 (3.81) cm/s. The DVM in this area exhibited a 3-layer vertical structure. Between the surface nighttime residence and the daytime residence below 300 m, there was a weak subsurface daytime residence probably formed by the assemblage of migrants avoiding aerobic predators. The variations in lower margin depth of surface nighttime residence and the upper margin depth of subsurface daytime residence were consistent with the variation in oxycline depth, which is closely related to thermocline variations. Compared with the premonsoon season, the MVBS was weaker, but the DVM was more active during the summer monsoon season, corresponding to the water clarity trend. Overall, equatorial Kelvin waves and monsoon winds presumably dominated the seasonal variations in DVM by modulating sea water properties such as oxygen concentration and transparency.

Modeling The Hydrodynamic Characteristics of Tidal And Monsoonal Currents In Pondok Dayung Port of Tanjung Priok Harbor, Jakarta

The Pondok Dayung port forms a significant segment of the Tanjung Priok harbor in the Jakarta coastal bay. Studies on the hydrodynamic characteristics of tidal and monsoonal currents appear very important to ship movement and laid/dock operations in port basins/jetties. These flow conditions have been simulated using a two-dimensional shallow water equation, while the tidal and monsoonal wind were coupled to model the ocean current. In general, the simulation results of the ocean current characteristics were dominated by tidal effects, as well as the interactions with the coastlines, jetties, and breakwaters. Also, the geometric replica has been validated satisfactorily, using time series sea elevation from the tidal station in the research area managed by the National Geospatial Agency (BIG). Strong RMSE and linear correlation values ranging from 0.0405-0.0458 m and 0.9648-0.9843 were obtained, respectively. During the flood tides, the ocean current is directed towards the basin area, while an outward flow is observed under ebb conditions. Furthermore, the maximum tidal current speed of ±0.26 m/s was recorded at the port waterways. A similar outcome was also reported during the west and east monsoon, in addition to a minimum ocean current speed of approximately 0.00 m/s. These conditions implied that the Pondok Dayung port and its breakwater system served as protective structures to the surrounding vessels and the harsh ocean current impacts.

Influence of variability to coastline dynamic in the small uninhabited reef islands of Kepulauan Seribu

Small reef islands provide habitable land for coastal communities in many parts of the world. However, the small, low lying reef islands are commonly considered among the most geomorphically sensitive landforms to changes in sea level, wave processes, sediment supply and anthropogenic impacts. Kepulauan Seribu in the Java Sea comprise of numerous reef islands. By 2019, the islands chain is host to more than 24 thousand people. Kepulauan Seribu is affected by monsoon wind cycle. The monsoon wind also known to interact with an interannual phenomenon such as Indian Ocean Dipole (IOD) which affecting regional and local wind circulation. This study aims to examine the reef shoreline response to seasonal and interannual climate variability using satellite data that encompasses yearly monsoon cycle and IOD event. Strengthens (weakens) of winds speed in the study area during the East (West) Monsoon, which in some year also coincides with a positive (negative) IOD event, are observed from 2009 to 2018 ERA - Interim by The European Centre for Medium - Range Weather Forecasts (ECMWF) data. This variability influences the shoreline shifting in the uninhabited reef islands of Kepulauan Seribu as identified based on satellite imagery analysis. More pronounce shifted of large sediment flux are perceptible on opposing monsoon which coincides with positive/negative IOD event. Small uninhabited reef islands have ecological and economical value. Hence, enhancing coastal resilience from erosion by using conservation-types approach should be taking into consideration. Ultimately, a good understanding of climate variability that controlled changes in beach systems of reef islands is important for adequate coastal management decisions.

Evidence of a chlorophyll “tongue” in the Malacca Strait from satellite observations

Remotely sensed surface chlorophyll-a concentration from the Moderate Resolution Imaging Spectroradiometer (MODIS) unveils signatures of a “tongue” like feature extending into the Malacca Strait from the west of Malaysia. A threefold increase of chlorophyll-a amplitudes is observed in the strait during the northeast monsoon (December–February) compared to the lowest values during the southwest monsoon (May–September). This seasonal variability of chlorophyll-a is linked with the seasonal variabilities of the meridional component of Ekman mass transport (M y ), sea surface temperature (SST), wind stress curl, and the sea surface height anomaly (SSHA). A multiple regression analysis indicates that the monsoonal winds and SST are the dominant contributors to the chlorophyll-a variability in the strait. The role of SSHA is limited to the presence of a seasonal cyclonic eddy in the strait during December–February and its associated upwelling. The monsoonal winds associated with the active phase of Madden Julian Oscillation (MJO) events during November induced strong coastal upwelling along the west coast of Malaysia. Later, strong upwelling associated with both wind-induced coastal upwelling and open ocean upwelling due to wind stress curl is observed in the strait during December–February, which is also well supported by the entrainment of cold and saline waters from the subsurface and advection of colder SST within the strait. The advection of higher chlorophyll-a in the north-westward extension of the “tongue” off the west coast of Malaysia during December – February is attributed to the Ekman mass transport due to higher wind stress. On the other hand, lower chlorophyll-a during May–September is due to the negative wind stress curl and downwelling. Rectified wavelet analysis shows higher correlations of chlorophyll-a variability with the active phases of the MJO events than with the ENSO and IOD events, indicating substantial impacts of the MJO events in the Malacca Strait. • First study to link Chl-a seasonality in Malacca Strait with winds, SST and SSH. • Highest Chl-a values during December–February manifest as a “tongue.” • Winds drive open ocean and coastal upwelling processes to generate the “tongue”. • MJO events influences chlorophyll-a variability more than ENSO and IOD events.

Characteristics and Vertical Profiles of Mean Wind and Turbulence for Typhoon, Monsoon, and Thunderstorm Winds

AbstractThe vast majority of current structural design codes and standards do not separately consider the wind and turbulence profiles for different storm types. Based on the 356-m-high Shenzhen Me...

Monthly and Interannual Variations in Winter Positive Surface‐Bottom Temperature Difference in Northeastern Coastal Waters of the Shandong Peninsula in the Yellow Sea

AbstractTraditionally, the Yellow Sea (YS) is believed to be well mixed throughout the water column or to experience significant temperature inversions in winter. Recently, we found a significant positive surface‐bottom temperature difference (SBTD) as large as 3.7°C in northeastern coastal waters of the Shandong Peninsula in the YS in winter. By analyzing 4 years (June 2016–September 2020) of online in situ observations, this study examined monthly and interannual variations in winter positive SBTD and the underlying dynamics. The winter positive SBTD generally formed in November, peaked in December/January, and disappeared in March. At the interannual time scale, this SBTD was strongest in 2018 and weakest in 2020. The underlying dynamics involved the combined effects of prevailing winter monsoon winds and resultant surface heat loss and current heat advection. When the surface northerly wind was strong, strengthened southward advection of cold air over the ocean cooled the water column intensely, whereas wind‐enhanced southward advection of warm surface water partly offset the sea surface cooling and resulted in surface temperature cooling that was considerably slower than bottom temperature or even surface temperature warming. These processes together generated strong positive SBTDs. When the surface northerly wind was weak, all of the above processes became weak and resulted in weak positive SBTDs. The relationship with Yellow River runoff was also discussed. This study enriches our knowledge of winter thermal structure in the YS. More observations and coupled physical‐biogeochemical simulations are needed to further clarify the impacts on climate and marine ecology.

Mass Beach Stranding of Blue Button Jellyfishes, Porpita porpita (Linnaeus 1758) from the Coast of Mandvi, Kutch, India during August, 2021

Present short communication reports about beach stranding of Porpita porpita (Linnaeus 1758) from the Coast of Mandvi, Kutch during August 2021. Also, this is the first record of the blue button jellyfishes for the northern Gulf of Kutch region. A study was carried out by primary observation and measurements of common environmental parameters such as Sea Surface Temperature (SST), Wind Direction & Wind Speed. Aboral and oral parts were observed and described. It is assumed that the large biomass of blue button jellyfish on the beach is due to strong shoreward Monsoon winds.

Fast local warming is the main driver of recent deoxygenation in the northern Arabian Sea

Abstract. The Arabian Sea (AS) hosts one of the most intense oxygen minimum zones (OMZs) in the world. Observations suggest a decline in O2 in the northern AS over the recent decades accompanied by an intensification of the suboxic conditions there. Over the same period, the local sea surface temperature has risen significantly, particularly over the Arabian Gulf (also known as Persian Gulf, hereafter the Gulf), while summer monsoon winds may have intensified. Here, we simulate the evolution of dissolved oxygen in the AS from 1982 through 2010 and explore its controlling factors, with a focus on changing atmospheric conditions. To this end, we use a set of eddy-resolving hindcast simulations forced with winds and heat and freshwater fluxes from an atmospheric reanalysis. We find a significant deoxygenation in the northern AS, with O2 inventories north of 20∘ N dropping by over 6 % per decade between 100 and 1000 m. These changes cause an expansion of the OMZ volume north of 20∘ N at a rate of 0.6 % per decade as well as an increase in the volume of suboxia and the rate of denitrification by 14 and 15 % per decade, respectively. We also show that strong interannual and decadal variability modulate dissolved oxygen in the northern AS, with most of the O2 decline taking place in the 1980s and 1990s. Using a set of sensitivity simulations we demonstrate that deoxygenation in the northern AS is essentially caused by reduced ventilation induced by the recent fast warming of the sea surface, including in the Gulf, with a contribution from concomitant summer monsoon wind intensification. This is because, on the one hand, surface warming enhances vertical stratification and increases Gulf water buoyancy, thus inhibiting vertical mixing and ventilation of the thermocline. On the other hand, summer monsoon wind intensification causes a rise in the thermocline depth in the northern AS that lowers O2 levels in the upper ocean. Our findings confirm that the AS OMZ is strongly sensitive to upper-ocean warming and concurrent changes in the Indian monsoon winds. Finally, our results also demonstrate that changes in the local climatic forcing play a key role in regional dissolved oxygen changes and hence need to be properly represented in global models to reduce uncertainties in future projections of deoxygenation.

Land-Ocean Interaction Affected by the Monsoon Regime Change in Western Taiwan Strait

The Taiwan Strait is a conduit between East China Sea (ECS) and South China Sea (SCS). Seasonal monsoon winds drive the southbound Zhejiang-Fujian Coastal Current and northbound SCS Warm Current through the strait. Water masses carried by these major current systems also carry fluvial signals from two major rivers, the Changjiang (Yangtze) River in ECS and the Zhujiang (Pearl) River in SCS through the strait. Here we show a switch occurred to signify the monsoon regime change on the western side of this conduit around 10:00 on May 8, 2015. Our data came from water mass properties and environmental proxies of N/P ratio in the surface water and 7Be and 210Pbex isotopes in surface sediments. The timings of the demarcation were identical in the water column and on the water-sediment interface. Our findings put a specific time point in the monsoon regime change in 2015.

Tropical cyclones over the Arabian Sea during the monsoon onset phase

AbstractGenerally, monsoon conditions are unfavourable for cyclogenesis in the Arabian Sea due to the strong vertical wind shear present over the basin which prevents the vertical development of cyclones. However, there are instances where tropical cyclones form over the basin during the onset phase of the Indian summer monsoon (ISM). The current study examines the evolution of the synoptic conditions in the years during 1979–2019 in which a cyclone forms during the onset phase of the ISM. The effect of various atmospheric and oceanic factors, the modulation of wind circulation over the Indian subcontinent and the north Indian Ocean region due to the possible influence of tropical and extratropical weather systems has been taken into consideration. Our analysis indicates that a weak mean monsoonal wind circulation caused by the southward intrusion of subtropical westerlies (at 200 hPa) is conducive for cyclogenesis over the Arabian Sea during the monsoon onset phase. Such a weak onset phase of the monsoon, coupled with the seasonal warm SSTs, may lead to cyclone formation in the Arabian Sea.

Identification of Marine Debris Sources in Kuta Beach, Bali, Indonesia

Maharta, I.P.R.F.; Radjawane, I.M.; Suprijo, T.; Park, H., and Hendrawan, I.G., 2021. Identification of marine debris sources in Kuta Beach, Bali, Indonesia. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 594–598. Coconut Creek (Florida), ISSN 0749-0208. Kuta Beach is one of the beaches with the biggest tourist arrivals in Bali. In recent years Kuta beach has received shipments of marine debris from the Bali Strait. Kuta Beach area gets an average of piles of marine debris reaching ± 30 tons/day and the peak occurred in January 2014 which reached ± 1,700 tons. Previous studies only carried out simulations with sources of marine debris from outside the Bali Strait and the coast in Bali. This study aims to determine the marine debris that reaches Kuta Beach with the source of debris from rivers in the west season (January 2019). The Finite Volume Coastal Ocean Model (FVCOM) is used to obtain the circulation of current patterns and patterns of movement of particles by using the Lagrangian Particle Tracking module, with the sources of the debris from 8 river in Bali Strait. In general, the pattern of movement of currents in the Bali Strait at west season is dominantly moving towards the east due to the influence of the west monsoon winds. The simulation results show that particles that reach Kuta Beach are dominated by rivers that flow near Kuta Beach, with the river that gives the most debris is the Tukad Penet, which is 68.89% of the total marine debris that reaches Kuta Beach.

Physical forces driving chlorophyll-a variability in the South Java Sea Shelf: a spatio-temporal analysis

The wind and current are two physical forces that strongly influence the biogeochemistry in coastal waters. Both of these forces could enhance the Chlorophyll-a (Chl-a) concentration through the upwelling process. Here we examine the contribution of the wind and current to the Chl-a variability in the South Java upwelling system in terms of wind stress and bottom stress respectively using satellite-derived and reanalysis data from 2002 to 2017. Ten longitudinally cells were used for further analysis. A long-term Chl-a shows a strong longitudinal gradient of Chl-a with the highest value on the shelf. Seasonal and Inter-annual Chl-a analysis shows the evidence of the monsoonal winds and other forcing effects relevant to the previous studies. Wind stress (τwx ) has a strong seasonal variation which is upwelling- favorable during southeast monsoon coincide with higher Chl-a suggesting wind as the main forces during that time, while bottom stress (τbx ) has more complicated variations, but it’s seen that τwx mostly downwelling-favorable or eastward circulations. There were about 39.92- 52.94% of positive Chl anomalous events generated by the combination of upwelling- favourable τwx and downwelling-favorable τbx , higher than other combinations. In terms of Oceanographic drivers, the wind has a higher effect on enhancing Chl-a through a negative correlation. τwx leads the Chl-a anomalies by about 15 – 24 days with a correlation coefficient of more than 0.6.

Regionalization of the Red Sea Based on Phytoplankton Phenology: A Satellite Analysis

AbstractThe current average state of Red Sea phytoplankton phenology needs to be resolved in order to study future variations that could be induced by climate change. Moreover, a regionalization of the Red Sea could help to identify areas of interest and guide in situ sampling strategies. Here, a clustering method used 21 years of satellite surface chlorophyll‐a concentration observations to characterize similar regions of the Red Sea. Four relevant phytoplankton spatiotemporal patterns (i.e., bio‐regions) were found and linked to biophysical interactions occurring in their respective areas. Two of them, located in the northern part the Red Sea, were characterized by a distinct winter‐time phytoplankton bloom induced by mixing events or associated with a convergence zone. The other two, located in the southern regions, were characterized by phytoplankton blooms in summer and winter which might be under the influence of water advected into the Red Sea from the Gulf of Aden in response to the seasonal monsoon winds. Some observed inter‐annual variabilities in these bio‐regions suggested that physical mechanisms could be highly variable in response to variations in air‐sea heat fluxes and ENSO phases in the northern and southern half of the Red Sea, respectively. This study reveals the importance of sustaining in situ measurements in the Red Sea to build a full understanding about the physical processes that contribute to phytoplankton production in this basin.

Redistribution of riverine and rainfall freshwater by the Bay of Bengal circulation

We use satellite-derived currents and a Lagrangian approach to investigate the redistribution of the precipitation minus evaporation (P-E) and river freshwater inputs into Bay of Bengal (BoB) by the oceanic circulation. We find a key role of Ekman transport in shaping the BoB freshwater distribution. Until September, the summer monsoon winds induce eastward Ekman transport, which maintains freshwater near its major rivers and rain sources in the northeastern BoB. The winter monsoon Ekman transport strongly contributes to the surface flow in many areas of the interior BoB. This ~ 0.15 m s−1 westward transport overcomes the weaker offshore transport by mesoscale motions and pushes a ~ 40/45% mixture of P-E and Ganges–Brahmaputra freshwater into the East Indian Coastal Current (EICC). In agreement with previous studies, we find that the EICC then transports Ganges–Brahmaputra freshwater southward, allowing the formation of a narrow freshwater tongue or “river in the sea” along the coast east of India in November. Ekman transport thus operates jointly with the EICC to allow the “river in the sea” formation. The EICC is nonetheless a “leaky pipe” as only ~ 22% of the Ganges–Brahmaputra, and ~ 9% of the P-E monsoonal freshwater inputs exit the BoB near Sri Lanka. The winter monsoon anticyclonic circulation in fact brings more rain freshwater from the equatorial Indian Ocean into the southeastern BoB than it exports freshwater through the EICC. As a result, the BoB circulation contributes to a net freshwater gain that amounts to 11% of the local rain and freshwater inputs.

Interconnection between the Southern South China Sea and the Java Sea through the Karimata Strait

This study aims to investigate the interconnection between the southern South China Sea (SSCS) and Java Sea (JS) by simulating seasonal circulations and associated transports using the Regional Ocean Modelling System (ROMS). The seasonal circulation was predominantly driven by monsoonal wind stress and water exchanges between the SSCS and the JS. During the boreal winter, cooler and saltier waters from the SSCS were advected into the JS, while during the boreal summer, cooler waters from the JS were advected into the SSCS, with the advection of fresher water onto the Peninsular Malaysia’s east coast in the SSCS being the new finding provided by this study. The various water transports were driven southward into the JS during the boreal winter and northward into the SSCS during the boreal summer. The various water transports estimated by ROMS peaked in May during the inflow months from the JS into the SSCS, which was attributed to the simulated anticyclonic eddy in the SSCS, which differed from previous studies that peaked between June and August. The annual mean volume, freshwater, heat, and salt transports were 0.96 Sv, 0.04 Sv, 0.10 PW, and 0.03 × 109 kg s−1, respectively, directed from the SSCS into the JS.

A Trade-Friendly Environment?: Newly Reconstructed Indian Summer Monsoon Wind Stress Curl Data for the Third Millennium BCE and Their Potential Implications Concerning the Development of Early Bronze Age Trans-Arabian Sea Maritime Trade

A Trade-Friendly Environment?: Newly Reconstructed Indian Summer Monsoon Wind Stress Curl Data for the Third Millennium BCE and Their Potential Implications Concerning the Development of Early Bronze Age Trans-Arabian Sea Maritime Trade

Initial Findings Suggest Box Jellyfish Encounters along Shallow Philippine Coastlines are Predictable

Jellyfish stings account for numerous deaths in the Philippines. Despite this, there is little scientific information on the identity, distribution, seasonality, and ecology of the box jellyfish species involved. We present initial findings of three months (April–June 2021) of monitoring the abundance of and envenomations by box jellyfishes in eastern and western Luzon. Emergent patterns suggest encounters between box jellyfish and people are more likely to occur in beach areas within a few kilometers from rivers when tidal ranges are large, particularly around the flood phase of high tide. Encounters are also more likely on coasts where the monsoon winds blow onshore during the warmer months, bringing these animals closer to beach areas. They then stay longer in the shallows when the seas are calm. Beachgoers are, thus, advised to plan their destinations and activities carefully and wear protective clothing when venturing into shallow coastal areas.

A 145 kyr record of upstream changes in Indian monsoon circulation and its link to southern high-latitude climate

The influence of northern high latitude climate variability on the South Asian Summer Monsoon has been extensively studied using both instrumental and proxy based climate data. In comparison, only a few studies have attempted to explore the southern high latitude association of the South Asian Summer Monsoon. Here we present a 145 kyr long new data (oxygen and carbon isotopic abundance of two depth-stratified species of foraminifera viz. Globigerinoides ruber and Globorotalia menardii) from a sediment core on sub-millennial to millennial scale resolution from the southwestern tropical Indian Ocean - a region swept by the southeasterly wind during boreal summer (referred to as ‘summer’ hereafter), which transforms to the southwest monsoon wind after crossing the equator. The available records of past summer monsoon variability are predominantly based on reconstruction of downstream hydrology, which is identifiable with the thermodynamics of the system. The present study is a reconstruction of the dynamics of the summer monsoon circulation from an upstream region which is ideally suited for exploring its link with the southern high-latitude climate. We identified several occurrences of interchanging intense and weak monsoon circulation events during the 145 kyr period. We further find that warm (cold) conditions in Antarctica show a near one-to-one coupling with weak (strong) monsoon phases, suggesting a strong mechanistic link between them during the period.

Study of Active and Break Spell Phenomena of Indian Summer Monsoon Using WRF Downscaled Data

This study evaluates the performance of a dynamically downscaled Weather Research and Forecasting (WRF) model by capturing the characteristics of the interseasonal variability in terms of active and break spells of the Indian summer monsoon during the period 1980–2014. We identify the active and break days based on the standard criteria of previous studies. Further, the composite means in the rainfall and different rainfall events, along with the thermal and dynamical features associated with active and break spells, are analyzed and discussed. Our results clearly show that the WRF model reproduces the observed features of monsoon circulation in active spells such as the wider and intensified lower tropospheric winds, the presence of mid-tropospheric cyclonic circulation, and the dominance of strong upper-level tropical easterlies along with the high influx of moisture towards the Indian subcontinent. Even in the break spells, the WRF model effectively simulates the observed features of the ERA, such as weaker monsoon winds at both low and upper levels and decreased strength of northwesterly winds of Shamal, the presence of a strong thermal inversion over the northwestern part of the Arabian Sea, and a significant increase in the African easterly jet. Moreover, our rainfall analysis during active and break spells reveals that the WRF model accurately reproduces the observed characteristics of the regional-scale precipitation. The results also reveal that the spatial distributions of moderate, heavy, and very heavy rainfall events over the monsoon core region are well captured by the WRF model, with only slight intensity variations compared to the observed distributions.

Seasonal Variability of Waves Within the Indonesian Seas and Its Relation With the Monsoon Wind

The previous studies have simulated the variability of the wave within the Indonesian seas which showed that the variability of wave follows the seasonal pattern. However, their analysis only consider the influence of local wind forcings. The bias and error of their simulated wave were also unclear. In the present study, we investigate the variability of wave within the Indonesian seas and its relation with the surface wind speed using the combination of reanalysis and remote sensing data with high accuracies. We split the analysis into swell and wind wave to obtain the influence of local and remote wind forcings. We show that at the inner seas (i.e., the South China Sea, Java Sea, Flores Sea, Banda Sea and Arafura Sea), the variability of significant wave height (SWH) is majorly influenced by the variability of the speed of monsoon wind. The maximum SWH during Northwest monsoon (NWM) season is located at the South China Sea while during Southeast monsoon (SEM) season is at Arafura Sea. This indicates that the wind wave (sea) is dominant at the inner seas. At the open seas (i.e., Pacific Ocean and Indian Ocean) the variability of SWH less corresponds to the the speed of monsoon wind. The remote wind forcings control the wave variability in the open ocean area. This indicates that swell is dominant at the open seas. In general, the magnitude of SWHswell is also more than SWHsea within the Indonesian seas.