Using 3‐D‐printed analogues to investigate the fall speeds and orientations of complex ice particles

Westbrook, C. D.; Sephton, E. K.

doi:10.1002/2017gl074130

Cited by 29 publications

(44 citation statements)

References 26 publications

(31 reference statements)

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“…Westbrook and Sephton () recently evaluated the fall speeds calculated with the Heymsfield and Westbrook () parameterization by comparison with laboratory measurements using 3‐D‐printed analogs of ice crystal habits including bullet rosettes and aggregates. The results showed good agreement (fall speeds within about 20% and no systematic bias) for Reynolds numbers relevant for this study.…”

Section: Ice Crystal Growth‐sedimentation Trajectoriesmentioning

confidence: 99%

“…We use the values for , , , and given by Mitchell (1996) and Heymsfield et al (1998) for bullet rosettes and aggregates, respectively (see Sölch & Kärcher, 2010, Table AII) to span the range of habit possibilities for ice detrained from deep convection. Westbrook and Sephton (2017) recently evaluated the fall speeds calculated with the Heymsfield and Westbrook (2010) parameterization by comparison with laboratory measurements using 3-D-printed analogs of ice crystal habits including bullet rosettes and aggregates. The results showed good agreement (fall speeds within about 20% and no systematic bias) for Reynolds numbers relevant for this study.…”

Section: Ice Crystal Fall Speeds and Vapor Deposition Growth Ratesmentioning

confidence: 99%

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The Life Cycles of Ice Crystals Detrained From the Tops of Deep Convection

2018

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Extensive anvil cirrus clouds generated by deep convection have important impacts on the Earth's radiation budget and climate. We use growth‐sedimentation trajectory calculations to investigate the life cycles of anvil ice crystals as they are advected downwind from their convective source. Temperature, water vapor, and wind fields from a cloud‐resolving model simulation of an isolated cumulonimbus cloud are used to drive the calculations. Ice crystals are initialized in the main upper‐level detrainment zone with a size distribution based on in situ measurements made in a convective core at about 12 km. Advection, deposition growth, and sedimentation of thousands of sample ice crystals are tracked over about 2.5 hr; neither aggregation of ice crystals nor radiative effects are included. Results support the importance of deposition growth and gravitational size sorting in the evolution of the anvil cirrus. Most ice crystals initialized with maximum dimensions larger than about 200 μm fall out of the anvil and sublimate in subsaturated air below within about 2 hr. Few small ice crystals are present in the lower part of the mature anvil. Vapor deposition growth accounts for about 50% of the ice mass remaining after about 2 hr. Ice crystals larger than about 50 μm in the mature anvil have grown substantially by deposition of vapor. This result is consistent with the predominance of bullet rosette habits observed in mature anvils. Variations in ice crystal fall speeds and growth rates associated with ice crystal habit assumptions have little impact on the ice crystal life cycles.

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Section: Ice Crystal Growth‐sedimentation Trajectoriesmentioning

confidence: 99%

Section: Ice Crystal Fall Speeds and Vapor Deposition Growth Ratesmentioning

confidence: 99%

The Life Cycles of Ice Crystals Detrained From the Tops of Deep Convection

2018

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“…For liquid drops, PAMTRA uses the relation provided by Khvorostyanov and Curry (2002) as a default. For ice and snow particles, the modified relation by Heymsfield and Westbrook (2010) is recommended because it is in better agreement with recent experiments using ice analogues (Westbrook and Sephton, 2017). For PAMTRA, v is defined such that positive values refer to particles moving towards the radar.…”

Section: Radar Simulatormentioning

confidence: 96%

PAMTRA 1.0: A Passive and Active Microwave radiative TRAnsfer tool for simulating radiometer and radar measurements of the cloudy atmosphere

Mech¹,

Maahn²,

Kneifel³

et al. 2020

Preprint

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Abstract. Forward models are a key tool to generate synthetic observations given the knowledge of the atmospheric state. In this way they are an integral part of inversion algorithms that aim to retrieve geophysical variables from observations or in data assimilation. Their application for the exploitation of the full information content of remote sensing observations becomes increasingly important when these are used to evaluate the performance of cloud resolving models (CRMs). Herein, CRMs profiles or fields provide the input to the forward model whose simulation results are subsequently compared to the observations. This paper introduces the freely available comprehensive microwave forward model PAMTRA (Passive and Active Microwave TRAnsfer), demonstrates its capabilities to simulate passive and active measurements across the microwave spectral region for up- and downward looking geometries, and illustrates how the forward simulations can be used to evaluate CRMs and to interpret measurements to improve our understanding of cloud processes. PAMTRA is unique as it treats passive and active radiative transfer (RT) in a consistent way with the passive forward model providing up- and down-welling polarized brightness temperatures and radiances for arbitrary observation angles. The active part is capable of simulating the full radar Doppler spectrum and its moments. PAMTRA is designed to be flexible with respect to instrument specifications, interfaces to many different formats of in- and output type, especially CRMs, spanning the range from bin-resolved microphysical output to one- and two-moment schemes, and to in situ measured hydrometeor properties. A specific highlight is the incorporation of the self-similar Rayleigh--Gans Approximation (SSRGA) both for active and passive applications which becomes especially important for the investigation of frozen hydrometeors.

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“…For Mie scattering, however, the irregular snow shape plays a more significant role. Westbrook et al (2006Westbrook et al ( , 2008 used the Rayleigh-Gans approximation to develop an analytical equation for the scattering cross sections of simulated snow aggregates of bullet rosettes using an empirical fit to the form factor that accounts for deviations from the Rayleigh limit. Here, we use two scattering models, one based on the soft spheroid with a fixed axis ratio and quasi-random orientation.…”

Section: Scattering Modelmentioning

confidence: 99%

Dual-wavelength radar technique development for snow rate estimation: a case study from GCPEx

et al. 2019

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Abstract. quantitative precipitation estimation (QPE) of snowfall has generally been expressed in power-law form between equivalent radar reflectivity factor (Ze) and liquid equivalent snow rate (SR). It is known that there is large variability in the prefactor of the power law due to changes in particle size distribution (PSD), density, and fall velocity, whereas the variability of the exponent is considerably smaller. The dual-wavelength radar reflectivity ratio (DWR) technique can improve SR accuracy by estimating one of the PSD parameters (characteristic diameter), thus reducing the variability due to the prefactor. The two frequencies commonly used in dual-wavelength techniques are Ku- and Ka-bands. The basic idea of DWR is that the snow particle size-to-wavelength ratio is falls in the Rayleigh region at Ku-band but in the Mie region at Ka-band. We propose a method for snow rate estimation by using NASA D3R radar DWR and Ka-band reflectivity observations collected during a long-duration synoptic snow event on 30–31 January 2012 during the GCPEx (GPM Cold-season Precipitation Experiment). Since the particle mass can be estimated using 2-D video disdrometer (2DVD) fall speed data and hydrodynamic theory, we simulate the DWR and compare it directly with D3R radar measurements. We also use the 2DVD-based mass to compute the 2DVD-based SR. Using three different mass estimation methods, we arrive at three respective sets of Z–SR and SR(Zh, DWR) relationships. We then use these relationships with D3R measurements to compute radar-based SR. Finally, we validate our method by comparing the D3R radar-retrieved SR with accumulated SR directly measured by a well-shielded Pluvio gauge for the entire synoptic event.

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Using 3‐D‐printed analogues to investigate the fall speeds and orientations of complex ice particles

Cited by 29 publications

References 26 publications

The Life Cycles of Ice Crystals Detrained From the Tops of Deep Convection

The Life Cycles of Ice Crystals Detrained From the Tops of Deep Convection

PAMTRA 1.0: A Passive and Active Microwave radiative TRAnsfer tool for simulating radiometer and radar measurements of the cloudy atmosphere

Dual-wavelength radar technique development for snow rate estimation: a case study from GCPEx

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