Research Highlights

Stereo Photogrammetry Reveals Substantial Drag on Cloud Thermals
Jun 25, 2015       
Fast updrafts within clouds can generate hail, lightning, and tornadoes at the surface, as well as clear-air turbulence that pose hazards for aircraft aloft. Despite these important impacts of fast updrafts, there is surprisingly large uncertainty about the forces that generate these updraft speeds. For example, do these cloud updrafts experience drag? If so, what [...]

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Sticky Thermals: Evidence for a Dominant Balance Between Buoyancy and Drag in Cloud Updrafts
Jun 25, 2015       
Quickly rising clouds are associated with many important phenomena, including hail, turbulence, and lightning. But, what sets the speeds of these rising clouds? In other words, what is the balance of forces giving rise to the observed cloud updraft speeds? Here, we answer this question by studying thousands of cloud thermals in a high-resolution large-eddy [...]

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Regime Analysis to Identify the Contribution of Clouds to Surface Temperature Errors in GCMs
Jun 16, 2015       
Many Global Circulation Models (GCMs) exhibit a persistent bias in the 2m-temperature (T2m) over the midlatitude continents, present in weather forecasts and climate simulations. A number of hypotheses have been proposed, from deficiencies in the soil-vegetation-atmosphere energy exchange, to poorly resolved boundary-layer clouds to misrepresentations of deep convection. This paper presents a new method to [...]

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Bimodal CCN Spectra
May 23, 2015       
Aerosol spectra under marine stratus are often bimodal and attributable to cloud processes. Sizes at the minima between the modes have inferred supersaturations (S) of nearby clouds (Hoppel et al. 1985, 1994). This was based on the principle that the lower critical S (Sc) particles that produced cloud droplets were increased by 1) chemical reactions [...]

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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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