Multiple Plumes Research Articles

Collective effect of thermal plumes on temperature fluctuations in a closed Rayleigh–Bénard convection cell

We report a systematic study of the collective effect of thermal plumes on the probability density function (p.d.f.) $P(\delta T)$ of temperature fluctuations $\delta T(t)$ in turbulent Rayleigh–Bénard convection. By decomposing $\delta T(t)$ into four basic fluctuation modes associated with single and multiple warm and cold plumes and a turbulent background, we derive an analytic form of $P(\delta T)$ based on the convolutions of the five independent modes. To test the derived form of $P(\delta T)$ in the multiple-plume regions, where the thermal plumes are heavily populated, we conduct time series measurements of temperature fluctuations in two convection cells; one is a vertical thin disk and the other is an upright cylinder of aspect ratio unity. For a given normalized position in most regions of the convection cell, all of the measured p.d.f.s $P(\delta T)$ for different Rayleigh numbers fall onto a single master curve, once $\delta T$ is normalized by its root-mean-square (r.m.s.) value $\sigma _T$ . It is found that the measured $P(\delta T/\sigma _T)$ at different locations along the symmetric horizontal and vertical axes of the convection cells can all be well described by the derived form of $P(\delta T/\sigma _T)$ . The fitted values of the parameters associated with the number of plumes in multiple plume clusters and their relative strengths and degrees of intermittency are closely linked to the spatial distribution of thermal plumes and local dynamics of the large-scale circulation in a closed convection cell. Our work thus provides a unified theoretical approach for understanding scalar p.d.f.s in a turbulent field, which is very useful not only for the present study but also for the study of many turbulent mixing problems of practical interest.

Hybrid Continuum/Rarefied Flow Simulations of Plume Interaction with Full-Sized Spacecraft

The present study performs hybrid Navier–Stokes (N-S) and direct simulation Monte Carlo (DSMC) simulations to predict surface pressures and heat fluxes imposed by plumes impinging on spacecraft in actual length scale. The first application was the impingement of H-II Transfer Vehicle main engine plumes on the International Space Station. It was found that the profiles of the surface pressure and heat flux imposed by the plume interactions strongly depend on the high-density regions generated by the interactions among multiple plumes and between plumes and upstream structures. The plume of a lunar lander was another application. A plume impinging on the lunar surface generated a strong shock wave near ground level, and some of the hot gases imposed larger pressures and heat fluxes as the altitude decreased. The third application was a cold-gas plume vented from rocket tanks. Although the nozzles were small, plumes expanded rapidly and subjected some rocket assemblies to various forces and cooling effects. Last, the last application to a thruster plume impinging on debris showed that the plume can impart enough torque to detumble the rotation of a debris. This study adequately demonstrated that the usefulness of the hybrid N-S/DSMC technique for assessing risks or exploring new ideas regarding plume impingement in actual spacecraft length scale, including the plume–plume and plume–surface interactions.

Variability of Natural Methane Bubble Release at Southern Hydrate Ridge

AbstractCurrent estimations of seabed methane release into the ocean (0.4–48 Tg yr−1) are based on short‐term observations and implicitly assume that fluxes are constant over time. However, the intensity of gas seepage varies significantly throughout a seep lifetime. We used instruments operated by the Ocean Observatories Initiative's Regional Cabled Array to monitor variations of gas emissions over the entire Southern Hydrate Ridge summit. We show that bubble plumes emanate from distinct and persistent vents. Multiple plumes can occur within each vent and the location of their outlets may shift progressively. Active bubble plumes vary temporally in number and intensity, even within single vents. Gas emission fluctuations are partly periodic and linked to the local tide. However, short‐term variability and high ebullition events unrelated to tidal cycles are also commonly observed. Our data indicate that small‐scale processes beneath or at the sediment surface are responsible for the short‐term variability of the venting activity that is otherwise modulated by tides. Furthermore, a decrease of venting at one vent may coincide with an increase in plume activity at other vents. Our results depict a spatially and temporally dynamic seep environment, the variability of which cannot be fully characterized without systematic and comprehensive monitoring of the entire area. These results indicate that flux estimations may be largely overestimated or underestimated depending on the time, duration, and place of observation. Although sudden ebullition bursts are hardly predictable, we argue that tidal cycles must be taken into consideration when estimating gas fluxes.

First retrieval of absorbing aerosol height over dark target using TROPOMI oxygen B band: Algorithm development and application for surface particulate matter estimates

Constraint of the vertical distribution of aerosol particles is crucial for the study of aerosol plume structure, aerosol radiative effects, and ultimately monitoring surface air pollution. We developed an algorithm to retrieve the aerosol optical central height (AOCH) of absorbing aerosols by using, for the first time, the oxygen (O2) A and B absorption band measurements from the TROPOspheric Monitoring Instrument (TROPOMI) over dark targets. For the retrieval, narrow band radiance at seven channels ranging from ultraviolet (UV) to shortwave infrared (SWIR) are convolved from TROPOMI hyperspectral measurements. Subsequently, cloudy pixels are screened out by using the slope of spectral reflectance, while aerosol types (dust and smoke) are classified by the wavelength dependence of aerosol path radiance in conjunction with UV aerosol index. Surface reflectance over land is derived from the MODIS surface bi-directional reflectance climatology, and over water from the GOME-2 surface Lambert-equivalent reflectivity (LER) database. The aerosol optical depth (AOD) and AOCH are retrieved through an approach of look-up-table accounting for AERONET-based dust and smoke optical properties. For multiple smoke and dust plume events around the world, our retrieved AOCH values agree with space-borne lidar CALIOP counterparts, with a mean bias of <0.15 km and a correlation coefficient of 0.85–0.87. Due in part to adding the O2 B band, our retrieval represents an aerosol extinction peak height better than the TROPOMI operational Level 2 aerosol layer height retrieved from only the O2 A band. The latter shows 0.5–2 km low bias, especially over land. Finally, the high potential of AOCH for improving surface PM2.5 estimates is also illustrated with a case study in which the high bias of surface PM2.5 in MERRA-2 data is corrected after being scaled by the retrieved AOCH.

Marine Electromagnetic Imaging and Volumetric Estimation of Freshwater Plumes Offshore Hawai'i

AbstractSubmarine groundwater discharge (SGD) is an important phenomenon that governs hydrological cycles at the land‐to‐ocean transition zone. SGD manifests as cold and buoyant freshwaters influx from the seafloor to the water column that contains carbon, nutrients, metals, and greenhouse gases, altering coastal areas' oceanographical and biochemical properties. Here, we present electromagnetic imaging of large‐scale freshwater plumes in high‐resolution, offshore west Hawai'i. Electrical resistivity models detect multiple vertical freshwater plumes extending from the seafloor to the ocean surface. Additionally, our models image extensive spatially distributed surface freshwater. The resistivity of these plumes and surface freshwater ranges from ∼1 to 30 Ωm. Resistivity‐to‐salinity calculation indicates a plume‐scale salinity range of ∼0.3–9.9, containing up to 87% of freshwater. Our results imply that substantial volumes of freshwater occupy water column plumes in Hawai'i. This study offers a new and effective method to elucidate hydrogeologic and ocean processes affecting biogeochemical cycles in coastal waters worldwide.

AFRP20: New P‐Wavespeed Model for the African Mantle Reveals Two Whole‐Mantle Plumes Below East Africa and Neoproterozoic Modification of the Tanzania Craton

AbstractAfrica's Cenozoic tectonism is often attributed to mantle plumes, particularly below East Africa, but their morphology, number, location, and impact on the African lithosphere are debated. The broad slow wavespeed African Superplume, ubiquitous in large‐scale tomographic models, originates below South Africa, reaching the surface somewhere below East Africa. However, whether the diverse East African mantle geochemistry is best reconciled with one heterogeneous upwelling, or current tomographic models lack the resolution to image multiple distinct plumes, remains enigmatic. S‐wavespeed tomographic images of Africa are legion, but higher frequency P‐wavespeed whole‐mantle models possessing complementary diagnostic capabilities are comparatively lacking. This hinders attempts to disentangle the effects of Cenozoic hotspot tectonism and Pan African (and older) tectonic events on the East African lithosphere. Here we develop a continental‐scale P‐wave tomographic model capable of resolving structure from upper‐to‐lower mantle depths using a recently developed technique to extract absolute arrival‐times from noisy, temporary African seismograph deployments. Shallow‐mantle wavespeeds are δVP ≈ −4% below Ethiopia, but less anomalous (δVP ≥–2%) below other volcanic provinces. The heterogeneous African Superplume reaches the upper mantle below the Kenyan plateau. Below Ethiopia/Afar we image a second sub‐vertical slow wavespeed anomaly rooted near the core‐mantle boundary outside the African LLVP, meaning multiple disparately sourced whole‐mantle plumes may influence East African magmatism. In contrast to other African cratons, wavespeeds below Tanzania are only fast to 90–135 km depth. When interpreted alongside Lower Eocene on‐craton kimberlites, our results support pervasive metasomatic lithospheric modification caused by subduction during the Neoproterozoic Pan‐African orogeny.

Australian New Year's PyroCb Impact on Stratospheric Composition

AbstractFollowing the Australian New Year's pyrocumulonimbus complex between 29 December 2019 and 4 January 2020, the Aura Microwave Limb Sounder (MLS) observed a plume with unprecedented enhancements of H2O and biomass‐burning products (CO, HCN, CH3Cl, CH3CN, and CH3OH) in the lower/middle stratosphere, accompanied by depressions in stratospheric species (O3and HNO3). The plume persisted for ∼110 days, circling the globe twice while ascending to 5.62 hPa (∼35 km). Air masses drawn off the main plume moved toward the developing Antarctic polar vortex but do not appear to have penetrated it. Comparison of species in the plume requires consideration of their measurements' spatial resolutions and background abundances. The apparent decay of some long‐lived plume constituents is largely attributable to their coarsening spatial resolution with height, which reduces observed peak values. Differing HCN/H2O signatures indicate that multiple early plumes originated from different stratospheric injection events.

Fate of river-borne floating litter during the flooding event in the northeastern part of the Black Sea in October 2018

This study is focused on delivery and fate of floating marine litter (FML) carried by rivers to coastal sea. We examine a large flooding event which happened in the northeastern part of the Black Sea in October 2018. A high resolution circulation model coupled with a Lagrangian particle model is applied to simulate transport of riverine FML in the coastal sea. During this flood multiple river plumes in the study area coalesced into one stripe of freshened water which occupied large segment of coastal sea along the shoreline. Riverine FML was transported within this stripe far off its sources in river mouths and remained arrested near the shore. As a result, approximately half of the discharged FML was washed ashore by the Stokes drift. FML, which remained in the sea, accumulated at convergence lines associated with large salinity gradients at the fronts between the river plumes and the ambient sea.

Enhanced hydrothermal activity on an ultraslow-spreading supersegment with a seismically detected melting anomaly

Seafloor hydrothermal venting fields occur on all ocean spreading ridges (OSRs) regardless of spreading rates. However, the distribution of seafloor hydrothermal activity such as frequency and spacing on ultraslow-spreading OSRs are poorly known. Chinese Dayang cruises from 2015 to 2016 conducted detailed water column surveys for seafloor hydrothermal activity using a towed system, with an array of turbidity sensors and a near-bottom camera, along the ultraslow-spreading Southwest Indian Ridge. Here we report the discovery of multiple hydrothermal plumes overlying segments 28, 29, and 30 between the Indomed and Gallieni fracture zones. From these data, and earlier explorations in segments 25–27, we identify nine active venting sites. The spatial density (Fs, sites/100 km) of active sites along the 394 km of ridge axis in our study area is thus 2.8, nearly 3× higher than predicted by the global trend of Fs for ultraslow OSRs in the InterRidge database. Previous studies concluded that an enhanced magma supply to the central Indomed–Gallieni supersegment 11–8 Ma is now limited to segment 27. Our results indicate that although hydrothermal activity may be most concentrated in segment 27, the discoveries of active venting in segments 25–30 implies the presence of additional magma bodies across a broad extent of the Indomed–Gallieni supersegment.

Optical and Chemical Analysis of Absorption Enhancement by Mixed Carbonaceous Aerosols in the 2019 Woodbury, AZ, Fire Plume

AbstractWildfires emit mixtures of light‐absorbing aerosols (including black and brown carbon, BC and BrC, respectively) and more purely scattering organic aerosol (OA). BC, BrC, and OA interactions are complex and dynamic and evolve with aging in the atmosphere resulting in large uncertainties in their radiative forcing. We report microphysical, optical, and chemical measurements of multiple plumes from the Woodbury Fire (AZ, USA) observed at Los Alamos, NM, after 11–18 hr of atmospheric transit. This includes periods where the plumes exhibited little entrainment as well as periods that had become more dilute after mixing with background aerosol. Aerosol mass absorption cross sections (MAC) were enhanced by a factor of 1.5–2.2 greater than bare BC at 870 nm, suggesting lensing by nonabsorbing coatings following a core‐shell morphology. Larger MAC enhancement factors of 1.9–5.1 at 450 nm are greater than core‐shell morphology can explain and are attributed to BrC. MAC of OA (MACOrg) at 450 nm was largest in intact portions of the plumes (peak value bounded between 0.6 and 0.9 m2/g [Org]) and decreased with plume dilution. We report a strong correlation between MACOrg(450 nm) with the fC2H4O2 (a tracer for levoglucosan‐like species) of coatings and of bulk OA indicating that BrC in the Woodbury Fire was coemitted with levoglucosan, a primary aerosol. fC2H4O2 and MACOrg(450 nm) are shown to vary between the edge and the core of plumes, demonstrating enhanced oxidation of OA and BrC bleaching near plume edges. Our process‐level finding can inform parameterizations of mixed BC, BrC, and OA properties for wildfire plumes in climate models.

Experimental research on aerodynamic force effect of multiple plumes based on pressure-sensitive paint technique

Experimental research on aerodynamic force effect of multiple plumes based on pressure-sensitive paint technique

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

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

Integral model for multiple forced plumes arranged around a circle in a linearly stratified environment

An integral model is developed to predict the mixing of multiple forced plumes evenly spaced around a circle in a stratified environment, e.g., buoyant plumes in nature. The model reasonably captures the significant plume boundary distortion caused by plume interactions at the touching height.

Remote sensing and identification of volcanic plumes using fixed‐wing UAVs over Volcán de Fuego, Guatemala

AbstractThis paper describes a series of proof‐of‐concept Beyond Visual Line Of Sight unmanned aerial vehicle flights which reached a range of up to 9 km and an altitude of 4,410 m Above Mean Sea Level over Volcán de Fuego in Guatemala, interacting with the volcanic plume on multiple occasions across a range of different conditions. Volcán de Fuego is an active volcano which emits gas and ash regularly, causing disruption to airlines operating from the international airport 50 km away and impacting the lives of the local population. Collection of data from within the plume develops scientists’ understanding of the composition of the volcano's output and is of use to scientists, aviation, and hazard management groups alike. This paper presents preliminary results of multiple plume interceptions with multiple aircraft, carrying a variety of sensors. A plume‐detection metric is introduced, which uses a combination of flight data and atmospheric sensor data to identify flight through a volcanic plume. Future work will develop the automation of plume tracking such that reliable scientific data sets can be gathered in a robust manner.

Effects of sloshing gas–liquid interface on dynamics of meandering bubble plumes and mixing in a shallow vessel: PIV and PLIF measurements

Gas–liquid shallow vessels are widely used in steel-making and refining processes in the steel industry. The efficiency of these processes or the quality of steel depends on the extent of gas–induced liquid–phase mixing achieved through top–blowing of oxygen and bottom–blowing of inert gases. In the present work, the effects of combined top and bottom gas injection and sloshing interface on the dynamics of gas–liquid flow, and their role in the liquid–phase mixing in a shallow vessel, that corresponds 1:6 scaled–down model of a ladle used in steel refining, are investigated. The effects of interface sloshing and top blowing on the motion of multiple meandering bubble plumes on the liquid–phase velocity distribution, recirculatory flow structures and turbulent kinetic energy are analyzed using the time–resolved Particle Image Velocimetry (PIV) measurements. Further, the role of the aforementioned parameters on the liquid–phase mixing is analyzed using the Planar Laser Induced Fluorescence (PLIF) measurements. The effects of coaxial and eccentric top blowing configuration on the liquid flow structures and mixing are also investigated. In the case of combined top and bottom gas injection, in which gas was injected very close to the interface, the liquid–phase mixing was found to be significantly faster than that of the other configurations considered in the present work, due to the formation of strong downward flow regions and higher turbulent kinetic energy provided by the top blowing. The present investigations help to understand and to quantify the effects of the different top gas injection configurations on the meandering motion of bubble plumes, liquid flow structures, turbulence and their contributions to liquid–phase mixing.

Calculating risk and payoff in planetary exploration and life detection missions

A framework for quantitative assessment of different mission architectures is described using historical data and formal (Bayesian) information value measures. The science value of the result is argued for binary questions (e.g. 'is there life on Europa?) to be proportional to the logarithm of the posterior likelihood ratio of the answers, and can be derived from estimates of the false positive rates of instrumentation and of the presence (PD) of biosignatures at a given site. The expectation payoff is the product of the sought result with Markovian success probabilities of the required steps of launch, landing, sample acquisition etc., and historical planetary mission data are reviewed to derive (sometimes dismaying) estimates of these probabilities, e.g. historical landing successes rates are of the order of 66% and when landing is successful, the conditional rates of individual sample acquisition/analysis/return have similar values. The history of seafloor exploration on Earth is used as an analog, and indicates that in the absence of close reconnaissance data, PD may have rather low values of the order of 1% or less. The data acquisition success framework is demonstrated on the value of single versus multiple landers, on the choice of flyby altitudes for multiple plume fly-through missions, and on the value of surface mobility, which for small values of PD multiplies the science return by the number of sites visited. Bayesian reasoning requires encapsulation of prior information: while such estimates (of biosignature presence, false alarm rates, etc.) are inevitably subjective, the decomposition of that information onto specific factors affords transparency into their contribution to the final result and provides a basis for rational mission evaluation.

Ultraviolet observation of Enceladus' plume in transit across Saturn, compared to Europa

Saturn's moon Enceladus is known to have a water vapor plume erupting from fissures across its south polar region. The plume was detectable in an observation of Enceladus transiting Saturn by Cassini's Ultraviolet Imaging Spectrograph (UVIS), but only at 1216 Å (Lyman alpha). Jupiter's moon Europa also may have multiple water vapor plumes, detected via similar ultraviolet observations of Europa transiting Jupiter (after being discovered via emission features) by Hubble Space Telescope. Comparison of the UVIS Enceladus transit observation to published Europa transit results reveals that Europa's plumes have very different properties than Enceladus' plume using the same observational technique. For example, the mass of water expelled is two orders of magnitude less at Enceladus compared to Europa.

Numerical study of natural convection in a horizontal concentric annulus using smoothed particle hydrodynamics

Natural convection is of great importance in many engineering applications. This paper presents a smoothed particle hydrodynamics (SPH) method for natural convection simulation. The conservation equations of mass, momentum and energy of fluid are discretized into SPH equations. The body force due to the change of density in a temperature field is considered by the Boussinesq approximation. The SPH method is validated by experimental results in temperature distribution. Then the SPH method is applied to characterize the natural convection in a horizontal cylindrical annulus with varying both Rayleigh number (102 to 107) and Prandtl number (0.01 to 10), while in literature the effect of Prandtl number was usually not considered. In general, the flow is stable at low Rayleigh number but unstable at high Rayleigh number. The numerical results show that the transition Rayleigh number, from stable to unstable, varies with Prandtl number. Four different convection states are identified from numerical simulations, namely, stable state with one plume, unstable state with one plume, stable state with multiple plumes, and unstable state with multiple plumes. The two one-plume states are observed for all Prandtl numbers, while the two multiple-plume states are observed only for Pr = 0.1 and 0.01. It is believed that high thermal diffusivity (low Pr) enhances heat transfer, which modifies the flow and induces instability. An exception case is observed at Pr = 0.1 – the flow is unstable at Ra = 104 but stable at Ra = 105, which can be explained by vortex interactions. Therefore, the flow states depend on not only the Rayleigh and Prandtl numbers but also the vortex interactions.

Roles of fault structures and regional formations on CO2 migration and distribution in shallow saline aquifer in Green River, Utah

Understanding CO2 migration and distribution in fault systems is essential to evaluate long-term secure CO2 storage and prevent hazardous effects caused by CO2 leakage. To elucidate the role of the fault system on subsurface CO2 migration and leakage processes, a two-dimensional multi-phase transport model was constructed to represent Little Grand Wash (LGW) and Salt Wash (SW) faults, where naturally originating CO2 is being leaked to the surface. According to simulation results, buoyant CO2 leaked through various pathways including the faults themselves, fault offsets, and damaged caprock. Because of both fault systems and caprocks serving as barriers, multiple trapped CO2 plumes were developed in this region. Presence of trapped CO2 plumes in the subsurface is supported by multiple field-observations (e.g., elevated soil CO2 fluxes, travertines, and CO2-driven cold-water geysers/CO2 springs) adjacent to both LGW and SW faults. Sensitivity studies were conducted with different permeabilities for faults and caprock, various CO2 source locations, and differing fault parameters (e.g., fault throw and cutoff angle), which affected subsurface CO2 distribution including size, shape, and location of trapped CO2 plumes. Finally, such trapped CO2 plumes have played a key role in the development of CO2-driven cold-water geysers in these regions.

Accountability of wind variability in AERMOD for computing concentrations in low wind conditions

Commonly large shifts of wind direction in low-wind conditions are poorly understood and are not sufficiently captured by air-quality dispersion model AERMOD. In the low-wind conditions, the observed concentration distribution is multi-peaked and non-Gaussian due to the large variability in the wind direction. To account the variability in the wind direction, a segmented approach is used by assuming that a shorter time period (2 min) mean wind direction estimate the plume more closely than the hourly mean wind. For illustration, concentration measurements from the low wind diffusion experiment conducted at Idaho are utilized. The qualitative performance of AERMOD with all the three options (FASTALL, LOW-WIND1, and LOW-WIND3) using segmented approach is reasonably good in terms of explaining the key characteristics such as multiple peaks and large plume spread of the observed concentration and is relatively better than the hourly approach (using hourly mean wind). The statistical measures for all the three options of AERMOD using segmented approach are found good in agreement with the observations, and a quantitative analysis based on ANOVA (analysis of variance) shows that the results from all the three options of AERMOD using segmented approach are found to be comparable at 5% significance level.