Roundness and Aspect Ratio of Particles in Ice Clouds

Korolev, Alexei; Isaac, George A.

doi:10.1175/1520-0469(2003)060<1795:raarop>2.0.co;2

Cited by 168 publications

(192 citation statements)

References 27 publications

Supporting

Mentioning

171

Contrasting

Order By: Relevance

“…Taking a typical horizontal aspect ratio of 0.6 (Korolev and Isaac, 2003) gives φ ≈ 0.82 for D obs = D SVI,f . A common estimate for β is 1.9 (Brown and Francis, 1995), resulting in a reflectivity ratio of 0.47.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Characterization of video disdrometer uncertainties and impacts on estimates of snowfall rate and radar reflectivity

et al. 2013

View full text Add to dashboard Cite

Abstract. Estimates of snow microphysical properties obtained by analyzing collections of individual particles are often limited to short timescales and coarse time resolution. Retrievals using disdrometer observations coincident with bulk measurements such as radar reflectivity and snowfall amounts may overcome these limitations; however, retrieval techniques using such observations require uncertainty estimates not only for the bulk measurements themselves, but also for the simulated measurements modeled from the disdrometer observations. Disdrometer uncertainties arise due to sampling and analytic errors and to the discrete, potentially truncated form of the reported size distributions. Imaging disdrometers such as the Snowflake Video Imager and 2-D Video Disdrometer provide remarkably detailed representations of snow particles, but view limited projections of their three-dimensional shapes. Particle sizes determined by such instruments underestimate the true dimensions of the particles in a way that depends, in the mean, on particle shape, also contributing to uncertainties. An uncertainty model that accounts for these uncertainties is developed and used to establish their contributions to simulated radar reflectivity and snowfall rate. Viewing geometry effects are characterized by a parameter, φ, that relates disdrometer-observed particle size to the true maximum dimension of the particle. Values and uncertainties for φ are estimated using idealized ellipsoidal snow particles. The model is applied to observations from seven snow events from the Canadian CloudSat/CALIPSO Validation Project (C3VP), a mid-latitude cold-season cloud and precipitation field experiment. Typical total uncertainties are 4 dB for reflectivity and 40-60 % for snowfall rate, are highly correlated, and are substantial compared to expected uncertainties for radar and precipitation gauge observations. The dominant sources of errors are viewing geometry effects and the discrete, truncated form of the size distributions. While modeled Ze-S relationships are strongly affected by assumptions about snow particle mass properties, such relationships are only modestly sensitive to φ owing to partially compensating effects on both the reflectivity and snowfall rate.

show abstract

Section: Discussionmentioning

confidence: 99%

“…For this work, the SVI size distributions were based on D SVI,f and the 2DVD fallspeeds on D 2DVD,w . Taking a typical horizontal aspect ratio of 0.6 (Korolev and Isaac, 2003) gives φ SVI ≈ 0.82 for D SVI,f with a range of about 0.65 to 1.0. For D 2DVD,w , φ 2DVD ≈ 0.93 with a range of about 0.88 to 1.0.…”

mentioning

confidence: 99%

Characterization of video disdrometer uncertainties and impacts on estimates of snowfall rate and radar reflectivity

et al. 2013

View full text Add to dashboard Cite

show abstract

“…There is some ambiguity in the definition of aspect ratio. Although aspect ratio has generally been defined as L/2R (Fu and Liou, 1993;Takano and Liou, 1995;Macke et al, 1996;Walden et al, 2003;Noel and Chepfer, 2004;Grenfell et al, 2005;Um and McFarquhar, 2007), it has sometimes been defined as L/R (Yang and Liou, 1996), R/L (Chen et al, 2006), or 2R/L (Fu et al, 1998;Fu, 2007) for pristine ice crystals, and as D w /D max for in situ measurements (Korolev and Isaac, 2003), where D max is the projected maximum dimension and D w is the length perpendicular to D max . Hence, caution must be taken when comparing aspect ratios from different studies.…”

Section: Geometry Of Ice Crystals and Ray-tracing Modelmentioning

confidence: 99%

Single‐scattering properties of aggregates of plates

McFarquhar

2009

Quart J Royal Meteoro Soc

View full text Add to dashboard Cite

During the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE) sponsored by the Atmospheric Radiation Measurement programme, the Scaled Composites Proteus aircraft executed spiral profiles and flew horizontal legs through aging anvils, fresh anvils, and cirrus of unknown origin in the vicinity of Darwin, Australia. Pristine ice crystals including both plates and bullet rosettes, their aggregates, and unclassifiable ice crystals were observed by a Cloud Particle Imager. The widths of observed plates ranged between 80 µm and 200 µm. When a fresh dissipating anvil was observed on 2 February, aggregates of plates contributed 46.2% of the total area of measured ice crystals with maximum dimensions greater than 200 µm, while it was only 7.2% and 1.0% for 27 and 29 January, respectively, when aged cirrus was sampled. Because aggregates of plates have been observed to make large contributions to projected ice crystal area near convection during TWP-ICE and other projects, their single-scattering properties that have not been previously examined are investigated here.The dependence of the scattering phase function P 11 , asymmetry parameter g, and single-scattering albedo ω 0 on three parameters (the area ratio AR, normalized projected area A n , and a newly defined aggregation index AI which varies between 0 and 1 with ice crystals with more compact shape having lower AI ) defining the three-dimensional shapes of aggregates of plates were calculated using a geometric ray-tracing code at wavelengths λ of 0.55, 1.38 and 2.13 µm. The scattering properties depended on the crystal morphology with, for example, the g of an aggregate of plates with a high AI of 0.818 differing by +6.89% (+6.44%; +4.55%) from that with a lower AI of 0.378 at λ of 0.55 µm (1.38 µm; 2.13 µm), but by only +0.29% (+0.25%; −0.03%) from those of the component plates. The ω 0 at absorbing λ increased with AI, 1 − AR, and A n . Adding ray distortion to the aggregates caused a decrease in forward scattering and an increase in lateral and backward scattering, decreasing g, an effect that weakened with λ due to absorption. The aggregates of plates with low AI were more influenced by ray distortion compared to those with high AI. The dependence of scattering properties on crystal morphology noted here should be considered when computing bulk scattering properties of ice clouds to determine its importance for climate and remote-sensing studies.

show abstract

“…Aspect ratios for individual particles can be larger than this, but for a particle ensemble population the aspect ratios are generally well below 2 (e.g. Korolev and Isaac, 2003). The aspect ratio is fixed for each particle shape for a given cloud, and is selected with an uniform probability.…”

Section: Chalmers Training Datasetmentioning

confidence: 99%

Performance simulations for a submillimetre-wave satellite instrument to measure cloud ice

Jiménez

Buehler

Rydberg

et al. 2007

Q.J.R. Meteorol. Soc.

View full text Add to dashboard Cite

ABSTRACT:The performance of a conically scanning satellite instrument for the measurement of cloud ice was studied. The instrument measures radiances in 12 channels placed around the 183, 325 and 448 GHz water vapour lines and the 243, 664 and 874 GHz window channels, and is designed to provide estimations of ice water path (IWP), the equivalent sphere diameter (DME), and the median ice mass height (ZME). Overall median relative errors of around 20% for IWP, 33 µm for DME, and 240 m for ZME for a midlatitude winter scenario, and 17% for IWP, 30 µm for DME, and 310 m for ZME for a tropical scenario were found. Detection limits (relative retrieval error reaching 100%) of around 2 gm −2 were estimated for both scenarios. The performance of a five-receiver instrument, where either the 664 or 874 GHz channel is dropped, was close, but with increased errors for very thin and high clouds. A trade-off between having the 874 GHz receiver or two infrared channels at 10.7 and 12 µm emerged, as very similar performance was found between the six-receiver instrument and the five-receiver instrument with the infrared channels. Another trade-off between receiver selection and noise was also apparent, with some of the four-receiver selections operating at half noise levels being able to compete with the standard six-receiver instrument. Dual-polarized measurements were also tested, but they did not significantly improve the retrievals of IWP or DME.

show abstract

Roundness and Aspect Ratio of Particles in Ice Clouds

Cited by 168 publications

References 27 publications

Characterization of video disdrometer uncertainties and impacts on estimates of snowfall rate and radar reflectivity

Characterization of video disdrometer uncertainties and impacts on estimates of snowfall rate and radar reflectivity

Single‐scattering properties of aggregates of plates

Performance simulations for a submillimetre-wave satellite instrument to measure cloud ice

Contact Info

Product

Resources

About