Energy Budget Analysis Research Articles

Electrohydrodynamic stability of a two-layer plane Poiseuille flow in the presence of interfacial surfactant: Energy budget analysis

Electrohydrodynamic stability of a two-layer plane Poiseuille flow in the presence of interfacial surfactant: Energy budget analysis

Understanding the Biases in Global Monsoon Simulations from the Perspective of Atmospheric Energy Transport

Abstract Understanding global monsoon (GM) variability and projecting its future changes rely heavily on climate models. However, climate models generally show pronounced biases in GM simulations, and the reasons for this remain unclear. Here, we evaluate the performance of 20 pairs of climate models that participated in both phase 5 of the Coupled Model Intercomparison Project (CMIP5) and phase 6 of CMIP (CMIP6) and identify the sources of their GM simulation biases from an energy transport perspective. The multimodel mean improvement in CMIP6 compared to CMIP5 is demonstrated by the increasing skill scores for various GM metrics from 0.20–0.79 to 0.48–0.83. More specifically, the dry biases in the Northern Hemisphere Summer Monsoon (NHSM) precipitation in CMIP5 [root-mean-square error (RMSE): 1.85 mm day−1] are reduced in CMIP6 (RMSE: 1.66 mm day−1). This higher simulation skill is associated with higher skill in simulating the precipitation-solstitial mode, monsoon intensity, and monsoon domains. The improvement in the NHSM precipitation simulation results from that in the meridional transport of atmospheric energy. Atmospheric energy budget analysis shows that the negative biases in downward surface longwave radiation and northward energy transport are smaller in CMIP6 than in CMIP5 in the boreal summer, resulting in a more realistic interhemispheric thermal contrast and meridional gradient of moist static energy. However, a major weakness of the CMIP6 models is found in the Southern Hemisphere Summer Monsoon precipitation simulation due to the positive bias in the top-of-the-atmosphere downward longwave radiation. This study shows that reasonably reproducing the meridional global atmospheric energy transportation is necessary for skillful GM simulation.

Submesoscale processes and their seasonality generated by freshwater discharge at the Yangtze estuary

As the intersection between land and sea, the estuary is a hotpot for natural and human-induced processes that affect its physical and chemical characteristics, as well as biodiversity and ecosystems. Due to a combination of freshwater discharge and the unique topography of river estuaries, submesoscales with a spatial scale of O(1) km can be easily generated due to the presence of strong salinity fronts at river estuaries. As the biggest river in Asia, the basically dynamical characteristics and their seasonal mechanisms of submesoscales at the Yangtze estuary remain unclear. Using a nested high-resolution (300 m) simulation established by the Coastal and Regional Ocean Community model (CROCO), the seasonal variability of submesoscales at the Yangtze estuary is investigated and the underlying generation mechanisms are analyzed based on the analysis of kinetic energy budget. The results of normalized relative vorticity, horizontal salinity gradient, and submesoscale kinetic energy (SMKE) show that submesoscale processes have a seasonal variation at the Yangtze estuary. This seasonality is tightly related to the freshwater input with a correlation coefficient of up to 0.66 (the confidence level >99%). To figure out the dominant energy sources that control the SMKE budget, five terms including the baroclinic term (BC), the barotropic term (BT), the advection of submesoscale kinetic energy term (ADK), the pressure work term (PW), and vertical mixing term (VM) are diagnosed. The results suggest that BC, BT, and PW are the source producing SMKE, while ADK and VM tend to dissipate SMKE. This work suggests the important role of submesoscale activities in the energy cascade and enhancing the transports of tracers at the estuary.

The Adiabatic Evolution of 3D Annular Vortices with a Double-Eyewall Structure

Tropical cyclones (TCs) can be characterized as a 3D annular structure of elevated potential vorticity (PV). However, strong mature TCs often develop a secondary eyewall, leading to a 3D annular vortex with a double-eyewall structure. Using 2D linear stability analysis, it is shown that three types of barotropic instability (BI) are present for annular vortices with a double-eyewall structure: Type-1 BI across the secondary eyewall, Type-2 BI across the moat of the vortex, and Type-3 BI across the primary eyewall. The overall stability of these vortices (and the type of BI that develops) depends principally upon five vortex parameters: the thickness of the primary eyewall, the thickness of the secondary eyewall, the moat width, the vorticity ratio between the eye and the primary eyewall, and the vorticity ratio between the primary and secondary eyewall. The adiabatic evolution of 3D annular vortices with a double-eyewall structure is examined using a primitive equation model in normalized isobaric coordinates. It is shown that Type-2 BI is the most common type of BI for 3D annular vortices whose vortex parameters mimic TCs with a double-eyewall structure. During the onset of Type-2 BI, eddy kinetic energy budget analysis indicates that barotropic energy conversion from the mean azimuthal flow is the dominant energy source of the eddies, which produces a radial velocity field with a quadrupole structure. Absolute angular momentum budget analysis indicates that Type-2 BI generates azimuthally averaged radial outflow across the moat, and the eddies transport absolute angular momentum radially outward towards the secondary eyewall. The combination of these processes leads to the dissipation of the primary eyewall and the maintenance of the secondary eyewall for the vortex.

Hydrodynamic stability of magnetic boundary layer flow of viscoelastic Walters' liquid B embedded in a porous medium

The present study investigates the linear stability of stagnation boundary layer flow of viscoelastic Walters' liquid B in the presence of magnetic field and porous medium by solving modified Orr–Sommerfeld equation numerically using the Chebyshev collocation method. The model is characterized mainly by the elasticity number (E), the magnetic number (Q), and the permeability parameter (K) in addition to the Reynolds number(Re). The Prandtl boundary layer equations derived for the present model are converted through appropriate similarity transformations, to an ordinary differential equation whose solution describes the velocity, which has oscillatory behavior. The solution of generalized eigenvalue problem governing the stability of the boundary layer has an interesting eigenspectrum. The spectra for different values of E, K, and Q are shown to be a continuation of Newtonian eigenspectrum with the instability belongs to viscoelastic wall mode for certain range of parameters. It is shown that the role of elasticity number is to destabilize the viscoelastic boundary layer flow, whereas both magnetic field and porous medium have the stabilizing effect on the flow. These interesting features are further confirmed by performing the energy budget analysis on the perturbed quantities. Region of negative production due to the Reynolds stress as well as production due to viscous dissipation and viscoelastic contributions in the positive region, and there is reduction in the growth rate of kinetic energy that causes stability. Other physical mechanisms related to flow stability are discussed in detail.

Growth of organized flow coherent motions within a single-stream shear layer: 4D-PTV measurements

This study investigates the evolution of a single-stream shear layer (SSSL) originating from a wall boundary layer past a backward-facing step. Utilizing a time-resolved 3D-Particle Tracking Velocimetry (4D-PTV) technique, we track the trajectories of fluorescent particles to gain insight into the flow characteristics of the SSSL. A compact water tunnel facility (Reτ=1240\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ extrm{Re}_\ au =1\\,240$$\\end{document}) is fabricated to obtain an SSSL with a perpendicular slow entrainment stream past the separation edge. A hybrid interpolation approach that combines ensemble binning and Gaussian weighting is implemented to derive minimally filtered mean and instantaneous lower- and higher-order flow field parameters. Spanwise-dominant coherent motion accompanied by finer flow scales is observed to grow due to flow entrainment through “nibbling” actions of small-scale vortices, “engulfing” by large-scale vortices, and vortex pairing events. Furthermore, the non-zero-speed stream edge grows relatively faster than the zero-speed stream edge, showing a strong asymmetry in mixing composition across a mixing layer. The SSSL reaches self-similarity at a streamwise distance of ≈55θ0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\approx 55\\,\ heta _{0}$$\\end{document}, where θ0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ heta _0$$\\end{document} is the initial momentum thickness from the separation edge, i.e., considerably shorter than reported in previous studies. A literature comparison of growth rate parameters raises intriguing questions regarding a potential inclusive growth scaling unifying the free shear layers. A turbulent kinetic energy (TKE) budget analysis reveals a negative production region immediately downstream of the separation edge attributed to a large positive streamwise gradient of streamwise velocity. In the self-similar region, the phase-averaged flow mapping demonstrates a larger concentration of turbulence production rate around the outer edges of spanwise vortices, specifically at the intersection of braids and vortices. Furthermore, a spatial separation exists in the regions of peak production and dissipation rates within the vortex core region favoring dissipation. The braids exhibit a larger concentration of turbulence diffusion rates, indicating their function as a conduit for exchanging turbulence between neighboring coherent motions.

Decadal Trends in the Southern Ocean Meridional Eddy Heat Transport

Abstract Meridional heat transport induced by oceanic mesoscale eddies (EHT) plays a significant role in the heat budget of the Southern Ocean (SO) but the decadal trends in EHT and its associated mechanisms are still obscure. Here, this scientific issue is investigated by combining concurrent satellite observations and Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) reanalysis data over the 24 years between 1993 and 2016. The results reveal that the surface EHTs from both satellite and ECCO2 data consistently show decadal poleward increasing trends in the SO, particularly in the latitude band of the Antarctic Circumpolar Current (ACC). In terms of average in the ACC band, the ECCO2-derived EHT over the upper 1000 m has a linear trend of 1.1 × 10−2 PW decade−1 or 16% per decade compared with its time-mean value of 0.07 PW. Diagnostic analysis based on “mixing length” theory suggests that the decadal strengthening of eddy kinetic energy (EKE) is the dominant mechanism for the increase in EHT in the SO. By performing an energy budget analysis, we further find that the decadal increase in EKE is mainly caused by the strengthened baroclinic instability of large-scale circulation that converts more available potential energy to EKE. For the strengthened baroclinic instability in the SO, it is attributed to the increasing large-scale wind stress work on the large-scale circulation corresponding to the positive phase of the Southern Annular Mode between 1993 and 2016. The decadal trends in EHT identified here may help understand decadal variations of heat storage and sea ice extent in the SO. Significance Statement Oceanic mesoscale-eddy-induced meridional heat transport (EHT) is a key process of heat redistribution in the Southern Ocean (SO), but the decadal variations of EHT and the associated mechanisms remain obscure. Here, by analyzing satellite and reanalysis data between 1993 and 2016, we find that the poleward EHT has significant decadal increasing trends in the SO, particularly in the Antarctic Circumpolar Current latitude band. Further analysis suggests that the increasing EHT is mainly caused by enhanced eddy kinetic energy converted by the strengthened baroclinic instability of large-scale circulation, which is attributed to the strengthening winds modulated by the Southern Annular Mode. The above findings may improve our understanding of the decadal variations of heat storage and sea ice extent in the SO.

Instability and transition control by steady local blowing/suction in a hypersonic boundary layer

The efficacy of steady large-amplitude blowing/suction on instability and transition control for a hypersonic flat plate boundary layer with Mach number 5.86 is investigated systematically. The influence of the blowing/suction flux and amplitude on instability is examined through direct numerical simulation and resolvent analysis. When a relatively small flux is used, the two-dimensional instability critical frequency that distinguishes the promotion/suppression mode effect closely aligns with the synchronisation frequency. For the oblique wave, as the spanwise wavenumber increases, the suppression effects would become weaker and the mode suppression bandwidth diminishes/increases in general in the blowing/suction control. Increasing the blowing/suction flux can effectively broaden the frequency bandwidth of disturbance suppression. The influence of amplitude on disturbance suppression is weak in a scenario of constant flux. To gain a deeper insight into disturbance suppression mechanism, momentum potential theory (MPT) and kinetic energy budget analysis are further employed in analysing disturbance evolution with and without control. When the disturbance is suppressed, the blowing induces the transport of certain acoustic components along the compression wave out of the boundary layer, whereas the suction does not. The velocity fluctuations are derived from the momentum fluctuations of the MPT. Compared with the momentum fluctuations, the evolutions indicated by each component's velocity fluctuations greatly facilitate the investigations of the acoustic nature of the second mode. The rapid variation of disturbance amplitude near the blowing is caused by the oscillations of the acoustic component and phase speed differences between vortical and thermal components. Kinetic energy budget analysis is performed to address the non-parallel effect of the boundary layer introduced by blowing/suction, which tends to suppress disturbances near the blowing. Moreover, viscous effects leading to energy dissipation are identified to be stronger in regions where the boundary layer is rapidly thickening. Finally, it is demonstrated that a flat plate boundary layer transition triggered by a random disturbance can be delayed by a blowing/suction combination control. The resolvent analysis further demonstrates that disturbances with frequencies that dominate the early transition stage are dampened in the controlled base flow.

Thermal convection of viscoelastic fluids in concentric rotating cylinders: Elastic turbulence and kinetic energy budget analysis

Thermal convection of viscoelastic fluids in concentric rotating cylinders: Elastic turbulence and kinetic energy budget analysis

A numerical study of rainfall effects on wind turbine wakes

Rainfall has significant impacts on the operations of wind turbines due to erosion of turbine blades and alterations in aerodynamic performance of wind turbines. However, little is understood in the influences of rainfall on wind turbine wakes. In this study, large-eddy simulation (LES) coupled with actuator-disk model with rotation (ADM-R) is used to investigate impacts of rainfall on wind turbine wakes. A double Euler method is employed in ADM-R to simulate the rainfall injection. The results of the model indicate that rainfall reduces wind speed in the sweep area and increases wind speed in the outer region of the top tip level by 2.1 %. Furthermore, rainfall reduces turbulence intensity in the near wake and outer wake region of the top tip (up to 2.0 %), with the influence extending up to 10 d (diameters of the wind turbine) in the downstream. These changes have a positive correlation with the rainfall intensity and an inverse correlation with the wind speed. The mean kinetic energy (MKE) and turbulent kinetic energy (TKE) budget analysis reveals that (1) the turbulent radial transport variation of MKE is the primary reason for the rainfall-induced wind speed change; (2) the change in shear production of TKE is responsible for the rainfall-induced turbulent intensity change; (3) the rainfall-induced Reynolds stress −u′w′‾ is the dominant factor of this dynamics.

Cold Surge Impacts on the Structure, Energy Budget, and Turbulence of the South China Sea Boundary Layer

Abstract Episodic cold surges in the East Asia winter monsoon can penetrate deep into the South China Sea (SCS), enhance consequent tropical rainfall, and further strengthen the East Asia meridional overturning circulation. These cold surges can promote strong surface fluxes and lead to a deeper marine boundary layer (MBL). However, there is a lack of boundary layer studies over the SCS, unlike many other well-studied regions such as the north Atlantic Ocean and the central-eastern Pacific Ocean. In this study, we use high resolution radiosonde data of temperature and humidity profiles over Dongsha Island (116.69E, 20.70N) to identify the inversion layer, mixed layer, cloud base, cloud top, and factors controlling low cloud cover for the period of December-January-February from 2010 to 2020. We perform an energy budget analysis with ERA-5 meteorological variables and surface fluxes. Here we show a strong turbulent flux convergence of both heat and moisture within the SCS MBL during cold surges, which leads to a lifting of the mixed layer to ~1.0 km and inversion layer to ~2.0 km and associated cloud development over Dongsha Island. The cold and dry horizontal advection is balanced by this vertical turbulent flux convergence in the energy budget. Overall, cold surges over the SCS enhance lower branch of winter monsoon meridional overturning circulation with stronger inversion and higher low cloud covers.

A Nature-Inspired Approach to Energy-Efficient Relay Selection in Low-Power Wide-Area Networks (LPWAN).

Despite the ability of Low-Power Wide-Area Networks to offer extended range, they encounter challenges with coverage blind spots in the network. This article proposes an innovative energy-efficient and nature-inspired relay selection algorithm for LoRa-based LPWAN networks, serving as a solution for challenges related to poor signal range in areas with limited coverage. A swarm behavior-inspired approach is utilized to select the relays' localization in the network, providing network energy efficiency and radio signal extension. These relays help to bridge communication gaps, significantly reducing the impact of coverage blind spots by forwarding signals from devices with poor direct connectivity with the gateway. The proposed algorithm considers critical factors for the LoRa standard, such as the Spreading Factor and device energy budget analysis. Simulation experiments validate the proposed scheme's effectiveness in terms of energy efficiency under diverse multi-gateway (up to six gateways) network topology scenarios involving thousands of devices (1000-1500). Specifically, it is verified that the proposed approach outperforms a reference method in preventing battery depletion of the relays, which is vital for battery-powered IoT devices. Furthermore, the proposed heuristic method achieves over twice the speed of the exact method for some large-scale problems, with a negligible accuracy loss of less than 2%.

Photosymbiont Density Is Correlated with Constitutive And Induced Immunity in The Facultatively Symbiotic Coral, Astrangia Poculata.

Scleractinian corals, essential ecosystem engineers that form the base of coral reef ecosystems, have faced unprecedented mortality in recent decades due to climate-change related stressors, including disease outbreaks. Despite this emergent threat to corals, many questions still remain regarding mechanisms underlying observed variation in disease susceptibility. Recent data suggests at least some degree of variation in disease response may be linked to variability in the relationship between host corals and their algal photosymbionts (Family Symbiodiniaceae). Still, the nuances of connections between symbiosis and immunity in cnidarians, including scleractinian corals, remain poorly understood. Here we leveraged an emergent model species, the facultatively symbiotic, temperate, scleractinian coral Astrangia poculata, to investigate associations between symbiont density and both constitutive and induced immunity. We used a combination of controlled immune challenges with heat-inactivated pathogens and transcriptomic analyses. Our results demonstrate that A. poculata mounts a robust initial response to pathogenic stimuli that is highly similar to responses documented in tropical corals. We document positive associations between symbiont density and both constitutive and induced immune responses, in agreement with recent preliminary studies in A. poculata. A suite of immune genes, including those coding for antioxidant peroxiredoxin biosynthesis, are positively associated with symbiont density in A. poculata under constitutive conditions. Furthermore, variation in symbiont density is associated with distinct patterns of immune response; low symbiont density corals induce preventative immune mechanisms whereas high symbiont density corals mobilize energetic resources to fuel humoral immune responses. In summary, our study reveals the need for more nuanced study of symbiosis-immune interplay across diverse scleractinian corals, preferably including quantitative energy budget analysis for full disentanglement of these complex associations and their effects on pathogen susceptibility.

Boundary-layer instability on a highly swept fin on a cone at Mach 6

The growth and characteristics of linear, oblique instabilities on a highly swept fin on a straight cone in Mach 6 flow are examined. Large streamwise pressure gradients cause doubly inflected cross-flow profiles and reversed flow near the wall, which necessitates using the harmonic linearized Navier–Stokes equations. The cross-flow instability is responsible for the most-amplified disturbances, however, not all disturbances show typical cross-flow characteristics. Distinct differences in perturbation structure are shown between small ( $\sim$ 3–5 mm) and large ( $\sim$ 10 mm) wavelength disturbances at the unit Reynolds number $Re' = 11 \times 10^6$ m $^{-1}$ . As a result, amplification measurements based solely on wall quantities bias a most-amplified disturbance assessment towards larger wavelengths and lower frequencies than would otherwise be determined by an off-wall total-energy approach. A spatial-amplification energy-budget analysis demonstrates (i) that wall-normal Reynolds-flux terms dictate the local growth rate, despite other terms having a locally larger magnitude and (ii) that the Reynolds-stress terms are responsible for large-wavelength disturbances propagating closer to the wall compared with small-wavelength disturbances. Additionally, the effect of free-stream unit Reynolds number and small yaw angles on the perturbation amplification and energy budget is considered. At a higher Reynolds number ( $Re' = 22 \times 10^6$ m $^{-1}$ ), the most-amplified wavelength shrinks. Perturbations do not behave self-similarly in the thinner boundary layer, and the shift in most-amplified wavelength is due to decreased dissipation relative to the lower-Reynolds-number case. Small yaw angles produce a streamwise shift in the boundary layer and disturbance amplification. The yaw results quantify a potential uncertainty source in experiments and flight.

Role of Air‐Sea Interaction in the Energy Balance of Anticyclonic and Cyclonic Eddies in the Kuroshio Extension

AbstractUsing eddy‐resolving Community Earth System Model (CESM) simulations, this study investigates mesoscale eddy energetics and the role of air‐sea interaction for both anticyclonic and cyclonic eddies (AEs and CEs) in the Kuroshio Extension (KE) region. Based on energy budget analysis and eddy tracking algorithm, it is found that eddy energy balance depicts similar characteristics for AEs and CEs. The eddy kinetic energy (EKE) is generated through barotropic instability, vertical buoyancy flux, as well as transported from the upper stream Kuroshio. In addition, the temperature variance, which is directly related to eddy potential energy, is maintained by baroclinic instability. Air‐sea heat flux and wind stress act as eddy killers to move energy from oceanic eddies. For both AEs and CEs, heat exchange between atmosphere and oceanic eddies dominates the dissipation of temperature variance and accounts for more than 60% and 72% of the total dissipation, respectively. In comparison, the role of wind power in damping the EKE is relatively small. Only 14% (5%) of EKE dissipation in AEs (CEs) is attributed to eddy wind power.

Benchmark Thermodynamic Contributors to the Growth and Decay of the Regional Extreme Surface Temperature

Abstract A thermodynamic energy budget analysis is applied to the lowest model level of the ERA5 dataset to investigate the mechanisms that drive the growth and decay of extreme positive surface air temperature (SAT) events. Regional and seasonal variation of the mechanisms are investigated. For each grid point on Earth’s surface, a separate composite analysis is performed for extreme SAT events, which are days when temperature anomaly exceeds the 95th percentile. Among the dynamical terms, horizontal temperature advection of the climatological temperature by the anomalous wind dominates SAT anomaly growth over the extratropics, while nonlinear horizontal temperature advection is a major factor over high-latitude regions and the adiabatic warming is important over major mountainous regions. During the decay period, advection of the climatological temperature by the anomalous wind sustains the warming while nonlinear advection becomes the dominant decay mechanism. Among diabatic heating processes, vertical mixing contributes to the SAT anomaly growth over most locations while longwave radiative cooling hinders SAT anomaly growth, especially over the ocean. However, over arid regions during summer, longwave heating largely contributes to SAT anomaly growth while the vertical mixing dampens the SAT anomaly growth. During the decay period, both longwave cooling and vertical mixing contribute to SAT anomaly decay with more pronounced effects over the ocean and land, respectively. These regional and seasonal characteristics of the processes that drive extreme SAT events can serve as a benchmark for understanding the future behavior of extreme weather.

Impact of wall-slip on the soluto-marangoni instability in a two-fluid system in a channel–Creeping flow scenario

The role of wall-slip on the soluto-Marangoni instability that emerges in a two-fluid creeping two-dimensional Poiseuille flow is assessed within the framework of Orr-Sommerfeld analysis and species-transport system. Different wall-slip scenarios, namely S1 (slip at the upper wall), S2 (slip at the lower wall), S1S2 (symmetric slip at the upper and lower walls) are considered. The system instability is characterized by identifying unstable and stable zones in the m-n (viscosity ratio - depth ratio) plane for each of the slip conditions at the wall using asymptotic analysis for long-wave disturbances. Numerical simulations based on Chebyshev spectral collocation method reveals the emergence of two modes (M1 and M2) and corresponding stability features are displayed for typical values of Marangoni numbers, n, m and slip lengths. The occurrence of short-wave modes and the features of exchanging dominance between the short-wave modes in the presence of wall-slip for different slip condition are elucidated and the physical mechanism responsible for triggering the instability in the system are revealed through energy budget analysis. The channel system hosting less viscous fluid adjacent to the upper wall demonstrates interesting characteristics such as (among other things): stabilizing/destabilizing the emerging M1/M2 modes in system with no-slip by imposing S1/S2/S1S2 wall conditions and increasing the slip length; exchange of dominance of unstable modes beyond a threshold slip length for S1 slip type. The study thus presents possible means of stabilizing/destabilizing a creeping channel flow system by designing the walls of the channel with appropriate slip type relevant to the application.

Unchannelized granular flows: Effect of initial granular column geometry on fluid dynamics

In recent years, significant progress has been made in modelling granular flows using the μI-rheology model, which connects the viscosity of a granular medium to the pressure and strain rate via a dimensionless quantity called the inertial number, I. This model allows treating the granular material as a non-Newtonian liquid with a yield stress, making it possible to model the flow using the continuum approach, which is less computationally expensive than discrete element methods.In this paper, we implement the μI-rheology model in a computational fluid dynamics (CFD) code and couple it with the volume of fluid (VOF) interface tracking approach to model the three-dimensional (3D) flow of monodisperse granular materials. After validating the model using experimental data, we briefly describe a trial-and-error method for evaluating the material properties of powders via a simple collapse experiment. Then, employing the CFD model, we investigate the physics of the unchannelized collapse of granular materials and perform an energy budget analysis to demonstrate the different stages of the granular collapse.To further investigate the effect of the initial shape of the pile on the spreading dynamics, we run a campaign of 3D simulations. Our results show that the μI-rheology model accurately reproduces the dynamics of the granular material during the collapse and can be used for risk assessment purposes in natural disasters. The findings from our simulations can also aid in developing preventative measures to minimize potential harm.

Observation of Near‐Inertial Waves Induced by Typhoon Lan in the Northwestern Pacific: Characteristics, Energy Fluxes and Impact on Diapycnal Mixing

AbstractBased on mooring observations from October 10 to 5 November 2017 at four stations in the Northwestern Pacific, the characteristics of four strong near‐inertial wave (NIW) packets generated by the typhoon Lan were examined. The wave‐packet analysis revealed that for the NIWs with larger horizontal wavelengths, as their interactions with the background currents were weakened, the observed frequency was close to the intrinsic frequency. The near‐inertial kinetic energy (NIKE) between two cyclonic eddies penetrated deeper (∼620 m) than that in a negative vorticity region. A ray‐tracing model suggested that it was the strong positive vorticity to the north that caused the northward propagating NIWs to be reflected, and then the reflected NIWs were accelerated to propagate downward at ∼70 m depth where the stratification was strongest. In these two cases, furthermore, the efficiency of the downward propagation of NIKE was at a comparable level of 21%–25%. Energy budget analysis indicated that about 5%–25% of the near‐inertial wind work was injected into the upper 50–200 m, approximately 6%–25% of which could be further radiated to the deeper ocean. On average, after the passage of the typhoon Lan, the dissipation rate increased by 3–8 times, and for the enhanced diapycnal mixing, ∼42% of the energy was provided by the typhoon‐induced strong NIWs.

The Extraordinary March 2022 East Antarctica “Heat” Wave. Part II: Impacts on the Antarctic Ice Sheet

Abstract Between 15 and 19 March 2022, East Antarctica experienced an exceptional heat wave with widespread 30°–40°C temperature anomalies across the ice sheet. In Part I, we assessed the meteorological drivers that generated an intense atmospheric river (AR) that caused these record-shattering temperature anomalies. Here, we continue our large collaborative study by analyzing the widespread and diverse impacts driven by the AR landfall. These impacts included widespread rain and surface melt that was recorded along coastal areas, but this was outweighed by widespread high snowfall accumulations resulting in a largely positive surface mass balance contribution to the East Antarctic region. An analysis of the surface energy budget indicated that widespread downward longwave radiation anomalies caused by large cloud-liquid water contents along with some scattered solar radiation produced intense surface warming. Isotope measurements of the moisture were highly elevated, likely imprinting a strong signal for past climate reconstructions. The AR event attenuated cosmic ray measurements at Concordia, something previously never observed. Last, an extratropical cyclone west of the AR landfall likely triggered the final collapse of the critically unstable Conger Ice Shelf while further reducing an already record low sea ice extent. Significance Statement Using our diverse collective expertise, we explored the impacts from the March 2022 heat wave and atmospheric river across East Antarctica. One key takeaway is that the Antarctic cryosphere is highly sensitive to meteorological extremes originating from the midlatitudes and subtropics. Despite the large positive temperature anomalies driven from strong downward longwave radiation, this event led to huge amounts of snowfall across the Antarctic interior desert. The isotopes in this snow of warm airmass origin will likely be detectable in future ice cores and potentially distort past climate reconstructions. Even measurements of space activity were affected. Also, the swells generated from this storm helped to trigger the final collapse of an already critically unstable Conger Ice Shelf while further degrading sea ice coverage.