Buoyant Plume Research Articles

Wind Effects on Small‐Scale River and Creek Plumes

AbstractIn contrast to large river plumes, Coriolis effects are weak, and inertia is quickly depleted so that the fate and structure of small‐scale plumes are more sensitive to tide and wind. Advected alongshore by reversing tidal currents in absence of wind forcing, small buoyant plumes are persistently deflected downwind in presence of alongshore winds and exhibit little tidal variability. The effect of different upwelling/downwelling winds on buoyant outflows ∼10 m3 s−1 is explored. With increasing wind, tidal variability decreases, as does asymmetry in plume characteristics—for strong winds upwelling/downwelling plume structure is similar as the plume is retained closer to the shore. Wind forcing is exerted directly by wind stress on the surface of the plume and indirectly by wind‐driven currents that deflect the upwind boundary of the plume. While inertia and buoyancy dominate the inner plume, and wind dominates the outer plume, the mid‐plume responds to an interaction of wind and buoyancy forcing that can be indexed by a Plume Wedderburn Number Wpl (wind stress vs. density gradients): for weaker winds (Wpl < 1) surface stress enhances stratification through straining, lengthening the reach of low‐salinity waters, whereas for stronger winds (Wpl > 1) surface stress mixes the plume vertically, shortening the reach of low‐salinity waters. However, dilute plume waters extend furthest in strong winds, passively advected several kilometers downwind. Shoreline exposure to outflow transitions from a quasi‐symmetrical tide‐averaged zone of impact under zero‐wind to a heavily skewed zone with persistent weak wind and a one‐sided zone for strong wind.

Puffing frequency of interacting buoyant plumes

Buoyant plumes are known to oscillate at a characteristic frequency, but little is known about how this frequency changes when two plumes are in close proximity. In this work, we conduct a series of high-fidelity simulations varying the spacing and width between two-dimensional helium plumes. We find that the global trends are similar to that of interacting reacting plumes, and four distinct regimes of interaction can be identified, most notably a scaling regime when the plumes are at moderate distances apart.

Dynamics of Two Caldera-Forming Eruptions (Banda Besar and Naira) in the Marine Conservation Zone of Banda, Maluku, Indonesia

This is the first study discussing the dynamics of two caldera-forming eruptions in the Banda volcanic complex (BVC) in the marine conservation zone of Banda, Maluku, Indonesia. The first and second caldera episodes are, hereafter, termed as Banda Besar and Naira, respectively. The formation of Banda Besar caldera (ca. 8 × 7 km) ejected homogeneous rhyolitic magmas (bulk-rock, 73.1–73.8 wt.% SiO2) in the following three stages: (1) sub-Plinian (BB-5a), (2) intra-sub-Plinian flow (BB-5b), and (3) caldera collapse (BB-5c and BB-5d). The BB-5a stage produced a reversely graded white pumice fall layer with moderate lithics (2–11%), which originated from a sub-Plinian eruption with an estimated plume height of 22–23 km. Subsequently, intensive erosion of wall rock (13–25%) causes conduit enlargement, leading to the partial collapse of the eruption columns, forming intra-sub-Plinian flow deposits (BB-5b). It is likely that conduit size surpassed the minimum threshold value for a buoyant plume during the final phase of the second stage, causing the complete formation of a pumice-rich pyroclastic density current (PDC) during the early-third stage (BB-5c). Finally, the evacuation of voluminous magma from the reservoir yields the first caldera collapse during the late-third stage, producing a lithic-dominated PDC with minor pumices (BB-5d). The formation of the Naira caldera (ca. 3 × 3 km) ejected homogeneous dacitic magmas (bulk-rock, 66.2–67.2 wt.% SiO2) in the following three stages: (1) early sub-Plinian (N-2a and 2b), (2) late sub-Plinian (N-2c, 2d, 2e), and (3) caldera collapse (N-2f). This research distinguishes the sub-Plinian into two stages on the basis of different vent locations (assumed from the isopach map). In particular, this research suggests that the early sub-Plinian stage (N-2a and 2b) erupted from the northern vent, producing 14 and 8 km eruption plume heights, respectively. Additionally, the late sub-Plinian stage (N-2c, 2d, 2e) was generated from a newly-formed conduit located in the relatively southern position, producing 12–17, 9, and 6 km eruption plume heights, respectively. Conduit enlargement is expected to occur during at both sub-Plinian stages, as lithic portions are considerably high (10–72%) and ultimately generate PDCs during the third stage (caldera collapse; N-2f). Because most of the erupted materials (for both caldera-forming eruptions) are emplaced in the ocean, estimating the erupted volume becomes difficult. However, with the assumption that the caldera dimension represents the erupted volume of magma (Vmagma), and that the total erupted volume (Vtotal) is a summation of Vmagma and the now-vanished pre-caldera island (Vvanished, represented by average lithic fractions), the first and second caldera might produce (at least) 35.2 and 2.4 km3 of erupted materials, scaling them as VEI (volcano explosivity index) 6 and 5, respectively. That VEI is more than enough to initiate a secondary hazard in the form of tsunamis triggered by volcanic activities.

A simple model for predicting dispersion characteristics of high-temperature airflow and particle distribution during smelting process in a thermally stratified foundry shop

The flow-field characteristics of high-temperature airflow and particle distributions generated from the running furnace during smelting process in foundry shop were studied by on-site measurements and theoretical analysis in this work. A theoretical model was proposed to describe the dispersion characteristics of the high-temperature buoyant jet flow and plume induced by the furnace with two typical opening modes. The coupling effects of the heat source features and environmental factors were emphatically discussed by comparing the trajectory, cross-section diameter, velocity and temperature decay, and volumetric flow rate during the dispersion process. Results show that in the large foundry shop with natural ventilation, there is a vertical temperature gradient of 0.1–0.4 °C/m, which can make the pollutant locked in the workshop and weaken the entrainment of the thermal flow. The crossflow is a non-negligible factor, which causes the dispersion trajectory of the pollutant flatter and induces a long travelling distance along the horizontal direction. The indoor particle concentration when the furnace opens concentration seriously exceeds the limits in the existing indoor air quality standard of China. This work is expected to give suggestions on ventilation designs and arrangements of the exhaust port or device in industrial environments.

Meltwater Discharge From Marine‐Terminating Glaciers Drives Biogeochemical Conditions in a Greenlandic Fjord

AbstractAn increasing body of work has shown the potential impacts of subglacial discharge from marine‐terminating glaciers on the marine environment around Greenland. Upwelling of nutrients associated with rising buoyant plumes near the front of marine‐terminating glaciers plays a key role in maintaining the high productivity of connected fjords. The response of protist communities to subglacial discharges into fjords nevertheless remains poorly understood. Here we show data of water properties, nutrients, and protist communities during two summers in 2018 and 2019 in a Greenlandic fjord system fed by marine‐terminating glaciers. This study included the period of intense summer melting of the Greenland Ice Sheet in 2019. The data revealed high nutrient concentrations in 2019 that were attributed to intensified upwelling of nutrients and dissolved iron into the subsurface layer. The source of the iron and the nutrients was subglacial discharge and deep fjord water, respectively. Intense glacial discharges in 2019 mitigated nitrate and phosphate limitations of phytoplankton in the fjord and resulted in an increase of chlorophyll a in the subsurface layer and growth of large diatoms. Heterotrophic protists such as dinoflagellates, tintinnids, and nanoflagellates were more abundant in the summer of 2019. We concluded that nutrient upwelling by subglacial discharges was the major driver of the structure of lower trophic levels in fjord ecosystems. We hypothesize that the more intense melting of glaciers and related increase in subglacial discharge will enhance nutrient upwelling, and increased summer productivity in fjords until the glaciers retreat and terminate on land.

Temporal Evolution of the Swell and Magmatic Fluxes Along the Louisville Hotspot Chain

AbstractHawaii and Louisville are the two long‐lived hotspot chains in the Pacific basin. Characterizing the swell flux, Qs, a measure of the plume buoyancy, and the flux of the magmatic material accumulated along the chain, Qm, brings important constraints on the plumes' temporal evolution and on their interaction with the lithosphere. Numerous studies focus on the temporal evolution of the Hawaiian chain, but no study investigates the temporal evolution along the Louisville chain. In the present study we constrain the temporal evolution of the swell and magmatism fluxes along the Louisville chain, from volcano ages and bathymetry data. The overall Louisville magmatism flux appears nearly constant, that is, Louisville plume activity has exhibited remarkably little variation over the past 30 m.y., in agreement with geochemical data. These results are also in agreement with recent studies along Hawaii, which show that the Qm increase is due to plume migration toward a more fertile mantle reservoir. This means that, in general, long term variations in Qm relate to variations in the deep source of the plume. Along Louisville, we find short‐term variations occurring with a periodicity of ∼5–10 m.y. in both Qm and Qs, similar to the short‐term variations observed along Hawaii by former studies. As these variations occur along hotspot chains associated with either a heterogenous or homogeneous chemical signature, they must be created by shallow phenomena. The tilt of the plume conduit by large‐scale mantle advection is our preferred model, as it can account for both the geophysical and geochemical observations.

Richardson and Reynolds number effects on the near field of buoyant plumes: temporal variability and puffing

Using numerical simulations, we investigate the near-field temporal variability of axisymmetric helium plumes as a function of inlet-based Richardson ( ${Ri}_0$ ) and Reynolds ( ${Re}_0$ ) numbers. Previous studies have shown that ${Ri}_0$ plays a leading-order role in determining the frequency at which large-scale vortices are produced (commonly called the ‘puffing’ frequency). By contrast, ${Re}_0$ dictates the strength of localized gradients, which are important during the transition from laminar to turbulent flow. The simulations presented here span a range of ${Ri}_0$ and ${Re}_0$ , and use adaptive mesh refinement to achieve high spatial resolutions. We find that as ${Re}_0$ increases for a given ${Ri}_0$ , the puffing motion undergoes a transition at a critical ${Re}_0$ , marking the onset of chaotic dynamics. Moreover, the critical ${Re}_0$ decreases as ${Ri}_0$ increases. When the puffing instability is non-chaotic, time series of different variables are well-correlated, exhibiting only modest changes in the dynamics (including period doubling and flapping). Once the flow becomes chaotic, denser ambient fluid penetrates the core of the plume, similar to penetrating ‘spikes’ formed by Rayleigh–Taylor instabilities, leading to only moderately correlated flow variables. These changes result in a non-trivial dependence of the puffing frequency on ${Re}_0$ . Specifically, at sufficiently low ${Re}_0$ , the puffing frequency falls below the prediction from Wimer et al. (J. Fluid Mech., vol. 895, 2020). As ${Re}_0$ increases beyond the critical ${Re}_0$ , the puffing frequency increases and then drops back down to the predicted scaling. The dependence of the puffing frequency on ${Re}_0$ provides a possible explanation for previously observed changes in the scaling of the puffing frequency for high ${Ri}_0$ .

The role of edge-driven convection in the generation ofvolcanism – Part 2: Interaction with mantle plumes, applied to the Canary Islands

Abstract. In the eastern Atlantic Ocean, several volcanic archipelagos are located close to the margin of the African continent. This configuration has inspired previous studies to suggest an important role of edge-driven convection (EDC) in the generation of intraplate magmatism. In a companion paper (Manjón-Cabeza Córdoba and Ballmer, 2021), we showed that EDC alone is insufficient to sustain magmatism of the magnitude required to match the volume of these islands. However, we also found that EDC readily develops near a step of lithospheric thickness, such as the oceanic–continental transition (“edge”) along the western African cratonic margin. In this work, we carry out 3D numerical models of mantle flow and melting to explore the possible interactions between EDC and mantle plumes. We find that the stem of a plume that rises close to a lithospheric edge is significantly deflected ocean-ward (i.e., away from the edge). The pancake of ponding hot material at the base of the lithosphere is also deflected by the EDC convection cell (either away or towards the edge). The amount of magmatism and plume deflection depends on the initial geometric configuration, i.e., the distance of the plume from the edge. Plume buoyancy flux and temperature also control the amount of magmatism, and influence the style and extent of plume–EDC interaction. Finally, comparison of model predictions with observations reveals that the Canary plume may be significantly affected and deflected by EDC, accounting for widespread and coeval volcanic activity. Our work shows that many of the peculiar characteristics of eastern Atlantic volcanism are compatible with mantle plume theory once the effects of EDC on plume flow are considered.

Pore-scale phenomena in carbon geological storage (Saline aquifers—Mineralization—Depleted oil reservoirs)

The injection of CO2 into geological formations triggers inherently coupled thermo-hydro-chemo-mechanical processes. The reservoir pressure and temperature determine the CO2 density, the CO2-water interfacial tension, and the solubility of CO2 in water (hindered by salts and competing gases). The CO2-water interface experiences marked pinning onto mineral surfaces, and contact angles can range from the asymptotic advancing to receding values, in contrast to the single contact angle predicted by Young’s equation. CO2 dissolves in water to form carbonic acid and the acidified water dissolves minerals; mineral dissolution enhances porosity and permeability, triggers settlement, may couple with advection to form “wormholes”, produces stress changes and may cause block sliding and shear bands. Convective currents can emerge beneath the CO2 plume and sustain CO2 and mineral dissolution processes. On the other hand, mineralization is a self-homogenizing process in advective regimes. The crystallization pressure can exceed the tensile capacity of the host rock and create new surfaces or form grain-displacive lenses. Within the rock matrix, coupled reactive-diffusion-precipitation results in periodic precipitation bands. Adequate seal rocks for CO2 geological storage must be able to sustain the excess capillary pressure in the buoyant CO2 plume without experiencing open-mode discontinuities or weakening physico-chemical interactions. CO2 injection into depleted oil reservoirs benefits from time-proven seals; in addition, CO2 can mobilize residual oil to simultaneously recover additional oil through oil swelling, ganglia destabilization, the reduction in oil viscosity and even miscible displacement. Rapid CO2 depressurization near the injection well causes cooling under most anticipated reservoir conditions; cooling can trigger hydrate and ice formation, and reduce permeability. In some cases, effective stress changes associated with the injection pressure and cooling thermoelasticity can reactivate fractures. All forms of carbon geological storage will require large reservoir volumes to hold a meaningful fraction of the CO2 that will be emitted during the energy transition.

Numerical study on the effect of buoyancy-driven pollution source on vortex ventilation performance

High-temperature buoyancy-driven pollutants that generally exist in industrial buildings and kitchens often be eliminated by local exhaust ventilation systems. The high-temperature pollutant plume driven by buoyancy significantly affects the local exhaust process, resulting in the change in the exhaust flow field and reduction of the pollutant capture efficiency. In this study, the effects of thermal buoyancy-driven pollution sources on the vortex flow field and pollutant removal efficiency of a vortex ventilation system are evaluated through experiments and numerical simulations. The results show that with an increase in the buoyancy flux of the pollution source, the minimum negative pressure and maximum tangential velocity in the vortex flow first increase and then decrease, that is, the buoyancy plume first enhances and then weakens the vortex flow. A critical buoyancy flux exists, and the value of the critical buoyancy flux increases with an increase in the vortex ventilation intensity. Furthermore, the capture of high-temperature pollutants by vortex flow can be categorized as “plume-dominated” and “vortex-dominated”. These two types exhibit significant differences in pollutant transport paths and pollutant capture times during pollutant removal. In addition, on the basis of the pollutant capture efficiency, the vortex airflow performance with respect to capturing high-temperature buoyancy-driven pollutants can be classified as low-efficiency, transition, high-efficiency, and invalid zones. In the process of capturing high-temperature pollutants, vortex ventilation systems should be avoided in the low-efficiency and invalid zones.

On the energy–consistent plume model in the convective boundary layer

The theoretical modeling of turbulent plumes in stratified environment is key for understanding the physics of convective systems of further complexity such as the atmospheric and oceanic convection. In this work we consider the round buoyancy plumes in stratified environments governed by the conservation of momentum, kinetic energy, and buoyancy, also referred to as energy-consistent plumes. Analytical solutions for the convective plumes for a particular case when the plume radius follows a linear grows with the height are presented. It is also shown that for this particular case the energy-consistent plume model gives the same type of equations as the well known one-dimensional Lagrangian model that is currently used to model the convection in the atmospheric boundary layer. Since in the atmospheric convection the assumption that the plume has a constant radius is a very common closure, the physical conditions that allow one to consider such an assumption are also discussed. In addition, a possible implementation of the energy-consistent plume model in the eddy-diffusivity mass-flux formulation is also presented in the last part of this work.

Experiments and modeling of the temperature profile of turbulent diffusion flames with large ullage heights

In the last decades, several major fire accidents involving storage tanks occurred, particularly for the tanks with a low fuel level (large ullage height). In case of a tank fire, the axial temperature profile is affected by the ullage because of the restriction in air entrainment by the tank sidewall. This work is aimed at examining the temperature profile of turbulent diffusion flames with large ullage heights. A series of experiments were conducted with different ullage heights (h = 16–42 cm) and fuel supply rates. The temperature profiles both inside and outside the fuel tray were measured and analyzed. Five regions were identified based on flame intermittencies: namely 1) fuel vapor, 2) down-reaching intermittent flame, 3) continuous flame (down-reaching and upper flame), 4) upper intermittent flame and 5) buoyant plume. It was found that for a given fuel supply rate the length of the fuel vapor region increases linearly with the ullage height. The lengths of the fuel vapor and continuous flame regions both increase with the fuel supply rate, whereas that of the down-reaching intermittent flame region shows an opposite trend. Based on the experimental data and dimensionless analysis, new correlations for the virtual origin were proposed, which were then incorporated in the predictions of the temperature profiles in both upper and down-reaching flames. The present results could not only contribute to the understanding the effects of the ullage height on the axial temperature profile in storage fuel tank fires with large ullage heights but are also of practical importance in the thermal hazard assessment of fire accidents involving tank liquid fuels.

The role of channelized basal melt in ice-shelf stability: recent progress and future priorities

AbstractBasal channels, which form where buoyant plumes of ocean water and meltwater carve troughs upwards into ice-shelf bases, are widespread on Antarctic ice shelves. The formation of these features modulates ice-shelf basal melt by influencing the flow of buoyant plumes, and influences structural stability through concentration of strain and interactions with fractures. Because of these effects, and because basal channels can change rapidly, on timescales similar to those of ice-shelf evolution, constraining the impacts of basal channels on ice shelves is necessary for predicting future ice-shelf destabilization and retreat. We suggest that future research priorities should include constraining patterns and rates of basal channel change, determining mechanisms and detailed patterns of basal melt, and quantifying the influence that channel-related fractures have on ice-shelf stability.

Systematic shift in plume bending direction at Grotto Vent, Main Endeavour Field, Juan de Fuca Ridge implies changes in venting output along the Endeavour Segment

Analysis of the time-dependent behavior of the buoyant plume rising above Grotto Vent (Main Endeavour Field, Juan de Fuca Ridge) as imaged by the Cabled Observatory Vent Imaging Sonar (COVIS) between September 2010 and October of 2015 captures long term time-dependent changes in the direction of background bottom currents independent of broader oceanographic processes, indicating a systematic evolution in vent output along the Endeavour Segment of the Juan de Fuca Ridge. The behavior of buoyant plumes can be quantified by describing the volume, velocity, and orientation of the effluent relative to the seafloor, which are a convolved expression of hydrothermal flux from the seafloor and ocean bottom currents in the vicinity of the hydrothermal vent. We looked at the azimuth and inclination of the Grotto plume, which was captured in three-dimensional acoustic images by the COVIS system, at 3-h intervals during October 2010 and between October 2011 and December 2014. The distribution of plume azimuths shifts from bimodal NW and SW to SE in 2010, 2011, and 2012 to single mode NW in 2013 and 2014. Modeling of the distribution of azimuths for each year with a bimodal Gaussian indicates that the prominence of southward bottom currents decreased systematically between 2010 and 2014. Spectral analysis of the azimuthal data showed a strong semi-diurnal peak, a weak or missing diurnal peak, and some energy in the sub-inertial and weather bands. This suggests the dominant current generating processes are either not periodic (such as the entrainment fields generated by the hydrothermal plumes themselves) or are related to tidal processes. This prompted an investigation into the broader oceanographic current patterns. The surface wind patterns in buoy data at two sites in the Northeast Pacific and the incidence of sea-surface height changes related to mesoscale eddies show little systematic change over this time-period. The limited bottom current data for the Main Endeavour Field and other parts of the Endeavour Segment neither confirm nor refute our observation of a change in the bottom currents. We hypothesize that changes in venting either within the Main Endeavour Field or along the Endeavour Segment have resulted in the changes in background currents. Previous numerical simulations (Thomson et al., J. Geophys. Res., 2009, 114 (C9), C09020) showed that background bottom currents were more likely to be controlled by the local (segment-scale) venting than by outside ocean circulation or atmospheric patterns.

Efficient algorithm for proper orthogonal decomposition of block-structured adaptively refined numerical simulations

Adaptive mesh refinement (AMR) is increasingly being used to simulate fluid flows that have vastly different resolution requirements throughout the computational domain. Proper orthogonal decomposition (POD) is a common tool to extract coherent structures from flow data and build reduced order models, but current POD algorithms do not take advantage of potential efficiency gains enabled by multi-resolution data from AMR simulations. Here, we explore a new method for performing POD on AMR data that eliminates repeated operations arising from nearest-neighbor interpolation of multi-resolution data onto uniform grids. We first outline our approach to reduce the number of computations with examples and provide the complete algorithms in the appendix. We examine the computational acceleration of the new algorithms compared to the standard POD method using synthetically generated AMR data and operation counting. We then use CPU times and operation counting to analyze data from an AMR simulation of an axisymmetric buoyant plume, finding that we are able to reduce the computational time by a factor of approximately 2−5 when using three levels of grid refinement. The new POD algorithm is the first to eliminate redundant operations for matrix multiplications with repeated values in each matrix, making it ideal for POD of data from AMR simulations.

Experimental study on transverse temperature profile of spill plume and thermal characteristic difference with lateral direction

The present research investigated theoretically and experimentally the transverse temperature profiles of spill buoyant plume ejected from a fire compartment, as well as the thermal characteristic difference between the transverse and lateral direction. The previous literatures only focused on the vertical and lateral (normal to facade) temperature profiles; although the transverse (parallel to facade) temperature profiles will also have a significant impact on the thermal expansion, and it could be essentially different from the lateral temperature profile due to the existence of facade (air entrainment restricted), however, this topic has not been revealed yet. Hence, in present study, the plume thickness of transverse direction was theoretically analyzed, and a model for transverse temperature profile using the Gaussian function was established using the new effective plume thickness. Experiments were then conducted by using a reduced-scaled fire compartment with one opening attached on the facade wall. The transverse and lateral temperature profile of the spill fire plume along the facade wall were measured and analyzed. The model for transverse temperature profile can be well verified by obtained data. And it is found that the transverse temperature decay slower than the lateral temperature due to the Coanda effect caused by the one-side air entrainment. The obtained experimental data and proposed transverse temperature profile function in this work provide a basic understanding for the thermal characteristics of spill buoyant plume ejected from a fire compartment, and the proposed function can be applied to predict the spread possibility of building facade fire.

Helium and oxygen isotopic variations in the Iceland plume source controlled by entrainment of recycled oceanic lithosphere

Icelandic basalts have low oxygen isotope (δ18O) values compared to other ocean island localities. While this observation is often ascribed to the assimilation of low-δ18O crust, a low-δ18O mantle beneath Iceland has also been suggested. To discern crustal from mantle-derived signals, high-quality in-situ and bulk crystal δ18O measurements have been obtained from olivine crystals covering 16 Ma of activity at the Iceland hotspot. The results are combined with olivine (ol) major, minor and trace element chemistry. Relationships between δ18Ool and indicators of melt evolution do not support a singular process responsible for lowering of δ18O values. However, correlations are observed between δ18Ool values and indicators of crustal processes. Such patterns are used to filter out data that are likely to reflect effects from crustal assimilation to highlight δ18Ool values indicative of source-derived variability only. Although filtered, the dataset reveals, that δ18Ool values, significantly lower than the canonical depleted upper mantle value, are derived from the Iceland mantle. Coupled δ18Ool and 3He/4Heol measurements done on olivine crystals from the same samples demonstrate that low-δ18O components (down to δ18Oolivine = 4.2‰) are a trait of the modern Iceland plume and that low-δ18O and low-3He/4He components have become more apparent in the hotspot products since 60 Ma. Olivine chemistry characteristics suggest that this low-δ18O component is best sampled in melts that reflect contributions from pyroxenitic mantle lithologies, likely related to the recycling of oceanic lithosphere within the plume. An increase in plume flux, as traced by increasing plume temperatures and plume buoyancy after 35 Ma, led to enhanced entrainment of lower mantle material carrying recycled low-δ18O oceanic lithosphere. Such material has become more apparent with time as is reflected in source-derived low-δ18O and high 3He/4He values in olivine from the modern Iceland plume. Moreover, the coincidence of the Iceland plume-head and the North Atlantic Rift at from ∼25 Ma likely assisted and further promoted enhanced plume-melting. Thus, the combination of changes in mantle upwelling and tectonic reorganisation of the North Atlantic led to the introduction of recycled oceanic lithosphere into the Iceland plume and the formation of the Iceland Plateau ∼25 Ma.

Continental Magmatism: The Surface Manifestation of Dynamic Interactions Between Cratonic Lithosphere, Mantle Plumes and Edge‐Driven Convection

AbstractSeveral of Earth's intra‐plate volcanic provinces lie on or adjacent to continental lithosphere. Although many are believed to mark the surface expression of mantle plumes, our limited understanding of how buoyant plumes interact with heterogeneous continental lithosphere prevents further progress in identifying mechanisms at the root of continental volcanism. In this study, using a suite of 3‐D geodynamical models, we demonstrate that the magmatic expression of plumes in continental settings is complex and strongly sensitive to the location of plume impingement, differing substantially from that expected beneath more homogeneous oceanic lithosphere. Within Earth's continents, thick cratonic roots locally limit decompression melting. However, they deflect plume conduits during their ascent, with plume material channeled along gradients in lithospheric thickness, activating magmatism away from the plume conduit, sometimes simultaneously at locations more than a thousand kilometres apart. This magmatism regularly concentrates at lithospheric steps, where it may be difficult to distinguish from that arising through edge‐driven convection. At times, the flow field associated with the plume enhances melting at these steps long before plume material enters the melting zone, implying that differentiating geochemical signatures will be absent. Beneath regions of thinner lithosphere, plume‐related flow can force material downwards at lithospheric steps, shutting off pre‐existing edge‐related magmatism. Additionally, variations in lithospheric structure can induce internal destabilization of ponding plume material, driving intricate magmatic patterns at the surface. Our analysis highlights the challenges associated with linking continental magmatism to underlying mantle dynamics, motivating an inter‐disciplinary approach in future studies.

Evaluation of a Revised AERMOD Treatment of Plume Dispersion in the Daytime Elevated Stable Layer

Advanced dispersion models such as AERMOD specifically address the portion of a plume emitted in convective conditions that is sufficiently buoyant to rise into the stable layer above the elevated inversion. This portion of the plume mass is often referred to as the “penetrated plume” because that plume component breaks through the elevated inversion and penetrates into the stable layer aloft. A pre-mature mixing of the penetrated plume to the ground has been identified in the current formulation of AERMOD, which is the USEPA-preferred short-range dispersion model and used in several other countries. This behavior has been observed based on data from field studies where the model is found to overpredict ground-level concentration events due to the penetrated plume component, with the timing of these peak predictions too early in the day. A proposed update to AERMOD to address the penetrated plume issue (referred to as “HBP” for modifications particularly important for “highly buoyant plume”) is documented and evaluated in this manuscript. The revised approach involves a check on the convective mixing height for the current hour as well as the next hour to determine how much of the penetrated plume has been captured by the convective boundary layer by the end of the current hour. The amount of the penetrated plume mass that is allowed to mix to the ground in the HBP modifications depends upon the result of this calculation. The HBP modification has been evaluated as an update to AERMOD for 3 databases along with a sensitivity analysis of the effects of the HBP changes on a variety of stack heights and buoyancy fluxes. The findings of the evaluation indicate that the HBP changes to AERMOD result in reduced overprediction tendencies. “Implications Statement” for the HBP paper being submitted to JAWMA A proposed enhancement to AERMOD to address a pre-mature mixing of penetrated plume material to the ground has been performed by implemented and evaluated by the authors. The enhancement, referred to as the highly buoyant plume (HBP) is based on work developed by Dr. Jeffrey Weil. HBP is designed to better characterize the penetrated plume behavior in the model such that it aligns more closely with observations based on data from field studies.

Framework for Improving Land Boundary Conditions in Ocean Regional Products

The coupling of coastal or regional ocean models to hydrological models or observed data is currently an uncommon practice in operational oceanography. Though hydrological models are regarded as a powerful and useful tool for estimating the quantity and quality of freshwater running in a watershed, they fail to provide accurate results for river flow reaching the coastal area due to water-management activities occurring within the river catchment, activities such as human consumption, irrigation, storage, etc. For this reason, many coastal and regional ocean models continue to impose surface zero-salinity discharges as land boundary conditions for representing such a dynamic boundary. Moreover, river flows are based in climatologies, thus neglecting seasonal and interannual variability. To achieve those objectives, this study proposes an integrated methodology ranging from watershed models to validation in the coastal area and passing through methods and proxies for integrating the freshwater flows into regional ocean models. The main objective of this study is to explore the results obtained by using more sophisticated land boundary conditions based on the capacities of state-of-the-art hydrologic models combined with observation networks. In addition to the evaluation of the source of river-flow data, this work also explores the use of estuarine proxies based on simple modelling grids. The estuarine proxies enable the incorporation of the mixing processes that take place in estuaries into the land fluxes and obtain the plume momentum. The watershed, estuarine proxies, and ocean were modelled using the MOHID Water modelling system and evaluated in western Iberia waters. The modelling results served to illustrate the sea surface salinity extension of the Western Iberia Buoyant Plume (WIBP) during an extreme event in March 2018.