Collision efficiencies empirically determined from laboratory investigations of collisional growth of small raindrops in a laminar flow field

Vohl, O.; Mitra, Subir K.; Wurzler, S.; Diehl, K.; Pruppacher, H. R.

doi:10.1016/j.atmosres.2006.12.001

Cited by 17 publications

(21 citation statements)

References 17 publications

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“…For its entire range of air speeds the tunnel shows a turbulence level of less than 0.5% (Vohl 1989). The wind tunnel facility allows the observation of single events without wall effects under controlled temperatures between 308C and 2308C, dew points from 2408C to saturation (ambient temperature), and wind speeds from 10 cm s 21 up to 40 m s 21 .…”

Section: Experimental Methodsmentioning

confidence: 99%

Riming of Graupel: Wind Tunnel Investigations of Collection Kernels and Growth Regimes

Blohn

Diehl

Mitra

et al. 2009

Journal of the Atmospheric Sciences

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Laboratory experiments were carried out in the vertical wind tunnel in Mainz, Germany, to study the collision coalescence growth of single spherical ice particles having initial radii between 290 and 380 mm while they were freely floated in a laminar flow containing a cloud of supercooled droplets with radii between 10 and 20 mm. The experiments were performed in a temperature range between 28 and 2128C, where riming proceeds in the atmosphere, and with cloud liquid water contents lying between 0.9 and 1.6 g m 23 (i.e., values typically found in mixed-phase clouds). The collection kernels were calculated from the mass increase of the rimed ice particles and the average liquid water content during the experiments. Surface temperature measurements of growing graupel indicated that a dry growth regime prevailed during the whole set of growth experiments. The collection kernels of rimed ice particles attained values between 0.9 and 2.3 cm 3 s 21 depending on their collector momenta (mass 3 fall velocity of the riming ice particles), which had values between 0.04 and 0.1 g cm s 21 . It was found that the collection kernels of ice particles determined from the present set of experiments were higher than the collection kernels of liquid drops. To correct for this discrepancy, an empirical factor depending on the cloud droplet radii was extracted from the newly measured data as well as from the old data. For the investigated size ranges of ice particles and droplets, these corrected collection kernels of ice particles can be incorporated in cloud models for the corresponding size ranges.

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Section: Experimental Methodsmentioning

confidence: 99%

Riming of Graupel: Wind Tunnel Investigations of Collection Kernels and Growth Regimes

Blohn

Diehl

Mitra

et al. 2009

Journal of the Atmospheric Sciences

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“…There are no data available for collectors larger than 300 µm in radius, a size range that has appreciable concentrations in medium to heavy rain, or for particles with size ratios less than 0.05, which can include particles from 0.5 to 10 µm in radius. As well, collision efficiencies for collectors smaller than 30 µm were later found to be underestimated (Vohl et al, 2007). These deficiencies appear to be the main causes of the lower values of rain for particles in the diameter range from 1.0 to 10.0 µm compared to the rest of the rain formulas.…”

Section: Mwmentioning

confidence: 99%

“…We thus removed the rain profiles based on the E(d, D p ) formulation of Park et al (2005) from further consideration since there was no easy way to fix the problem. We noticed, however, that Vohl et al (2007) had updated the Hall (1980) table with new experimental results that provided more realistic collision efficiencies for wider size ranges for both collector and collected particles. Thus, we chose to keep the rain profiles based on the E(d, D p ) scheme of Ackerman et al (1995) for further analysis, but these were modified profiles based on the updated collision efficiency table of Vohl et al (2007) in place of the Hall (1980) With this finalized selection of the available E(d, D p ) formulas (Table 1), there are 320 rain profiles based on different combinations of the product terms that are retained for further analysis (Fig.…”

Section: Mwmentioning

confidence: 99%

Development of a new semi-empirical parameterization for below-cloud scavenging of size-resolved aerosol particles by both rain and snow

Wang¹,

Zhang

Moran

2014

Geosci. Model Dev.

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Abstract.A parameter called the scavenging coefficient is widely used in aerosol chemical transport models (CTMs) to describe below-cloud scavenging of aerosol particles by rain and snow. However, uncertainties associated with available size-resolved theoretical formulations for span one to two orders of magnitude for rain scavenging and nearly three orders of magnitude for snow scavenging. Two recent reviews of below-cloud scavenging of size-resolved particles recommended that the upper range of the available theoretical formulations for should be used in CTMs based on uncertainty analyses and comparison with limited field experiments. Following this recommended approach, a new semiempirical parameterization for size-resolved has been developed for below-cloud scavenging of atmospheric aerosol particles by both rain ( rain ) and snow ( snow ). The new parameterization is based on the 90th percentile of values from an ensemble data set calculated using all possible "realizations" of available theoretical formulas and covering a large range of aerosol particle sizes and precipitation intensities (R). For any aerosol particle size of diameter d, a strong linear relationship between the 90th-percentile log 10 ( ) and log 10 (R), which is equivalent to a power-law relationship between and R, is identified. The log-linear relationship, which is characterized by two parameters (slope and y intercept), is then further parameterized by fitting these two parameters as polynomial functions of aerosol size d. A comparison of the new parameterization with limited measurements in the literature in terms of the magnitude of and the relative magnitudes of rain and snow suggests that it is a reasonable approximation. Advantages of this new semiempirical parameterization compared to traditional theoretical formulations for include its applicability to belowcloud scavenging by both rain and snow over a wide range of particle sizes and precipitation intensities, ease of implementation in any CTM with a representation of size-distributed particulate matter, and a known representativeness, based on the consideration in its development, of all available theoretical formulations and field-derived estimates for (d) and their associated uncertainties.

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“…The collection efficiency differs from unity if hydrodynamic effects (e.g. Vohl et al, 2007) or van der Waals forces (Rogers and Davis, 1990) are considered. The whole coalescence kernel may take a different form (in particular, may be nonzero for drops of equal terminal velocity) if turbulence effects are taken into account (Grabowski and Wang, 2013, and references therein).…”

Section: Coalescencementioning

confidence: 99%

libcloudph++ 1.0: a single-moment bulk, double-moment bulk, and particle-based warm-rain microphysics library in C++

et al. 2015

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Abstract. This paper introduces a library of algorithms for representing cloud microphysics in numerical models. The library is written in C + +, hence the name libcloudph++. In the current release, the library covers three warm-rain schemes: the single-and double-moment bulk schemes, and the particle-based scheme with Monte Carlo coalescence. The three schemes are intended for modelling frameworks of different dimensionalities and complexities ranging from parcel models to multi-dimensional cloudresolving (e.g. large-eddy) simulations. A two-dimensional (2-D) prescribed-flow framework is used in the paper to illustrate the library features. The libcloudph++ and all its mandatory dependencies are free and open-source software. The Boost.units library is used for zero-overhead dimensional analysis of the code at compile time. The particlebased scheme is implemented using the Thrust library that allows one to leverage the power of graphics processing units (GPU), retaining the possibility of compiling the unchanged code for execution on single or multiple standard processors (CPUs). The paper includes a complete description of the programming interface (API) of the library and a performance analysis including comparison of GPU and CPU set-ups.

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Collision efficiencies empirically determined from laboratory investigations of collisional growth of small raindrops in a laminar flow field

Cited by 17 publications

References 17 publications

Riming of Graupel: Wind Tunnel Investigations of Collection Kernels and Growth Regimes

Riming of Graupel: Wind Tunnel Investigations of Collection Kernels and Growth Regimes

Development of a new semi-empirical parameterization for below-cloud scavenging of size-resolved aerosol particles by both rain and snow

libcloudph++ 1.0: a single-moment bulk, double-moment bulk, and particle-based warm-rain microphysics library in C++

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