The role of ice particle shape and size distributions in polarimetric radar measurands at 95 GHz

AbstractThe role of new particle formation (NPF) events and their contribution to haze formation through subsequent growth in polluted megacities is still controversial. To improve the understanding of the sources, meteorological conditions, and chemistry behind air pollution, we performed simultaneous measurements of aerosol composition and particle number size distributions at ground level and at 260 m in central Beijing, China, during a total of 4 months in 2015–2017. Our measurements show a pronounced decoupling of gas-to-particle conversion between the two heights, leading to different haze processes in terms of particle size distributions and chemical compositions. The development of haze was initiated by the growth of freshly formed particles at both heights, whereas the more severe haze at ground level was connected directly to local primary particles and gaseous precursors leading to higher particle growth rates. The particle growth creates a feedback loop, in which a further development of haze increases the atmospheric stability, which in turn strengthens the persisting apparent decoupling between the two heights and increases the severity of haze at ground level. Moreover, we complemented our field observations with model analyses, which suggest that the growth of NPF-originated particles accounted up to ∼60% of the accumulation mode particles in the Beijing–Tianjin–Hebei area during haze conditions. The results suggest that a reduction in anthropogenic gaseous precursors, suppressing particle growth, is a critical step for alleviating haze although the number concentration of freshly formed particles (3–40 nm) via NPF does not reduce after emission controls.

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Evaluation of convective cloud microphysics in numerical weather predictionmodel with dual-wavelength polarimetric radar observations

10.5194/dach2022-281 ◽

2021 ◽

Author(s):

Gregor Köcher ◽

Florian Ewald ◽

Martin Hagen ◽

Christoph Knote ◽

Eleni Tetoni ◽

...

Keyword(s):

Particle Size ◽

Weather Prediction ◽

Cloud Microphysics ◽

Dual Wavelength ◽

Size Distributions ◽

Polarimetric Radar ◽

Particle Size Distributions ◽

Numerical Weather ◽

High Impact Weather ◽

Radar Signals

The representation of microphysical processes in numerical weather prediction models remains a main source of uncertainty until today. To evaluate the influence of cloud microphysics parameterizations on numerical weather prediction, a convection permitting regional weather model setup has been established using 5 different microphysics schemes of varying complexity (double-moment, spectral bin, particle property prediction (P3)). A polarimetric radar forward operator (CR-SIM) has been applied to simulate radar signals consistent with the simulated particles. The performance of the microphysics schemes is analyzed through a statistical comparison of the simulated radar signals to radar measurements on a dataset of 30 convection days. The observational data basis is provided by two polarimetric research radar systems in the area of Munich, Germany, at C- and Ka-band frequencies and a complementary third polarimetric C-band radar operated by the German Weather Service. By measuring at two different frequencies, the dual-wavelength ratio is derived that facilitates the investigation of the particle size evolution. Polarimetric radars provide in-cloud information about hydrometeor type and asphericity by measuring, e.g., the differential reflectivity ZDR. Within the DFG Priority Programme 2115 PROM, we compare the simulated polarimetric and dual-wavelength radar signals with radar observations of convective clouds. Deviations are found between the schemes and observations in ice and liquid phase, related to the treatment of particle size distributions. Apart from the P3 scheme, simulated reflectivities in the ice phase are too high. Dual-wavelength signatures demonstrate issues of most schemes to correctly represent ice particle size distributions. Comparison of polarimetric radar signatures reveal issues of all schemes except the spectral bin scheme to correctly represent rain particle size distributions. The polarimetric information is further exploited by applying a hydrometeor classification algorithm to obtain dominant hydrometeor classes. By comparing the simulated and observed distribution of hydrometeors, as well as the frequency, intensity and area of high impact weather situations (e.g., hail or heavy convective precipitation), the influence of cloud microphysics on the ability to correctly predict high impact weather situations is examined.

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2D-3D conversion method for assessment of multiple characteristics of particle shape and size

Powder Technology ◽

10.1016/j.powtec.2018.11.019 ◽

2019 ◽

Vol 343 ◽

pp. 287-295 ◽

Cited By ~ 6

Author(s):

Takao Ueda ◽

Tatsuya Oki ◽

Shigeki Koyanaka

Keyword(s):

Particle Shape ◽

Conversion Method ◽

Multiple Characteristics ◽

Shape And Size

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Size-mediated, density-dependent cannibalism in the signal crayfish Pacifastacus leniusculus (Dana, 1852) (Decapoda, Astacidea), an invasive crayfish in Britain

Crustaceana ◽

10.1163/15685403-00003653 ◽

2017 ◽

Vol 90 (4) ◽

pp. 417-435 ◽

Cited By ~ 6

Author(s):

R. J. Houghton ◽

C. Wood ◽

X. Lambin

Keyword(s):

Relative Size ◽

Pacifastacus Leniusculus ◽

Gut Contents ◽

Size Distributions ◽

Signal Crayfish ◽

Density Dependent ◽

Invasive Crayfish ◽

The Relationship ◽

Best Fit

The role of cannibalism in crayfish populations is not well understood, despite being a potentially key density-dependent process underpinning population dynamics. We studied the incidence of cannibalism in an introduced signal crayfish Pacifastacus leniusculus population in a Scottish lowland river in September 2014. Animals were sampled using six different sampling techniques simultaneously, revealing variable densities and size distributions across the site. Cannibalism prevalence was estimated by analysing the gut contents of crayfish >20 mm CL for the presence of crayfish fragments, which was found to be 20% of dissected individuals. When seeking evidence of relationships between the sizes of cannibals and ‘prey’, the density of conspecifics <56% the size of a dissected individual yielded the best fit. The relationship between cannibalism probability and crayfish size and density was equally well described by three different metrics of crayfish density. Cannibalism increased with crayfish size and density but did not vary according to sex. These results suggest that large P. leniusculus frequently cannibalize smaller (prey) conspecifics, and that the probability of cannibalism is dependent upon the relative size of cannibal-to-prey and the density of the smaller crayfish. We suggest that removing large individuals, as targeted by many traditional removal techniques, may lead to reduced cannibalism and therefore a compensatory increase in juvenile survival.

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