Plume Distribution Research Articles

Three-dimensional distribution of aerosols of multiple types at daily scale using TROPOMI spaceborne observations

We present new satellite-based daily observations of the 3D distribution of aerosols from most common types and origins, both over land and ocean, derived from TROpospheric Ozone Monitoring Instrument (TROPOMI) measurements. This is done using the so-called AEROS5P (AEROsol Sentinel 5 Precursor) approach which retrieves vertical profiles of aerosol extinction from passive measurements of high-resolution spectral reflectance in the visible and near infrared for cloud-free conditions. Previous work demonstrated the potential of this approach, but it was initially applicable only to biomass burning aerosols with limited spatial coverage over ocean. The new methodology presented here generalizes the method for the most common aerosol types and improves spatial coverage. We take advantage of an operational aerosol type product derived from Visible Infrared Imaging Radiometer Suite (VIIRS) observations, combined with those from TROPOMI, to choose a priori aerosol set of intensive properties (particle size and refractive index). AEROS5P shows good agreement in aerosol optical depth, when compared to observations from AErosol RObotic NETwork and other widely used satellite measurements. Additionally, the vertical distribution of aerosol plumes of different types derived from AEROS5P agrees well with lidar coincident observations from the Advanced Topographic Laser Altimeter System spaceborne sensor and ground-based measurements. We utilize AEROS5P to analyze the three-dimensional distribution of aerosols for four different scenarios. It traces the three-dimensional pathways of smoke from Canadian wildfires reaching the Eastern USA in July 2023, desert dust from the Namibian deserts over the southeast Atlantic Ocean confined near the surface during the same month, fine aerosol pollution over Western Europe during June 2019, and an extreme dust event mixed with fine aerosol pollution over Northern China in March 2021. These observations provide valuable insights into aerosol transport patterns, surface-level air quality impacts, and can potentially be used to assess the radiative effects at various atmospheric layers.

Identification of tephra horizons in a glacier on the Ushkovsky volcano (Kamchatka)

Identification of tephra and its allocation (association) with known eruptive events allows obtainng chronostratigraphic markers, on the basis of which an age scale for dating glacial strata can be developed. To determine the sources of ash in the ice core obtained in 2022 during drilling of glacier in the crater of the Ushkovsky volcano in Kamchatka, the chemical composition of volcanic glass in individual ash particles was analyzed. The accuracy of determination of the volcanic glass composition was verified by analyzing of international standard samples of volcanic and synthetic glass. Based on a comparison of the data we obtained with published data on the composition of tephra glasses from the present-day eruptions in Kamchatka, we determined affiliation of each tephra horizon to specific volcano-source. We have found that the main source of tephra in the ice core of the Ushkovsky Glacier is the Kliuchevskoi volcano, which is the closest and the most productive one among the Kamchatka volcanoes. Ash particles from Bezymyannyi volcano were identified in two horizons. A mixed population of particles was found in one of the horizons, including the ash particles from volcanoes Kizimen, Kliuchevskoi and Bezymyannyi. Analysis of published data on the chronology and distribution of ash plumes from known eruptive events made it possible to confidently correlate the tephra horizon at a depth of 762–777 cm with the initial phase of the eruption of the Kizimen volcano in late 2010–early 2011. Ash from the uppermost tephra buried in the glacier at depths of 89–94 cm belongs to the Bezymyannyi volcano eruption, which the most likely occurred in October 2020. Single particles with rhyolitic composition of glass in the sample from the depth of 348–354 cm may belong to the eruption of the Shiveluch volcano in December 2018. The results of our work can be used on further studying of the ice core from the Ushkovsky volcano, in particular for comparison and correlation with the chronostratigraphic data obtained by glacio-chemical and isotope methods.

Impact of ventilated tunnels on smoke peculiarities in train carriage fires with multiple lateral openings

This research investigates the dynamics of smoke dispersion in a subway train carriage with multiple lateral openings within a ventilated subway tunnel. Numerous extensive full-scale numerical simulations were conducted to analyze the thermal plume distribution within multiple lateral openings of a train carriage, and the longitudinal and transverse maximum excess ceiling temperature. The results reveal that the heat release rates have a greater impact on the airflow in the carriage than velocities ,even when the longitudinal ventilation velocity reaches 8 m/s or the heat release rate reaches 15 MW. The multiple lateral openings cause significant differences in smoke flow characteristics compared to tunnels with both ends open. Additionally, the transverse maximum ceiling excess temperature inclines towards the lateral opening side due to asymmetrical air entrainment. The analysis of longitudinal maximum ceiling excess temperature identified two regions based on the dimensionless heat release rate, showing a linear increase followed by a constant phase dependent on the heat release rate, with a maximum longitudinal excess gas temperature of 1242 K. Additionally, a relationship between the dimensionless heat release rate and the transverse dimensionless maximum ceiling excess temperature was established. This study can be used as a guide for smoke exhaust mitigation and fire safety measures in the event of subway train carriage fires.

The Analysis of Permeability Influence on CO2 Plume based on Reservoir Simulation

Abstract Permeability is critical in site characterization and geoscience studies for carbon capture and storage projects. There is significant uncertainty of CO2 movement in the subsurface caused by permeability. This study aims to analyze the influence of permeability on the movement of CO2 plumes using a synthetic single-porosity model based on reservoir simulation. By simplifying geomechanics, employing tornado experimental design, as well as utilizing Pearson and Spearman correlations from 30,000 neural network proxy models based on Latin Hypercube and Monte Carlo experimental design, this research successfully explains the impact of permeability on CO2 movement. The reservoir can withstand pressures up to 6500 psi without rock failure. The total CO2 injection with a 90% probability is ∼1.3 TSCF equivalent, with an injection rate of 30 MMSCFD, optimized for a duration of 120 years. Initially, the CO2 movement tends to be upward during injection due to gravitational effects, but over time, it tends to move laterally. Vertical permeability exhibits a negative correlation with total CO2 injection, lateral distribution of CO2 plumes, and CO2 solubility in water. On the other hand, horizontal permeability shows a positive correlation with total CO2 injection. Factors such as perforation location and layer thickness also influence the extent of permeability’s role. However, the lateral and vertical movement of CO2 in this study has not been fully identified, and more complex quantification formulas are needed in commercial simulators. Despite the limitations in data and computational resources, this research successfully explains the movement of CO2 plumes and highlights the importance of other factors such as porosity, perforation location, layer thickness, among others. The recommendations of this study include the use of more complex quantification formulas to model the movement of CO2 plumes, along with increasing the complexity of the model.

The characteristics of the vertical distribution of radionuclide in free troposphere from simplified release scenarios: a case study

Dose estimation in the upper air is not studied as much as on ground level or in boundary layer. However, there is a need from stakeholders in aviation industry for a reasonable estimation of the radioactive plume impact at cruising levels. This study aims to provide a quantitative estimation of the dose and how reliable it is for dispersion processes up to seven days. A Lagrangian atmospheric dispersion model is used to estimate quantitively the vertical extension of radionuclides from simplified hypothetical radionuclide release scenarios. Sources at different latitudes are selected for simulation in a boreal winter case. Three meteorological data are examined to test the sensitivity of vertical plume distribution to driving meteorological data. The vertical distribution of air concentration of radionuclides is investigated and the associated uncertainties are analysed. It is found that the vertical extension of plumes is sensitive to meteorological data being used where vertical turbulent velocities play an important role. It is therefore necessary to address the uncertainties of air concentration or dose in the free troposphere and caution must be taken when providing the results to stakeholders.

Assimilation of Geophysics-Derived Spatial Data for Model Calibration in Geologic CO2 Sequestration

Summary Uncertainty in geological models usually leads to large uncertainty in the predictions of risk-related system properties and/or risk metrics (e.g., CO2 plumes and CO2/brine leakage rates) at a geologic CO2 storage site. Different types of data (e.g., point measurements from monitoring wells and spatial data from 4D seismic surveys) can be leveraged or assimilated to reduce the risk predictions. In this work, we develop a novel framework for spatial data assimilation and risk forecasting. Under the U.S. Department of Energy’s National Risk Assessment Partnership (NRAP), we have developed a framework using an ensemble-based data assimilation approach for spatial data assimilation and forecasting. In particular, we took CO2 saturation maps interpreted from 4D seismic surveys as inputs for spatial data assimilation. Three seismic surveys at Years 1, 3, and 5 were considered in this study. Accordingly, three saturation maps were generated for data assimilation. The impact from the level of data noise was also investigated in this work. Our results show increased similarity between the updated reservoir models and the “ground-truth” model with the increased number of seismic surveys. Predictive accuracy in CO2 saturation plume increases with the increased number of seismic surveys as well. We also observed that with the increase in the level of data noise from 1% to 10%, the difference between the updated models and the ground truth does not increase significantly. Similar observations were made for the prediction of CO2 plume distribution at the end of the CO2 injection period by increasing the data noise.

Experimental and numerical investigation of the effect of deep-sea mining vehicles on the discharge plumes

During mining activities, deep-sea mining vehicles (DSMVs) are highly susceptible to causing massive disturbance to the seafloor sediment, resulting in the formation of plumes due to underlying turbulence and currents. To gain a better understanding of the dispersion mechanism of sediment plumes, both experimental and numerical methods were employed. The numerical model was primarily used to characterize the solidity and liquidity of the sediment plume through volume of fluid and discrete phase model methods, respectively. The experimental data were validated against the numerical results. The plume distribution was studied in physical experiments for three different DSMV parameters. The study findings indicate that the discharge of the plume in the near field occurs in three stages due to a combination of plume release inertial forces, negative buoyancy in the water column, and wall restoring forces. Additionally, the increase in the travel velocity of the DSMV reduces the propagation of the plume in the direction of discharge and instead increases its lateral spread across the bottom surface. As the size of the DSMV decreases in three dimensions, changes in the vertical vortex structure become dominant in the plume distribution. This leads to a reduction in the length of the plume head and a faster sinking of the plume. When the wake Froude number Frw is between 0.7 and 6.8, representing the wake turbulence effect of DSMV on plume discharge, the diffusion width of the plume on the bottom surface is linearly related to Frw.

Numerical modelling of CO2 leakage through fractured caprock using an extended numerical manifold method

In this study, the cohesive element-based numerical manifold method (Co-NMM) and unified pipe network method (UPM) are further developed and integrated to analyze the CO2 leakage through fractured caprock considering CO2-water two-phase flow, CO2 adsorption and deformation of both caprock matrix and fractures. First, the Co-NMM is modified to better treat complex discrete fracture networks (DFNs) problems, while the CO2 adsorption effect is introduced into the UPM governing equation of two-phase seepage. And then, a two-phase seepage-stress coupling model and an implicit sequential solution are successively adopted to combine the Co-NMM and UPM tightly to capture the interplay between the two-phase flow and fractured caprock accurately and flexibly. The extended Co-NMM formulation is verified by reproducing the CO2 plume distribution evolution process in deep brine aquifers for geological sequestration. Finally, we conduct a series of simulations where CO2 displaces water through caprock formation with different DFNs that serve as a dominant conduit for potential CO2 leakage from storage reservoirs. The effects of DFN connectivity and hydraulic characteristics on the CO2 leakage through caprock are discussed. The research results can offer a reference for the evaluation of caprock sealing efficiency and also indicate that the modified hybrid NMM-UPM method is a potentially effective tool for analyzing CO2 leakage through fractured caprock under complex DFN conditions.

Time-lapse attenuation variations using distributed acoustic sensing vertical seismic profile data during CO2 injection at CaMI Field Research Station, Alberta, Canada

For seismic monitoring of geologic [Formula: see text] storage, it is useful to measure time-lapse (TL) variations of seismic attenuation. Seismic attenuation directly connects to different petrophysical parameters within the [Formula: see text] storage complex. We have developed an approach to derive smooth time-variant amplitude spectra from seismic signals by using the sparse strongest signal peaks, and then measuring two different attributes (conventional Q factor and its “geometric” counterpart) characterizing the path effects of seismic attenuation from the smooth spectra. This approach is straightforward and does not require sophisticated algorithms or parameterization schemes. We apply this approach to TL distributed acoustic sensing (DAS) vertical seismic profile (VSP) data from the Field Research Station (FRS) [Formula: see text] injection project in southern Alberta, Canada. High-quality stacked reflection records are obtained from the baseline and monitor DAS VSP surveys at the FRS and TL attenuation-attribute differences are derived from these reflection records. TL variations of attenuation are observed within the injection zone at the FRS, which are interpreted as being related to the injected [Formula: see text]. Although there is always a significant trade-off between the accuracy and temporal resolution of the measured attenuation parameters, reliable attenuation measurements around the injection zone are still achieved with an in-use reflection signal of a sufficient length and bandwidth. Attenuation attributes measured from this approach can be an advantageous tool for monitoring the distribution and migration of [Formula: see text] plumes.

Simultaneous identification of a non-point contaminant source with Gaussian spatially distributed release and heterogeneous hydraulic conductivity in an aquifer using the LES-MDA method

Space-temporal distribution of the contaminant plumes and aquifer properties is critical for groundwater management. However, most previous studies have focused on point source identification, barely exploring the identification of non-point sources. Xu et al. (2022) proposed to identify non-point sources but did not consider uncertainties in aquifer properties and release mass loading. In this work, we have implemented an application of the localized ensemble smoother with multiple data assimilation (LES-MDA) for the simultaneous identification of Gaussian hydraulic conductivities and non-point source parameters including Gaussian release mass-loading by assimilating both piezometric head and concentration observations in a synthetic confined aquifer. The results prove that the LES-MDA is not only capable of providing accurate identification of the spatial architecture of non-point contaminant sources and related release parameters (such as initial release time, and release duration) but also spatially heterogeneous release mass-loading and hydraulic conductivities.

Advancing spatiotemporal forecasts of CO[formula omitted] plume migration using deep learning networks with transfer learning and interpretation analysis

Accurate and timely forecasts of CO2 plume distribution throughout the injection and post-injection phases are crucial for detecting plume migration, assessing leakage risks, and supporting operational decisions in geologic carbon storage (GCS). Current convolutional neural network-based approaches primarily focus on spatial information and overlook temporal dependencies in plume distributions, thus limiting their ability to capture dynamic movement effects and provide accurate predictions of plume migration. In this work, we propose two deep learning models, Auto-Encoder (AE)-LSTM and Encoder-Decoder (ED)-ConvLSTM, each uniquely designed to capture both spatial and temporal features. We apply the proposed methods to forecast the dynamic distribution of CO2 plumes based on 108 reservoir simulations over a 30-year injection and a 30-year post-injection period. The results indicate that the ED-ConvLSTM model outperforms the AE-LSTM model in accurately predicting the spatiotemporal dynamics of CO2 plume migration, achieving R2 values above 0.99. To provide a deeper understanding of these model predictions, we employ a gradient-based explanation method on the trained models. This approach provides insights into the influence of input variables on plume migration forecasts and uncovers the underlying prediction mechanisms of the proposed models. Furthermore, we introduce a transfer learning technique, enabling fast and accurate plume migration forecasting in the post-injection phase by leveraging the trained model during the injection phase. This reduces the necessity for extensive data collection or re-training. The methods proposed in our work enhances the performance and interpretability of CO2 plume migration forecasts, thereby facilitating informed decision-making throughout the entire lifecycle of GCS applications.

Numerical simulation study on combustion characteristics of square hollow oil pool fire in ship cabins

To study the combustion phenomenon of square hollow fire sources in ship cabins, PyroSim software was used to establish numerical models of different inner and outer edge lengths of the same fire source area. FDS software was used to numerically simulate fire temperature and smoke spread, observe and record the flame and smoke spread characteristics in cabins under different working conditions, and analyze the temperature distribution of flame plumes and the temperature field characteristics inside the cabin. The results indicate that: During the combustion process of a square hollow fire source in a ship’s cabin, a typical flame convergence phenomenon occurs, and the flame temperature of the fire source combustion first increases significantly and then gradually stabilizes. The smaller the inner edge length of a square hollow, the higher the combustion temperature of the fire source, the faster the heating rate, the more obvious the phenomenon of fire convergence, and the more intense the flame combustion. As the inner edge length increases, the influence of flame combustion at the center of the square decreases, and the peak temperature of the flame decreases with a smaller amplitude and tends to concentrate.

Delineation of LNAPL plumes in a clay-rich site in Gyeongsangnam-do Province, South Korea: integration of geophysical survey data with borehole data and soil sampling information.

To effectively delineate the spatial distribution of oil contaminant plumes, geophysical methods indirectly measure the physical properties of the subsurface and can provide spatial information and images on a large scale, as opposed to traditional direct methods such as borehole drilling, sampling, and chemical analysis, which are time-consuming and costly. However, interpreting geophysical responses over non-aqueous phase liquid (NAPL)-contaminated sites is not straightforward due to inconsistent responses from biodegraded oil contaminants. In this study, we performed multi-geophysical surveys including seismic refraction, ground-penetrating radar, electrical resistivity tomography (ERT), and induced polarization (IP) surveys, to locate NAPL-contaminated zones in a clay-rich site. To reduce ambiguity in discriminating between oil contaminants and clay layers, we first figure out the geological structure of the site by interpreting geophysical data incorporating with borehole data. The ERT data highlighted the heavily contaminated regions in the unsaturated zone but were less distinctive below groundwater levels. Conversely, IP responses revealed potential hotspots within the clay layers, extending beneath the groundwater. Considering the 3D geological model, NAPL-contaminated zones are properly delineated through interpretation of ERT and IP data together with borehole data, and the contaminant source zone was properly estimated within the site.

On the numerical assessment of engine exhaust plumes with a scaled cowling

The ability to predict the characteristics of engine exhaust is important to determining heat signatures on various components of the aircraft body. This is often obtained through numerical means such as RANS, which however relies closely on the choice of the turbulence model for accurate predictions. In this study, predictions of exhaust plumes from four turbulence models are compared against results from particle image velocimetry of a scaled helicopter engine exhaust. These models include the standard k − ϵ, realizable k − ϵ, shear-stress transport (SST) k − ω, and Durbin’s turbulence models. All four turbulence models managed to capture the general shape of the exhaust when analyzed through the velocity contours at two measurement windows. However, the comparisons of velocity contours fail to describe the shift of the predicted plume from the experiments, which is important for fuselage/tail impingement. To obtain further insights to the shifts, a visual correlation in the form of a confidence ellipse through principal component analysis (PCA) is introduced and plotted for the predicted plumes. All the models’ plume predictions showed quantifiable shifts in their mean-centers when compared to the measurements. In terms of matching the measurements’ statistical maximum variance of the plume distribution at the furthermost plane, it was found that the realizable k − ϵ performed the best among the models. On the other hand, the SST k − ω and Durbin’s model performed the best in predicting bivariate ( x and y coordinates) distribution of the plume at the furthermost plane.

Feasibility Assessment of Acid Gas Injection in an Iranian Offshore Aquifer

Acid gas injection operations function as the commercial equivalent of certain aspects within the realm of geological CO2 storage. Acid gas, composed of H2S and CO2, alongside minor quantities of hydrocarbon gases stemming from either petroleum production or processing, constitute the composition of acid gas. The primary aim of acid gas injection operations lies in the disposal of H2S. Nevertheless, substantial volumes of CO2 are concurrently injected due to the economic impracticality of segregating the two gases. This investigation delves into the comprehensive, step-by-step procedure that can be employed to determine the suitability of a field or formation for acid gas injection, utilizing all accessible data, including the literature and data from neighboring fields. This approach incorporates sensitivity analysis of various parameters to ascertain the feasibility of AGI while minimizing costs and time consumption. The focus of this study centers on evaluating the feasibility of Acid Gas Injection (AGI) in a saline aquifer offshore in Iran. The assessment encompasses the examination of reservoir properties, geomechanical aspects, caprock integrity, and gas plume dynamics. The Surmeh formation emerges as a promising candidate for AGI due to the presence of upper dolomite and lower carbonate within the rock formations. Geomechanical analysis reveals a pore pressure of 3800 psi and a fracture pressure of 6100 psi. Caprock integrity, particularly within the Hith formation, emerges as pivotal for both containment and long-term stability. Seismic mapping highlights variations in caprock thickness, influencing containment effectiveness. Capillary trapping emerges as a significant factor in short-term gas entrapment and plume distribution. Numerical simulations elucidate the impact of heterogeneous rock properties on capillary trapping and gas plume movement. The projection estimates approximately 2 TCF (Trillion Cubic Feet) of acid gas injection into the Surmeh formation. Based on the acid gas content and the gas in place at the source of injection, the recommended injection rate stands at 180 MMSCFD (million standard cubic feet per day). The formation’s inherent tightness limits injectivity, allowing for a maximum achievable rate of 7 MMSCFD with a permeability of 1 mD (millidarcy). However, a higher porosity (12%) and a permeability of 100 mD enable more efficient injection without fracturing the formation. To achieve this, it becomes imperative to implement two injection wells, each with a capacity of 90 MMSCFD.

Enhanced impact of prolonged MHWs on satellite-observed chlorophyll in the South China Sea

Marine heatwaves (MHWs) are period of extreme ocean temperatures that can last from a few days to several years. The increasing frequency and intensity of MHWs have devastating impacts on marine ecosystems. This study explores the characteristics of MHWs from 1982 to 2021 and their effects on chlorophyll (Chl) from 1998 to 2021 in the South China Sea (SCS), utilizing satellite data and reanalysis products. MHWs were classified into short-duration MHWs (SMHWs) and long-duration MHWs (LMHWs) based on their duration to analyze their effects. High-intensity and frequent MHWs were observed in the coastal regions of China, the western SCS (WSCS, average depth more than 200 m), and southwest of the Luzon Strait (LS, average depth more than 200 m). MHWs have increased by 14 days (R2 = 0.42, p < 0.01) and 0.99 times (R2 = 0.36, p < 0.01) per decade over the past four decades. The per-decade rate of increase is 44 % of the average MHWs days, and 36 % of the frequency in entire SCS.LMHWs contributed the most to this increase at a rate of 6.5 days (R2 = 0.43, p < 0.01) and 0.25 times (R2 = 0.45, p < 0.01) per decade. The trend of MHWs in the Pearl River estuary (PRE, On the coastal continental shelf, average depth <200 m) is noteworthy for cause for concern, increasing by 19 days and 1.4 times per decade.During SMHWs, the Chl response was relatively insignificant, with roughly 3 % negative anomalies across the entire SCS. However, LMHWs had a more profound impact on Chl,which decliend 8 % over the SCS, especially in the WSCS, PRE, and southwest of LS. During summer in the WSCS and winter southwest of LS, the negative anomalies of Chl varied between 20 % and 40 % of its daily climatology for each grid. In contrast, a noteworthy positive Chl response was observed in the PRE and adjacent waters during summer. The duration and intensity of MHWs in these regions affected Chl, and the suppression of Chl was more prominent as the intensity and duration increased, except in the PRE, where MHWs promoted Chl during both spring and summer. We identified various mechanisms by which MHWs impacted Chl in these regions, including weakened upwelling and eddies in the WSCS, changes in plume distribution along the PRE, and shallow mixed layer and weakened cyclonic circulation in the LS during winter. Our study underscores the need for immediate conservation measures to mitigate the effects of MHWs on marine ecosystems, particularly in the PRE and adjacent regions where harmful algal blooms (HABs) are a frequent and ongoing threat.

Development of a circumferential-scanning tomography system for the measurement of 3-D plume distribution of the spacecraft plasma thrusters

Plasma thruster—currently used on many spacecraft—is intensively developing to meet the new demands of space propulsion. The spatial distribution of the thruster plume is essential for thruster study. However, it is difficult to construct plume distribution due to the traditionally-used probe method's time-consuming point-by-point scanning procedure. In this work, a circumferential-scanning tomography (CST) system is developed as a powerful tool to characterize the plume distribution. The CST system is installed inside the vacuum chamber, rotates around the thruster, and takes plume images from different circumferential angles. The 3-D plume distribution is reconstructed using a filtered back-projection method from these images. The CST system is demonstrated on a plasma thruster. The thruster plume—twisting in three-dimensional space—is successfully reconstructed by the CST system. The reconstructed ion density of the plume is compared with a Faraday probe. The overall root mean square difference is ∼11 % along the trajectory.

Modelling Plume Development with Annual Pulses of Contaminants Released from an Airport Runway to a Layered Aquifer, Evaluation of an In Situ Monitoring System

In cold climates, the use of de-icing chemicals in the winter can lead to groundwater contamination, especially when used in large quantities, such as at airports. Oslo Airport, Gardermoen, is situated on Norway’s largest rain-fed aquifer. Potassium formate is used to remove ice from runways and propylene glycol from airplanes; the organic parts are degradable. Most of the wells to monitor the spread of de-icing chemicals in the underlying aquifer have well screens near the groundwater level, while the runways and the source of de-icing chemicals are near the groundwater divides, where vertical flow is expected. The objective of this study is to demonstrate the importance of layers and time-varying recharge on the spreading of contaminant plumes in an aquifer near a groundwater divide. This is done with numerical modelling. The model results show increased vertical transport of the added tracer in the presence of horizontal layers, both continuous and discontinuous, in the aquifer. With certain distributions of hydraulic conductivity, Ks, we demonstrate that deeper monitoring wells are required. With the scenarios modelled here, time-varying recharge has a weaker effect on plume distribution. Measured concentrations of potassium and total organic carbon show the cyclic effect of seasonally varying recharge of contaminants, and an asymptotic accumulation of concentration over time, that is consistent with the model runs. In conclusion, groundwater monitoring systems near a groundwater divide should include multi-level samplers to ensure control of the vertical plume movement.

Two Decades of Monitoring Hydrothermal Plumes at the Brothers Submarine Volcano, Kermadec Arc, New Zealand

Abstract Brothers volcano is arguably the most well-studied submarine arc volcano on Earth. Between 1996, when massive sulfides were first recovered by dredging, and 2018, when International Ocean Discovery Program (IODP) Expedition 376 recovered cores from as deep as 453 m below the sea floor at two chemically distinct hydrothermal upflow zones, over 60 conductivity-temperature-depth (CTD) vertical casts and tow-yo operations mapped hydrothermal plumes over and around the edifice by employing hydrothermal tracer-specific sensors. These surveys started in 1999 and were completed during nine separate expeditions at one- to three-year intervals, except for a six-year gap between 2011 and 2017. Hydrothermal plume distributions over this two-decade period show variability in the intensity and vertical rise height of plumes from the four main vent fields (Upper Cone, Lower Cone, NW Caldera, and Upper Caldera, with the latter not discovered until 2017). Upper Cone plumes were more intense than all other sites in 1999, 2002, 2007, and 2009, then significantly diminished from 2011 to 2018. The Lower Cone plume was the most intense in 2004, then the NW Caldera site became the dominant source of hydrothermal particles from 2011 to 2018. Despite the gap of six years between 2011 and 2017, hydrothermal output appears to have increased within the caldera sometime after the 2009 survey while simultaneously decreasing in intensity at the cone sites. This supports other evidence of linkages between the cone and caldera sites in the deep hydrothermal circulation system, and may be related to the predicted deepening of hydrothermal circulation, infiltration of seawater to facilitate “mining” of magmatic brines, and modulation of subseafloor mineralization processes associated with a modeled, pulsed injection of magmatic gasses. The surveys also revealed ways in which the highly variable regional hydrographic environment impacts the flux of hydrothermal products to the surrounding ocean. Plumes from sources located above the caldera rim disperse hydrothermal components without hindrance, but particles and heat from sources within the caldera become trapped and are dispersed episodically by caldera-flushing events. While on site for 18 days in 2018, repeat CTD casts into the deepest part of the caldera, which was isolated from the surrounding ocean, showed a progressive increase in temperature, representing a net heat flux of 79 MW from conductive and advective sources deeper than 1,570 m.

Vortex structure and small scale characteristics in turbulent Rayleigh–Bénard convection with mixed isothermal–adiabatic bottom boundary

Turbulent Rayleigh–Bénard convection with a mixed isothermal–adiabatic bottom boundary is simulated to investigate the effect of a nonideal thermal boundary on vortex structure and small-scale characteristics in turbulent convection. Simulations of convection with element aspect ratios of the mixed isothermal–adiabatic boundary cell ranging from 116 to 14 are performed at fixed Rayleigh and Prandtl numbers. Within the parameters adopted in this paper, the large-scale circulation under the mixed boundary condition is found to be consistent with that under the classical isothermal condition. However, the shape characteristics and distribution of plumes are strongly affected by the presence of a mixed isothermal–adiabatic boundary. Compared with the isothermal system, the mixed boundary breaks up the corner vortex structures and reduces the vortex intensity at the corners. Some complex vortex structures, such as a horseshoe vortex, appear in the case of a mixed isothermal–adiabatic thermal boundary. The vortices in side and face regions are governed by an enhancement rule that is related to the ratio of the element width to the typical plume size. The structure functions of scales above the element scale are greatly affected by the presence of a mixed boundary. The temperature structure function exhibits discrete characteristics, especially in the near-bottom region. However, the velocity structure function of the velocity retains continuous characteristics in all regions. The small-scale characteristics observed here help provide better understanding of the effect of a discrete boundary on buoyancy-driven turbulent convection.