scholarly journals The NCAR–FAA Snow Machine: An Artificial Snow-Generation System

2018 ◽  
Vol 35 (11) ◽  
pp. 2159-2168
Author(s):  
Scott D. Landolt ◽  
Roy M. Rasmussen ◽  
Alan J. Hills ◽  
Warren Underwood ◽  
Charles A. Knight ◽  
...  
Keyword(s):  
Mass Balance ◽  
Size Distribution ◽  
Liquid Water ◽  
Generation System ◽  
Fall Velocity ◽  
Atmospheric Research ◽  
Controlled Conditions ◽  
Precipitation Gauge ◽  
Cold Chamber ◽  
Over Time

AbstractThe National Center for Atmospheric Research (NCAR) developed an artificial snow-generation system designed to operate in a laboratory cold chamber for testing aircraft anti-icing fluids under controlled conditions. Flakes of ice are produced by shaving an ice cylinder with a rotating carbide bit; the resulting artificial snow is dispersed by turbulent airflows and falls approximately 2.5 m to the bottom of the device. The resulting fine ice shavings mimic snow in size, distribution, fall velocity, density, and liquid water equivalent (LWE) snowfall rate. The LWE snowfall rate can be controlled using either a mass balance or a precipitation gauge, which measures the snowfall accumulation over time, from which the computer derives the LWE rate. LWE snowfall rates are calculated every 6 s, and the rate the ice cylinder is fed into the carbide bit is continually adjusted to ensure that the LWE snowfall rate matches a user-selected value. The system has been used to generate LWE snowfall rates ranging from 0 to 10 mm h−1 at temperatures from −2 to −30°C and densities of approximately 0.1–0.5 g cm−3. Comparisons of the snow-machine fluid tests with the outdoor fluid tests have shown that the snow machine can mimic natural outdoor rates under a broad range of conditions.

scholarly journals Inertial Measures of Motion for Clinical Biomechanics: Comparative Assessment of Accuracy under Controlled Conditions – Changes in Accuracy over Time

PLoS ONE ◽  
2015 ◽  
Vol 10 (3) ◽  
pp. e0118361 ◽  
Author(s):  
Karina Lebel ◽  
Patrick Boissy ◽  
Mathieu Hamel ◽  
Christian Duval
Keyword(s):  
Comparative Assessment ◽  
Controlled Conditions ◽  
Over Time

scholarly journals Future surface mass balance and surface melt in the Amundsen sector of the West Antarctic Ice Sheet

2021 ◽  
Vol 15 (2) ◽  
pp. 571-593
Author(s):  
Marion Donat-Magnin ◽  
Nicolas C. Jourdain ◽  
Christoph Kittel ◽  
Cécile Agosta ◽  
Charles Amory ◽  
...  
Keyword(s):  
Mass Balance ◽  
Liquid Water ◽  
Ice Sheet ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
Ice Shelves ◽  
Net Production ◽  
West Antarctic ◽  
Surface Liquid ◽  
Surface Melt

Abstract. We present projections of West Antarctic surface mass balance (SMB) and surface melt to 2080–2100 under the RCP8.5 scenario and based on a regional model at 10 km resolution. Our projections are built by adding a CMIP5 (Coupled Model Intercomparison Project Phase 5) multi-model-mean seasonal climate-change anomaly to the present-day model boundary conditions. Using an anomaly has the advantage to reduce CMIP5 model biases, and a perfect-model test reveals that our approach captures most characteristics of future changes despite a 16 %–17 % underestimation of projected SMB and melt rates. SMB over the grounded ice sheet in the sector between Getz and Abbot increases from 336 Gt yr−1 in 1989–2009 to 455 Gt yr−1 in 2080–2100, which would reduce the global sea level changing rate by 0.33 mm yr−1. Snowfall indeed increases by 7.4 % ∘C−1 to 8.9 % ∘C−1 of near-surface warming due to increasing saturation water vapour pressure in warmer conditions, reduced sea-ice concentrations, and more marine air intrusion. Ice-shelf surface melt rates increase by an order of magnitude in the 21st century mostly due to higher downward radiation from increased humidity and to reduced albedo in the presence of melting. There is a net production of surface liquid water over eastern ice shelves (Abbot, Cosgrove, and Pine Island) but not over western ice shelves (Thwaites, Crosson, Dotson, and Getz). This is explained by the evolution of the melt-to-snowfall ratio: below a threshold of 0.60 to 0.85 in our simulations, firn air is not entirely depleted by melt water, while entire depletion and net production of surface liquid water occur for higher ratios. This suggests that western ice shelves might remain unaffected by hydrofracturing for more than a century under RCP8.5, while eastern ice shelves have a high potential for hydrofracturing before the end of this century.

scholarly journals A Synergy Approach to Estimate Properties of Raindrop Size Distributions Using a Doppler Lidar and Cloud Radar

2010 ◽  
Vol 27 (6) ◽  
pp. 1095-1100 ◽  
Author(s):  
Katja Träumner ◽  
Jan Handwerker ◽  
Andreas Wieser ◽  
Jens Grenzhäuser
Keyword(s):  
Size Distribution ◽  
Analytical Description ◽  
Doppler Lidar ◽  
Fall Velocity ◽  
Rayleigh Approximation ◽  
Size Dependent ◽  
Cloud Radar ◽  
Raindrop Size Distribution ◽  
Remote Sensing Systems ◽  
Raindrop Size

Abstract Remote sensing systems like radars and lidars are frequently used in atmospheric measurement campaigns. Because of their different wavelengths, they operate in different scattering regimes. Combined use may result in new measurement options. Here, an approach to estimate raindrop size distribution using vertical velocities measured by a lidar–radar combination is introduced and tested using a 2-μm Doppler lidar and a 35.5-GHz cloud radar. The lidar spectra are evaluated to deduce air motion from the aerosol peak and the fall velocity of the raindrops from the rain peak. The latter is weighted by the area (D2) of the scatters. The fall velocity derived from radar measurements is weighted by D6 (Rayleigh approximation). Assuming a size-dependent fall velocity and an analytical description of the drop size distribution, its parameters are calculated from these data. Comparison of the raindrop size distribution from the lidar–radar combination with in situ measurements on the ground yields satisfying results.

Soft Computing Techniques in Civil Engineering

2010 ◽  
pp. 143-159
Author(s):  
Juan L. Pérez ◽  
Juan R. Rabuñal ◽  
Fernando Martínez Abella
Keyword(s):  
Genetic Programming ◽  
Evolutionary Computation ◽  
Soft Computing ◽  
Civil Engineering ◽  
Structural Concrete ◽  
Controlled Conditions ◽  
Classical Algorithm ◽  
Soft Computing Techniques ◽  
Over Time

Soft computing techniques are applied to a huge quantity of problems spread in several areas of science. In this case, Evolutionary Computation (EC) techniques are applied, in concrete Genetic Programming (GP), to a temporary problem associated to the field of Civil Engineering. The case of study of this technique has been centered in the prediction, over time, of the behavior of the structural concrete in controlled conditions. Given the temporary nature of the case of study, it has been necessary to make several changes to the classical algorithm of GP, among whom it can be emphasized the incorporation of a new operator that gives the GP the ability to be able to solve problems with temporary behavior. The obtained results shown that the proposed method has succeeded in improving the adjustment to the current regulations about creep in the structural concrete.

Soft Computing Techniques in Civil Engineering

2012 ◽  
pp. 1982-1997
Author(s):  
Juan L. Pérez ◽  
Juan Rabuñal ◽  
Fernando Martínez Abella
Keyword(s):  
Genetic Programming ◽  
Evolutionary Computation ◽  
Soft Computing ◽  
Civil Engineering ◽  
Structural Concrete ◽  
Controlled Conditions ◽  
Classical Algorithm ◽  
Soft Computing Techniques ◽  
Over Time

Soft computing techniques are applied to a huge quantity of problems spread in several areas of science. In this case, Evolutionary Computation (EC) techniques are applied, in concrete Genetic Programming (GP), to a temporary problem associated to the field of Civil Engineering. The case of study of this technique has been centered in the prediction, over time, of the behavior of the structural concrete in controlled conditions. Given the temporary nature of the case of study, it has been necessary to make several changes to the classical algorithm of GP, among whom it can be emphasized the incorporation of a new operator that gives the GP the ability to be able to solve problems with temporary behavior. The obtained results shown that the proposed method has succeeded in improving the adjustment to the current regulations about creep in the structural concrete.

scholarly journals Dataset on raindrop size distribution, raindrop fall velocity and precipitation data measured by disdrometers and rain gauges over Peruvian central Andes (12.0°S)

Data in Brief ◽  
2020 ◽  
Vol 29 ◽  
pp. 105215
Author(s):  
Jairo M. Valdivia ◽  
Kevin Contreras ◽  
Daniel Martinez-Castro ◽  
Elver Villalobos-Puma ◽  
Luis F. Suarez-Salas ◽  
...  
Keyword(s):  
Size Distribution ◽  
Central Andes ◽  
Precipitation Data ◽  
Fall Velocity ◽  
Rain Gauges ◽  
Raindrop Size Distribution ◽  
Raindrop Size

Geometrical Thickness, Liquid Water Content, and Radiative Properties of Stratocumulus Clouds over the Western North Pacific

1995 ◽  
Vol 34 (2) ◽  
pp. 460-470 ◽  
Author(s):  
Tadahiro Hayasaka ◽  
Teruyuki Nakajima ◽  
Yasushi Fujiyoshi ◽  
Yutaka Ishizaka ◽  
Takao Takeda ◽  
...  
Keyword(s):  
Size Distribution ◽  
Liquid Water ◽  
North Pacific ◽  
Western North Pacific ◽  
Near Infrared ◽  
North Pacific Ocean ◽  
Microwave Radiometer ◽  
Radiative Properties ◽  
Liquid Water Path ◽  
Water Vapor Absorption

Abstract An algorithm was developed for retrieving cloud geometrical thickness from a measured liquid water path and equivalent width of 0.94-µm water vapor absorption band. The algorithm was applied to aircraft observations obtained by a microwave radiometer and a spectrometer in the winter of 1991 over the western North Pacific Ocean. Retrieved values of the cloud geometrical thickness are apt to be smaller than those observed by eye, especially for horizontally inhomogeneous clouds. Measured cloud albedos in the visible and near-infrared spectral region were also compared with calculated values. For homogeneous clouds there exists a single droplet size distribution that satisfies both spectral regions. However, for inhomogeneous clouds no single size distribution exists that satisfies the albedo observed in both spectral regions.

scholarly journals A New Criterion to Improve Operational Drizzle Detection with Ground-Based Remote Sensing

2019 ◽  
Vol 36 (5) ◽  
pp. 781-801 ◽  
Author(s):  
Claudia Acquistapace ◽  
Ulrich Löhnert ◽  
Maximilian Maahn ◽  
Pavlos Kollias
Keyword(s):  
Liquid Water ◽  
Positive Zero ◽  
Doppler Spectrum ◽  
Fall Velocity ◽  
Cloud Droplets ◽  
Particle Sedimentation ◽  
Boundary Layer Dynamics ◽  
Cloud Evolution ◽  
New Criterion

AbstractLight shallow precipitation in the form of drizzle is one of the mechanisms for liquid water removal, affecting cloud lifetime and boundary layer dynamics and thermodynamics. The early formation of drizzle drops is of particular interest for quantifying aerosol–cloud–precipitation interactions. In models, drizzle initiation is represented by the autoconversion, that is, the conversion of liquid water from a cloud liquid water category (where particle sedimentation is ignored) into a precipitating liquid water category. Various autoconversion parameterizations have been proposed in recent years, but their evaluation is challenging due to the lack of proper observations of drizzle development in the cloud. This work presents a new algorithm for Classification of Drizzle Stages (CLADS). CLADS is based on the skewness of the Ka-band radar Doppler spectrum. Skewness is sensitive to the drizzle growth in the cloud: the observed Gaussian Doppler spectrum has skewness zero when only cloud droplets are present without any significant fall velocity. Defining downward velocities positive, skewness turns positive when embryonic drizzle forms and becomes negative when drizzle starts to dominate the spectrum. CLADS identifies spatially coherent structures of positive, zero, and negative skewness in space and time corresponding to drizzle seeding, drizzle growth/nondrizzle, and drizzle mature, respectively. We test CLADS on case studies from the Jülich Observatory for Cloud Evolution Core Facility (JOYCE-CF) and the Barbados Cloud Observatory (BCO) to quantitatively estimate the benefits of CLADS compared to the standard Cloudnet target categorization algorithm. We suggest that CLADS can provide additional observational constraints for understanding the processes related to drizzle formation better.

scholarly journals A level-set method for modeling the evolution of glacier geometry

2004 ◽  
Vol 50 (171) ◽  
pp. 485-491 ◽  
Author(s):  
Antoine Pralong ◽  
Martin Funk
Keyword(s):  
Steady State ◽  
Mass Balance ◽  
Level Set Method ◽  
Level Set ◽  
Numerical Solutions ◽  
Glacier Surface ◽  
Surface Evolution ◽  
Proposed Model ◽  
Steady State Solutions ◽  
Over Time

AbstractA level-set method is proposed for modeling the evolution of a glacier surface subject to a prescribed mass balance. This leads to a simple and versatile approach for computing the evolution of glaciers: the description of vertical fronts and overriding phenomena presents no difficulties, topological changes are handled naturally and steady-state solutions can be calculated without integration over time. A numerical algorithm is put forth as a means of solving the proposed model of glacier surface evolution. It is evaluated by comparing different numerical solutions of the model with analytical and published numerical solutions. The level-set method appears to be a reliable approach for dealing with different glaciological problems.

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