Special Issue "Microphysics of Precipitation Particles: Raindrops, Hail, and Snow"

A special issue of Atmosphere (ISSN 2073-4433). This special issue belongs to the section "Meteorology".

Deadline for manuscript submissions: closed (15 August 2020).

Special Issue Editor

Dr. Miklós Szakáll
E-Mail Website
Guest Editor
Institut für Physik der Atmosphäre, Johannes Gutenberg-Universität Mainz, Becherweg, Germany

Special Issue Information

Dear Colleagues,

Precipitation, both solid and liquid, plays a central role in the Earth’s water cycle. On the one hand, it is the primary source of life-giving freshwater, and on the other hand, hail storms, freezing rain, severe rainfall and the associated floods, and landslides are among the most hazardous weather phenomena, having harmful economic, societal, and natural impacts. Hence, precipitation prediction, adequate observation, and short-term forecast at regional and global scales under changing climatic conditions are crucially important scientific issues. Nevertheless, the tools used for such approaches, such as numerical weather models, or radar-based remote sensing precipitation facilities, suffer from the still inadequately understood microphysics of precipitation particles.

This Special Issue aims to advance our understanding on the microphysics of single precipitation particles (e.g., hail, graupel, snow, rain, and cloud droplets), as well as the interactions among these hydrometeors. We invite contributors to submit original articles on laboratory and field measurements, numerical simulations, and theoretical studies on precipitation microphysics and aerodynamics. Articles on atmospheric phenomena related to precipitation microphysics (e.g., rainbow and halos) are also welcome.

Dr. Miklós Szakáll
Guest Editor

Manuscript Submission Information

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Keywords

  • raindrop
  • hail stone
  • graupel
  • snow
  • riming
  • freezing
  • melting
  • collision, coalescemce, and breakup
  • ventilation

Published Papers (5 papers)

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Research

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Article
Contribution of Phoretic and Electrostatic Effects to the Collection Efficiency of Submicron Aerosol Particles by Raindrops
Atmosphere 2020, 11(10), 1028; https://doi.org/10.3390/atmos11101028 - 24 Sep 2020
Cited by 2 | Viewed by 602
Abstract
This article presents an experimental study, performed in the BERGAME setup, dedicated to studying the collection of submicron aerosol particles by raindrops. The initial aim was to focus on the influence of the electrical charges of raindrops on the efficiency with which they [...] Read more.
This article presents an experimental study, performed in the BERGAME setup, dedicated to studying the collection of submicron aerosol particles by raindrops. The initial aim was to focus on the influence of the electrical charges of raindrops on the efficiency with which they collect aerosol particles. However, in the relative humidity range considered in this article (26–36%), measurements highlight a first-order role of phoretic effect for submicron aerosol particles. Indeed, measurements highlight a 100% increase in the collection efficiency for each percentage decrease in the atmospheric relative humidity. Phoretic effects are known to play a role in collection by drops; however, none of the models found in the literature predicts the same magnitude as the one presently measured. Characterization of the aerosol trajectories around the drop, accelerated to terminal velocity, seems to show a coupling between phoretic effects and rear capture. This interaction, already suggested by Grover et al., is a line of explanation for such a sharp unpredicted increase of the collection efficiency with moisture decrease. Full article
(This article belongs to the Special Issue Microphysics of Precipitation Particles: Raindrops, Hail, and Snow)
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Article
Hurricane Dorian Outer Rain Band Observations and 1D Particle Model Simulations: A Case Study
Atmosphere 2020, 11(8), 879; https://doi.org/10.3390/atmos11080879 - 18 Aug 2020
Cited by 1 | Viewed by 934
Abstract
The availability of high quality surface observations of precipitation and volume observations by polarimetric operational radars make it possible to constrain, evaluate, and validate numerical models with a wide variety of microphysical schemes. In this article, a novel particle-based Monte-Carlo microphysical model (called [...] Read more.
The availability of high quality surface observations of precipitation and volume observations by polarimetric operational radars make it possible to constrain, evaluate, and validate numerical models with a wide variety of microphysical schemes. In this article, a novel particle-based Monte-Carlo microphysical model (called McSnow) is used to simulate the outer rain bands of Hurricane Dorian which traversed the densely instrumented precipitation research facility operated by NASA at Wallops Island, Virginia. The rain bands showed steady stratiform vertical profiles with radar signature of dendritic growth layers near −15 °C and peak reflectivity in the bright band of 55 dBZ along with polarimetric signatures of wet snow with sizes inferred to exceed 15 mm. A 2D-video disdrometer measured frequent occurrences of large drops >5 mm and combined with an optical array probe the drop size distribution was well-documented in spite of uncertainty for drops <0.5 mm due to high wind gusts and turbulence. The 1D McSnow control run and four numerical experiments were conducted and compared with observations. One of the main findings is that even at the moderate rain rate of 10 mm/h collisional breakup is essential for the shape of the drop size distribution. Full article
(This article belongs to the Special Issue Microphysics of Precipitation Particles: Raindrops, Hail, and Snow)
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Article
Secondary Ice Formation in Idealised Deep Convection—Source of Primary Ice and Impact on Glaciation
Atmosphere 2020, 11(5), 542; https://doi.org/10.3390/atmos11050542 - 23 May 2020
Cited by 1 | Viewed by 817
Abstract
Secondary ice production via rime-splintering is considered to be an important process for rapid glaciation and high ice crystal numbers observed in mixed-phase convective clouds. An open question is how rime-splintering is triggered in the relatively short time between cloud formation and observations [...] Read more.
Secondary ice production via rime-splintering is considered to be an important process for rapid glaciation and high ice crystal numbers observed in mixed-phase convective clouds. An open question is how rime-splintering is triggered in the relatively short time between cloud formation and observations of high ice crystal numbers. We use idealised simulations of a deep convective cloud system to investigate the thermodynamic and cloud microphysical evolution of air parcels, in which the model predicts secondary ice formation. The Lagrangian analysis suggests that the “in-situ” formation of rimers either by growth of primary ice or rain freezing does not play a major role in triggering secondary ice formation. Instead, rimers are predominantly imported into air parcels through sedimentation form higher altitudes. While ice nucleating particles (INPs) initiating heterogeneous freezing of cloud droplets at temperatures warmer than −10 °C have no discernible impact of the occurrence of secondary ice formation, in a scenario with rain freezing secondary ice production is initiated slightly earlier in the cloud evolution and at slightly different places, although with no major impact on the abundance or spatial distribution of secondary ice in the cloud as a whole. These results suggest that for interpreting and analysing observational data and model experiments regarding cloud glaciation and ice formation it is vital to consider the complex vertical coupling of cloud microphysical processes in deep convective clouds via three-dimensional transport and sedimentation. Full article
(This article belongs to the Special Issue Microphysics of Precipitation Particles: Raindrops, Hail, and Snow)
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Article
A Wind Tunnel Investigation into the Aerodynamics of Lobed Hailstones
Atmosphere 2020, 11(5), 494; https://doi.org/10.3390/atmos11050494 - 12 May 2020
Cited by 2 | Viewed by 924
Abstract
The complex surface geometries of hailstones affect their fall behavior, fall speeds, and growth. Systematic experimental investigations on the influence of the number and length of lobes on the fall velocity and the drag coefficient of hailstones were performed in the Mainz vertical [...] Read more.
The complex surface geometries of hailstones affect their fall behavior, fall speeds, and growth. Systematic experimental investigations on the influence of the number and length of lobes on the fall velocity and the drag coefficient of hailstones were performed in the Mainz vertical wind tunnel to provide relationships for use in numerical models. For this purpose, 3D prints of four artificial lobed hailstone models as well as spheres were used. The derived drag coefficients show no dependency in the Reynolds number in the range between 25,000 and 85,000. Further, the drag coefficients were found to increase with increasing length of lobes. All lobed hailstones show higher or similar drag coefficients than spheres. The terminal velocities of the the hailstones with short lobes are very close to each other and only reduced by about 6% from those of a sphere. The terminal velocities from the long lobed hailstones deviate up to 21% from a sphere. The results indicate that lobes on the surface of hailstones reduce their kinetic energy by a factor of up to 3 compared to a sphere. This has important consequences for the estimation of the destructive potential of hailstones. Full article
(This article belongs to the Special Issue Microphysics of Precipitation Particles: Raindrops, Hail, and Snow)
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Review

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Review
Some Aspects of the Scattering of Light and Microwaves on Non-Spherical Raindrops
Atmosphere 2020, 11(5), 531; https://doi.org/10.3390/atmos11050531 - 21 May 2020
Cited by 1 | Viewed by 748
Abstract
A review of the author’s work on the study of the microphysics of rain is carried out. The effect of an anomalously high modulation of light scattered by oscillating drops of water, which consists in the formation of powerful pulses of light when [...] Read more.
A review of the author’s work on the study of the microphysics of rain is carried out. The effect of an anomalously high modulation of light scattered by oscillating drops of water, which consists in the formation of powerful pulses of light when illuminating an oscillating drop with continuous light and observation at scattering angles near a first-order rainbow, is described and explained. The anomalous scattering tracks obtained in the photographs provide information on the mass, average shape, mode, and amplitude of oscillations for each drop, by analogy with the Wilson camera. In field measurements, spatial selection of droplets by size was detected, when droplets of different sizes were grouped in different parts of space. The theoretical substantiation of the grouping of rain particles in space under the influence of wind gusts is carried out. It has been shown that the grouping and clustering of raindrops affects the relationship between radar reflectivity Z and rain intensity R. The influence of non-sphericity and oscillation of raindrops on the scattering of microwave radiation is studied. Polarization methods are proposed for enhancing or sharply reducing the contributions of the asphericity of raindrops to reflected radar signals. Full article
(This article belongs to the Special Issue Microphysics of Precipitation Particles: Raindrops, Hail, and Snow)
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