Plume Layer Research Articles

High‐Resolution Simulations of the Plume Dynamics in an Idealized 79°N Glacier Cavity Using Adaptive Vertical Coordinates

AbstractFor better projections of sea level rise, two things are needed: an improved understanding of the contributing processes and their accurate representation in climate models. A major process is basal melting of ice shelves and glacier tongues by the ocean, which reduces ice sheet stability and increases ice discharge into the ocean. We study marine melting of Greenland's largest floating ice tongue, the 79° North Glacier, using a high‐resolution, 2D‐vertical ocean model. While our fjord model is idealized, the results agree with observations of melt rate and overturning strength. Our setup is the first application of adaptive vertical coordinates to an ice cavity. Their stratification‐zooming allows a vertical resolution finer than 1 m in the entrainment layer of the meltwater plume, which is important for the plume development. We find that the plume development is dominated by entrainment only initially. In the stratified upper part of the cavity, the subglacial plume shows continuous detrainment. It reaches neutral buoyancy near 100 m depth, detaches from the ice, and transports meltwater out of the fjord. Melting almost stops there. In a sensitivity study, we show that the detachment depth depends primarily on stratification. Our results contribute to the understanding of ice–ocean interactions in glacier cavities. Furthermore, we suggest that our modeling approach with stratification‐zooming coordinates will improve the representation of these interactions in global ocean models. Finally, our idealized model topography and forcing are close to a real fjord and completely defined analytically, making the setup an interesting reference case for future model developments.

Genome-resolved metagenomic analysis of Great Amazon Reef System sponge-associated Latescibacterota bacteria and their potential contributions to the host sponge and reef

The Great Amazon Reef System (GARS) is an extensive biogenic reef influenced by a plume layer of sediments. This creates an extreme environment where light is reduced, thus affecting physicochemical properties as well as living organisms such as sponges and their microbiomes. The sponge’s microbiome has numerous ecological roles, like participation in biogeochemical cycles and host nutrition, helping the sponge thrive and contributing to the ecosystem. Also, sponges and sponge-associated microorganisms are rich sources of bioactive compounds, and their products are applied in different areas, including textile, pharmaceutical, and food industries. In this context, metagenome-assembled genomes (MAG), obtained from GARS sponges microbiota, were analyzed to predict their ecological function and were prospected for biotechnological features. Thus, in this work, tissues of GARS sponges were collected, their metagenomes were sequenced and assembled, and 1,054 MAGs were recovered. Ten of those MAGs were selected based on their taxonomic classification in the candidate phylum Latescibacterota and this group’s abundance in GARS sponges. The workflow consisted of MAG’s quality definition, taxonomic classification, metabolic reconstruction, and search for bioactive compounds. Metabolic reconstruction from medium to high-quality MAGs revealed genes related to degradation and synthesis pathways, indicating functions that may be performed by GARS sponge-associated Latescibacterota. Heterotrophy, a recurring attribute in Latescibacterota that might be crucial for GARS sponge holobiont nutrition, was verified by the presence of genes related to respiration and fermentation. Also, the analyzed bacteria may contribute to the host’s survival in multiple ways, including host protection via defense systems; aid in nutrient consumption by breaking complex substrates and producing essential nutrients like vitamins and certain amino acids; and detoxification of mercury, arsenic, ammonia, and hydrogen sulfide. Additionally, genes linked to persistent organic pollutant degradation, including glyphosate, and biogeochemical cycles reactions, such as ammonification, sulfate reduction, thiosulfate disproportionation, phosphorus remineralization, and complex organic matter degradation, were identified, suggesting the participation of these Latescibacterota in bioremediation and nutrient cycling. Finally, the investigated MAGs contain genes for numerous bioactive compounds, including industrial enzymes, secondary metabolites, and biologically active peptides, which may have biotechnological value.

Ice Shelf Basal Melt Sensitivity to Tide‐Induced Mixing Based on the Theory of Subglacial Plumes

AbstractTidal currents are known to influence basal melting of Antarctic ice shelves through two types of mechanisms: local processes taking place within the boundary current adjacent to the ice shelf‐ocean interface and far‐field processes influencing the properties of water masses within the cavity. The separate effects of these processes are poorly understood, limiting our ability to parameterize tide‐driven ice shelf‐ocean interactions. Here we focus on the small‐scale processes within the boundary current. We apply a one‐dimensional plume model to a range of ice base geometries characteristic of Antarctic ice shelves to study the sensitivity of basal melt rates to different representations of tide‐driven turbulent mixing processes. Our simulations demonstrate that tides can either increase or decrease melt rates depending on the approach chosen to parameterize entrainment of ambient water into the turbulent plume layer, a process not yet well constrained by observations. A theoretical assessment based on an analogy with tidal bottom boundary layers suggests that tide‐driven shear at the ice shelf‐ocean interface enhances mixing through the pycnocline. Under this assumption our simulations predict a tide‐induced increase in melt and freeze rates along the base of the ice shelf, with the strongest plume path‐integrated effects for cold cavities (up to +400% in the realistic set up). An approximation is provided to account for this response in basal melt rate parameterizations that neglect the effect of tide‐induced turbulent mixing.

Characteristics of Unorganized Hydrogen Sulfide Dispersion for Industrial Building Layout Optimization

Hydrogen sulfide (H2S) is the main toxic pollutant emitted to the atmosphere from auto-coating wastewater. Its unorganized dispersion poses a health challenge for workers. Defining safe working distance, which transfers the H2S occupational exposure limit into industrial construction design regulation, would be a useful approach for reducing H2S exposure risk. Therefore, in this study, an H2S dispersion prediction, within 25 m, was performed by a computational fluid dynamics (CFD) method to explore the influence of temperature and wind speed on H2S dispersion. With the temperature changes from 288 K to 303 K, the H2S concentration at different observing points decreased. With wind speed changes from 2 m/s to 20 m/s, the plume layer structure was studied in the whole process. According to the H2S distribution characteristics, when the sedimentation tank treatment capacity is less than or equal to 10 m3/h, the safe working distance of H2S unorganized dispersion is 10 m. Hence, when there are workplaces within 10 m of the tank, closed measures should be taken for the sedimentation tank, or the manufacturer layout should be optimized to protect the environment and human health.

Large Eddy Simulation of Inclined Negatively Buoyant Jets with Sloped Beds

The effluents produced by reverse osmosis desalination plants are usually disposed under the surface of the sea as inclined negatively buoyant jets (INBJ), to achieve the highest mixing rate. Bed slope in the local environment is one of the contributing factors in the behavior of INBJs. The aim of the present study is to utilize large eddy simulation (LES) to study the effects of the bed slope on the dilution and spreading of INBJs with 30°, 45°, and 60° nozzle angles. In this regard, five down slopes, 0°, 5°, 10°, 15°, and 20° were considered for the bed, and the mixing and geometrical properties of INBJs were studied in both jet plume and spreading layer regions. Present simulations show that the increase in the bed slope for all the three nozzle angles favorably increases the dilution of the INBJs at return point, concentration buildup point (CBP), impact point, and on the bed. For a 20° increase in the bed slope, the relative increase in the dilution at CBP of 30°, 45°, and 60° INBJs is calculated as 167.75%, 81.13%, and 107.43%, respectively. Also, the centerline dilution is the highest for the 60° nozzle angle at each bed inclination. The distribution of the mean concentration on the bed shows that an increase in the nozzle and bed inclination results in a significant decrease in the mean concentration and the area in which the effluent alters the ambient water quality. Present results suggest that the INBJs should be discharged into the ambient water in sloped environments, and the nozzle angle of 60° is preferred to 30° and 45° regardless of the bed inclination.

Volatile‐Rich Hydrothermal Plumes Over the Southern Central Indian Ridge, 24°49’S: Evidence for a New Hydrothermal Field Hosted by Ultramafic Rocks

AbstractWater column physico‐chemical studies were conducted over the southern Central Indian Ridge between 24°44’S and 25°52’S to identify and chemically characterize seafloor hydrothermal activity. High turbidity values were observed between 2300 and 2700 m with two distinct layers, between water depths of 2320–2500 m and 2510–2650 m, at two closely spaced CTD stations at 24°48.62’S (CTD‐17‐P5) and 24°48.68’S (CTD‐17‐P8). Elevated concentrations of dissolved Mn (DMn: 19–112 nM), dissolved Fe (DFe: 33–88 nM), methane (CH4: 32–246 nM), elevated δ3He values (28%–88%), and stable carbon isotope ratios of CH4 confirm the hydrothermal origin. In plume layer‐1, the maximum concentrations were observed at 2375m at P8 and in plume layer‐2, the maximum concentrations were observed at 2570 m at P5. The stable isotope ratios of methane (δ13C‐CH4) show that heavier isotopes are enriched (−13.2‰ to −14.7‰) in the plume waters and are similar to vent fluids on the global mid‐oceanic ridges. Further, morphological and mineralogical studies of plume particles, collected from the plume layer‐2 maxima, clearly show the presence of barite, pyrite, chalcopyrite, and indicate possible venting of high‐temperature fluids in the vicinity of P5. Enrichment in methane relative to the other tracers and the general geochemical characteristics of these two plume layers, CH4/Mn (1.8–2.2); CH4/Δ3He (85–97 × 106), Mn/Δ3He (44–46 × 106), Fe/Δ3He (52–54 × 106), indicate that these plumes are formed from fluids released at the seafloor that circulated through ultramafic/gabbroic rocks. The high concentrations of dissolved gases and metals combined with the presence of sulfide particles in the water column provide evidence for a new ultramafic/gabbroic‐hosted hydrothermal vent field, at 24°49’S on the southern Central Indian Ridge.

Evolving Interior Mixing Regimes in a Tidal River Plume

AbstractMicrostructure profiling was utilized to estimate vertical mixing (via vertical turbulent buoyancy flux) during a tidal pulse in the interior Merrimack River plume in calm winds. Multiple stratified shear mixing regimes appear and evolve with time. Initially the plume acts as a nearfield jet, with mixing in the plume (plume layer mixing) and over the plume‐ambient interface (nearfield interfacial mixing). As the plume grows, interfacial mixing is suppressed offshore of the nearfield as currents slow, diminishing turbulent exchange between plume and shelf. At the end of ebb, ambient tidal currents reverse direction below plume, initiating another mode of internal, interfacial mixing (coined here as tidal interfacial mixing), allowing exchange between plume and ambient waters offshore. This work highlights previously unreported tidally modulated mixing within the near and midfield of a river plume.

Using a collision-radiation model with extended excitation rates to calculate the OH spectrum in the ultraviolet band

To improve the calculation accuracy of the ultraviolet (UV) nonequilibrium radiation spectrum in the plume and shock layer, an extended transition process collision-radiation model of hydroxyl (OH) is proposed. The transition processes for the vibrational level of the OH(A) state in the exchange reaction are extended, including both the fundamental band (Δν=1) and the universal band (Δν=2). Eight air components (N2, O2, H2, H2O, CO2, CO, H and O) are used instead of two components (N2 and O2) in the quenching and exchange reactions to make the extended model applicable to both a plume and shock layer. The accuracy of the extended model is verified by comparing the calculated number density for the OH(A) state of an Atlas III plume and the calculated spectral radiance of a BSUV-2 shock layer against experimental data. By comparing with the Atlas plume and error analysis, the results show that the calculated results of the extended C-R model are in better agreement with the experimental data than that of the original model. The accuracy of the developed spectral-line prediction model is higher than that the existing model, which is very important for research on target early warning, detection and recognition.

Plume Layer Influences the Amazon Reef Sponge Microbiome Primary Producers

Symbiont relationships between corals and photosynthetic microorganisms sustain coral reef existence. However, the Great Amazon Reef System (GARS) stays under a plume layer that attenuates the entry of light, and instead of corals, sponges are the major reef epifauna, for which little is known about the function of the associated microbiome. Here, we used genome-resolved metagenomics to investigate how the sponge microbiome supports its host and overcomes the reduced light availability, recovering 205 MAGs from Agelas and Geodia sponges with completeness >70% and contamination <10%. Beta diversity estimates based on the 16S rRNA genes indicated the microbiomes of Amazon and Caribbean sponges to be distinct (P<0.01), with heterotrophic lifestyles being prevalent in Amazon sponge microbiomes (P<0.05). Nevertheless, genes indicating the carbon fixation pathways 3-Hydroxypropionate/4-Hydroxybutyrate cycle, 3-Hydroxypropionate bicycle, Reductive Tricarboxylic Acid Cycle, and Calvin-Benson-Bassham cycle could be recovered in low abundance. The presence of Cyanobacteria, represented by both 16S rRNA analyses and low-quality MAGs indicated light incidence on the reef. The metabolic profile shows that the GARS sponge microbiome had genes for sulfate reduction, sulfur oxidation, nitric oxide reduction, ammonia oxidation, nitrate reduction, nitrite ammonification, nitrite oxidation, and nitrite reduction, indicating that the microbiome might play a role in detoxification of the holobiont. We conclude, that neither the plume-limited photosynthesis of the sponge microbiome nor the primary producers sustain the organic carbon input for the sponges, which likely live off plume-associated organic carbon and their heterotrophic microbiota.

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.

Connection Between a Subcontinental Plume and the Mid‐Lithospheric Discontinuity Leads to Fast and Intense Craton Lithospheric Thinning

AbstractRemoval and thinning of cratonic lithosphere is believed to have occurred under different tectonic settings, for example, near subduction zones and above mantle plumes. Subduction‐induced cratonic modification has been widely discussed; however, the mechanisms and dynamic processes of plume‐induced lithospheric removal remain elusive and require further systematic investigation. In this study, we use a series of 2‐D thermo‐mechanical models to explore the dynamics of the removal and thinning of cratonic lithosphere due to the interaction between a mantle plume and a weak mid‐lithosphere discontinuity (MLD) layer. Our modeling results suggest that the interaction between a mantle plume and weak MLD layer can lead to a large‐scale removal of the cratonic lithosphere once a connection between the hot upwelling and weak MLD layer is established. The presence of a vertical lithospheric weak zone and its closeness to the plume center play critical roles in creating a connection between the weak MLD and hot plume/asthenosphere. Furthermore, delamination of cratonic lithosphere is favored by a larger plume radius/volume, a higher plume temperature anomaly, and a lower viscosity of the MLD layer. A systematic comparison between subduction‐induced and plume‐induced lithospheric thinning patterns was also conducted. We summarize their significant differences on the origin and migration of melt generation, the water content in melts, and topographic evolution. The combination of numerical models and geological/geophysical observations indicates that mantle plume‐MLD interactions may have played a crucial role in lithospheric removal beneath the South Indian, South American, and North Siberian Cratons.

Mechanisms of Lateral Spreading in a Near-Field Buoyant River Plume Entering a Fjord

Observations collected from a fast-flowing buoyant river plume entering the head of Doubtful Sound, New Zealand, were analysed to examine the drivers of plume lateral spreading. The near-field plume is characterised by flow speeds of over 2 ms−1, and strong stratification (N2 > 0.1 s−2), resulting in enhanced shear which supports the elevated turbulence dissipation rates (ϵ > 10−3 W kg−1). Estimates of plume lateral spreading rates were derived from the trajectories of Lagrangian GPS surface drifters and from cross-plume hydrographic transects. Lateral spreading rates derived from the latter compared favourably with estimates derived from a control volume technique in a previous study. The lateral spreading of the plume was driven by a baroclinic pressure gradient toward the base of the plume. However, spreading rates were underestimated by the surface drifters. A convergence of near-surface flow from the barotropic pressure gradient concentrated the drifters within the plume core. The combination of enhanced internal turbulence stress and mixing at the base of the surface layer, and the presence of steep fjord sidewalls likely reduced the rate of lateral spreading relative to the theoretical spreading rate. The estimates of plume width from the observations provided evidence of scale-dependent dispersion which followed a 4/3 power law. Two theoretical models of dispersion, turbulence and shear flow dispersion, were examined to assess which was capable of representing the observed spreading. An analytical horizontal shear-flow dispersion model generated estimates of lateral dispersion that were consistent with the observed 4/3 law of dispersion. Therefore, horizontal shear dispersion appeared to be the dominant mechanism of dispersion, thus spreading, in the surface plume layer.

BTEX biodegradation is linked to bacterial community assembly patterns in contaminated groundwater ecosystem

The control of degrader populations and the stochasticity and certainty of the microbial community in contaminated groundwater are not well-understood. In this study, a long-term contaminated groundwater ecosystem was selected to investigate the impact of BTEX on microbial communities and how microbial communities respond to BTEX pollution. 16S rRNA gene sequencing and metagenomic sequencing provided insights on microbial community assemblage patterns and their role in BTEX cleaning. The operational taxonomy units (OTUs) in the contaminated groundwater ecosystem were clustered distinguishably between the Plume and the Deeper Zone (lower contaminated zone). βNTI analysis revealed that the assembly strategies of abundant and rare OTU subcommunities preferred deterministic processes. Redundancy Analysis (RDA) and mantel testing indicated that benzene, toluene, ethylbenzene, and xylenes (BTEX) strongly drove the abundant OTU subcommunity, while the rare OTU subcommunity was only weakly affected. Deltaproteobacteria, the most dominant degrading microorganism, contains the complete degradation genes in the plume layer. In summary, our finding revealed that BTEX was the major factor in shaping the microbial community structure, and functional bacteria contribute greatly to water cleaning. Investigating the pattern of microbial community assembly will provide insights into the ecological controls of contaminant degradation in groundwater.

An improved collision - radiation model of the OH spectrum in the ultraviolet band

In order to calculate the spectral radiation characteristics of OH(A2∑) molecules more accurately, an improved collision-radiation (C-R) model is proposed to determine the excited states OH(A) number density. The six-components air model (CO, CO2, H2, H2O, N2, and O2) instead of the two-components air model (N2 and O2) are used as other plume products in the excitation/de-excitation radiation reaction, and the rate of the four reactions are modified to improve the accuracy and applicability of the number density. Effects of temperature and other plume products on the number density of excited states are analyzed in the experiment, and the spectral radiation characteristics of OH(A) can be obtained by using this improved C-R model. Results of these calculations are then compared with other series of experimental data of exhaust plume and shock layer, the results show that both the original model and the improved model can be used to calculate the radiation characteristics in shock layer, however, due to the great error, the original model not apply to calculation of the OH(A) number density in exhaust plume, and the result of the improved model is in good agreement with the Atlas experimental data. As the vibrational-rotational level distribution number density has a close relationship with radiative spectral characteristics, a more focused OH(A) particle number density model will be more helpful to the hypersonic target detection and recognition.

Influence of reservoir-scale heterogeneities on the growth, evolution and migration of a CO2 plume at the Sleipner Field, Norwegian North Sea

New analysis of the baseline (pre-injection) seismic data at Sleipner has revealed large-scale, roughly north-trending, channelled ‘fairways’ at a range of stratigraphical levels in the Utsira Sand. The baseline data also reveal localised stratigraphical ‘point discontinuities’ within the reservoir, some of which show evidence of having provided vertical conduits for earlier natural gas flow. The repeat time-lapse seismic datasets, where finer details of reservoir geology are illuminated by the reflective CO2, show smaller-scale, north-trending and sometimes sinuous channels within the larger channel fairways. They also show a number of vertical CO2 pathways within the CO2 plume, corresponding to the point discontinuities seen on the baseline data.Reservoir flow models were set up with flow properties constrained only by the observed levels of CO2 accumulation in the reservoir and the arrival time of CO2 at the reservoir top just prior to the first repeat seismic survey in 1999. The initial model with laterally homogeneous sand units separated by thin semi-permeable mudstones achieved only a moderate match to the observed time-lapse seismic data. Subsequent flow models, progressively incorporating higher permeability vertical CO2 pathways through the mudstones and large-scale channel fairways within the reservoir sands, yielded a progressive and marked improvement in the history-match of key CO2 layers within the plume. Crucially, no layer-specific model calibration was employed to achieve this improvement.New geophysical measurements from Utsira Sand core have recently become available. These measurements provide important constraints on rock physics models of CO2 and brine mixtures in the Utsira Sand. An empirical Brie fluid mixing law for intermediate fluid saturations provides a good fit to the new laboratory data, allowing measurements of CO2 saturation to be converted into seismic velocity. This rock physics model was used to convert CO2 saturation distributions predicted by the most realistic reservoir model into a seismic velocity model of the CO2 plume. Synthetic seismic reflectivity profiles generated using this velocity model show a striking resemblance to the observed time-lapse seismic data, both in terms of plume layer reflectivity and also of time-shifts within and beneath the CO2 plume. This provides confidence in the fidelity of the preferred reservoir model solution.These results represent a significant breakthrough in the understanding and modelling of CO2 plume development at Sleipner. We emphasise that the improvements were brought about not by fine tuning reservoir properties to fit the observed time-lapse data, but simply by incorporating geological permeability features that can reasonably be inferred from the baseline seismic data.

Multi-Sensor Analysis of a Weak and Long-Lasting Volcanic Plume Emission

Volcanic emissions are a well-known hazard that can have serious impacts on local populations and aviation operations. Whereas several remote sensing observations detect high-intensity explosive eruptions, few studies focus on low intensity and long-lasting volcanic emissions. In this work, we have managed to fully characterize those events by analyzing the volcanic plume produced on the last day of the 2018 Christmas eruption at Mt. Etna, in Italy. We combined data from a visible calibrated camera, a multi-wavelength elastic/Raman Lidar system, from SEVIRI (EUMETSAT-MSG) and MODIS (NASA-Terra/Aqua) satellites and, for the first time, data from an automatic sun-photometer of the aerosol robotic network (AERONET). Results show that the volcanic plume height, ranging between 4.5 and 6 km at the source, decreased by about 0.5 km after 25 km. Moreover, the volcanic plume was detectable by the satellites up to a distance of about 400 km and contained very fine particles with a mean effective radius of about 7 µm. In some time intervals, volcanic ash mass concentration values were around the aviation safety thresholds of 2 × 10−3 g m−3. Of note, Lidar observations show two main stratifications of about 0.25 km, which were not observed at the volcanic source. The presence of the double stratification could have important implications on satellite retrievals, which usually consider only one plume layer. This work gives new details on the main features of volcanic plumes produced during low intensity and long-lasting volcanic plume emissions.

The role of turbulence and internal waves in the structure and evolution of a near-field river plume

Abstract. An along-channel momentum budget is quantified in the near-field plume region of a controlled river flow entering Doubtful Sound, New Zealand. Observations include highly resolved density, velocity and turbulence, enabling a momentum budget to be constructed over a control volume. Estimates of internal stress (τ) were made from direct measurements of turbulence dissipation rates (ϵ) using vertical microstructure profiles. High flow speeds of the surface plume over 2 m s−1 and strong stratification (N2∼10-1 s−2) resulted in enhanced turbulence dissipation rates (ϵ>10-3 W kg−1) and internal stress (τ>10-2 m2 s−2) at the base of the surface layer. Internal waves were observed propagating along the base of the plume, potentially released subsequent to a hydraulic jump in the initial 1 km downstream of the plume discharge point. The momentum flux divergence of these internal waves suggests that almost 15 % of the total plume momentum can be transported out of the system by wave radiation, therefore playing a crucial role in the redistribution of momentum within the near-field plume. Observations illustrate that the evolution of the momentum budget components vary between the distinct surface plume layer and the turbulent, shear-stratified interfacial layer. Within the surface plume, a momentum balance was achieved. The dynamical balance demonstrates that the deceleration of the plume, driven by along-channel advection, is controlled by turbulence stress from the plume discharge point to as far as 3 km downstream. In the interfacial layer, however, the momentum equation was dominated by the turbulence stress term and the balance was not closed. The redistribution of momentum within the shear-stratified layer by internal wave radiation and other hydraulic features could account for the discrepancy in the budget.

Modeling the Dynamics of Small‐Scale River and Creek Plumes in Tidal Waters

AbstractThe fate of discharges from small rivers and mountainous streams are little studied relative to the dynamics of large river plumes. Flows from small watersheds are episodic, forming transient low‐salinity surface plumes that vary tidally due to interaction of outflow inertia with buoyancy and ambient tidal currents. An implementation of the Regional Ocean Modeling System (ROMS v3.0), a three‐dimensional, free‐surface, terrain‐following numerical model, is applied to small river outflows (≤10 m3 s−1) entering a tidal ocean, where they form small plumes of scale ~103 m or smaller. Analysis of the momentum balance points to three distinct zones: (i) an inertia‐driven near field, where advection, pressure gradient, and vertical stress divergence control the plume dynamics, (ii) a buoyancy‐driven midfield, where pressure gradient, lateral stress divergence, and rotational accelerations are dominant, and (iii) an advective far field, where local accelerations induced by ambient tidal currents determine the fate of the river/estuarine discharge. The response of these small tidal plumes to different buoyancy forcing and outflow rate is explored. With increasing buoyancy, plumes change from narrow/elongated, bottom‐attached flows to radially expanding, surface‐layer flows. Weak outflow promotes stratification within the plume layer, and with stronger outflow, the plume layer becomes thinner and well‐mixed. When compared with prototypical large‐river plumes in which Coriolis effects are important, (i) in these small plumes, there is no bulge and no coastal buoyancy current, that is, shore contact is mostly absent, and (ii) the plume is strongly influenced by ambient tidal currents, forming a tidal plume that is deflected upcoast/downcoast from the river mouth.

Spatial and temporal variability of turbulent mixing in the near-field of the Changjiang River

Based on field hydrological, microstructural, and shipboard Acoustic Doppler Current Profiler data, we quantified the spatial and temporal variability of turbulent mixing in the near-field Changjiang (Yangtze) River plume. The surface dissipation rate (e) changed by three orders of magnitude from near-field (10-4 W/kg) to far-field (10-7 W/kg) plumes, indicating a decrease with distance from the river mouth. Below the river plume, e changed with depth to 10-8 W/kg, and increased to 10-6 W/kg at the layer where the Taiwan Warm Current (TWC) intruded. Thus, e in the near-field plume showed three layers:surface layer in the river plume, middle layer, and lower TWC layer. In the river plume, the strongest e and turbulent diffusivity (Kz) were greater than 10-4 W/kg and 10-2 m2/s, respectively, during strong ebb tides. A three-orders-of-magnitude change in e and Kz was observed in the tidal cycle. The depth of the halocline changed with tidal cycles, and stratification (N2) varied by one order of magnitude. Stratification in the TWC layer followed the distribution of the halocline, which is opposite to the dissipation structure. Tidal currents led to intrusion and turbulent mixing in the TWC layer. During ebb tides, e and Kz were as strong as those measured in the river plume, but did not last as long. The structure of the velocity shear was similar to the dissipation rate in both the river plume and TWC layer, whereas the velocity shear in the TWC layer did not match the stratification structure. In the high dissipation rate area, the gradient Richardson number was smaller than the critical value (Rig < 1/4). The Rig structure was consistent with shear and dissipation distributions, indicating that turbulent mixing in the near-field plume was controlled by a combination of shear induced by the discharged river flow and tidal current.

The 2018 fire season in North America as seen by TROPOMI: aerosol layer height intercomparisons and evaluation of model-derived plume heights

Abstract. Before the launch of the TROPOspheric Monitoring Instrument (TROPOMI), only two other satellite instruments were able to observe aerosol plume heights globally, the Multi-angle Imaging SpectroRadiometer (MISR) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). The TROPOMI aerosol layer height is a potential game changer, since it has daily global coverage, and the aerosol layer height retrieval is available in near real time. The aerosol layer height can be useful for aviation and air quality alerts, as well as for improving air quality forecasting related to wildfires. Here, TROPOMI's aerosol layer height product is evaluated with MISR and CALIOP observations for wildfire plumes in North America for the 2018 fire season (June to August). Further, observing system simulation experiments were performed to interpret the fundamental differences between the different products. The results show that MISR and TROPOMI are, in theory, very close for aerosol profiles with single plumes. For more complex profiles with multiple plumes, however, different plume heights are retrieved; the MISR plume height represents the top layer, and the plume height retrieved with TROPOMI tends to have an average altitude of several plume layers. The comparison between TROPOMI and MISR plume heights shows that, on average, the TROPOMI aerosol layer heights are lower, by approximately 600 m, compared to MISR, which is likely due to the different measurement techniques. From the comparison to CALIOP, our results show that the TROPOMI aerosol layer height is more accurate over dark surfaces, for thicker plumes, and plumes between approximately 1 and 4.5 km. MISR and TROPOMI are further used to evaluate the plume height of Environment and Climate Change Canada's operational forecasting system FireWork with fire plume injection height estimates from the Canadian Forest Fire Emissions Prediction System (CFFEPS). The modelled plume heights are similar compared to the satellite observations but tend to be slightly higher with average differences of 270–580 and 60–320 m compared to TROPOMI and MISR, respectively.