Plume Structure Research Articles

Variability of the Spreading of the Patos Lagoon Plume Using Numerical Drifters

The Patos Lagoon coastal plume is a small-scale outflow that is strongly controlled by meteorological tides. However, the riverine discharge of the lagoon is subject to high decadal variability. Hence, the discharge amount alters the scale of this coastal plume and its effects over the inner shelf environment. This study uses hydrodynamic simulations and a Lagrangian model to estimate the spreading of the plume under two different discharge conditions.Through scale parameters, we characterized the contrasts of the plume structure between high discharge and low discharge conditions. During a strong discharge regime, the width and thickness of the plume are enhanced, and the inertial processes increase against the frictional effect of the wind. The consequences of these differences include higher values of alongshore and cross-shore spreading of the drifters for the strong discharge regime. These findings indicate that under similar wind conditions, different amounts of riverine discharges alter the extent to which the material delivered by the plume can spread over the inner continental shelf.

Acoustic spectrometry of bubbles in an estuarine front: Sound speed dispersion, void fraction, and bubble density.

Estuaries constitute a unique waveguide for acoustic propagation. The spatiotemporally varying three-dimensional front between the seawater and the outflowing freshwater during both flood and ebb constitutes an interfacial sound speed gradient capable of supporting significant vertical and horizontal acoustic refraction. The collision of these two water masses often produces breaking waves, injecting air bubbles into the water column; the negative vertical velocities of the denser saltwater often subduct bubbles to the bottom of these shallow waveguides, filling the water column with a bubbly mixture possessing a significantly lower effective sound speed. A field experiment was carried out in the mouth of Mobile Bay, Alabama in June 2021 to characterize estuarine bubble clouds in terms of their depth-dependent plume structure, frequency-dependent sound speed and attenuation, bubble size distribution, bubble number density, and void fraction. Results demonstrate that sound speed in the bubbly liquid consistently falls below the intrinsic sound speed of bubble-free water; specifically, the bubbly liquid 1.3 m below the surface in a front in this environment possesses effective sound speeds, void fractions, and bubble number densities of approximately 750 m/s, 0.001%, and 2 × 106 bubbles/m3, respectively.

Исследование пароводяного шлейфа градирни в окружающей среде

Studies of the transformation of steam-water emissions of a cooling tower in the ambient atmospheric environment, depending on meteorological factors, is carried out. It is revealed that the structure of the steam-water plume is heterogeneous. There are three zones in which the character of thermo-aerodynamic processes and their flow conditions change significantly: the zone of active aerodynamic processes, the transition zone, and the flare zone. It is established that dilution of the steam-water plume with polluted air is carried out throughout the volume due to its turbulence. Using the above methodological developments allows determining the main design parameters of the cooling tower steam-water plum, in particular, temperature and humidity conditions.

Multi‐Scale Density Structures in the Plasmaspheric Plume During a Geomagnetic Storm

AbstractEvolution of large‐scale and fine‐scale plasmaspheric plume density structures was examined using space‐ground coordinated observations of a plume during the 7–8 September 2015 storm. The large‐scale plasmaspheric plume density at Van Allen Probes A was roughly proportional to the total electron content (TEC) along the satellite footprint, indicating that TEC distribution represents the large‐scale plume density distribution in the magnetosphere. The plasmaspheric plume contained fine‐scale density structures and subauroral polarization streams (SAPS) velocity fluctuations. High‐resolution TEC data support the interpretation that the fine‐scale plume structures were blobs with ∼300 km size and ∼500–800 m/s in the ionosphere (∼3,000 km size and ∼5–8 km/s speed in the magnetosphere), emerging at the plume base and drifting to the plume. The short‐baseline Global Navigation Satellite System receivers detected smaller‐scale (∼10 km in the ionosphere, ∼100 km in the magnetosphere) TEC gradients and their sunward drift. Fine‐scale density structures were associated with enhanced phase scintillation index. Velocity fluctuations were found to be spatial structures of fine‐scale SAPS flows that drifted sunward with density irregularities down to ∼10 s of meter‐scale. Fine‐scale density structures followed a power law with a slope of ∼−5/3, and smaller‐scale density structures developed slower than the larger‐scale structures. We suggest that turbulent SAPS flows created fine‐scale density structures and their cascading to smaller scales. We also found that the plume fine‐scale density structures were associated with whistler‐mode intensity modulation, and localized electron precipitation in the plume. Structured precipitation in the plume may contribute to ionospheric heating, SAPS velocity reduction, and conductance enhancements.

Data‐Driven Method With Numerical Model: A Combining Framework for Predicting Subtropical River Plumes

AbstractNumerical models are of fundamental usage for estuarine and coastal sciences. Although numerical simulations are widely applied, analyzing and improving them are often challenging tasks given their large volume and huge parameter space. In this study, a novel data‐driven framework is introduced to study the Minjiang River Plume (MJRP). The framework combines Self‐Organizing Map (SOM) clustering with a Hidden Markov Model (HMM). A three‐dimensional Regional Ocean Model System for MJRP is first configurated with realistic atmospheric, oceanic, and riverine forcings. By applying SOM clustering to the modeled sea surface salinity (SSS) with ∼2,000 2‐day averaged records from 2010 to 2020, we identify six major patterns of MJRP. Each pattern exhibits distinct circulation and plume structures. These MJRP patterns contain not only seasonal signals, but also rich short‐term variabilities driven by the riverine inputs and oceanic dynamics. Then, the SOM‐HMM method was applied to predict the future of the hidden state (i.e., patterns of MJRP) from the observable states (wind and river runoff). With a hypothetic SSS product from a geostationary satellite as the ground truth, we show that the SOM‐HMM method can predict MJRP patterns considerably high prediction accuracy and computational efficiency. Further, these patterns were translated back to SSS with high forecast skills. Combining a conventional numerical model with a data‐driven method, this approach can be promisingly applied in the short‐term marine forecast to support the utilization and management of other estuaries.

The Vertical Structure and Entrainment of Subglacial Melt Water Plumes

AbstractBasal melting of marine‐terminating glaciers, through its impact on the forces that control the flow of the glaciers, is one of the major factors determining sea level rise in a world of global warming. Detailed quantitative understanding of dynamic and thermodynamic processes in melt‐water plumes underneath the ice‐ocean interface is essential for calculating the subglacial melt rate. The aim of this study is therefore to develop a numerical model of high spatial and process resolution to consistently reproduce the transports of heat and salt from the ambient water across the plume into the glacial ice. Based on boundary layer relations for momentum and tracers, stationary analytical solutions for the vertical structure of subglacial non‐rotational plumes are derived, including entrainment at the plume base. These solutions are used to develop and test convergent numerical formulations for the momentum and tracer fluxes across the ice‐ocean interface. After implementation of these formulations into a water‐column model coupled to a second‐moment turbulence closure model, simulations of a transient rotational subglacial plume are performed. The simulated entrainment rate of ambient water entering the plume at its base is compared to existing entrainment parameterizations based on bulk properties of the plume. A sensitivity study with variations of interfacial slope, interfacial roughness and ambient water temperature reveals substantial performance differences between these bulk formulations. An existing entrainment parameterization based on the Froude number and the Ekman number proves to have the highest predictive skill. Recalibration to subglacial plumes using a variable drag coefficient further improves its performance.

Modelling extinction/re-ignition processes in fire plumes under oxygen-diluted conditions using flamelet tabulation approaches

The main objective of this article is to investigate the capability of the flamelet progress variable (FPV) model to capture the extinction processes observed in under-ventilated fire scenarios. To this end, large eddy simulation (LES) of the methane line fire plumes in oxygen-reduced environments down to global extinction, investigated experimentally at the University of Maryland (UMD), is performed. Two experimental burner configurations, that differ by the presence (anchored) or not (non-anchored) of an oxygen anchor to stabilise the flame base, are considered leading to two different extinction modes. Both the FPV and the steady laminar flamelet (SLF) model coupled with a presumed filtered density function (FDF) are considered. The Rank Correlated Full Spectrum k-distribution (RCFSK) model is used as a gas radiative property model. In both non-anchored and anchored scenarios, the FPV model reproduces with fidelity the evolution of the fire plume structure, radiative loss, and combustion efficiency with decreasing down to global extinction, without introducing any adjustable constant. The extinction in the non-anchored scenario occurs owing to flame-based detachment coupled to the generation of a buoyancy-driven vortex and is found to be very sensitive to the grid resolution in the near burner region. The present results suggest that these processes can be adequately resolved with a spatial resolution of 2.5 mm in this region. The SLF model, for its part, provides reliable predictions comparable to the FPV as long as no local extinction/re-ignition process occurs.

The Impacts of Freshwater Input and Surface Wind Velocity on the Strength and Extent of a Large High Latitude River Plume

Arctic Ocean physical and biogeochemical properties are strongly influenced by freshwater input from land and through the Bering Strait, where the mean currents transport water northward from the Bering Sea. The Yukon River is one of the largest rivers in North America and the Arctic, contributing large quantities of freshwater and terrigenous material to the coastal ocean in the northern Bering Sea. However, a detailed analysis of the coastal hydrodynamics at the outflow of the river has not been conducted in this remote but regionally important river. A three-dimensional hydrodynamic model was built to represent the lower Yukon River and coastal ocean for the ice-free months in 7 years. On average, a large anticyclonic eddy persisted at the main outflow of the Yukon that recirculates water back toward the coast where the currents converge to form a mean northward transport along the delta. Interannual spatial variance in salinity was relatively small, while there was substantial variance in u and v current velocity. u velocity spatial variance was correlated to the volume of freshwater discharge across years, while v velocity spatial variance was correlated to the N–S wind velocity. During strong wind events, plume structure was substantially altered: southerly winds deepened the plume and enhanced northward transport, while northerly winds shoaled and strengthened the pycnocline, and reversed the flow toward the south. The variability in plume dispersion on short time scales due to wind forcing has implications for where terrigenous material is processed in and settles out of the water column.

Onset Conditions and Features of Equatorial F Region Irregularities: New Insight From Collocated Digisonde and Radar Observations From Gadanki

AbstractIn this paper, we study the onset conditions and features of equatorial F region irregularities linked with equatorial plasma bubbles (EPBs) using observations made simultaneously by using a DPS‐4D digisonde and the Gadanki Ionospheric Radar Interferometer (GIRI), both collocated at Gadanki. Importantly, we have employed specific analysis tools on DPS‐4D observations, providing range‐time displays of radio frequency and signal‐to‐noise ratio (SNR) of the reflected/backscattered echoes and the angle‐of‐arrival of the echoes, to characterize the echoes and to study the ambient and disturbed states of the ionosphere. Observations clearly show noticeably different background conditions, in terms of the height of the F layer base, electron density gradient and vertical drift, for the freshly generated and drifting EPBs. The zonal wavelengths of the pre‐sunset large‐scale wave structures (LSWS) observed using the DPS‐4D, however, are found to show a close connection with EPB spacings for freshly generated and drifting EPBs, consistent with earlier findings. The satellite traces were observed just prior to the equatorial spread F (ESF) and were found to be associated with the bottomside upwellings. Comparison of the range‐time displays of radio frequency and SNR of the DPS‐4D observations and the height‐time variations of SNR of the GIRI observations demonstrates that the relatively weak echoes in the DPS‐4D observations, which represent the ESF echoes, correlate fairly well temporally with the plume structures observed by the GIRI. The GIRI observations also reproduce the bottomside upwellings observed by the DPS‐4D. We propose that the bottomside upwellings are due to the growth of the LSWS and these bottomside upwellings are instrumental for the growth of the Rayleigh‐Taylor instability generating EPBs. Finally, the new aspects of the digisonde observations are discussed with regard to their usefulness in understanding and forecasting EPBs/ESF.

Strong ULVZ and Slab Interaction at the Northeastern Edge of the Pacific LLSVP Favors Plume Generation

AbstractStrong waveform complexities, including multipathing of the S diffracted phase and rapid changes in differential ScS‐S times, are observed for multiple deep Fiji earthquakes recorded at the USArray. The complexities occur at the northeastern edge of the Pacific Large Low Shear Velocity Province (LLSVP), about 12 degrees southeast of present‐day Hawaiʻi. Waveform modeling of the multipathing provides good constraints on an ultra‐low velocity zone (ULVZ) with a width of 5 degree located near the inner edge of the LLSVP. Based on the mineralogical‐modeling of the ULVZ as a solid iron‐rich magnesiowüstite‐bearing assemblage with compatible morphology predicted from geodynamical simulations, a ULVZ model with a thickness of 30 km and a shear wave velocity reduction of 18% is preferred. The rapid change in differential ScS‐S travel time is best explained by having both the aforementioned ULVZ and an adjacent high velocity structure near the LLSVP. Furthermore, a low‐velocity plume‐like structure could potentially explain the observed S travel time delay independent of ScS. These seismic features are proposed to be a ULVZ driven toward the edge of the LLSVP while potentially pushed by a subducted slab. This configuration may trigger plume generation due to strong thermal instabilities and is in the same vicinity where mantle flow models place the present‐day Hawaiian plume source. Multiple ScS can potentially be used to verify vertical plume structure in tomographic models but the accuracy of upper mantle structure, which is a key reflection point, needs to be considered.

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.

Turbulent Statistics of a Hot, Overexpanded Rectangular Jet

The near-field dynamics of a rectangular heated overexpanded jet of aspect ratio two is examined with an implicit large-eddy simulation using experimental data for validation purposes. The conical nozzle, representative of practical configurations, results in multiple shock trains from the throat region as well as the overexpanded operating condition. Each train introduces unsteadiness that influences the external shock cell and plume structure. A detailed analysis of the terms contributing to the turbulent kinetic energy (TKE) is performed to examine the evolution of the plume. The major-axis shear layer experiences significant amplification of the TKE compared with the minor axis, particularly near the core collapse region, and thus pressure fluctuations in the near acoustic field are correspondingly larger in that direction. The most prominent source of TKE in this region is associated with strong mean flow gradients across the major-axis shear layer, and larger corresponding cross-correlations of velocity fluctuations. These effects are shown to be consistent with protrusions of vortical perturbations arising in the minor-axis shear layer into the potential core. The evolution of pressure perturbations from asymmetric to axisymmetric occurs relatively quickly, to achieve agreement with far-field experimental data.

Non-synaptic interactions between olfactory receptor neurons, a possible key feature of odor processing in flies.

When flies explore their environment, they encounter odors in complex, highly intermittent plumes. To navigate a plume and, for example, find food, they must solve several challenges, including reliably identifying mixtures of odorants and their intensities, and discriminating odorant mixtures emanating from a single source from odorants emitted from separate sources and just mixing in the air. Lateral inhibition in the antennal lobe is commonly understood to help solving these challenges. With a computational model of the Drosophila olfactory system, we analyze the utility of an alternative mechanism for solving them: Non-synaptic ("ephaptic") interactions (NSIs) between olfactory receptor neurons that are stereotypically co-housed in the same sensilla. We find that NSIs improve mixture ratio detection and plume structure sensing and do so more efficiently than the traditionally considered mechanism of lateral inhibition in the antennal lobe. The best performance is achieved when both mechanisms work in synergy. However, we also found that NSIs decrease the dynamic range of co-housed ORNs, especially when they have similar sensitivity to an odorant. These results shed light, from a functional perspective, on the role of NSIs, which are normally avoided between neurons, for instance by myelination.

Large River Plumes Detection by Satellite Altimetry: Case Study of the Ob–Yenisei Plume

Satellite altimetry is an efficient instrument for detection dynamical processes in the World Ocean, including reconstruction of geostrophic currents and tracking of mesoscale eddies. Satellite altimetry has the potential to detect large river plumes, which have reduced salinity and, therefore, elevated surface level as compared to surrounding saline sea. In this study, we analyze applicability of satellite altimetry for detection of the Ob–Yenisei plume in the Kara Sea, which is among the largest river plumes in the World Ocean. Based on the extensive in situ data collected at the study area during oceanographic surveys in 2007–2019, we analyze the accuracy and efficiency of satellite altimetry in reproducing, first, the outer boundary of the plume and, second, the internal structure of the plume. We reveal that the value of positive level anomaly within the Ob–Yenisei plume strongly depends on the vertical plume structure and is prone to significant synoptic and seasonal variability due to wind forcing and mixing of the plume with subjacent sea. As a result, despite generally high statistical correlation between the ADT and surface salinity, straightforward usage of ADT for detection of the river plume is incorrect and produces misleading results. Satellite altimetry could provide correct information about spatial extents and shape of the Ob–Yenisei plume only if it is validated by synchronous in situ measurements.

Structure and mixing of a meandering turbulent chemical plume: turbulent mixing and eddy diffusivity

Structure and mixing of a meandering turbulent chemical plume: turbulent mixing and eddy diffusivity

Novel Analysis to Quantify Plume Crosswind Heterogeneity Applied to Biomass Burning Smoke.

We present a novel method, the Gaussian observational model for edge to center heterogeneity (GOMECH), to quantify the horizontal chemical structure of plumes. GOMECH fits observations of short-lived emissions or products against a long-lived tracer (e.g., CO) to provide relative metrics for the plume width (wi/wCO) and center (bi/wCO). To validate GOMECH, we investigate OH and NO3 oxidation processes in smoke plumes sampled during FIREX-AQ (Fire Influence on Regional to Global Environments and Air Quality, a 2019 wildfire smoke study). An analysis of 430 crosswind transects demonstrates that nitrous acid (HONO), a primary source of OH, is narrower than CO (wHONO/wCO = 0.73-0.84 ± 0.01) and maleic anhydride (an OH oxidation product) is enhanced on plume edges (wmaleicanhydride/wCO = 1.06-1.12 ± 0.01). By contrast, NO3 production [P(NO3)] occurs mainly at the plume center (wP(NO3)/wCO = 0.91-1.00 ± 0.01). Phenolic emissions, highly reactive to OH and NO3, are narrower than CO (wphenol/wCO = 0.96 ± 0.03, wcatechol/wCO = 0.91 ± 0.01, and wmethylcatechol/wCO = 0.84 ± 0.01), suggesting that plume edge phenolic losses are the greatest. Yet, nitrophenolic aerosol, their oxidation product, is the greatest at the plume center (wnitrophenolicaerosol/wCO = 0.95 ± 0.02). In a large plume case study, GOMECH suggests that nitrocatechol aerosol is most associated with P(NO3). Last, we corroborate GOMECH with a large eddy simulation model which suggests most (55%) of nitrocatechol is produced through NO3 in our case study.

Structure and mixing of a meandering turbulent chemical plume: concentration and velocity fields

Structure and mixing of a meandering turbulent chemical plume: concentration and velocity fields

Sensing of Airborne Infochemicals for Green Pest Management: What Is the Challenge?

One of the biggest global challenges for our societies is to provide natural resources to the rapidly expanding population while maintaining sustainable and ecologically friendly products. The increasing public concern about toxic insecticides has resulted in the rapid development of alternative techniques based on natural infochemicals (ICs). ICs (e.g., pheromones, allelochemicals, volatile organic compounds) are secondary metabolites produced by plants and animals and used as information vectors governing their interactions. Such chemical language is the primary focus of chemical ecology, where behavior-modifying chemicals are used as tools for green pest management. The success of ecological programs highly depends on several factors, including the amount of ICs that enclose the crop, the range of their diffusion, and the uniformity of their application, which makes precise detection and quantification of ICs essential for efficient and profitable pest control. However, the sensing of such molecules remains challenging, and the number of devices able to detect ICs in air is so far limited. In this review, we will present the advances in sensing of ICs including biochemical sensors mimicking the olfactory system, chemical sensors, and sensor arrays (e-noses). We will also present several mathematical models used in integrated pest management to describe how ICs diffuse in the ambient air and how the structure of the odor plume affects the pest dynamics.

Natural convection over vertical and horizontal heated flat surfaces: A review of recent progress focusing on underpinnings and implications for heat transfer and environmental applications

Natural convection arising over vertical and horizontal heated flat surfaces is one of the most ubiquitous flows at a range of spatiotemporal scales. Despite significant developments over more than a century contributing to our fundamental understanding of heat transfer in natural convection boundary layers, certain “hidden” characteristics of these flows have received far less attention. Here, we review scattered progress on less visited fundamental topics that have strong implications to heat and mass transfer control. These topics include the instability characteristics, laminar-to-turbulent transition, and spatial flow structures of vertical natural convection boundary layers and large-scale plumes, dome, and circulating flows over discretely and entirely heated horizontal surfaces. Based on the summarized advancements in fundamental research, we elaborate on the selection of perturbations and provide an outlook on the development of perturbation generators and methods of altering large-scale flow structures as a potential means for heat and mass transfer control where natural convection is dominant.

Periodic forced flow in a nanosecond pulsed cold atmospheric pressure argon plasma jet

This paper is devoted to the study of the argon flow modification in a cold atmospheric pressure plasma jet driven by nanosecond high voltage (HV) pulses, from single to multiple HV shots applications. A schlieren optical bench has been designed in order to visualize the argon flow downstream expansion in quiescent air, for moderate flow rates below 1 standard liter per minute. A coupled approach is used between charge coupled device (CCD) schlieren imaging and intensified CCD (ICCD) plasma plume imaging, both time-resolved. It is shown that the application of only one HV pulse (i.e. single HV shot) is enough to disturb the flow. The disturbed flow exhibits ripple propagation, on a timescale similar to the flow velocity. When operating in double HV shots, the second ionization wave can be used as a probe, to instantly visualize the flow structure any time after the first HV pulse application. For some flow rates, the ripple can increase in amplitude up to the point when it strongly deforms, or even stops, the plasma plume expansion, after which it is entrained by the flow and the plasma plume retrieves its full usual expansion. When a series of HV pulses are applied, the maximal disturbance of the flow is achieved for a certain pulse repetition frequency (PRF), specific of each flow rate. It is associated with ripples alternation in the plasma plume, in a 3D helical-like arrangement. For greater PRF, the ripples progressively vanish, and the flow is clearly less disturbed. Once the ripples have vanished, increasing further the PRF does not change the plasma plume and flow structures. We suggest that the repetitive plasma ignition mechanically forces the flow inside the capillary with consequences on the global flow structure, similarly to a forced backward-facing step flow with actuator.