A Case Study of Cloud-top Kelvin–Helmholtz Instability Waves near the Dendritic Growth Zone

2021 ◽  
Keyword(s):  
Dendritic Growth ◽  
Supercooled Liquid ◽  
Growth Zone ◽  
Helmholtz Instability ◽  
Instability Waves ◽  
Cloud Radar ◽  
Surface Liquid ◽  
The Impact

Abstract Kelvin-Helmholtz instability (KH) waves have been broadly shown to affect the growth of hydrometeors within a region of falling precipitation, but formation and growth from KH waves at cloud top needs further attention. Here, we present detailed observations of cloud-top KH waves that produced a snow plume that extended to the surface. Airborne transects of cloud radar aligned with range height indicator scans from ground-based precipitation radar track the progression and intensity of the KH wave kinetics and precipitation. In-situ cloud probes and surface disdrometer measurements are used to quantify the impact of the snow plume on the composition of an underlying supercooled liquid water (SLW) cloud and the snowfall observed at the surface. KH wavelengths of 1.5 km consisted of ~750-m-wide up- and downdrafts. A distinct fluctus region appeared as a wave-breaking cloud top where the fastest updraft was observed to exceed 5 m s−1. Relatively weaker updrafts of 0.5-1.5 m s−1 beneath the fluctus and partially overlapping the dendritic growth zone were associated with steep gradients in reflectivity of −5 to 20 dBZe in as little as 500 m depths due to rapid growth of pristine planar ice crystals. The falling snow removed ~80% of the SLW content from the underlying cloud and led to a twofold increase in surface liquid equivalent snowfall rate from 0.6 to 1.3 mm hr−1. This paper presents the first known study of cloud-top KH waves producing snowfall with observations of increased snowfall rates at the surface.

scholarly journals Fuel economy assessment tool for auxiliary kite propulsion of merchant ship

2018 ◽  
pp. 5-7 ◽  
Author(s):  
Vincent Podeur ◽  
Damien Merdrignac ◽  
Morgan Behrel ◽  
Kostia Roncin ◽  
Caroline Fonti ◽  
...  
Keyword(s):  
Fuel Economy ◽  
Assessment Tool ◽  
Round Trip ◽  
Merchant Ship ◽  
Added Resistance In Waves ◽  
The Mean ◽  
The Impact ◽  
Engine Power

A tool dedicated to assess fuel economy induced by kite propulsion has been developed. To produce reliable results, computations must be performed on a period over several years, for several routes and for several ships. In order to accurately represent the impact of meteorological trends variations on the exploitability of the kite towing concept, a time domain approach of the problem has been used. This tool is based on the weather database provided by the ECMWF. Two sailing strategies can be selected for assessing the performance of the kite system. For a given kite area, the simulation can be run either at constant speed or at constant engine power. A validation has been made, showing that predicted consumption is close from in-situ measurement. It shows an underestimation of 11.9% of the mean fuel consumption mainly due to auxiliary consumption and added resistance in waves that were not taken into account. To conclude, a case study is performed on a 2200 TEU container ship equipped with an 800m² kite on a transatlantic route between Halifax and Le Havre. Round trip simulations, performed over 5 years of navigation, show that the total economy predicted is of around 12% at a speed of 16 knots and around 6.5% at a speed of 19 knots.

scholarly journals Assessing the efficiency of a “buried wall” barrier in the establishment of near-surface long-term storage and disposal facilities for RW

2021 ◽  
Vol 14 (1) ◽  
pp. 96-105
Author(s):  
V. V. Suskin ◽  
◽  
I. V. Kapyrin ◽  
F. V. Grigorev ◽  
◽  
...  
Keyword(s):  
Near Surface ◽  
Transfer Processes ◽  
Long Term Storage ◽  
Mass Transfer Processes ◽  
High Degree ◽  
The Impact ◽  
Term Storage

The article evaluates the impact of a “buried wall” barrier on the long-term safety during the long-term storage1 or in-situ disposal of nuclear legacy facilities, in particular, industrial reservoirs, as well as during the development of near-surface disposal facilities for radioactive waste (RWDF). For assessment purposes, filtration and mass transfer processes have been numerically modelled in the GeRa code based on a case study of a reference near-surface facility. The study explores in which way the available covering screen affects the dynamics of contaminant spread. It evaluates the sensitivity of the results to the dispersion parameter commonly characterized by a high degree of uncertainty.

scholarly journals Meiofauna winners and losers of coastal hypoxia: case study harpacticoid copepods

2014 ◽  
Vol 11 (2) ◽  
pp. 281-292 ◽  
Author(s):  
M. Grego ◽  
B. Riedel ◽  
M. Stachowitsch ◽  
M. De Troch
Keyword(s):  
Harpacticoid Copepod ◽  
Recovery Phase ◽  
Harpacticoid Copepods ◽  
The Family ◽  
Juvenile Stages ◽  
Males And Females ◽  
Gravid Females ◽  
The Impact

Abstract. The impact of anoxia on meiobenthic copepod species was assessed by means of a field experiment. Four plexiglass chambers were deployed in situ in 24 m depth to simulate an anoxic event of 9 days, 1 month, 2 months and 10 months. From normoxic to anoxic conditions, we recorded a drop in copepod density and species richness. With increasing duration of anoxia the relative abundance of the individuals of the family Cletodidae increased, and they survived the 1 month and 2 month anoxia, the latter with few specimens. They were the true "winners" of the experimentally induced anoxia. Dominance did not increase in the deployments because not one, but several species from this family were tolerant to anoxia. The overall rate of survival was the same for males and females, but no juvenile stages of copepods survived in anoxia. During a recovery phase of 7 days after a short-term anoxia of 9 days, harpacticoid copepod density did not increase significantly, and there was only a slight increase in species diversity. We concluded that no substantial colonisation from the surrounding sediment took place. The survivors, however, showed a high potential for recovery according to the number of gravid females, whose number increased significantly once the oxygen was available again. These findings imply that substantial energy is allocated to reproduction in the recovery phase.

scholarly journals Properties of Impact-Related Pseudotachylite and Associated Shocked Zircon and Monazite in the Upper Levels of a Large Impact Basin: a Case Study From the Vredefort Impact Structure

Minerals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1053
Author(s):  
Elizaveta Kovaleva ◽  
Roger Dixon
Keyword(s):  
Impact Crater ◽  
Shock Pressure ◽  
Initial Structure ◽  
Impact Structure ◽  
Near Surface ◽  
X Ray ◽  
Host Rocks ◽  
The Impact

The Vredefort impact structure in South Africa is deeply eroded to its lowermost levels. However, granophyre (impact melt) dykes in such structures preserve clasts of supracrustal rocks, transported down from the uppermost levels of the initial structure. Studying these clasts is the only way to understand the properties of already eroded impactites. One such lithic clast from the Vredefort impact structure contains a thin pseudotachylite vein and is shown to be derived from the near-surface environment of the impact crater. Traditionally, impact pseudotachylites are referred to as in situ melt rocks with the same chemical and isotopic composition as their host rocks. The composition of the sampled pseudotachylite vein is not identical to its host rock, as shown by the micro-X-ray fluorescence (µXRF) and energy-dispersive X-ray (EDX) spectrometry mapping. Mapping shows that the melt transfer and material mixing within pseudotachylites may have commonly occurred at the upper levels of the structure. The vein is spatially related to shocked zircon and monazite crystals in the sample. Granular zircons with small granules are concentrated within and around the vein (not farther than 6–7 mm from the vein). Zircons with planar fractures and shock microtwins occur farther from the vein (6–12 mm). Zircons with microtwins (65°/{112}) are also found inside the vein, and twinned monazite (180°/[101]) is found very close to the vein. These spatial relationships point to elevated shock pressure and shear stress, concentrated along the vein’s plane during impact.

scholarly journals Fingerprints of a riming event on cloud radar Doppler spectra: observations and modeling

2016 ◽  
Vol 16 (5) ◽  
pp. 2997-3012 ◽  
Author(s):  
Heike Kalesse ◽  
Wanda Szyrmer ◽  
Stefan Kneifel ◽  
Pavlos Kollias ◽  
Edward Luke
Keyword(s):  
Supercooled Liquid ◽  
Relative Role ◽  
Traditional Use ◽  
Radar Observations ◽  
Atmospheric Radiation Measurement ◽  
Air Motion ◽  
Biogenic Aerosols

Abstract. Radar Doppler spectra measurements are exploited to study a riming event when precipitating ice from a seeder cloud sediment through a supercooled liquid water (SLW) layer. The focus is on the "golden sample" case study for this type of analysis based on observations collected during the deployment of the Atmospheric Radiation Measurement Program's (ARM) mobile facility AMF2 at Hyytiälä, Finland, during the Biogenic Aerosols – Effects on Clouds and Climate (BAECC) field campaign. The presented analysis of the height evolution of the radar Doppler spectra is a state-of-the-art retrieval with profiling cloud radars in SLW layers beyond the traditional use of spectral moments. Dynamical effects are considered by following the particle population evolution along slanted tracks that are caused by horizontal advection of the cloud under wind shear conditions. In the SLW layer, the identified liquid peak is used as an air motion tracer to correct the Doppler spectra for vertical air motion and the ice peak is used to study the radar profiles of rimed particles. A 1-D steady-state bin microphysical model is constrained using the SLW and air motion profiles and cloud top radar observations. The observed radar moment profiles of the rimed snow can be simulated reasonably well by the model, but not without making several assumptions about the ice particle concentration and the relative role of deposition and aggregation. This suggests that in situ observations of key ice properties are needed to complement the profiling radar observations before process-oriented studies can effectively evaluate ice microphysical parameterizations.

scholarly journals The FluxEngine air–sea gas flux toolbox: simplified interface and extensions for in situ analyses and multiple sparingly soluble gases

Ocean Science ◽  
2019 ◽  
Vol 15 (6) ◽  
pp. 1707-1728 ◽  
Author(s):  
Thomas Holding ◽  
Ian G. Ashton ◽  
Jamie D. Shutler ◽  
Peter E. Land ◽  
Philip D. Nightingale ◽  
...  
Keyword(s):  
Gas Transfer ◽  
Illustrative Case ◽  
Observation Data ◽  
Co2 Fluxes ◽  
In Situ Data ◽  
First Case ◽  
Gas Fluxes ◽  
The Impact

Abstract. The flow (flux) of climate-critical gases, such as carbon dioxide (CO2), between the ocean and the atmosphere is a fundamental component of our climate and an important driver of the biogeochemical systems within the oceans. Therefore, the accurate calculation of these air–sea gas fluxes is critical if we are to monitor the oceans and assess the impact that these gases are having on Earth's climate and ecosystems. FluxEngine is an open-source software toolbox that allows users to easily perform calculations of air–sea gas fluxes from model, in situ, and Earth observation data. The original development and verification of the toolbox was described in a previous publication. The toolbox has now been considerably updated to allow for its use as a Python library, to enable simplified installation, to ensure verification of its installation, to enable the handling of multiple sparingly soluble gases, and to enable the greatly expanded functionality for supporting in situ dataset analyses. This new functionality for supporting in situ analyses includes user-defined grids, time periods and projections, the ability to reanalyse in situ CO2 data to a common temperature dataset, and the ability to easily calculate gas fluxes using in situ data from drifting buoys, fixed moorings, and research cruises. Here we describe these new capabilities and demonstrate their application through illustrative case studies. The first case study demonstrates the workflow for accurately calculating CO2 fluxes using in situ data from four research cruises from the Surface Ocean CO2 ATlas (SOCAT) database. The second case study calculates air–sea CO2 fluxes using in situ data from a fixed monitoring station in the Baltic Sea. The third case study focuses on nitrous oxide (N2O) and, through a user-defined gas transfer parameterisation, identifies that biological surfactants in the North Atlantic could suppress individual N2O sea–air gas fluxes by up to 13 %. The fourth and final case study illustrates how a dissipation-based gas transfer parameterisation can be implemented and used. The updated version of the toolbox (version 3) and all documentation is now freely available.

Geomechanically Driven Casing Deformation During Multistage Perf and Plug Fracturing Operations: Investigation and Mitigation

2021 ◽  
Author(s):  
Arjang Gandomkar ◽  
David Katz ◽  
Ricardo Gomez ◽  
Anders Gundersen
Keyword(s):  
Active Tectonics ◽  
Oil Fields ◽  
Hydraulic Stimulation ◽  
Limited Entry ◽  
Stress States ◽  
Failure Conditions ◽  
Casing Deformation ◽  
The Impact

Abstract Casing Deformation has presented itself in numerous unconventional basins. Severe deformation interferes with multistage fracturing, in particular with plug-and-perforation (also known as plug-and-perf) operations, the most common stage isolation method in unconventional development. Casing Deformation can greatly impact 20-30% of field productivity of horizontal wells in certain US shale and tight oil fields (Jacobs, 2020). Reservoir accessibility and well integrity are the two separate issues when considering casing deformation. In this paper, the impact of geomechanically driven casing deformation on reservoir accessibility that in turn affects production and economics, will be discussed. Origin of casing deformation within a target zone lies in natural fractures placed in highly anisotropic stress regimes. When these fractures are perturbed by hydraulic stimulation, slow slip or dynamic failure of the rock may occur. This phenomenon is intensified by active tectonics, high anisotropic in-situ stresses, and poor completion practices, i.e., poor cement. This paper evaluates these processes by demonstrating failure conditions of wellbores in different stress states and well orientations representative of unconventional basins. It reviews how these conditions can be evaluated in the reservoir, so risk can be estimated. The mitigation procedures to reduce casing deformation impact to operations through either well planning or completions design are discussed. Finally, this paper will also review an alternative completion method to plug-and-perf that allows limited entry completion technique in restricted ID casing due to casing deformation with a field case study.

scholarly journals Meiofauna winners and losers of coastal hypoxia: case study harpacticoid copepods

2013 ◽  
Vol 10 (7) ◽  
pp. 12385-12416 ◽  
Author(s):  
M. Grego ◽  
B. Riedel ◽  
M. Stachowitsch ◽  
M. De Troch
Keyword(s):  
Harpacticoid Copepod ◽  
Recovery Phase ◽  
Harpacticoid Copepods ◽  
The Family ◽  
Juvenile Stages ◽  
Males And Females ◽  
Gravid Females ◽  
The Impact

Abstract. The impact of anoxia on meiobenthic copepod species was assessed by means of a field experiment. Four plexiglass chambers were deployed in situ in 24 m depth to simulate an anoxic event of 9 days, 1 month, 2 months and 10 months. From normoxic to anoxic conditions, we recorded a drop in copepod density and species richness. With increasing duration of anoxia the relative abundance of the individuals of the family Cletodidae increased, and they survived the 1 month and 2 month anoxia, the latter with few specimens. They were the true "winners" of the experimentally induced anoxia. Dominance did not increase throughout all deployments because; not one, but several species from this family were tolerant to anoxia. The overall rate of survival was the same for males and females, but no juvenile stages of copepods survived in anoxia. During a recovery phase of 7 days after a short-term anoxia of 9 days, harpacticoid copepod density did not increase significantly, and there was only a slight increase in species diversity. We concluded that there was no substantial colonisation from the surrounding sediment. The survivors, however, showed a high potential for recovery according to the number of gravid females, whose number increased significantly once the oxygen was available again. These finding imply that a substantial amount of energy is allocated to reproduction in the recovery phase.

scholarly journals Decolonising Namibian Arts and Design through Improvisation

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Melanie SARANTOU ◽  
Caoimhe Isha BEAULÉ ◽  
Satu MIETTINEN
Keyword(s):  
Focus Group ◽  
Case Study Research ◽  
For Profit ◽  
Not For Profit ◽  
Start Up ◽  
Group Members ◽  
The Impact

The research investigates the role of service design and improvisation as decolonising practice. It is based on case study research with a focus group consisting of Namibian artists, designers, artisans and arts organisations who participated in artistic and cultural exchange activities of the Art South-South Trust (ASST), a start-up Namibian not for profit (NFP) organisation. The goal of ASST was to increase visibility of the focus group members, enable global exposure and create an arena for multi-vocality. The paper creates a practical framework for decolonising practices in Namibian arts and design by drawing on reflective practice to analyse the activities of ASST alongside interview data collected from Namibian and Australian partner organisations and participants in the program. Critical thinking is used to evaluate the impact of realised activities and processes both in situ in Namibia and in exchange in Australia. This paper explores practices that can enable decolonising processes in Namibian arts and design spheres

Sign in / Sign up

Export Citation Format

Share Document