scholarly journals A linear stability analysis of two-layer moist convection with a saturation interface

2021 ◽  
Vol 928 ◽  
Author(s):  
Hao Fu
Keyword(s):  
Evaporative Cooling ◽  
Convective Cell ◽  
Marginal Stability ◽  
Prototype Model ◽  
Moist Convection ◽  
Interface Position ◽  
Physical Mechanisms ◽  
Relative Contribution ◽  
Air Interface ◽  
Saturated Layer

The linear convective instability of a mixture of dry air, water vapour and liquid water, with a stable unsaturated layer residing on an unstable saturated layer, is studied. It may serve as a prototype model for understanding the instability that causes mixing at the top of stratocumulus cloud or fog. Such a cloud-clear air interface is modelled as an infinitely thin saturation interface where radiative and evaporative cooling take place. The interface position is determined by the Clausius–Clapeyron equation, and can undulate with the evolution of moisture and temperature. In the small-amplitude regime two physical mechanisms are revealed. First, the interface undulation leads to the undulation of the cooling source, which destabilizes the system by superposing a vertical dipole heating anomaly on the convective cell. Second, the evolution of the moisture field induces non-uniform evaporation at the interface, which stabilizes the system by introducing a stronger evaporative cooling in the ascending region and vice versa in the descending region. These two mechanisms are competing, and their relative contribution to the instability is quantified by theoretically estimating their relative contribution to buoyancy flux tendency. When there is only evaporative cooling, the two mechanisms break even, and the marginal stability curve remains the same as the classic two-layer Rayleigh–Bénard convection with a fixed cooling source.

Quasi-idealized numerical simulations of processes involved in orogenic convection initiation over the Sierras de Córdoba mountains

2021 ◽  
Author(s):  
Christopher A. Davis
Keyword(s):  
Numerical Simulations ◽  
Mountain Range ◽  
Moist Convection ◽  
Low Level ◽  
Physical Mechanisms ◽  
Convergence Line ◽  
Synoptic Conditions ◽  
Deep Moist Convection ◽  
Outflow Boundary ◽  
Convection Initiation

Abstract The Sierras de Córdoba (SDC) mountain range in Argentina is a hotspot of deep moist convection initiation (CI). Radar climatology indicates that 44% of daytime CI events that occur near the SDC in spring and summer seasons and that are not associated with the passage of a cold front or an outflow boundary involve a northerly LLJ, and these events tend to preferentially occur over the southeast quadrant of the main ridge of the SDC. To investigate the physical mechanisms acting to cause CI, idealized convection-permitting numerical simulations with a horizontal grid spacing of 1 km were conducted using CM1. The sounding used for initializing the model featured a strong northerly LLJ, with synoptic conditions resembling those in a previously postulated conceptual model of CI over the region, making it a canonical case study. Differential heating of the mountain caused by solar insolation in conjunction with the low-level northerly flow sets up a convergence line on the eastern slopes of the SDC. The southern portion of this line experiences significant reduction in convective inhibition, and CI occurs over the SDC southeast quadrant. Thesimulated storm soon acquires supercellular characteristics, as observed. Additional simulations with varying LLJ strength also show CI over the southeast quadrant. A simulation without background flow generated convergence over the ridgeline, with widespread CI across the entire ridgeline. A simulation with mid- and upper-tropospheric westerlies removed indicates that CI is minimally influenced by gravity waves. We conclude that the low-level jet is sufficient to focus convection initiation over the southeast quadrant of the ridge.

scholarly journals Craig-Gordon model validation using observed meteorological parameters and measured stable isotope ratios in water vapor over the Southern Ocean

2019 ◽  
Author(s):  
Shaakir Shabir Dar ◽  
Prosenjit Ghosh ◽  
Ankit Swaraj ◽  
Anil Kumar
Keyword(s):  
Water Vapor ◽  
Surface Water ◽  
Southern Ocean ◽  
Isotopic Composition ◽  
Isotope Ratios ◽  
Mixing Processes ◽  
Relative Contribution ◽  
Molecular Diffusivity ◽  
Air Interface ◽  
Evaporation Flux

Abstract. The stable isotopic composition of water vapor over the ocean is governed by the isotopic composition of surface water, ambient vapor isotopic composition, exchange and mixing processes at the water-air interface as well as the local meteorological conditions. In this study we present water vapor and surface water isotope ratios in samples collected across the latitudinal transect from Mauritius to Prydz Bay in the Antarctic coast. The samples were collected on-board the ocean research vessel SA Agulhas during the 9th (Jan-2017) and 10th (Dec-2017 to Jan-2018) Southern Ocean expeditions. The inter annual variability of the meteorological factors governing water vapor isotopic composition is explained. The parameters governing the isotopic composition of evaporation flux from the oceans can be considered separately or simultaneously in the Craig-Gordon (CG) models. The Traditional Craig-Gordon (TCG) (Craig and Gordon, 1965) and the Unified Craig-Gordon (UCG) (Gonfiantini et al., 2018) models were used to evaluate the isotopic composition of evaporation flux for the molecular diffusivity ratios suggested by Merlivat (1978) (MJ), Cappa et al. (2003) (CD) and Pfahl and Wernli (2009) (PW) and for different ocean surface conditions. We found that the UCG model with CD molecular diffusivity ratios where equal contribution from molecular and turbulent diffusion is the best match for our observations. By assigning the representative end member isotopic compositions and solving the two-component mixing model, a relative contribution from locally generated and advected moisture was calculated along the transect. Our results suggest varying contribution of advected westerly component with an increasing trend upto 65° S. Beyond 65° S, the proportion of Antarctic moisture was found to be increasing linearly towards the coast.

scholarly journals Solar p-mode damping rates: Insight from a 3D hydrodynamical simulation

2019 ◽  
Vol 625 ◽  
pp. A20 ◽  
Author(s):  
K. Belkacem ◽  
F. Kupka ◽  
R. Samadi ◽  
H. Grimm-Strele
Keyword(s):  
Normal Modes ◽  
Turbulent Convection ◽  
Time Duration ◽  
Definitive Answer ◽  
Physical Mechanisms ◽  
Relative Contribution ◽  
Hydrodynamical Simulation ◽  
Red Giant ◽  
Hydrodynamical Simulations ◽  
Mixing Length Theory

Space-borne missions such as CoRoT and Kepler have provided a rich harvest of high-quality photometric data for solar-like pulsators. It is now possible to measure damping rates for hundreds of main-sequence and thousands of red-giant stars with an unprecedented precision. However, among the seismic parameters, mode damping rates remain poorly understood and thus barely used for inferring the physical properties of stars. Previous approaches to model mode damping rates were based on mixing-length theory or a Reynolds-stress approach to model turbulent convection. While they can be used to grasp the main physics of the problem, such approaches are of little help to provide quantitative estimates as well as a definitive answer on the relative contribution of each physical mechanism. Indeed, due to the high complexity of the turbulent flow and its interplay with the oscillations, those theories rely on many free parameters which inhibits an in-depth understanding of the problem. Our aim is thus to assess the ability of 3D hydrodynamical simulations to infer the physical mechanisms responsible for damping of solar-like oscillations. To this end, a solar high-spatial resolution and long-duration hydrodynamical 3D simulation computed with the ANTARES code allows probing the coupling between turbulent convection and the normal modes of the simulated box. Indeed, normal modes of the simulation experience realistic driving and damping in the super-adiabatic layers of the simulation. Therefore, investigating the properties of the normal modes in the simulation provides a unique insight into the mode physics. We demonstrate that such an approach provides constraints on the solar damping rates and is able to disentangle the relative contribution related to the perturbation (by the oscillation) of the turbulent pressure, the gas pressure, the radiative flux, and the convective flux contributions. Finally, we conclude that using the normal modes of a 3D numerical simulation is possible and is potentially able to unveil the respective role of the different physical mechanisms responsible for mode damping provided the time-duration of the simulation is long enough.

scholarly journals Soil water regulates the control of photosynthesis on diel hysteresis between soil respiration and temperature

2016 ◽  
Author(s):  
Ben Wang ◽  
TianShan Zha ◽  
Xin Jia ◽  
Jinnan Gong ◽  
Charles Bourque ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Soil Respiration ◽  
Soil Water ◽  
Volumetric Soil Water Content ◽  
Desert Shrub ◽  
Physical Mechanisms ◽  
Relative Contribution ◽  
Diel Variations ◽  
Volumetric Soil Water

Abstract. Causes for diel hysteresis between soil respiration (Rs) and temperature remain highly controversial. Explanations for the occurrence of hysteresis have involved both biological and physical mechanisms. The specifics of these explanations, however, tend to vary with the particular ecosystem or biome being studied. This study examined the seasonal variation in diel hysteresis and its controlling factors in a desert-shrub ecosystem in northwest (NW) China. The study was based on continuous measurements of Rs, air temperature (Ta), soil temperature at the surface and below (Tsurf and Ts), volumetric soil water content (SWC), and photosynthesis over a year 2013. Trends in diel Rs were observed to vary with SWC over the growing season. Diel variations in Rs were more closely associated with Tsurf than with photosynthesis as SWC increased, leading to Rs being in phase with Tsurf, particularly when SWC > 0.08 m3 m−3. However, as SWC decreased below 0.08 m3 m−3, diel variations in Rs were more closely related to variations in photosynthesis, leading to a pronounced diel hysteresis and asynchronicity between Rs and Tsurf. It was indicated that SWC regulates the relative control between photosynthesis and temperature on diel Rs by changing the relative contribution of autotrophic and heterotrophic respiration to total Rs, and thus, causing seasonal variation in diel hysteresis between Rs and temperature. Our findings highlight the importance of biologically-based mechanisms and the role of SWC in regulating diel hysteresis between Rs and temperature.

Design of a neural network aimed at predicting meteotsunamis in Ciutadella harbour (Balearic Islands, Spain)

2020 ◽  
Author(s):  
Maria-del-Mar Vich ◽  
Romualdo Romero
Keyword(s):  
Balearic Islands ◽  
Moist Convection ◽  
Probabilistic Forecasting ◽  
Physical Mechanisms ◽  
Port Facilities ◽  
Wave Heights ◽  
The Difference ◽  
Input Variables ◽  
Wind Profiles ◽  
Atmospheric Gravity

<p>This work explores the applicability of neural networks (NN) for forecasting atmospherically-driven tsunamis affecting Ciutadella harbor in Menorca (Balearic Islands). These meteotsunamis can lead to wave heights around 1 m, and several episodes in the modern history have reached 2-4 m with catastrophic consequences. A timely and skilled prediction of these phenomena could significantly help to mitigate the damages inflicted to the port facilities and moored vessels. We examine the relevant physical mechanisms that promote meteotsunamis in Ciutadella harbour and choose the input variables of the NN accordingly. Two different NNs are devised and tested: a dry and wet scheme. The difference between schemes resides on the input layer; while the first scheme is exclusively focused on the triggering role of atmospheric gravity waves (governed by temperature and wind profiles across the tropospheric column), the second scheme also incorporates humidity as input information with the purpose of accounting for the occasional influence of moist convection. We train both NNs using resilient backpropagation with weight backtracking method. Their performance is tested by means of classical deterministic verification indexes. We also compare both NN results against the performance of a substantially different prognostic method that relies on a sequence of atmospheric and oceanic numerical simulations. Both NN schemes show a skill comparable to that of computationally expensive approaches based on direct numerical simulation of the physical mechanisms. The expected greater versatility of the wet scheme over the dry scheme cannot be clearly proved owing to the limited size of the training database. The results emphasize the potential of a NN approach and open a clear path to an operational implementation, including probabilistic forecasting strategies.</p>

Measurement System for Oil-Water-Air Interface Position and Oil Layer Thickness

2014 ◽  
Vol 701-702 ◽  
pp. 518-521
Author(s):  
Yue Feng Li ◽  
Jie Sun ◽  
Hao Ren
Keyword(s):  
Layer Thickness ◽  
Measurement System ◽  
Optical Amplification ◽  
Interface Position ◽  
Air Interface ◽  
Amplification System ◽  
Oil Water ◽  
The Difference ◽  
Physical And Chemical ◽  
Air Interfaces

The measurement system adopts linear CCD as photographic element. Through the optical amplification system, the images of oil-water and oil-air interfaces were clearly imaged onto CCD chip. CCD transforms optical signals into electronically signals, and then submits data to PC through USB channel. After Savitzky-Golay smoothing on light intensity data, the software analyzes the data and calculate out the positions of oil-water-air interfaces. By calculating the difference between two positions, the oil layer thickness is gotten. The experiment results that the measurement system given in this paper is reasonable, stable, effective and accurate. This measurement system has wide application in the physical and chemical industry field.

scholarly journals Craig–Gordon model validation using stable isotope ratios in water vapor over the Southern Ocean

2020 ◽  
Vol 20 (19) ◽  
pp. 11435-11449
Author(s):  
Shaakir Shabir Dar ◽  
Prosenjit Ghosh ◽  
Ankit Swaraj ◽  
Anil Kumar
Keyword(s):  
Water Vapor ◽  
Surface Water ◽  
Southern Ocean ◽  
Isotopic Composition ◽  
Isotope Ratios ◽  
Mixing Processes ◽  
Vapor Flux ◽  
Relative Contribution ◽  
Molecular Diffusivity ◽  
Air Interface

Abstract. The stable oxygen and hydrogen isotopic composition of water vapor over a water body is governed by the isotopic composition of surface water and ambient vapor, exchange and mixing processes at the water–air interface, and the local meteorological conditions. These parameters form inputs to the Craig–Gordon models, used for predicting the isotopic composition of vapor produced from the surface water due to the evaporation process. In this study we present water vapor, surface water isotope ratios and meteorological parameters across latitudinal transects in the Southern Ocean (27.38–69.34 and 21.98–66.8∘ S) during two austral summers. The performance of Traditional Craig–Gordon (TCG) (Craig and Gordon, 1965) and the Unified Craig–Gordon (UCG) (Gonfiantini et al., 2018) models is evaluated to predict the isotopic composition of evaporated water vapor flux in the diverse oceanic settings. The models are run for the molecular diffusivity ratios suggested by Merlivat (1978), Cappa et al. (2003) and Pfahl and Wernli (2009), referred to as MJ, CD and PW, respectively, and different turbulent indices (x), i.e., fractional contribution of molecular vs. turbulent diffusion. It is found that the UCGx=0.8MJ, UCGx=0.6CD, TCGx=0.6MJ and TCGx=0.7CD models predicted the isotopic composition that best matches with the observations. The relative contribution from locally generated and advected moisture is calculated at the water vapor sampling points, along the latitudinal transects, assigning the representative end-member isotopic compositions, and by solving the two-component mixing model. The results suggest a varying contribution of the advected westerly component, with an increasing trend up to 65∘ S. Beyond 65∘ S, the proportion of Antarctic moisture was found to be prominent and increasing linearly towards the coast.

Mathematical modelling of moist convection and transport of gaseous pollutants and aerosols in clouds

2015 ◽  
Vol 30 (3) ◽  
Author(s):  
Artash E. Aloyan ◽  
Vardan O. Arutyunyan ◽  
Alexander N. Yermakov
Keyword(s):  
Gas Phase ◽  
Transport Model ◽  
Liquid Droplet ◽  
Three Dimensional ◽  
Medium Size ◽  
Moist Convection ◽  
Convective Clouds ◽  
Physical Mechanisms ◽  
Mechanisms Of Formation ◽  
Microphysical Processes

AbstractA joint three-dimensional numerical model of formation of convective clouds in the atmosphere is constructed with a detailed description of microphysical processes. A transport model of multicomponent gaseous admixtures and aerosols is also a constructed subject to gas-phase and liquid-phase chemical reactions. Basic physical mechanisms of formation of liquid droplet clouds of medium size and the transport of gases with different reactivity and solubility are considered. The calculations performed with the use of the data on emission of NO

Oscillatory flow regimes for a circular cylinder near a plane boundary

2018 ◽  
Vol 844 ◽  
pp. 127-161 ◽  
Author(s):  
Chengwang Xiong ◽  
Liang Cheng ◽  
Feifei Tong ◽  
Hongwei An
Keyword(s):  
Boundary Layer ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Oscillatory Flow ◽  
Flow Regimes ◽  
Plane Boundary ◽  
Marginal Stability ◽  
Hysteresis Phenomenon ◽  
Physical Mechanisms ◽  
Large Hysteresis

Oscillatory flow around a circular cylinder close to a plane boundary is numerically investigated at low-to-intermediate Keulegan–Carpenter ($KC$) and Stokes numbers ($\unicode[STIX]{x1D6FD}$) for different gap-to-diameter ratios ($e/D$). A set of unique flow regimes is observed and classified based on the established nomenclature in the ($KC,\unicode[STIX]{x1D6FD}$)-space. It is found that the flow is not only influenced by $e/D$ but also by the ratio of the thickness of the Stokes boundary layer ($\unicode[STIX]{x1D6FF}$) to the gap size (e). At relatively large $\unicode[STIX]{x1D6FF}/e$ values, vortex shedding through the gap is suppressed and vortices are only shed from the top of the cylinder. At intermediate values of $\unicode[STIX]{x1D6FF}/e$, flow through the gap is enhanced, resulting in horizontal gap vortex shedding. As $\unicode[STIX]{x1D6FF}/e$ is further reduced below a critical value, the influence of $\unicode[STIX]{x1D6FF}/e$ becomes negligible and the flow is largely dependent on $e/D$. A hysteresis phenomenon is observed for the transitions in the flow regime. The physical mechanisms responsible for the hysteresis and the variation of marginal stability curves with $e/D$ are explored at $KC=6$ through specifically designed numerical simulations. The Stokes boundary layer over the plane boundary is found to be responsible for the relatively large hysteresis range over $0.25<e/D<1.0$. Three mechanisms have been identified to the change of the marginal stability curve over $e/D$, which are the blockage effect due to the geometry setting, the favourable pressure gradient over the gap and the location of the leading eigenmode relative to the cylinder.

Strain analysis with nanometer resolution using a conventional transmission electron microsopy technique: electron diffraction contrast imaging revisited

1995 ◽  
Vol 53 ◽  
pp. 168-169
Author(s):  
Koenraad G F Janssens ◽  
Omer Van der Biest ◽  
Jan Vanhellemont ◽  
Herman E Maes ◽  
Robert Hull
Keyword(s):  
Electron Diffraction ◽  
Strain Field ◽  
Elastic Strain ◽  
Strain Analysis ◽  
Local Strain ◽  
Contrast Imaging ◽  
Strain Characterization ◽  
Physical Mechanisms ◽  
Diffraction Contrast ◽  
Transmission Electron

There is a growing need for elastic strain characterization techniques with submicrometer resolution in several engineering technologies. In advanced material science and engineering the quantitative knowledge of elastic strain, e.g. at small particles or fibers in reinforced composite materials, can lead to a better understanding of the underlying physical mechanisms and thus to an optimization of material production processes. In advanced semiconductor processing and technology, the current size of micro-electronic devices requires an increasing effort in the analysis and characterization of localized strain. More than 30 years have passed since electron diffraction contrast imaging (EDCI) was used for the first time to analyse the local strain field in and around small coherent precipitates1. In later stages the same technique was used to identify straight dislocations by simulating the EDCI contrast resulting from the strain field of a dislocation and comparing it with experimental observations. Since then the technique was developed further by a small number of researchers, most of whom programmed their own dedicated algorithms to solve the problem of EDCI image simulation for the particular problem they were studying at the time.

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