Frontogenesis and Frontolysis of a Cold Filament Driven by the Cross-Filament Wind and Wave Fields Simulated by a Large Eddy Simulation

The variations of the frontogenetic trend of a cold filament induced by the cross-filament wind and wave fields are studied by a non-hydrostatic large eddy simulation. Five cases with different strengths of wind and wave fields are studied.The results show that the intense wind and wave fields further break the symmetries of submesoscale flow fields and suppress the levels of filament frontogenesis. The changes of secondary circulation directions—that is, the conversion between the convergence and divergence of the surface cross-filament currents with the downwelling and upwelling jets in the filament center—are associated with the inertial oscillation. The filament frontogenesis and frontolysis caused by the changes of secondary circulation directions may periodically sharpen and smooth the gradient of submesoscale flow fields.The lifecycle of the cold filament may include multiple stages of filament frontogenesis and frontolysis.

Westerlies Affecting the Seasonal Variation of Water Vapor Transport over the Tibetan Plateau Induced by Tropical Cyclones in the Bay of Bengal

This study investigates the activity of tropical cyclones(TCs)in the Bay of Bengal(BOB)from 1979 to 2018 to discover the mechanism affecting the contribution rate to the meridional moisture budget anomaly(MMBA)over the southern boundary of the Tibetan Plateau(SBTP).May and October–December are the bimodal phases of BOB TC frequency,which decreases month by month from October to December and is relatively low in May.However,the contribution rate to the MMBA is the highest in May.The seasonal variation in the meridional position of the westerlies is the key factor affecting the contribution rate.The relatively southern(northern)position of the westerlies in November and December(May)results in a lower(higher)contribution rate to the MMBA.This mechanism is confirmed by the momentum equation.When water vapor enters the westerlies near the trough line,the resultant meridional acceleration is directed north.It follows that the farther north the trough is,and the farther north the water vapor can be transported.When water vapor enters the westerlies from the area near the ridge line,for Type-T(Type-R)TCs,water vapor enters the westerlies downstream of the trough(ridge).Consequently,the direction of the resultant meridional acceleration is directed south and the resultant zonal acceleration is directed east(west),which is not conducive to the northward transport of water vapor.This is especially the case if the trough or ridge is relatively south,as the water vapor may not cross the SBTP.

Formation of the front-gradient bandgap in the Ag doped CZTSe thin films and solar cells

The graded bandgap of kesterite based absorber layer is an important way to achieve high efficiency solar cells. Incorporation of Ag into CZTSSe thin films can adjust the bandgap and thus reduce the VOC-deficit and improve the quality of crystallization. However, the distribution of Ag is difficult to control due to the quick diffusion of Ag under the high temperature. In this study, we achieve the front Ag-gradient in kesterite structured compound films by prealloying followed by selenization process at 550 °C. AgZn3,Ag3Sn, and Sn–Ag–Cu alloy phases were formed during prealloying stage at 250 °C. After prealloying process, Ag tends to distribute at the front surface of the ACZTSe thin films. Combining the results of experiment and SCAPS simulation, the significantly VOCimprovement of devices is ascribed to the formation of the front Ag-gradient bandgap structure in the absorber layer. This facile prealloying selenization process affords a feasible method to design the graded bandgap structure absorber layers, which will promote the fabrication of high efficient graded bandgap structure solar cells.

An Extreme Drought over South China in 2020/21 Concurrent with an Unprecedented Warm Northwest Pacific and La Niña

An extreme drought appeared in South China from October 2020 to March 2021.During that time,sea surface temperatures exhibited an unprecedented warm center over the northwest Pacific(NWP)and a cold center over the tropical eastern Pacific(La Niña).This study demonstrates the combined effects of an exceptionally warm NWP and a moderate La Niña are closely linked to the anomalous drought in South China.The sea surface temperature anomaly in these two regions induced a steeper horizontal geopotential height gradient over South China.As a result,anomalous northeasterly winds prevailed over South China,altering water vapor transport and moisture convergence.A simplified atmospheric general circulation model also verifies the influence of the NWP warm anomaly on South China precipitation.This study points out that the sea surface temperature variation in the NWP was important to the occurrence of extreme drought in South China from October 2020 to March 2021.

Path towards high-efficient kesterite solar cells

Kesterite structure semiconductor Cu2ZnSn（S,Se）4 is one of the most promising candidate as a light absorber material to overtake the next generation of thin film solar cells, owing to its low cost, non-toxic, and earth abundant source materials. The Sbockley-Queisser limit of the single junction Cu2ZnSn（S,Se）4 solar cell is over 30%, signifying a large potential of this family of solar cells. In the past years, with the development of synthesis techniques, Cu2ZnSn（S,Se）4 solar cells have attracted considerable atten- tion and the power conversion efficiency of Cu2ZnSn（S,Se）4 solar cell has experienced a rapid progress. Presently, the certified champion efficiency of CZTSSe solar cells has reached to 12.6%, which is far below the efficiency of Cu（ln,Ga）Se2 solar cell. In this review, the developments of Cu2ZnSn（S,Se）4 solar cells in recent years are briefly reviewed. Then the fundamental understanding of Cu2ZnSn（S,Se）4 solar cells is introduced, including materials and device structure, as well as the band alignment of hetero-junction and their impacts on device performance. After that, we mainly review the progress and achievements in the preparation processes, through vacuum and non-vacuum based processes. Finally, we outline the challenges and perspectives of this promising solar cell.

Influence of Coriolis Parameter Variation on Langmuir Turbulence in the Ocean Upper Mixed Layer with Large Eddy Simulation

Langmuir turbulence is a complex turbulent process in the ocean upper mixed layer.The Coriolis parameter has an important effect on Langmuir turbulence through the Coriolis-Stokes force and Ekman effect,however,this effect on Langmuir turbulence has not been systematically investigated.Here,the impact of the Coriolis parameter on Langmuir turbulence with a change of latitude(LAT)from 20°N to 80°N is studied using a non-hydrostatic large eddy simulation model under an ideal condition.The results show that the ratio of the upper mixed layer depth to Ekman depth scale(RME)RME=0.266(LAT=50°N)is a key value(latitude)for the modulation effect of the Coriolis parameter on the mean and turbulent statistics of Langmuir turbulence.It is found that the rate of change of the sea surface temperature,upper mixed layer depth,entrainment flux,crosswind velocity,downwind vertical momentum flux,and turbulent kinetic energy budget terms associated with Langmuir turbulence are more evident at RME≤0.266(LAT≤50°N)than at RME≥0.266(LAT≥50°N).However,the rate of change of the depth-averaged crosswind vertical momentum flux does not have a clear variation between RME≤0.266 and RME≥0.266.The complex changes of both Langmuir turbulence characteristics and influence of Langmuir turbulence on the upper mixed layer with latitude presented here may provide more information for further improving Langmuir turbulence parameterization.

Influence of the upper mixed layer depth on Langmuir turbulence characteristics

The upper mixed layer depth(h)has a significant seasonal variation in the real ocean and the low-order statistics of Langmuir turbulence are dramatically influenced by the upper mixed layer depth.To explore the influence of the upper mixed layer depth on Langmuir turbulence under the condition of the wind and wave equilibrium,the changes of Langmuir turbulence characteristics with the idealized variation of the upper mixed layer depth from very shallow(h=5 m)to deep enough(h=40 m)are studied using a non-hydrostatic large eddy simulation model.The simulation results show that there is a direct entrainment depth induced by Langmuir turbulence(h_(LT))within the thermocline.The normalized depthaveraged vertical velocity variance is smaller and larger than the downwind velocity variance for the ratio of the upper mixed layer to a direct entrainment depth induced by Langmuir turbulence h/h_(LT)<1 and h/h_(LT)>1,respectively,indicating that turbulence characteristics have the essential change(i.e.,depth-averaged vertical velocity variance(DAVV)DADV for Langmuir turbulence)between h/h_(LT)<1 and h/h_(LT)>1.The rate of change of the normalized depth-averaged low-order statistics for h/h_(LT)<1 is much larger than that for h/h_(LT)>1.The reason is that the downward pressure perturbation induced by Langmuir cells is strongly inhibited by the upward reactive force of the strong stratified thermocline for h/h_(LT)<1 and the eff ect of upward reactive force on the downward pressure perturbation becomes weak for h/h_(LT)>1.Hence,the upper mixed layer depth has significant influences on Langmuir turbulence characteristics.

Seasonal variation in the three-dimensional structures of coastal thermal front off western Guangdong

The seasonal structure and dynamic mechanism of oceanic surface thermal fronts(STFs)along the western Guangdong coast over the northern South China Sea shelf were analyzed using in situ observational data,remote sensing data,and numerical simulations.Both in situ and satellite observations show that the coastal thermal front exhibits substantial seasonal variability,being strongest in winter when it has the greatest extent and strongest sea surface temperature gradient.The winter coastal thermal front begins to appear in November and disappears after the following April.Although runoff water is more plentiful in summer,the front is weak in the western part of Guangdong.The frontal intensity has a significant positive correlation with the coastal wind speed,while the change of temperature gradient after September lags somewhat relative to the alongshore wind.The numerical simulation results accurately reflect the seasonal variation and annual cycle characteristics of the frontal structure in the simulated area.Based on vertical cross-section data,the different frontal lifecycles of the two sides of the Zhujiang(Pearl)River Estuary are analyzed.

Dissimilarity among Ocean Reanalyses in Equatorial Pacific Upper-Ocean Heat Content and Its Relationship with ENSO

This study focuses on the temporal variation of dissimilarity in heat content(HC)anomalies in the upper 300 m of ocean(HC300A)in the equatorial Pacific(±10°N)and its response to the El Ni?o-Southern Oscillation(ENSO).The HC300A anomalies are derived from four ocean reanalyses that are commonly used in ENSO studies and are compared using a simple differencing method.The dissimilarity in HC300A is found to vary closely with the magnitude of ENSO(regardless of phase),meaning that it tends to be greater during strong ENSO events.However,the dissimilarity among ocean reanalyses persists after the event decays.This effect is more pronounced after strong events.The persistence of the dissimilarity after ENSO events is a result of a late maturation of the ENSO signal,its persistence,and the interruption of the signal decay due to follow-up ENSO events.The combined effect of these three factors slows down the decay of HC300A in the region and hence results in the slow decay of dissimilarity.It is also found that areas with a significant spread in vertical temperature profiles collocate with the ENSO signal during warm ENSO phases.Thus,differences in subsurface process reconstruction are a significant factor in the dissimilarity among ocean reanalyses during warm ENSO events.

Interannual variability in the sea surface cooling induced by tropical cyclones in the South China Sea

Sea surface cooling induced by tropical cyclones(TCs)is an important component of air-sea interactions.Using coordinate transformation and composite analysis methods,we examined the interannual variability in TCinduced sea surface cooling(TCSSC)in the South China Sea(SCS).The frequency of surface cooling cases was over 86%and that of surface warming cases was less than 14%.The magnitude of TCSSC was defined as the absolute value of TCSSC.The maximum magnitude of TCSSC occurred on the right side of the TC track,and the mean magnitude of TCSSC decreased by 0.04℃/a from 2006 to 2018.The interannual variability in TCSSC was highly correlated with the TC translation speed and pre-TC mixed layer depth.Notably,TCSSC got enhanced in El Nino years of 2007,2010,and 2015.The El Nino types were suggested to determine the occurring periods of strong TCSSC via controlling the positions of SCS anticyclones,which brought pre-TC shallow mixed layer and caused strong TCSSC via vertical mixing process during El Nino events.To quantify how the anticyclone influences TCSSC,we need to use mixed layer heat balances model in the next study.

Extended Impact of Cold Air Invasions in East Asia in Response to a Warm South China Sea and Philippine Sea

During boreal winter,the invasion of cold air can lead to remarkable temperature drops in East Asia which can result in serious socioeconomic impacts.Here,we find that the intensity of strong synoptic cold days in the East China Sea and Indochina Peninsula are increasing.The enhanced synoptic cold days in these two regions are attributed to surface warming over the South China Sea and Philippine Sea(SCSPS).The oceanic forcing of the SCSPS on the synoptic cold days in the two regions is verified by numerical simulation.The warming of the SCSPS enhances the baroclinicity,which intensifies meridional wind and cold advection on synoptic timescales.This leads to a more extended region that is subject to the influence of cold invasion.

Effect of seasonal barrier layer on mixed-layer heat budget in the Bay of Bengal

Time series measurements (2010–2017) from the Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA) moorings at 15°N,90°E and 12°N,90°E are used to investigate the effect of the seasonal barrier layer (BL) on the mixed-layer heat budget in the Bay of Bengal (BoB).The mixed-layer temperature tendency (?T/?t) is primarily controlled by the net surface heat flux that remains in the mixed layer(Q’) from March to October,while both Q’and the vertical heat flux at the base of the mixed layer (Q_(h)),estimated as the residual of the mixed-layer heat budget,dominate during winter (November–February).An inverse relation is observed between the BL thickness and the mixed-layer temperature (MLT).Based on the estimations at the moorings,it is suggested that when the BL thickness is≥25 m,it exerts a considerable influence on ?T/?t through the modulation of Q_(h) (warming) in the BoB.The cooling associated with Q_(h) is strongest when the BL thickness is≤10 m with the MLT exceeding 29°C,while the contribution from Q_(h) remains nearly zero when the BL thickness varies between 10 m and 25 m.Temperature inversion is evident in the BoB during winter when the BL thickness remains≥25 m with an average MLT<28.5°C.Furthermore,Q_(h) follows the seasonal cycle of the BL at these RAMA mooring locations,with r>0.72 at the 95%significance level.

A new presentation of the Indian Ocean shallow overturning circulation from a vertical perspective

The calculation of the meridional overturning streamfunction in the southern Indian Ocean is biased by the Indonesian Throughflow.Therefore,this study applies the vertical overturning streamfunction to diagnose the shallow overturning circulation in the Indian Ocean.Using the Ocean General Circulation Model for the Earth simulator output,improvements with the vertical overturning streamfunction compared with the meridional overturning streamfunction are explored.The results show that the vertical overturning streamfunction smoothly connects the shallow overturning circulations of the northern Indian Ocean and the southern Indian Ocean with the whole cycle of the subtropical cell and the cross-equatorial cell.The vertical overturning streamfunction shows a much cleaner shallow overturning circulation,which is underestimated by the meridional overturning streamfunction.It shows that the shallow overturning circulation has a magnitude of~13 Sv(1 Sv≡106 m 3 s−1),of which the subtropical cell accounts for~8 Sv.In addition,the vertical overturning streamfunction captures a clockwise overturning cell in the upper 600 m layer between 30°S and 34°S.This cell has a magnitude of about−5 Sv and probably corresponds to the wind-forced subtropical gyre.Therefore,the vertical overturning streamfunction provides a new approach for estimating the shallow overturning circulation in the Indian Ocean.

Multi-agent mobile networking observation experiment at the air-sea interface of ocean eddy

Current climate forecasting has advanced to the stage of investigating mesoscale air-sea interactions. Recent studies have identified significant structural differences between the cores and edges of mesoscale eddies;however, the effects of these structural variations on air-sea fluxes and the Marine Atmospheric Boundary Layer(MABL) remain underexplored. Traditional observations often fail to capture the detailed structures of eddies, necessitating enhanced observations at high spatiotemporal resolution for mesoscale eddies. To address this, efforts have been made to develop multi-agent platforms and expendable air-sea interface observation technologies. A task-oriented observation scheme was developed to monitor the spatial characteristics of mesoscale eddies. The South China Sea(SCS) is rich in mesoscale eddies with rapid motion changes, requiring enhanced observations of the air-sea interface using multi-agent mobile networking. An anticyclonic eddy was observed in the eastern region of the Xisha Islands in the SCS, and we examined variations in air-sea fluxes across different regions within the eddy.

MoO_(x) nanoclusters on Mo-doped TiO_(2) nanosheets with enhanced singlet oxygen generation and sulfide conversion abilities for photocatalytic aerobic oxidative desulfurization

Photocatalytic aerobic oxidation desulfurization(PAODS)is a promising and sustainable alternative to conventional,energyintensive desulfurization techniques for petroleum products.However,its development is greatly plagued by the low capability in generating highly reactive oxygen species and sluggish kinetics of sulfide oxidation of reported photocatalysts.Here we report a class of MoO_(x)nanocluster decorated on ultrathin Mo-doped TiO_(2)nanosheet(MoO_(x)/MoTiO)catalyst for efficiently facilitating the photocatalytic aerobic oxidation of sulfides.We demonstrate that MoO_(x)/MoTiO can not only promote the generation of highly reactive singlet oxygen(^(1)O_(2))but also enhance the aerobic conversion of sulfides,which leads to a record dibenzothiophene oxidation activity of 3.90 mmol g^(-1)h^(-1).The multiple experimental characterizations and density functional theory calculations collectively reveal that the doped-Mo sites can interact with the photogenerated excitons,enabling directly energy transfer generation of^(1)O_(2)through a new exciton modulation mechanism,and the coordination unsaturated MoO_(x)clusters play the role of co-catalyst to enhance the separation of charge carriers,and effectively catalyze the reaction between sulfides and1O_(2)to form sulfones.

Field-observation for an anticyclonic mesoscale eddy consisted of twelve gliders and sixty-two expendable probes in the northern South China Sea during summer 2017

An intensive field observation experiment using 12 Chinese gliders equipped with conductivity-temperature-depth (CTD) sensors and 62 expendable CTD probes (XCTDs) was performed to investigate the 3-D structure and time evolution of an anticyclonic eddy in the northern South China Sea (NSCS). The observed results showed that the anticyclonic eddy had a horizontal radius of about 80 km at surface and a vertical depth of impact of more than 1000 m. The largest temperature and salinity anomalies compared with the averaged values of the temperature and salinity profiles were 3.5°C and 0.4 psu at 120 m depth, respectively. Combined analysis of altimeter sea level and water mass properties indicated that the anticyclonic eddy was shed from the Kuroshio loop current. The vertical axis of the anticyclonic eddy tilted from surface to the observed maximum depth (1000 m) along its translation direction against the 2000 m isobath. The center of the anticyclonic eddy remained in the region east of Dongsha Island for more than half a month. During this time, the long axis direction of the eddy changed from across the slope to along the slope. Then, the eddy moved southward along the 2000 m isobaths. Both the geostrophic current and temperature distribution revealed that the eddy intensity weakened during the observation period gradually. These observations indicated strong interaction between the anticyclonic eddy and the slope topography of Dongsha Island.

Advances in research of the mid-deep South China Sea circulation

The South China Sea(SCS)is a large marginal sea connecting the Indian and Pacific oceans.Under the factors of monsoons,strait transport,and varied bathymetry,the SCS presents a three-layer structure and strong diapycnal mixing which is far greater than that in the open ocean.Theoretical analysis and observations reveal that internal tides,internal solitary waves,and strong winds are the sources of the strong mixing in the northern SCS.A major consequence of the strong mixing is an active mid-deep circulation system.This system promotes exchange of water between the SCS and adjacent oceans,and also regulates the upper layer of wind-driven circulation,making the 3 dimensional SCS circulation clearly different from that in other tropical and subtropical marginal seas.The mass transport capacity of the mid-deep circulation has a substantial impact on marine sedimentation,the biogeochemical cycle,and other processes in the SCS.This paper summarizes the recent advances in middeep sea circulation dynamics of the SCS,and discusses the opportunities and challenges in this area.

Carbon pools and fluxes in the China Seas and adjacent oceans

The China Seas include the South China Sea, East China Sea, Yellow Sea, and Bohai Sea. Located off the Northwestern Pacific margin, covering 4700000 km^2 from tropical to northern temperate zones, and including a variety of continental margins/basins and depths, the China Seas provide typical cases for carbon budget studies. The South China Sea being a deep basin and part of the Western Pacific Warm Pool is characterized by oceanic features; the East China Sea with a wide continental shelf, enormous terrestrial discharges and open margins to the West Pacific, is featured by strong cross-shelf materials transport; the Yellow Sea is featured by the confluence of cold and warm waters; and the Bohai Sea is a shallow semiclosed gulf with strong impacts of human activities. Three large rivers, the Yangtze River, Yellow River, and Pearl River, flow into the East China Sea, the Bohai Sea, and the South China Sea, respectively. The Kuroshio Current at the outer margin of the Chinese continental shelf is one of the two major western boundary currents of the world oceans and its strength and position directly affect the regional climate of China. These characteristics make the China Seas a typical case of marginal seas to study carbon storage and fluxes. This paper systematically analyzes the literature data on the carbon pools and fluxes of the Bohai Sea,Yellow Sea, East China Sea, and South China Sea, including different interfaces(land-sea, sea-air, sediment-water, and marginal sea-open ocean) and different ecosystems(mangroves, wetland, seagrass beds, macroalgae mariculture, coral reefs, euphotic zones, and water column). Among the four seas, the Bohai Sea and South China Sea are acting as CO_2 sources, releasing about0.22 and 13.86–33.60 Tg C yr^(-1) into the atmosphere, respectively, whereas the Yellow Sea and East China Sea are acting as carbon sinks, absorbing about 1.15 and 6.92–23.30 Tg C yr^(-1) of atmospheric CO_2, respectively. Overall, if only the CO_2 exchange at the sea-air interface is considered, the Chinese marginal seas appear to be a source of atmospheric CO_2, with a net release of 6.01–9.33 Tg C yr^(-1), mainly from the inputs of rivers and adjacent oceans. The riverine dissolved inorganic carbon (DIC) input into the Bohai Sea and Yellow Sea, East China Sea, and South China Sea are 5.04, 14.60, and 40.14 Tg C yr^(-1),respectively. The DIC input from adjacent oceans is as high as 144.81 Tg C yr^(-1), significantly exceeding the carbon released from the seas to the atmosphere. In terms of output, the depositional fluxes of organic carbon in the Bohai Sea, Yellow Sea, East China Sea, and South China Sea are 2.00, 3.60, 7.40, and 5.92 Tg C yr^(-1), respectively. The fluxes of organic carbon from the East China Sea and South China Sea to the adjacent oceans are 15.25–36.70 and 43.93 Tg C yr^(-1), respectively. The annual carbon storage of mangroves, wetlands, and seagrass in Chinese coastal waters is 0.36–1.75 Tg C yr^(-1), with a dissolved organic carbon(DOC) output from seagrass beds of up to 0.59 Tg C yr^(-1). Removable organic carbon flux by Chinese macroalgae mariculture account for 0.68 Tg C yr^(-1) and the associated POC depositional and DOC releasing fluxes are 0.14 and 0.82 Tg C yr^(-1), respectively. Thus, in total, the annual output of organic carbon, which is mainly DOC, in the China Seas is 81.72–104.56 Tg C yr^(-1). The DOC efflux from the East China Sea to the adjacent oceans is 15.00–35.00 Tg C yr^(-1). The DOC efflux from the South China Sea is 31.39 Tg C yr^(-1). Although the marginal China Seas seem to be a source of atmospheric CO_2 based on the CO_2 flux at the sea-air interface, the combined effects of the riverine input in the area, oceanic input, depositional export,and microbial carbon pump(DOC conversion and output) indicate that the China Seas represent an important carbon storage area.

Interdecadal variability in the tropical Indian Ocean and its dynamic explanation

Interdecadal variability in the tropical Indian Ocean has been analyzed based on the long-term climatic observational data. Case study showed that strong interannual signals formed at the surface can penetrate the depth of seasonal thermocline, where the anomalies last a couple of years. Artificial time series based on damping with exponential decay of selected strong events agree well with the detected interdecadal variability in the tropical Indian Ocean.

Hydrographic field investigations in the Northern South China Sea by open cruises during 2004-2013

In the past 10 years （2004-2013）, annual open cruise during late summer provided new opportunities for comprehensive studies in the Northern South China Sea （NSCS）. The 10-year field investigation program was carried out by the South China Sea Institute of Oceanology, Chinese Academy of Sciences （SCSIO, CAS）. Measurements inclu- ded water mass property, ocean circulation, atmospheric structure, and chemical and biological elements. The observation data collected during these open cruises have been intensively used in the studies of marine oceanographic, meteorological, chemical, and biological processes in the NSCS. In this study, comprehensive assessment of data application in oceanographic and meteorological studies is provided： （1） the property and variability of water masses in different layers; （2） the distribution of main currents and three-dimensional structure of mesoscale eddies; and （3） atmospheric structure and its feedback to the ocean. With the continuance of open cruises, it is feasible to construct high- quality, gridded climatological marine meteorological datasets in the NSCS in the near future.