Buoyant Plume Research Articles

Mixed convection around two vertically aligned horizontal cylinders: A numerical, experimental, and modeling investigation on the effect of local conditions on heat transfer

Experimental and numerical studies were performed to assess the effects of buoyancy driven flows from lower cylinders in a tube array on the heat transfer of higher-elevation cylinders. First, PIV and LIF experiments were performed for a single 13.4 mm diameter cylinder submerged in water at atmospheric conditions to measure velocity and temperature fields. Then the effect of buoyancy from a lower heater was studied by arranging two horizontal cylinders at different vertical displacements from each other (P/D = 1.5, 2.15, 6.45). Wall temperatures were measured as a function of pitch and power. CFD analysis was performed for the same configurations using an LES model. Using a combination of CFD and experimental measurements, mechanistic models for velocity and temperature behaviour in the plume were developed. These models are used to determine the impact of buoyant plumes from cylinders at lower elevations on heat transfer from heated cylinders at higher elevations. Since the plumes from cylinders at lower elevation are imposed on the natural convection from higher-elevation cylinders there is a combined effect from the momentum and temperature of the lower plume as it interacts with the natural convection phenomena from the upper-elevation heater. A model to predict the NuD of the upper cylinder in the case of horizontal vertically aligned pair of tubes was developed based on superposition of the convection caused by the lower cylinder and the natural convection from the higher-elevation cylinder. This model was found to predict the cylinder NuD with an RMS error of 2.8 and an absolute deviation of 2.31 as compared to the experimental data obtained in this study. It was also found to agree well with independent data available in literature.

Palynological analysis of sandy hyperpycnal deposits of the Middle Jurassic, Lajas Formation, Neuquén Basin, Argentina

The basal succession of the Lajas Formation at Trasandino section, Arroyo Covunco area, constitutes an excellent example of proximal prodelta facies cut by sediment-waves formed during a complete acceleration-deceleration hyperpycnal discharge cycle. The main outcome of this contribution was to present a new studied locality in which the Lajas Formation outcrops. Nine mudstones and fine-grained heterolites levels deposited during the waning stage, were sampled to palynological analysis. The recovered assemblages are dominated by sporomorphs, which are characterized by a great diversity of the trilete spores. Among them, is interesting to highlight the first mention of Manumia variverrucata and the extension of the last occurrence of Striatella seebergensis until to Callovian in Argentina. Based on selected key taxa a Late Bathonian–Callovian age is proposed for the Lajas Formation at the Trasandino section in this area. The Trasandino section spore assemblages show the greatest similarity with the Arroyo Covunco section spore associations when they are compared with the Lajas Formation of other studied localities. The endemic development of certain types of bryophyte (sensu lato) spores, e.g. Taurocusporites quattrocchiensis, was favored by locally humid conditions inferred at the Arroyo Covunco area. Large abundance of phytoclasts, sporomorphs and fresh-water algae characterize the recovered organic matter suggesting a high input of continental organic particles to the basin, as the result of fluvial-derived density discharges. Three palynofacies type (PT) had been identified which allow to evaluate the hydrodynamic characteristics of the flow, taking into account the differential buoyancy of the opaque particles. The large amount of equidimensional opaque particles recognized at the PT-B, characterizes the beginning of the deceleration phase of the flow and the abundance of blade-shape opaque particles, identified in the PT-A, point out a deposition from the final buoyant plume of hyperpycnal flow. The PT-C shows transitional features between these two conditions.

Characteristic Depths, Fluxes, and Timescales for Greenland's Tidewater Glacier Fjords From Subglacial Discharge‐Driven Upwelling During Summer

AbstractGreenland's glacial fjords are a key bottleneck in the earth system, regulating exchange of heat, freshwater and nutrients between the ice sheet and ocean and hosting societally important fisheries. We combine recent bathymetric, atmospheric, and oceanographic data with a buoyant plume model to show that summer subglacial discharge from 136 tidewater glaciers, amounting to 0.02 Sv of freshwater, drives 0.6–1.6 Sv of upwelling. Bathymetric analysis suggests that this is sufficient to renew most major fjords within a single summer, and that these fjords provide a path to the continental shelf that is deeper than 200 m for two‐thirds of the glaciers. Our study provides a first pan‐Greenland inventory of tidewater glacier fjords and quantifies regional and ice sheet‐wide upwelling fluxes. This analysis provides important context for site‐specific studies and is a step toward implementing fjord‐scale heat, freshwater and nutrient fluxes in large‐scale ice sheet and climate models.

Differential Behavior of Metal Sulfides in Hydrothermal Plumes and Diffuse Flows

Extensive sampling of high-temperature hydrothermal fluids and diffuse flows within <2 m of the vent orifices at the 9°50′N East Pacific Rise (EPR) hydrothermal vent field reveals formation of nanoparticulate phases and rapid precipitation/aggregation of metal sulfide minerals upon mixing of vent fluid with ambient seawater. Here, we characterize metal sulfide phases via scanning and transmission electron microscopy (SEM, TEM) in addition to quantifying the concentrations of major and trace metals in filtered and unfiltered fluid samples. Analyses demonstrate that, despite coprecipitation in phases such as chalcopyrite, iron speciation and transport is decoupled from that of copper and zinc. We observe the formation of ∼10–500 nm diameter (nano)particulate Zn and Cu sulfide phases that are near-quantitatively removed by filtration. Iron sulfides, conversely, are typically present in SEM images as larger particles up to tens of microns in diameter. Few small nanoparticles (20–100 nm diameter) are captured on the filter, but determination of nitric-acid-soluble iron in 0.2 μm filtered samples indicates the presence of pyrite nanoparticles. Physical mixing and temperature play a larger role in determining the extent of nanoparticulate pyrite formation than fluid chemistry. In diffuse flow environments, Fe and Cu more commonly co-occur as aggregates of very small crystallites, with the Zn sulfide phases occurring separately. Sample pH and the ZPC (zero point of charge) of metal sulfides exhibit chemical control on nanoparticle and large particle formation versus aggregation. The concentrations of the additional trace metals analyzed vary between vent sites, despite the short distances between the sites and likely similar magmatic sources. Measured trace metal concentrations highlight the importance of diffuse flow systems in hydrothermal metal emissions. These near-vent behavioral differences have implications for the long-distance transport of metals away from vent fields in buoyant and nonbuoyant plumes.

A dual-mesh hybrid Reynolds-averaged Navier-Stokes/Large eddy simulation study of the buoyant flow between coaxial cylinders

This study is concerned with the investigation of the suitability of the dual-mesh method for the buoyancy driven flow inside a cylindrical annulus with one internal cylinder. This flow situation can occur, for instance, in gas cooled nuclear reactors and is characterized by complex features, including a buoyant plume and a negatively buoyant wall-jet. The buoyancy forces in this flow are generated by the temperature difference between the inner and outer cylinders. The dual-mesh approach is a hybrid RANS-LES method in which an unsteady Reynolds-averaged Navier-Stokes (RANS) simulation and a coarse Large eddy simulation (i.e. an LES that is under-resolved near walls) are run simultaneously on two different grids. In this approach, a criterion is used to determine the locations at which each simulation is expected to perform better than the other. Consequently, at every location the less accurate simulation is forced and corrected towards the more accurate one. This correction is done using source terms that are included in the equations of the flow and thermal fields of the two simultaneous simulations. It is observed that the buoyancy-extended lengthscale resolution criterion behaves satisfactorily in defining the regions where the LES is corrected towards the RANS and vice versa. Moreover, both quantitative and qualitative analyses of the results are conducted using quasi direct numerical simulation results from the literature. It is shown that the dual-mesh method has the potential to yield results that are better than the results of the pure RANS and the pure coarse LES simulations.

Influence of Depositional and Diagenetic Processes on Caprock Properties of CO2 Storage Sites in the Northern North Sea, Offshore Norway

Characterization of caprock shale is critical in CO2 storage site evaluation because the caprock shale acts as a barrier for the injected buoyant CO2 plume. The properties of shales are complex and influenced by various processes; hence, it is challenging to evaluate the caprock quality. An integrated approach is therefore necessary for assessing seal integrity. In this study, we investigated the caprock properties of the Lower Jurassic Drake Formation shales from the proposed CO2 storage site Aurora (the Longship/Northern Lights CCS project), located in the Horda Platform area, offshore Norway. Wireline logs from 50 exploration wells, various 2D seismic lines, and two 3D seismic cubes were used to investigate the variations of the caprock properties. The Drake Formation was subdivided into upper and lower Drake units based on the lithological variations observed. Exhumation and thermal gradient influencing the caprock properties were also analyzed. Moreover, rock physics diagnostics were carried out, and caprock property maps were generated using the average log values to characterize the Drake Formation shales. In addiiton, pre-stack seismic-inverted properties and post-stack seismic attributes were assessed and compared to the wireline log-based analysis. The sediment source controlled at 61° N significantly influenced the depositional environment of the studied area, which later influenced the diagenetic processes and had various caprock properties. The upper and lower Drake units represent similar geomechanical properties in the Aurora area, irrespective of significant lithological variations. The Drake Formation caprock shale near the injection site shows less-ductile to less-brittle brittleness values. Based on the caprock thickness and shaliness in the Aurora injection site, Drake Formation shale might act as an effective top seal. However, the effect of injection-induced pressure changes on caprock integrity needs to be evaluated.

Compositions of dissolved organic matter in the ice-covered waters above the Aurora hydrothermal vent system, Gakkel Ridge, Arctic Ocean

Abstract. Hydrothermal vents modify and displace subsurface dissolved organic matter (DOM) into the ocean. Once in the ocean, this DOM is transported together with elements, particles, dissolved gases and biomass along with the neutrally buoyant plume layer. Considering the number and extent of actively venting hydrothermal sites in the oceans, their contribution to the oceanic DOM pool may be substantial. Here, we investigate the dynamics of DOM in relation to hydrothermal venting and related processes at the as yet unexplored Aurora hydrothermal vent field within the ultraslow-spreading Gakkel Ridge in the Arctic Ocean at 82.9∘ N. We examined the vertical distribution of DOM composition from sea ice to deep waters at six hydrocast stations distal to the active vent and its neutrally buoyant plume layer. In comparison to background seawater, we found that the DOM in waters directly affected by the hydrothermal plume was molecularly less diverse and 5 %–10 % lower in number of molecular formulas associated with the molecular categories related to lipid and protein-like compounds. On the other hand, samples that were not directly affected by the plume were chemically more diverse and had a higher percentage of chemical formulas associated with the carbohydrate-like category. Our results suggest that hydrothermal processes at Aurora may influence the DOM distribution in the bathypelagic ocean by spreading more thermally and/or chemically induced compositions, while DOM compositions in epipelagic and mesopelagic layers are mainly governed by the microbial carbon pump dynamics and surface-ocean–sea-ice interactions.

Trait phenology and fire seasonality co-drive seasonal variation in fire effects on tree crowns.

The plume of hot gases rising above a wildfire can heat and kill the buds in tree crowns. This can reduce leaf area and rates of photosynthesis, growth, and reproduction, and may ultimately lead to mortality. These effects vary seasonally, but the mechanisms governing this seasonality are not well understood. A trait-based physical model combining buoyant plume and energy budget theories shows the seasonality of bud necrosis height may originate from temporal variation in climate, fire behaviour, and/or bud functional traits. To assess the relative importance of these drivers, we parameterized the model with time-series data for air temperature, fireline intensity, and bud traits from Pinus contorta, Picea glauca, and Populus tremuloides. Air temperature, fireline intensity, and bud traits all varied significantly through time, causing significant seasonal variation in predicted necrosis height. Bud traits and fireline intensity explained almost all the variation in necrosis height, with air temperature explaining relatively minor amounts of variation. The seasonality of fire effects on tree crowns appears to originate from seasonal variation in functional traits and fire behaviour. Our approach and results provide needed insight into the physical mechanisms linking environmental variation to plant performance via functional traits.

Export of Ice Sheet Meltwater from Upernavik Fjord, West Greenland

Abstract Meltwater from Greenland is an important freshwater source for the North Atlantic Ocean, released into the ocean at the head of fjords in the form of runoff, submarine melt, and icebergs. The meltwater release gives rise to complex in-fjord transformations that result in its dilution through mixing with other water masses. The transformed waters, which contain the meltwater, are exported from the fjords as a new water mass Glacially Modified Water (GMW). Here we use summer hydrographic data collected from 2013 to 2019 in Upernavik, a major glacial fjord in northwest Greenland, to describe the water masses that flow into the fjord from the shelf and the exported GMWs. Using an optimum multi-parameter technique across multiple years we then show that GMW is composed of 57.8% ± 8.1% Atlantic Water (AW), 41.0% ± 8.3% Polar Water (PW), 1.0% ± 0.1% subglacial discharge, and 0.2% ± 0.2% submarine meltwater. We show that the GMW fractional composition cannot be described by buoyant plume theory alone since it includes lateral mixing within the upper layers of the fjord not accounted for by buoyant plume dynamics. Consistent with its composition, we find that changes in GMW properties reflect changes in the AW and PW source waters. Using the obtained dilution ratios, this study suggests that the exchange across the fjord mouth during summer is on the order of 50 mSv (1 Sv ≡ 106 m3 s−1) (compared to a freshwater input of 0.5 mSv). This study provides a first-order parameterization for the exchange at the mouth of glacial fjords for large-scale ocean models.

Geological storage of CO2 and acid gases dissolved at surface in production water

During geological CO2 storage traditionally CO2 is injected subsurface into a high permeability reservoir capped by a low permeability seal to trap the buoyant supercritical plume. Wastewater from oil and gas production is also currently disposed of by subsurface injection into suitable reservoirs, most notably in the USA and Canada. Injection of CO2 dissolved in water may both increase storage security by reducing vertical migration and enhancing dissolution and mineral trapping. There is potential for surface dissolution of CO2 into wastewater that is already being stored subsurface. CO2-water-rock reactions in different sandstone or limestone reservoir rocks with either saline coal production water or low salinity water were geochemically modelled. The geochemical potential for mineral trapping of CO2, and associated changes to pH for potential reservoirs is compared. For a mineralogically clean quartz-rich saline sandstone reservoir only 0.18 and 0.20 kg/m3 CO2 was mineral trapped as ankerite and calcite over 30 or 1000 years. Feldspars, clays and carbonate minerals were converted to kaolinite, calcite, ankerite and smectites, as pH increased to 5.65. The specific silicate minerals present controlled mineral trapping potential e.g. with an Fe-rich chlorite present rather than a clinochlore chlorite 6.3 and 6.8 kg/m3 CO2 was trapped at 30 and 1000 years respectively as siderite and ankerite. Dissolution trapping dominated in the low salinity or limestone reservoirs with minor mineral trapping. The presence of small amounts of SO2 or H2S in the CO2 stream resulted in dissolved S sequestered as elemental S, pyrite, barite, and anhydrite. The effects of low CO2 content or potential reservoir cooling induced by injection fluids were also investigated. The low pH of the injection fluid could potentially corrode legacy wellbores, one solution is a form of amendment such as liming to neutralise pH.

Experiment and Simulation of One Deep Sewage Discharge Type: Transport of Low‐Salinity Sediment‐Laden Flow Discharged

AbstractDeep sewage discharge leads to inestimable damage to the ambient water (lakes, oceans and reservoirs), which has caused widespread social concern. In the current paper, a three‐dimensional (3D) buoyancy plume model for deep sewage discharge was developed. It simulates sediment‐laden flow with the effects of temperature and salinity differences. Taking the turbulent diffusion coefficient of salinity (αsal) as the calibration parameter, a comparison between the RNG k‐ε and the standard k‐ε models was performed. The proposed model was verified well and agreement with experiment, which proved that the RNG model with the αsal value of 0.4 was the optimal calibration. Then the model was applied to quantify the behavior of the buoyant plume in the ambient fluid (salt water) with respect to different contours of turbulent kinetic energy (k), temperature, salinity and sediment. The dimensionless centerline trajectory positions and boundary positions of them were determined. The results indicated that the discharge of low‐salinity sediment‐bearing water influenced the deep ambient water spatially, both near the free surface and in the vertical plane. Different diffusion and spreading shapes (butterfly, Ginkgo biloba, bean) can be observed on the surface. Accurately evaluating the impact of deep discharge on ambient water has great significance for maintaining healthy and sustainable environments in offshore areas, deep lakes and reservoirs.

Dynamics of deep-submarine volcanic eruptions

Deposits from explosive submarine eruptions have been found in the deep sea, 1–4 km below the surface, with both flow and fall deposits extending several km’s over the seafloor. A model of a turbulent fountain suggests that after rising 10–20 m above the vent, the erupting particle-laden mixture entrains and mixes with sufficient seawater that it becomes denser than seawater. The momentum of the resulting negatively buoyant fountain is only sufficient to carry the material 50–200 m above the seafloor and much of the solid material then collapses to the seafloor; this will not produce the far-reaching fall deposits observed on the seabed. However, new laboratory experiments show that particle sedimentation at the top of the fountain enables some of the hot, buoyant water in the fountain to separate from the collapsing flow and continue rising as a buoyant plume until it forms a radially spreading intrusion higher in the water column. With eruption rates of 10^6–10^7hbox {kg s}^{-1}, we estimate that this warm water may rise a few 100’s m above the fountain. Some of the finer grained pyroclasts can be carried upwards by this flow and as they spread out in the radial intrusion, they gradually sediment to form a fall deposit which may extend 1000’s m from the source. Meanwhile, material collapsing from the dense fountain forms aqueous pyroclastic flows which may also spread 1000’s m from the vent forming a flow deposit on the seabed. Quantification of the controls on the concurrent fall and flow deposits, and comparison with field observations, including from the 2012 eruption of Havre Volcano in the South Pacific, open the way to new understanding of submarine eruptions.

River Plume Rooted on the Sea-Floor: Seasonal and Spring-Neap Variability of the Pearl River Plume Front

The buoyant river plume front exhibits substantial variability in the sea surface under energetic external forcing. Although highly dynamic, the river plume is often “rooted” at specific locations through the bottom river plume front. In this study, we addressed this mechanism using the Pearl River plume as an example based on a well-validated numerical model. With this model, we described the spatiotemporal characteristics of the Pearl River salinity front. It was found that, although the surface Pearl River plume features bimodal extension in summer and winter seasons, owing to the reversal of the seasonal monsoon wind, there is a relatively stable bottom front extending from the river mouth to the downstream region (i.e., in the direction of propagation of Kelvin Wave). The occurrence probability of the bottom front showed that the front location varies only slightly and fixes at ∼8-m isobath. The Empirical Orthogonal Function (EOF) analysis demonstrated that runoff, wind, and tide are major regulating factors. These three factors jointly control the strength and position of the bottom front. In particular, the bottom front moves offshore during the spring tide but onshore during the neap tide, respectively, indicating a different mechanism from the classic frontal trapping theory. The sensitivity experiment without tide indicated that the bottom plume front shrinks significantly, and the river plume becomes more dynamic since it is no longer rooted on the seafloor.

Effect of tunnel slope on the critical velocity of densimetric plumes and fire plumes in ventilated tunnels

To control the harmful releases in a tunnel, a longitudinal ventilation flow has to be imposed. The concept of critical velocity has been the focus of numerous tunnel fire studies, with researches focus on horizontal tunnels and tunnels with inclination have received much less attention. Due to the stack effect, smoke movement in inclined tunnels (with inclination angle θ) is different from that in horizontal tunnels and the critical velocity can be affected. In this study, we tackle the problem of critical velocity theoretically, experimentally and numerically. The theoretical model relies on a top-hat plume impinging on the ceiling, and predicts a dependence, in case of buoyancy-driven releases, of the form Vc/Vc0=1+Cksinθ. Experiments are performed in a reduced scale tunnel, inclined from -5° to +5°, and using light gas mixture (air/helium) to simulate the presence of light smokes. Numerical simulations are performed using FDS (Fire Dynamics Simulator) with hot-air plume and propane fire. Experimental results show that the dynamical condition at the source affects the critical velocity: when the buoyant plume is momentum-driven, the influence of slope is small; when the buoyant plume is buoyancy-driven, the influence of slope is large. This feature is conveniently reproduced by the analytical model adopting Ck=2.1. Similar influence of Γi has been observed in the hot-air plume simulation with that in the experiment. Finally, in the numerical simulation of propane fire, results show that the influence of the slope on the ratio Vc/Vc0 is not affected by the heat release rate.

Observations and Modeling of a Buoyant Plume Exiting Into a Tidal Cross‐Flow and Exhibiting Along‐Front Instabilities

AbstractAerial image sequences of an ebbing river plume propagating into a tidal cross‐flow demonstrate the presence of along‐front instabilities at multiple scales, which appear to propagate along‐front in the direction of the shear flow. We hypothesize the instabilities are due to cross‐front shear in the along‐front velocity field. Image analysis quantifies the horizontal shear across the plume front as well as the length scales and propagation speeds of the instabilities. In situ measurements from cross‐front ship transects are also used to examine shear and the width of the shear layer. A non‐hydrostatic numerical simulation of an ebb plume in an idealized tidal cross‐flow was conducted using comparable flow parameters and confirms the presence of shear instabilities. An additional numerical simulation without a tidal‐cross flow demonstrates that shear instabilities are not present; rather, lobe‐and‐cleft structures on the nose of the gravity current emerge. According to the scaling of White and Helfrich (2013), utilizing both the observed and modeled parameters, it is shown that shear instabilities are likely in the observed and modeled cross‐flow scenario, and confirms that they are unlikely to emerge in the no cross‐flow model case.

Meltwater drainage and iceberg calving observed in high-spatiotemporal resolution at Helheim Glacier, Greenland

AbstractMarine-terminating glaciers lose mass through melting and iceberg calving, and we find that meltwater drainage systems influence calving timing at Helheim Glacier, a tidewater glacier in East Greenland. Meltwater feeds a buoyant subglacial discharge plume at the terminus of Helheim Glacier, which rises along the glacial front and surfaces through the mélange. Here, we use high-resolution satellite and time-lapse imagery to observe the surface expression of this meltwater plume and how plume timing and location compare with that of calving and supraglacial meltwater pooling from 2011 to 2019. The plume consistently appeared at the central terminus even as the glacier advanced and retreated, fed by a well-established channelized drainage system with connections to supraglacial water. All full-thickness calving episodes, both tabular and non-tabular, were separated from the surfacing plume by either time or by space. We hypothesize that variability in subglacial hydrology and basal coupling drive this inverse relationship between subglacial discharge plumes and full-thickness calving. Surfacing plumes likely indicate a low-pressure subglacial drainage system and grounded terminus, while full-thickness calving occurrence reflects a terminus at or close to flotation. Our records of plume appearance and full-thickness calving therefore represent proxies for the grounding state of Helheim Glacier through time.

A modeling study of water and sediment flux partitioning through the major passes of Mississippi Birdfoot Delta and their plume structures

The Mississippi River Delta consists of six major passes and numerous small crevasses through which water and sediments are transported to the continental shelf of northern Gulf of Mexico. The water and sediment fluxes through individual passes are not routinely monitored due to the complex morphology and challenging environment. However, they are critical factors in determining the highly nonlinear near-field characteristics of freshwater plumes, fronts, possible internal hydraulic jumps, nutrient dispersal and rapid initial deposition of fine sand and mud. The flux partitioning and flow/sediment dispersal characteristics near the modern Mississippi River Delta were investigated using a high-resolution (~ 100 m horizontally) unstructured-grid, three-dimensional coupled hydrodynamic-wave-sediment numerical model. Model result analysis for the period of April–June 2010 revealed that Southwest Pass is the main conduit among the six major passes, through which 64% and 32% of the Mississippi River water and sediment, respectively, are transported to the coastal ocean. In contrast, South Pass has the lowest water and sediment fluxes among the tri-furcation channels downstream of the Head of Passes. Due to the more energetic flow at Southwest Pass compared to other passes, an elongated freshwater/sediment jet is typically present in the near-field. The average width of the plume originating from Southwest Pass, 5 km away from the mouth, is approximately 8 km, while the high sediment concentration within the plume (SSC > 10−2 kg/m3) is maintained in the upper 4 m of the water column for more than 8 km. The pattern of the plume in the far-field varies with wind direction, and the buoyant plume bends towards the coast/mid-shelf in response to downwelling/upwelling favorable winds.

Effect of rotation on buoyant plume dynamics

Effect of rotation on buoyant plume dynamics

Impact of Flash Flood Events on the Coastal Waters Around Madeira Island: The “Land Mass Effect”

The Island Mass Effect has been primarily attributed to nutrient enhancement of waters surrounding oceanic islands due to physical processes, whereas the role of land runoff has seldom been considered. Land runoff can be particularly relevant in mountainous islands, highly susceptible to torrential rainfall that rapidly leads to flash floods. Madeira Island, located in the Northeast Atlantic Ocean, is historically known for its flash flood events, when steep streams transport high volumes of water and terrigenous material downstream. A 22-year analysis of satellite data revealed that a recent catastrophic flash flood (20 February 2010) was responsible for the most significant concentration of non-algal Suspended Particulate Matter (SPM) and Chlorophyll-a at the coast. In this context, our study aims to understand the impact of the February 2010 flash flood events on coastal waters, by assessing the impact of spatial and temporal variability of wind, precipitation, and river discharges. Two specific flash floods events are investigated in detail (2 and 20 February 2010), which coincided with northeasterly and southwesterly winds, respectively. Given the lack of in situ data documenting these events, a coupled air-sea-land numerical framework was used, including hydrological modeling. The dynamics of the modeled river plumes induced by flash floods were strongly influenced by the wind regimes subsequently affecting coastal circulation, which may help to explain the differences between observed SPM and Chlorophyll-a distributions. Model simulations showed that during northeasterly winds, coastal confinement of the buoyant river plume persisted on the island’s north coast, preventing offshore transport of SPM. This mechanism may have contributed to favorable conditions for phytoplankton growth, as captured by satellite-derived Chlorophyll-a in the northeastern coastal waters. On the island’s south coast, strong ocean currents generated in the eastern island flank promoted strong vertical shear, contributing to vertical mixing. During southwesterly winds, coastal confinement of the plume with strong vertical density gradient was observed on the south side. The switch to eastward winds spread the south river plume offshore, forming a filament of high Chlorophyll-a extending 70 km offshore. Our framework demonstrates a novel methodology to investigate ocean productivity around remote islands with sparse or absent field observations.

Review on buoyancy-driven natural ventilation in an enclosure with various types of heat sources

This paper reviews indoor heat convection and buoyancy-driven natural ventilation in enclosed space with heat sources in different forms such as point, line, plane, volume or combination of them. The indoor thermal flow is driven by these heat sources and accumulated in the enclosure. Thermal plume evolves based on its dynamic law above heat sources and is conversely affected by the thermal environment and geometric structure. Therefore, the dynamic of thermal-driven flows and the restriction by the thermal environment and geometric framework are both of interest in the field of indoor heat convection and buoyancy-driven natural ventilation. Based on this fact, the indoor thermal convection can be divided into two basic components which are buoyant plume above the heat source and indoor thermal stratification flow. Research and analysis on these laws and restriction are of significance in not only the advances in building thermal environment technology but also further cognition and effective solutions for current engineering practice.