Showing papers on "Convection published in 2022"

Atmospheric Convection

Abstract: ABSTRACT Convective parameterization is the long-lasting bottleneck of global climate modelling and one of the most difficult problems in atmospheric sciences. Uncertainty in convective parameterization is the leading cause of the widespread climate sensitivity in IPCC global warming projections. This paper reviews the observations and parameterizations of atmospheric convection with emphasis on the cloud structure, bulk effects, and closure assumption. The representative state-of-the-art convection schemes are presented, including the ECMWF convection scheme, the Grell scheme used in NCEP model and WRF model, the Zhang-MacFarlane scheme used in NCAR and DOE models, and parameterizations of shallow moist convection. The observed convection has self-suppression mechanisms caused by entrainment in convective updrafts, surface cold pool generated by unsaturated convective downdrafts, and warm and dry lower troposphere created by mesoscale downdrafts. The post-convection environment is often characterized by “diamond sounding” suggesting an over-stabilization rather than barely returning to neutral state. Then the pre-convection environment is characterized by slow moistening of lower troposphere triggered by surface moisture convergence and other mechanisms. The over-stabilization and slow moistening make the convection events episodic and decouple the middle/upper troposphere from the boundary layer, making the state-type quasi-equilibrium hypothesis invalid. Right now, unsaturated convective downdrafts and especially mesoscale downdrafts are missing in most convection schemes, while some schemes are using undiluted convective updrafts, all of which favour easily turned-on convection linked to double-ITCZ (inter-tropical convergence zone), overly weak MJO (Madden-Julian Oscillation) and precocious diurnal precipitation maximum. We propose a new strategy for convection scheme development using reanalysis-driven model experiments such as the assimilation runs in weather prediction centres and the decadal prediction runs in climate modelling centres, aided by satellite simulators evaluating key characteristics such as the lifecycle of convective cloud-top distribution and stratiform precipitation fraction.

Modules for Experiments in Stellar Astrophysics (MESA): Time-dependent Convection, Energy Conservation, Automatic Differentiation, and Infrastructure

Abstract: We update the capabilities of the open-knowledge software instrument Modules for Experiments in Stellar Astrophysics (MESA). The new auto_diff module implements automatic differentiation in MESA, an enabling capability that alleviates the need for hard-coded analytic expressions or finite-difference approximations. We significantly enhance the treatment of the growth and decay of convection in MESA with a new model for time-dependent convection, which is particularly important during late-stage nuclear burning in massive stars and electron-degenerate ignition events. We strengthen MESA’s implementation of the equation of state, and we quantify continued improvements to energy accounting and solver accuracy through a discussion of different energy equation features and enhancements. To improve the modeling of stars in MESA, we describe key updates to the treatment of stellar atmospheres, molecular opacities, Compton opacities, conductive opacities, element diffusion coefficients, and nuclear reaction rates. We introduce treatments of starspots, an important consideration for low-mass stars, and modifications for superadiabatic convection in radiation-dominated regions. We describe new approaches for increasing the efficiency of calculating monochromatic opacities and radiative levitation, and for increasing the efficiency of evolving the late stages of massive stars with a new operator-split nuclear burning mode. We close by discussing major updates to MESA’s software infrastructure that enhance source code development and community engagement.

Numerical thermal featuring in γAl2O3-C2H6O2 nanofluid under the influence of thermal radiation and convective heat condition by inducing novel effects of effective Prandtl number model (EPNM)

Abstract: The investigation of thermal transport in the nanofluid attained much interest of the researchers due to their extensive applications in automobile, mechanical engineering, radiators, aerodynamics, and many other industries. Therefore, a nanofluid model is developed for γAl2O3-C2H6O2 by incorporating the novel effects of Effective Prandtl Number Model (EPNM), thermal radiations, and convective heat condition. The model discussed numerically and furnished the results against the governing flow quantities. It is examined that the nanofluid velocity alters significantly due to combined convection and stretching parameter. Induction of thermal radiation in the model significantly contributed in the temperature of nanofluids and high temperature is observed by strengthen thermal radiation (Rd) parameter. Further, convection from the surface (convective heat condition) provided extra energy to the fluid particles which boosts the temperature of γAl2O3-C2H6O2. The comparison of nanofluid (γAl2O3-C2H6O2) temperature with base fluid (C2H6O2) revealed that γAl2O3-C2H6O2 has high temperature and would be fruitful for future industrial applications. Moreover, the study is validated with previously reported literature and found reliability of the study.

On the relative temperatures of Earth’s volcanic hotspots and mid-ocean ridges

Abstract: Description Hotspot cool down Deep-seated mantle plumes are responsible for volcanic island chains such as Hawai’i. Upwelling from the deep interior requires that the plumes are hotter than the surrounding mantle to make it all the way up to the surface. However, Bao et al. found that some of these “hotspots” are surprisingly cool. The temperature is actually low enough to challenge a deep mantle origin for some hotspots. In these specific cases, deep plumes may be entrained and cooled or possibly originate in the upper mantle instead. —BG Some hotspots that feed volcanos are surprisingly cool and may not originate from deep plumes in Earth’s mantle. Volcanic hotspots are thought to be fed by hot, active upwellings from the deep mantle, with excess temperatures (Tex) ~100° to 300°C higher than those of mid-ocean ridges. However, Tex estimates are limited in geographical coverage and often inconsistent for individual hotspots. We infer the temperature of oceanic hotspots and ridges simultaneously by converting seismic velocity to temperature. We show that while ~45% of plume-fed hotspots are hot (Tex ≥ 155°C), ~15% are cold (Tex ≤ 36°C) and ~40% are not hot enough to actively upwell (50°C ≤ Tex ≤ 136°C). Hot hotspots have an extremely high helium-3/helium-4 ratio and buoyancy flux, but cold hotspots do not. The latter may originate at upper mantle depths. Alternatively, the deep plumes that feed them may be entrained and cooled by small-scale convection.

Magneto-hydrothermal triple-convection in a W-shaped porous cavity containing oxytactic bacteria

Abstract: Bioconvective heat and mass transport phenomena have recently been the subject of interest in diverse fields of applications pertaining to the motion of fluids and their thermophysical properties. The transport processes in a system involving triple convective phenomena, irregular geometry, and boundary conditions constitute a complex phenomenon. This work aims to explore the mixed thermo-bioconvection of magnetically susceptible fluid containing copper nanoparticles and oxytactic bacteria in a novel W-shaped porous cavity. The buoyant convention is generated due to the isothermal heating at the wavy bottom wall, whereas the mixed convection is induced due to the shearing motion of the top-cooled sliding wall. Furthermore, the bioconvection is induced due to the manifestation of oxytactic bacteria or organisms. The inclined sidewalls are insulated. The geometry is packed with water based Cu nanoparticle mixed porous structure, which is subjected to a magnetizing field acted horizontally. The complex transport equations are transformed into nondimensional forms, which are then computed using the finite volume-based developed code. The coupled triple-convective flow physics are explored for a wide range of involved controlling parameters, which could provide helpful insight to the system designer for its proper operation. The shape of geometry can be considered one of the important parameters to control the heat and mass transport phenomena. In general, the influence of amplitude (δ) is more compared to the waviness number (m) of the undulations. The magnitude of heat (Nu) and mass (Sh) transfer rate for the W-shaped cavity is high compared to conventional square and trapezoidal-shaped cavities. The output of the analysis could be very helpful for the designer for modeling devices operating on nanotechnology-based bioconvection, microbial fuel cells, and others.

Sustaining Earth’s magnetic dynamo

Abstract: Earth’s magnetic field is generated by fluid motions in the outer core. This geodynamo has operated for over 3.4 billion years. However, the mechanism that has sustained the geodynamo for over 75% of Earth’s history remains debated. In this Review, we assess the mechanisms proposed to drive the geodynamo (precession, tides and convection) and their ability to match geomagnetic and palaeomagnetic observations. Flows driven by precession are too weak to drive the geodynamo. Flows driven by tides could have been strong enough in the early Earth, before 1.5 billion years ago, when tidal deformation and Earth’s spin rate were larger than they are today. Evidence that the thermal conductivity of Earth’s core could be as high as 250 W m−1 K−1 calls the ability of convection to maintain the dynamo for over 3.4 billion years into question. Yet, convection could supply enough power to sustain a long-lived geodynamo if the thermal conductivity is lower than 100 W m−1 K−1. Exsolution of light elements from the core increases this upper conductivity limit by 15% to 200%, based on the exsolution rates reported so far. Convection, possibly aided by the exsolution of light elements, remains the mechanism most likely to have sustained the geodynamo. The light-element exsolution rate, which remains poorly constrained, should be further investigated. The mechanisms that sustain Earth’s long-lived geodynamo remain under scrutiny. This Review assesses the potential candidates—convection, precession and tides—revealing that convection, possibly helped by the exsolution of light elements, is the most likely scenario.

GEFSv12 reforecast dataset for supporting subseasonal and hydrometeorological applications

Abstract: For the newly implemented Global Ensemble Forecast System version 12 (GEFSv12), a 31-year (1989-2019) ensemble reforecast dataset has been generated at the National Centers for Environmental Prediction (NCEP). The reforecast system is based on NCEP’s Global Forecast System version 15.1 and GEFSv12, which uses the Finite Volume 3 dynamical core. The resolution of the forecast system is ∼25 km with 64 vertical hybrid levels. The Climate Forecast System (CFS) reanalysis and GEFSv12 reanalysis serve as initial conditions for the Phase 1 (1989–1999) and Phase 2 (2000–2019) reforecasts, respectively. The perturbations were produced using breeding vectors and ensemble transforms with a rescaling technique for Phase 1 and ensemble Kalman filter 6-h forecasts for Phase 2. The reforecasts were initialized at 0000 (0300) UTC once per day out to 16 days with 5 ensemble members for Phase 1 (Phase 2), except on Wednesdays when the integrations were extended to 35 days with 11 members. The reforecast data set was produced on NOAA’s Weather and Climate Operational Supercomputing System at NCEP. This study summarizes the configuration and dataset of the GEFSv12 reforecast and presents some preliminary evaluations of 500hPa geopotential height, tropical storm track, precipitation, 2-meter temperature, and MJO forecasts. The results were also compared with GEFSv10 or GEFS Subseasonal Experiment reforecasts. In addition to supporting calibration and validation for the National Water Center, NCEP Climate Prediction Center, and other National Weather Service stakeholders, this high-resolution subseasonal dataset also serves as a useful tool for the broader research community in different applications.

Metal foams application to enhance the thermal performance of phase change materials: A review of experimental studies to understand the mechanisms

Abstract: One of the main drawbacks of Phase change materials (PCMs) is their weak heat transfer performance. Introducing open-cell metal foams (MFs) into PCM has been among the most promising and effective methods to address this known shortfall. MFs can significantly improve the thermal performance of PCMs by offering a highly conductive and sturdy structure. The composites made of PCMs and MFs have been widely studied in the literature. However, the literature lacks consistency in describing the mechanisms under which these composites thermally perform in practice. The present article tries to shed light on this matter by reviewing the experimental studies presented in the literature. In this regard and directed by the literature, both heat transfer and heat storage capabilities of the PCM-MF composites are reviewed and compared with those of pure PCMs; both conduction and convection heat transfer mechanisms inside the composites are investigated in detail; the existing methods for measuring and calculation of different composite thermophysical properties are discussed; the current gaps in the field are identified, and suggestions for further studies are provided.

Heat transfer inspection in [(ZnO-MWCNTs)/water-EG(50:50)]hnf with thermal radiation ray and convective condition over a Riga surface

Abstract: The composition of hybrid nanoparticles in the base solvent is a way to improve the thermal efficiency of regular liquids which makes them more effective to cope with the heat transport problems faced by the modern technological world. Enhanced heat transfer in hybrid nanofluids opened the barrier towards applied thermal engineering, mechanical and chemical engineering regarding heat transfer. Therefore, this research is conducted to examine the improved thermal efficiency of [(ZnO-MWCNTs)/water-EG (50:50)]hnf and [(ZnO)/water-EG (50:50)]nf over a Riga surface; similarity transforms and hybrid nanoliquid correlations exercised to achieve the model. The constitutive model was modified by inducing thermal radiation effects and convective heat conditions. A numerical scheme is utilized as a mathematical tool and furnished the results for velocity gradient, thermal behavior and shear stresses under the physical constraints that appeared during the research. The results exposed that induction of novel thermal radiations (Rd) is a prime source to improve heat capability of [(ZnO-MWCNTs)/water-EG(50:50)]hnf. Further, an outstanding improvement in the temperature of [(ZnO-MWCNTs)/water-EG(50:50)]hnf was achieved due to convective heat conditions. As Bi number (due to the convectively heated surface) involves thermal conductivity of the surface materials, extra heat transferred from the surface material to the fluid which significantly contributed to the heat transfer mechanism of [(ZnO-MWCNTs)/water-EG(50:50)]hnf.