Research Highlights

Assessing Impact of Shattered Artifacts on Measured Size Distributions
May 12, 2015       
Model parameterizations of ice clouds have typically been derived from observations of ice particle size distributions (PSDs), collected by optical array probes, mounted on the wings of aircraft. Many recent studies have shown PSDs can potentially be contaminated by particles shattering on the tips of these probes, with shattered artifacts subsequently entering the probe sample [...]

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Characterizing Uncertainties in Ice Particle Size Distributions
May 10, 2015       
In many parameterization schemes for numerical models or remote sensing retrievals, particle size distributions (SDs) are represented by gamma functions. Empirical relations, determined from in-situ measurements of SDs, are sometimes needed to determine how the parameters of the gamma function (slope lambda, intercept N0 and shape factor mu) depend on environmental conditions such as temperature, [...]

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The Shapes and Phases of Small Particles in Mixed-Phase Clouds
May 10, 2015       
Mixed-phase clouds, in which supercooled water droplets and ice crystals co-exist, are ubiquitous throughout the troposphere over all regions of the Earth, and especially over polar regions. Because these clouds are radiatively significant, because radiative properties depend significantly on particle phase, and because particles with maximum dimensions D < 60 micrometers contribute up to [...]

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Single Particle Database of Natural Ice Crystals: Dimensions and Aspect Ratios
May 09, 2015       
Accurate knowledge of dimensions and of length (L)–width (W) relationships for ice crystals is important because it is needed to construct shape models for calculating the single-scattering (e.g., scattering phase function and asymmetry parameter) and microphysical (e.g., area and fall velocity) properties of ice crystals. Prior studies have shown that the assumed L–W relationship impacts [...]

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Making Sense of Convective Updrafts: Mass Flux and Microphysics
May 07, 2015       
Cloud-resolving and large-eddy simulation results are often used to inform convective parameterization development for climate models simply owing to the fact that, in theory, all aspects of a simulated system are known. However, high-resolution model simulations contain a variety of complex dynamical structures that often do not map directly to the structural elements of convective [...]

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Developing and Evaluating Ice Cloud Parameterizations by Combining Radar and in Situ Observations
Apr 22, 2015       
One of the main challenges to measure ice clouds by remote sensing is that the transfer functions which relate the observables (e. g., radar Doppler spectrum) to cloud properties (e. g., ice water content, or IWC) are not uniquely defined. To overcome this challenge, this study has two main objectives: 1) estimate a mass-size relation [...]

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Light Absorption of Primary Organic Aerosol Paper Named ACS Editors' Choice
Apr 20, 2015       
Organic aerosols (OAs) in the atmosphere affect Earth’s energy budget by not only scattering but also absorbing solar radiation due to the presence of the so-called “brown carbon” (BrC) component. However, the absorptivities of OAs are not represented or are poorly represented in current climate and chemical transport models. Most models still treat primary OA [...]

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The Two Faces of Aerosols
Apr 15, 2015       
It's a double dose of climate disturbance. Tiny particles of pollution—also known as aerosols—both cool and warm the planet. Now, a team of scientists from Pacific Northwest National Laboratory and NASA identified how current climate models may be far off in estimating the actual amounts of these particles and their total impact on the atmosphere. [...]

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Intersecting Cold Pools: Convective Cloud Organization by Cold Pools over Tropical Ocean
Apr 06, 2015       
As rain drops descend to the surface, they can evaporate and cool the air. The cold air then spreads horizontally and forms pools at the surface that displace surrounding warm air. The dynamics of cold pools are an important mechanism of organizing convection. Researchers, including Department of Energy scientists at Pacific Northwest National Laboratory, [...]

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Comparison of Vertical Velocities in Cirrus Derived from Aircraft and Ground-based Radar
Mar 31, 2015       
Vertical velocities and turbulence in the upper troposphere are key elements affecting the microphysical properties and dynamical evolution of cirrus clouds. In particular, vertical velocities contribute to the cooling rates in the upper troposphere thereby affecting the values of ice supersaturations, the number concentrations of ice crystals formed by ice nucleation, and the growth rates [...]

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Satellite Inference of Thermals and Cloud Base Updraft Speeds
Mar 30, 2015       
Thermals transfer and distribute heat, moisture, momentum, and pollutant materials from the surface layer to the upper part of the convective mixed layer. Thermals also play a central role in the formation of convective clouds and precipitation. Cloud base updrafts govern water vapor supersaturation there, determining the concentration of cloud condensation nuclei (CCN) activated into [...]

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Are Increases in Thunderstorm Activity in Southeast China Related to Air Pollution?
Mar 12, 2015       
Pollution aerosols are thought to have an invigorative effect on convective clouds by suppressing warm precipitation in moist and convectively unstable environments. As clouds develop to above the freezing level, mixed-phase clouds containing ice and supercooled water can grow further more readily and induce cloud electrification and thunderstorms during summertime. In southeastern China, the summer [...]

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Strongly Absorbing Aerosols Affect Retrievals of Cloud Optical Depth
Mar 12, 2015       
Surface-based and satellite remote sensing techniques have proven indispensable for learning more about cloud temporal and spatial variations. Comparisons between cloud properties retrieved from surface and spaceborne platforms are commonly done as a way of validating satellite retrievals. Observations made at the surface are often treated as the “ground-truth” with respect to satellite retrievals. Both [...]

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Filling Gaps Within Instrument Records
Mar 09, 2015       
The ARM SGP site in Lamont, Oklahoma, is home to one of the longest records of actively sensed cloud information anywhere on the planet. Despite the best efforts of the program, instruments occasionally misbehave or are taken down for maintenance, resulting in holes within this record. Utilizing the Active Remote Sensing of Clouds Value-Added Product [...]

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Quantifying the Importance of Cold Pool Mechanisms for Convection Triggering
Mar 09, 2015       
The organization of the subcloud layer into cold pools, areas of evaporatively cooled downdraft air spreading on the surface, is one of the key processes that help sustainin deep convection. It has long been known cold pools can spawn new convective cells by mechanically lifting air along their gust front. Such lifting could be the [...]

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Modeling Precipitating Cumulus Congestus Observed by the ARM Radar Suite During the MC3E Field Campaign
Mar 04, 2015       
Much of the uncertainty in climate model projections stems from the limited understanding of cloud and precipitation processes and the parameterization of these processes in global climate models (GCMs). Typically, results from cloud-resolving models (CRMs) or large-eddy simulation (LES) models serve as benchmarks for developing and tuning single-column models (SCMs), which, in turn, form the [...]

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Evaluation of Trigger Functions for Convective Parameterization Schemes
Mar 03, 2015       
In a convective parameterization scheme, the trigger function activates the onset of convection. Hence, an accurate trigger function is important to the correct simulation of convection in global climate models (GCMs). However, the formulation of trigger functions in many of convective schemes is ad hoc and convection is often activated too easily. The over-activation of [...]

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