Shapes and oscillations of falling raindrops — A review

Szakáll, Miklós; Mitra, Subir K.; Diehl, K.; Borrmann, Stephan

doi:10.1016/j.atmosres.2010.03.024

Cited by 102 publications

(69 citation statements)

References 51 publications

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“…However, Beard (1974) proposed this transition for perfectly spherical drops, and the experiments highlight that 2 mm drops falling at terminal velocity are slightly oblate (Fig. 3), and moreover oscillate at high frequencies (Szakáll et al, , 2010. As a consequence, it can be expected from current experiments that eddy shedding should start only at Reynolds numbers greater than 800.…”

Section: Resultsmentioning

confidence: 99%

“…Finally, an additional uncertainty, according to Wang and Pruppacher (1977), involves the lack of knowledge on the collection efficiencies of large raindrops (with a diameter larger than 1 mm). First, large drops oscillate during their fall (Szakáll et al, , 2010; additionally, eddies develop downstream of large drops allowing small aerosol to be embedded in that secondary circulation and be captured at the rear of the drops or shed with the eddies (Beard, 1974). These two phenomena are the reason why modelling of the flow around a large drop is not feasible and that those collection efficiencies cannot be theoretically determined.…”

Section: Introductionmentioning

confidence: 95%

See 1 more Smart Citation

An experiment to measure raindrop collection efficiencies: influence of rear capture

Quérel¹,

Lemaître

Monier

et al. 2014

Atmos. Meas. Tech.

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Abstract. In the case of severe accident with loss of containment in a nuclear plant, radionuclides are released into the atmosphere in the form of both gases and aerosol particles (Baklanov and Sørensen, 2001). The analysis of radioactive aerosol scavenged by rain after the Chernobyl accident highlights certain differences between the modelling studies and the environmental measurements. Part of these discrepancies can probably be attributed to uncertainties in the efficiencies used to calculate aerosol particle collection by raindrops, particularly drops with a diameter larger than one millimetre. In order to address the issue of these uncertainties, an experimental study was performed to close the gaps still existing for this key microphysical parameter. In this paper, attention is first focused on the efficiency with which aerosol particles in the accumulation mode are collected by raindrops with a diameter of 2 mm. The collection efficiencies measured for aerosol particle in the sub-micron range are quantitatively consistent with previous theoretical model developed by Beard (1974) and thus highlight the major role of rear capture in the submicron range.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

An experiment to measure raindrop collection efficiencies: influence of rear capture

Quérel¹,

Lemaître

Monier

et al. 2014

Atmos. Meas. Tech.

View full text Add to dashboard Cite

show abstract

“…The higher-frequency fluctuations that are also evident are more difficult to ascertain, but have been noted to occur in highly controlled wind tunnel studies (12,13,15) where they have been attributed to naturally occurring drop oscillations of the type examined by (21,22). As alluded to by (12,23), additional impacts on the characteristics of the oscillations in the real atmosphere can be expected to result from turbulent motion of the air, electrical effects, or the presence of other drops.…”

Section: Resultsmentioning

confidence: 99%

Radar observations of individual rain drops in the free atmosphere

Schmidt¹,

Flatau²,

Harasti³

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Atmospheric remote sensing has played a pivotal role in the increasingly sophisticated representation of clouds in the numerical models used to assess global and regional climate change. This has been accomplished because the underlying bulk cloud properties can be derived from a statistical analysis of the returned microwave signals scattered by a diverse ensemble comprised of numerous cloud hydrometeors. A new Doppler radar, previously used to track small debris particles shed from the NASA space shuttle during launch, is shown to also have the capacity to detect individual cloud hydrometeors in the free atmosphere. Similar to the traces left behind on film by subatomic particles, larger cloud particles were observed to leave a well-defined radar signature (or streak), which could be analyzed to infer the underlying particle properties. We examine the unique radar and environmental conditions leading to the formation of the radar streaks and develop a theoretical framework which reveals the regulating role of the background radar reflectivity on their observed characteristics. This main expectation from theory is examined through an analysis of the drop properties inferred from radar and in situ aircraft measurements obtained in two contrasting regions of an observed multicellular storm system. The observations are placed in context of the parent storm circulation through the use of the radar's unique high-resolution waveforms, which allow the bulk and individual hydrometeor properties to be inferred at the same time.microphysics | convection | cumulonimbus | backscatter

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“…3. Note that the size error is exclusively related to the limitation of the image resolution and does not consider other sources of errors such as the asymmetric modes of large drops due to oscillation and collision (Szakáll et al, 2010(Szakáll et al, , 2014. However, this uncertainty would be relatively minor because the drops captured by the HSC in the indoor experiment is expected to reach terminal velocities with equilibrium-shaped status.…”

Section: Quantitative Comparisonsmentioning

confidence: 99%

“…A HSC has been used to investigate the behavior of raindrop oscillations and the impact of water drops on the Earth's surface, as described in a number of articles (Fukada and Fujiwara, 1989;Ghadiri, 2006;Testik et al, 2006;Licznar et al, 2008;Szakáll et al, 2010). However, these HSC published works did not address the possible application of the HSC to the investigation of atmospheric DFSs.…”

Section: Introductionmentioning

confidence: 99%

Measuring droplet fall speed with a high-speed camera: indoor accuracy and potential outdoor applications

Hsieh

Yuter

et al. 2016

Atmos. Meas. Tech.

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Abstract. Acquisition of accurate raindrop fall speed measurements outdoors in natural rain by means of moderatecost and easy-to-use devices represents a long-standing and challenging issue in the meteorological community. Feasibility experiments were conducted to evaluate the indoor accuracy of fall speed measurements made with a high-speed camera and to evaluate its capability for outdoor applications. An indoor experiment operating in calm conditions showed that the high-speed imaging technique can provide fall speed measurements with a mean error of 4.1-9.7 % compared to Gunn and Kinzer's empirical fall-speed-size relationship for typical sizes of rain and drizzle drops. Results obtained using the same apparatus outside in summer afternoon showers indicated larger positive and negative velocity deviations compared to the indoor measurements. These observed deviations suggest that ambient flow and turbulence play a role in modifying drop fall speeds which can be quantified with future outdoor high-speed camera measurements. Because the fall speed measurements, as presented in this article, are analyzed on the basis of tracking individual, specific raindrops, sampling uncertainties commonly found in the widely adopted optical disdrometers can be significantly mitigated.

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Shapes and oscillations of falling raindrops — A review

Cited by 102 publications

References 51 publications

An experiment to measure raindrop collection efficiencies: influence of rear capture

An experiment to measure raindrop collection efficiencies: influence of rear capture

Radar observations of individual rain drops in the free atmosphere

Measuring droplet fall speed with a high-speed camera: indoor accuracy and potential outdoor applications

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