Plume Structure Research Articles

Observations Show Charge Density of Volcanic Plumes is Higher Than Thunderstorms

AbstractWe analyze slow electric field change and lightning mapping measurements to provide insight into the characteristics of volcanic lightning and the associated implications on charging processes and the charge structure of a Vulcanian eruption plume. Data were obtained during a multi‐instrumental field campaign at Sakurajima volcano in 2015 when the Showa crater was active. We combine the electric field change and lightning mapping data from one explosive eruption on June 6, 2015 to identify individual flashes. From this, we interpret the flash type and polarity. In addition, the long‐time constant of the electric field change instrument allowed measurement of the quasi‐static field associated with charge separation in the eruption plume. We find that both intracloud and cloud‐to‐ground discharges occurred, and the polarity of cloud‐to‐ground discharges were all negative. The quasi‐static field measurement showed the plume carried a net negative charge. We calculate both the total charge transferred by cloud‐to‐ground discharges and the net charge density of the eruption plume. We find that cloud‐to‐ground discharges transfer an average of −0.41C per flash and the net charge density was −33C/. The percent error is at least 200%, due to uncertainty in the antenna gain. We show that these estimates are consistent with lightning that is 100 m in length. Further, the average flash rate during the first 8 s following the onset of eruption was five flashes per second. After that time, the flash rate abruptly decreased, which may be related to the end of gas‐thrust forcing.

Mantle convection and possible mantle plumes beneath Antarctica – insights from geodynamic models and implications for topography

Abstract This chapter describes large-scale mantle flow structures beneath Antarctica as derived from global seismic tomography models of the present-day state. In combination with plate reconstructions, the time-dependent pattern of palaeosubduction can be simulated and is shown from the rarely seen Antarctic perspective. Furthermore, a dynamic topography model demonstrates which kind and scales of surface manifestations can be expected as a direct and observable result of mantle convection. The last section of this chapter features an overview of the classical concept of deep-mantle plumes from a geodynamic point of view and how recent insights, mostly from seismic tomography, have changed the understanding of plume structures and dynamics over past decades. The long-standing and controversial hypothesis of a mantle plume beneath West Antarctica is summarized and addressed with geodynamic models, which estimate the excess heat flow of a potential plume at the bedrock surface. However, the predicted heat flow is small, while differences in surface heat-flux estimates are large; therefore, the results are not conclusive with regard to the existence of a West Antarctic mantle plume. Finally, it is shown that global mantle flow would cause the tilting of whole-mantle plume conduits beneath West Antarctica such that their base is predicted to be displaced about 20° northward relative to the surface position, closer to the southern margin of the Pacific Large Low-Shear Velocity Province.

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.

Large eddy fire simulation applications from nuclear industry

Abstract A computational study has been carried out for predicting the behaviour of a pool fire source using the field-model based code Fire Dynamics Simulator (FDS). Time dependent velocity and temperature fields are predicted along with the resulting changes in the plume structure and its width. Firstly, a grid study was performed to find out the best grid size for this purpose. Then calculations were done which showed a very good agreement with earlier reported experimental based correlations for the temperature of the plume region. These studies have been extended to use this field-model based tools for modelling particular separate effect phenomena like puffing frequency and to validate against experimental data. There are several applications in nuclear industry like room fires, wildland fires, smoke or ash disposal, hydrogen transport in nuclear reactor containment, natural convection in building flows etc. In this paper the use of FDS with the advanced Large Eddy Simulation (LES) based CFD turbulence model is described for various applications: Fire simulation for Alpha storage, Bhabhatran teletherapy, pool fire for transport casks, fire PSA of a representative NPP, exhaust air fan buildings of a process plant and smoke dispersion in large fires around NPPs.

Extracting turbulence parameters of smoke via video analysis

Turbulence can be observed in almost all the smoke videos, so turbulence parameters can be extracted as features of smoke in the video smoke detection system. A video-based turbulence parameter measuring method is proposed in this paper. Turbulence can be regarded as a series of irregular flow states with instantaneous velocity fluctuations. First, the instantaneous turbulent velocity field is obtained from the real-time video using an optical flow method, and based on the velocity field information, the turbulence kinetic energy (TKE) and dissipation rate are calculated using large eddy simulation and sub-grid scale (SGS) models. Three different methods, Smagorinsky model, gradient model, and dimensional analysis, are used to obtain the dissipation rate. The results obtained using different methods are compared. The dissipation rate estimated using the SGS models shows high consistency and that estimated by the dimensional analysis has a similar distribution, which shows that the choice of the SGS model is not important for the dissipation rate estimation. Then the TKE is calculated, and the processed images show that each plume structure has its own life cycle and the rising velocity of each plume structure is steady. This method is efficient for the plume turbulence measurement, and it provides benefits to the experimental study of fire plumes. Furthermore, the measured parameters can be analyzed for video-based fire detection. It is a useful method in both scientific research and industrial development.

A Turbulent Magmatic Density Current and the Origin of the Anastomosing UG-1 Chromitites at Dwars River in the Bushveld Complex

AbstractThe origin of the enigmatic UG-1 chromitites at Dwars River in the eastern limb of the Bushveld Complex has been vigorously debated. The UG-1 chromitites form an anastomosing network of multiple layers that are hosted in poikilitic anorthosites and their formation has previously been explained by depositional, erosional, and intrusive processes. We propose that the UG-1 chromitites formed in response to the emplacement of a turbulent magmatic density current into the developing chamber. We use theoretical constraints in fluid mechanics to describe the evolution of the current and in this context, we provide an explanation for the enigmatic igneous features that are preserved at Dwars River. The current was emplaced as an instantaneous single pulse (fixed volume) of dense plagioclase-charged magma (i.e. a plagioclase slurry) that turbulently propagated along the chamber floor. Settling of the initial cargo of entrained plagioclase laths resulted in the formation of a thick sequence of feldspathic mush. The remaining melt turbulently outruns on the chamber floor ahead of the feldspathic mush. This led to the density current becoming stratified into two layers: (1) a basal granular layer, and (2) an upper melt-rich layer. Both layers evolved in a viscous-dominated regime from a Newtonian to a non-Newtonian behaviour (i.e. a power law fluid). In the current’s propagation stage, the resident magma in the chamber was entrained and efficiently admixed into the melt-dominated upper layer, producing a superheated chromite-saturated hybrid melt. Chromite precipitation from this hybrid melt led to the formation of a series of chromite-laden slurries that flowed in the turbulent current and were split (‘bifurcated’) as they passed around rising buoyant plagioclase diapirs that were developing in the back of the current. This led to the anastomosing and bifurcating nature of the UG-1 chromitites. The chromite slurries merged in the tail of the current and eventually back-injected into the deposited plagioclase cumulates on the chamber floor—forming the main ∼2-m thick UG-1 chromitite layer. The cooling and crystallization of the propagating upper layer of the current led to an increase in its viscosity that slowed its velocity until it eventually stagnated on the chamber floor. The mechanical sorting of crystals in plume structures became dominant at the stagnation stage. We argue that spatial variations in crystal packing controlled the heterogeneous distribution of brittle and ductile deformation features that are observed at Dwars River. In situ crystallization of trapped pore melts led to the nucleation of large orthopyroxene and plagioclase oikocrysts that cemented the anorthosite and the chromitite layers, respectively. The emplacement of magmatic density currents and intra-chamber magma mixing may be pertinent to the development of stratiform chromitites in incrementally constructed magma chambers.

Experimental study on the temperature and structure of the exhaust plume in valveless pulse detonation engines

The experiments of multi-cycle detonation were carried out based on a direct-connected pulse detonation engine (PDE) and an air-breathing PDE. The ignition energy was less than 50 mJ generated by a spark plug. The gasoline and air were used as the fuel and oxidizer. The pressure variation along the length of the direct-connected PDE and air-breathing PDE at several different operating frequencies was measured by the piezoelectric pressure sensors. The temperature of the exhaust plume from the PDEs was measured by the temperature and water vapor concentration instrument based on infrared spectrum measurement principle. Meanwhile, the average thrust of the air-breathing PDE with three different nozzles, including convergent nozzle, divergent nozzle, and convergent-divergent nozzle was measured by the force sensor. The experimental results indicated that there was a reflected shock wave propagating upstream when the detonation wave reached the convergent nozzle, while there was no reflected shock wave for the divergent nozzle. The exhaust plume temperature increased slightly with the increasing operating frequency. The exhaust plume temperature of the PDE with the convergent nozzle was lower than that of the divergent nozzle and convergent-divergent nozzle, while the PDE with divergent nozzle obtained the highest exhaust plume temperature. Analogously, the average thrust of PDE with the convergent nozzle was the largest while the PDE with the divergent nozzle obtained the minimum average thrust. The spontaneous flow field of the exhaust plume under the condition of multi-cycle was observed by a high speed camera. Several Mach disks looked like diamonds were generated at the center of exhaust plume and the flow was supersonic for a while. The flow field was similar to that of the supersonic unexpanded free jet.

Response of freshwater transport during typhoons with wave-induced mixing effects in the Pearl River Estuary, China

We examined the response of freshwater transport in the Pearl River Estuary (PRE) to typhoons in 2017 to investigate the effects of wave-induced mixing under extreme conditions using a 1D-3D coupled river-ocean model with a wave-induced mixing module. The results show that wave-induced mixing trapped more freshwater in coastal regions by narrowing the plume width and increasing the freshwater thickness. The freshwater volume in the coastal region increased by 10%–60% and the flushing time increased from 5–42 days to 10–50 days. The trapping effect of wave-induced mixing was modulated by alongshore wind, wave and river flow, and it was sensitive to the initial freshwater thickness before typhoon. Cross-shore and eastward freshwater transport was substantially altered during typhoons by wave-induced mixing, whereas westward freshwater transport exhibited only minor changes. It was found that wave-induced mixing caused a change in vertical/horizontal density gradient, and thereby altered the freshwater volume, ocean current and freshwater flux. The effects of wave-induced mixing on the plume structure and flushing time scale were further investigated by applying a salinity coordinate system. The results show that wave-induced mixing significantly increased/reduced the plume area and freshwater volume in the far field (26–32)/near field (19–26) during typhoons. As a consequence, the flushing time in the near field/far field was reduced/increased. Shorter flushing times inside the estuary and longer flushing times on the shelf induced by wave-induced mixing have important implications for the fate of nutrients, sediments, and other pollutants. This study highlights that wave-induced mixing effects are important in modulating freshwater transport and flushing time scales, which are of great significance in regional coastal management to protect the marine environment.

Cavitation and charge separation in laser-produced copper and carbon plasma in transverse magnetic field

In the present work, we report the dynamics and geometrical features of the plasma plume formed by the laser ablation of copper and graphite (carbon) targets in the presence of different transverse magnetic field. This work emphasizes on the effect of atomic mass of the plume species on the diamagnetic behaviour and geometrical aspect of the expanding plasma plume in the magnetic field. The time-resolved analysis of the simultaneously captured two directional images in orthogonal to the expansion axis is carried out for the comparative study of projected three-dimensional structure of copper and carbon plasma plume. In the presence of magnetic field, sharp differences are observed between the copper and carbon plasma plumes in terms of formation of diamagnetic cavity and structure formation. An elliptical cavity-like structure is observed in case of copper plasma plume which attains the sharp conical shape with increasing the time delay or magnetic field strength. On the other hand, splitted carbon plasma plume appears as a Y-shape structure in the presence of magnetic field where the cavity-like structure is not observed for the considered time and magnetic field. Based on the modified energy balance relation for the elliptic cylindrical geometry, we have also simulated the dynamics of the plume which is in close agreement with observed plasma expansion in diamagnetic and non-diamagnetic regions.

Evaluation of Novel NASA Moderate Resolution Imaging Spectroradiometer and Visible Infrared Imaging Radiometer Suite Aerosol Products and Assessment of Smoke Height Boundary Layer Ratio During Extreme Smoke Events in the Western USA

AbstractWe analyze new aerosol products from NASA satellite retrievals over the western USA during August 2013, with special attention to locally generated wildfire smoke and downwind plume structures. Aerosol optical depth (AOD) at 550 nm from MODerate Resolution Imaging Spectroradiometer (MODIS) (Terra and Aqua Collections 6 and 6.1) and Visible Infrared Imaging Radiometer Suite (VIIRS) Deep Blue (DB) and MODIS (Terra and Aqua) Multi‐Angle Implementation of Atmospheric Correction (MAIAC) retrievals are evaluated against ground‐based AErosol RObotic NETwork (AERONET) observations. We find a significant improvement in correlation with AERONET and other metrics in the latest DB AOD (MODIS C6.1 r2 = 0.75, VIIRS r2 = 0.79) compared to MODIS C6 (r2 = 0.62). In general, MAIAC (r2 = 0.84) and DB (MODIS C6.1 and VIIRS) present similar statistical evaluation metrics for the western USA and are useful tools to characterize aerosol loading associated with wildfire smoke. We also evaluate three novel NASA MODIS plume injection height (PIH) products, one from MAIAC and two from the Aerosol Single scattering albedo and layer Height Estimation (ASHE) (MODIS and VIIRS) algorithm. Both Terra and Aqua MAIAC PIHs statistically agree with ground‐based and satellite lidar observations near the fire source, as do ASHE, although the latter is sensitive to assumptions about aerosol absorption properties. We introduce a first‐order approximation Smoke Height Boundary Layer Ratio (SHBLR) to qualitatively distinguish between aerosol pollution within the planetary boundary layer and the free troposphere. We summarize the scope, limitations, and suggestions for scientific applications of surface level aerosol concentrations specific to wildfire emissions and smoke plumes using these novel NASA MODIS and VIIRS aerosol products.

Mantle plumes and their role in Earth processes

The existence of mantle plumes was first proposed in the 1970s to explain intra-plate, hotspot volcanism, yet owing to difficulties in resolving mantle upwellings with geophysical images and discrepancies in interpretations of geochemical and geochronological data, the origin, dynamics and composition of plumes and their links to plate tectonics are still contested. In this Review, we discuss progress in seismic imaging, mantle flow modelling, plate tectonic reconstructions and geochemical analyses that have led to a more detailed understanding of mantle plumes. Observations suggest plumes could be both thermal and chemical in nature, can attain complex and broad shapes, and that more than 18 plumes might be rooted in regions of the lowermost mantle. The case for a deep mantle origin is strengthened by the geochemistry of hotspot volcanoes that provide evidence for entrainment of deeply recycled subducted components, primordial mantle domains and, potentially, materials from Earth’s core. Deep mantle plumes often appear deflected by large-scale mantle flow, resulting in hotspot motions required to resolve past tectonic plate motions. Future research requires improvements in resolution of seismic tomography to better visualize deep mantle plume structures at smaller than 100-km scales. Concerted multi-proxy geochemical and dating efforts are also needed to better resolve spatiotemporal and chemical evolutions of long-lived mantle plumes.

Experimental and numerical study of gas to liquid ratio in stratified gas-saturated liquid blowouts’ plumes

During underwater live-oil blowouts, some fraction of dissolved gas separates from oil upon pressure drop. The excessive buoyancy flux caused by free gas, as well as dominated gas bubbles slip velocity, heightens the plume peeling level when compared with pure-liquid blowouts. A series of laboratory experiments with CO2 saturated water and pure water blowout in an open-top stratified basin was carried out. The structure of the single-phase plume has coherent eddies around it due to instabilities. These coherent eddies are mainly responsible for entrainment, and hence widening of the plume as expected. Visual observation of gas-saturated liquid plumes compared with pure-liquid plumes suggests that the instabilities are hampered, hence generating weaker more elongated coherent structures and less entrainment. This lets the plume widen less and contributes to heightening the plume peeling level to a greater extent. This seems to be due to off-source buoyancy enhancement as a result of off-source bubble formation in the plume. Experimental results were also compared with a series of equivalent numerical simulations conducted with OSCAR and Gas Track modules of SINTEF MEMW. In different steps of the experiments, the amount of dissolved CO2 in water, as well as volumetric gas to liquid ratio in numerical simulations, was changed. Non-dimensional form of plume peeling heights shows that peeling heights in numerical results would be more compatible with the experimental results when the volumetric gas to liquid ratio was set equal to the amount of gas separates due to pressure drop across the opening.

On the structure of the Enceladus plume

ABSTRACT The detection of a water-rich plume erupting from ‘tiger stripes’ near the Enceladus south polar region is an important discovery of geologically active satellites within the Solar system. In this work, we apply an analytical approach to model the plume structure, using as a diagnostic the CO2 distribution extracted from the Cassini Ion and Neutral Mass Spectrometer measurements made during the E14, E17, and E18 flybys. Special focus is placed on the modelling of the spike-like structures by including only sources with substantial contributions to the plume densities. Such a procedure reduces greatly the model complexity and helps to better constrain the source parameters. Both the model source rate and Mach number are found to vary considerably among different sources during the same flyby and also among different flybys for the same source, revealing a complicated spatio-temporal variability in the plume structure. Our analysis suggests a total escape rate of (1.0–7.1) × 1026 s−1 for CO2 and (2.4–6.6) × 1028 s−1 for H2O, in broad agreement with previous estimates. Of particular interest is our identification of a tentative correlation between the Mach number and thermal brightness, of which the latter is a tracer of the geological activity of the emission source. Such a relation should be able to provide more insights into the nature of geyser emission along the ‘tiger stripes’.

Mobile Ka-Band Polarimetric Doppler Radar Observations of Wildfire Smoke Plumes

ABSTRACTRemote sensing techniques have been used to study and track wildfire smoke plume structure and evolution; however, knowledge gaps remain because of the limited availability of observational datasets aimed at understanding fine-scale fire–atmosphere interactions and plume microphysics. Meteorological radars have been used to investigate the evolution of plume rise in time and space, but highly resolved plume observations are limited. In this study, we present a new mobile millimeter-wave (Ka band) Doppler radar system acquired to sample the fine-scale kinematics and microphysical properties of active wildfire smoke plumes from both wildfires and large prescribed fires. Four field deployments were conducted in autumn of 2019 during two wildfires in California and one prescribed burn in Utah. Radar parameters investigated in this study include reflectivity, radial velocity, Doppler spectrum width, differential reflectivity ZDR, and copolarized correlation coefficient ρHV. Observed radar reflectivity ranged between −15 and 20 dBZ in plume, and radial velocity ranged from 0 to 16 m s−1. Dual-polarimetric observations revealed that scattering sources within wildfire plumes are primarily nonspherical and oblate-shaped targets as indicated by ZDR values measuring above 0 and ρHV values below 0.8 within the plume. Doppler spectrum width maxima were located near the updraft core region and were associated with radar reflectivity maxima.

Mechanism analysis and experimental verification of electromagnetic sail, a new solar propulsion system without propellent

The electromagnetic sail, a new space propulsion system without propellant, which propels a spacecraft by deflecting solar wind with an electromagnetic field, is proposed. The thrust mechanism and the performance variations of the electromagnetic sail are analyzed with both particles in cell and magnetohydrodynamic models, and the interaction between the incoming plasma fluid and the electromagnetic field is investigated by tests on the ground experimental system. The simulation results demonstrate that a magnetosphere is created in front of the sail and its area increases with magnetic field intensity; with appropriate dipole moment, the thrust of the electromagnetic sail is higher than a pure magnetic sail or a pure electric sail. In test experiments, the plume structure of a helicon plasma source changes obviously with coil current and metal mesh voltage, which verifies the repulsion of the magnetic field and electric field to the incoming plasma. These results indicate that the combination of the magnetic sail and electric sail can increase the utilization efficiency of solar wind, which means the electromagnetic sail is a feasible propulsion system.

The Crustacean Antennule: A Complex Organ Adapted for Lifelong Function in Diverse Environments and Lifestyles.

AbstractThe crustacean first antenna, or antennule, has been an experimental model for studying sensory biology for over 150 years. Investigations have led to a clearer understanding of the functional organization of the antennule as an olfactory organ but also to a realization that the antennule is much more than that. Across the Crustacea, the antennules take on many forms and functions. As an example, the antennule of reptantian decapods has many types of sensilla, each with distinct structure and function and with hundreds of thousands of chemosensory neurons expressing hundreds of genes that code for diverse classes of receptor proteins. Together, these antennular sensilla represent multiple chemosensory pathways, each with its own central connections and functions. The antennule also has a diversity of sensors of mechanical stimuli, including vibrations, touch, water flow, and the animal's own movements. The antennule likely also detects other environmental cues, such as temperature, oxygen, pH, salinity, and noxious stimuli. Furthermore, the antennule is a motor organ-it is flicked to temporally and spatially sample the animal's chemo-mechanical surroundings-and this information is used in resolving the structure of chemical plumes and locating the odor source. The antennule is also adapted to maintain lifelong function in a changing environment. For example, it has specific secretory glands, grooming structures, and behaviors to stay clean and functional. Antennular sensilla and the annuli on which they reside are also added and replaced, leading to a complete turnover of the antennule over several molts. Thus, the antennule is a complex and dynamic sensory-motor integrator that is intricately engaged in most aspects of the lives of crustaceans.

Variations in the canopy shock structures of massive extraterrestrial plumes: Parametric DSMC simulation of 2007 Tvashtar observations

The New Horizons flyby of the Jovian system yielded multiple images of the erupting Pele-class volcanic plume, Tvashtar. These images include a unique five-frame sequence or “movie” taken over 8 min that revealed short-term dynamical activity in the form of a traveling wave and evolving plume structure. The high-latitude Tvashtar plume was observed from various aspects during the flyby to exhibit a canopy shock and a depositional ring with thermal vent emission. The movie frames and other high-resolution images of Io taken during the New Horizons flyby by the Long Range Reconnaissance Imager (LORRI) were deconvolved to aid analysis of the plume dynamics.While our previous work (Hoey et al., 2016) modeled this plume's gas field in its steady state with rarefied gas dynamic methods, Tvashtar's virtual vent conditions were underconstrained by observation. Therefore, to constrain thermodynamic and geometric parameters at the virtual vent, we extend our models of the Tvashtar plume to perform a parametric series of 3-D simulations at much improved resolution. These simulations vary virtual vent aspect ratio and stagnation temperature, and implement new models for gas opacity in SO2 flows and for the condensation and sublimation of particles entrained in the plume.We arrive at a set of virtual vent conditions that incorporate or satisfy all available observational constraints and several novel ones, including the gas canopy height and aspect ratio and the depositional ring extent and orientation. The 2007 Tvashtar gas plume is shown to be consistent with a virtual vent of aspect ratio less than or equal to 3; stagnation temperature 1287 K; area 30 km2; and mass flow rate 2.0 × 105 kg/s SO2. Alternate canopy shock and depositional ring configurations are evaluated across a range of vent aspect ratios from 1 to 15 with results that will help to constrain the sources of other observed gas plumes.Finally, we develop an alternate hypothesis for the New Horizons observations of canopy unsteadiness in the Tvashtar plume; namely, that transient perturbations in the structure of the gas canopy shock itself produce a traveling notch-like structure that may even grow unstable, inducing temporary canopy collapse. This is as opposed to a high-amplitude density pulse at the source, or to source-entrained dust in a condensate model coupled to steady gas-field solutions.

Supergranule aggregation for constant heat flux-driven turbulent convection

Turbulent convection processes in nature are often found to be organized in a hierarchy of plume structures and flow patterns. The gradual aggregation of convection cells or granules to a supergranule which eventually fills the whole horizontal layer is reported and analysed in spectral element direct numerical simulations of three-dimensional turbulent Rayleigh-B\'{e}nard convection at an aspect ratio of $60$. The formation proceeds over a time span of more than $10^4$ convective time units for the largest accessible Rayleigh number and occurs only when the turbulence is driven by a constant heat flux which is imposed at the bottom and top planes enclosing the convection layer. The resulting gradual inverse cascade process is observed for both temperature variance and turbulent kinetic energy. An additional analysis of the leading Lyapunov vector field for the full turbulent flow trajectory in its high-dimensional phase space demonstrates that turbulent flow modes at a certain scale continue to give rise locally to modes with longer wavelength in the turbulent case. As a consequence successively larger convection patterns grow until the horizontal extension of the layer is reached. This instability mechanism, which is known to exist near the onset of constant heat flux-driven convection, is shown here to persist into the fully developed turbulent flow regime thus connecting weakly nonlinear pattern formation with the one in fully developed turbulence. We discuss possible implications of our study for observed, but not yet consistently numerically reproducible, solar supergranulation which could lead to improved simulation models of surface convection in the Sun.

СВЯЗЬ ТЕПЛОВОГО ПОТОКА С ЗОНАМИ РЕОЛОГИЧЕСКОГО РАЗУПЛОТНЕНИЯ В ВЕРХНЕЙ МАНТИИ ВОСТОЧНОЙ ОКРАИНЫ АЗИИ

Results of the correlation analysis of heat flow anomalies with distributions of density contrast (µz-parameter) in rifting and plume structures on eastern margin of Asia which prove selective return correlation of these parameters in intervals of depths corresponding to the provision of the subcrustal viscous layer (the deep interval 25–45 км) and astenosphere (the deep interval 70–90 км) are considered. The South-Okhotsk rift has anomalous characteristic, where subcrustal layer locates at the depth of 10–25 km, and astenosphere – 45–55 km. In most regions (South Okhotsk, Sea of Japan, Cathaysia) main contribution to the heat flow brings a subcrustal viscous layer, but in the Indigiro-Kolimsky – asthenosphere contribution is prevailed over subcrustal one. The heat flow from an asthenosphere on Ceinozoic borders of lithospheric plates is screened by subduction’s slabs. In the Chenzhou–Linwu fault zone at the boundary of the Yangtze plate and Cathaysia block the wide stretch-shear zone in lithosphere is revealed. The late is displayed by the density contrast minima at the depth interval of 30–100 km and heat flow anomalies. in this zone, on geological data, manifestations of stretching, viscous shear and oblique subduction are detected. The main contribution to thermal anomalies in rift structures is made by a subcrustal viscous layer. Identical correlation of Q and µz-параметра in the areas removed from each other testifies to an identical deep structure and universality of tectonic states on eastern margins of the Asia where in space and time subduction’s rifting and plume processes are interfaced. Key words: heat flow, upper mantle, density contrast, rheology, Eastern Asia.

Plumelets: Dynamic Filamentary Structures in Solar Coronal Plumes

Abstract Solar coronal plumes long seemed to possess a simple geometry supporting spatially coherent, stable outflow without significant fine structure. Recent high-resolution observations have challenged this picture by revealing numerous transient, small-scale, collimated outflows (“jetlets”) at the base of plumes. The dynamic filamentary structure of solar plumes above these outflows, and its relationship with the overall plume structure, have remained largely unexplored. We analyzed the statistics of continuously observed fine structure inside a single representative bright plume within a mid-latitude coronal hole during 2016 July 2–3. By applying advanced edge-enhancement and spatiotemporal analysis techniques to extended series of high-resolution images from the Solar Dynamics Observatory's Atmospheric Imaging Assembly, we determined that the plume was composed of numerous time-evolving filamentary substructures, referred to as “plumelets” in this paper, that accounted for most of the plume emission. The number of simultaneously identifiable plumelets was positively correlated with plume brightness, peaked in the fully formed plume, and remained saturated thereafter. The plumelets had transverse widths of 10 Mm and intermittently supported upwardly propagating periodic disturbances with phase speeds of 190–260 km s−1 and longitudinal wavelengths of 55–65 Mm. The characteristic frequency (≈ 3.3 mHz) is commensurate with that of solar p-modes. Oscillations in neighboring plumelets are uncorrelated, indicating that the waves could be driven by p-mode flows at spatial scales smaller than the plumelet separation. Multiple independent sources of outflow within a single coronal plume should impart significant fine structure to the solar wind that may be detectable by Parker Solar Probe and Solar Orbiter.