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The rate of change of mass of a hailstone by diffusion is affected by its motions. In a stationary pure diffusive case the water vapor distribution around a spherical hailstone is spherically symmetric having rather weak water vapor... more
The rate of change of mass of a hailstone by diffusion is affected by its motions. In a stationary pure diffusive case the water vapor distribution around a spherical hailstone is spherically symmetric having rather weak water vapor gradients. However, when a hailstone falls in the air, the flow field and hence the water vapor distribution around the hailstone is asymmetric showing much stronger water vapor gradients which are high at the upstream side and lower at the rear side of the hailstone. When averaged over the whole surface area of the hailstone the mass transfer to or from the falling hailstone surface is always higher compared to a pure diffusive case. This convective enhancement is given by the ventilation coefficient. Thus, to reliably quantify growth or sublimation rates of falling hailstones with models, it is necessary to know their ventilation coefficients. The rate of change of mass is proportional to the rate of change of heat. Therefore, the growth or sublimation...
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Research Interests: Aerosol and Particle Size
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Vertical wind tunnel experiments were carried out to investigate the melting of low-density lump graupel while floating at their terminal velocities. The graupel characteristics such as maximum dimension, density, and axis ratio were 0.39... more
Vertical wind tunnel experiments were carried out to investigate the melting of low-density lump graupel while floating at their terminal velocities. The graupel characteristics such as maximum dimension, density, and axis ratio were 0.39 ± 0.06 cm, 0.41 ± 0.07 g cm−3, and 0.89 ± 0.06. The airstream of the wind tunnel was gradually heated simulating lapse rates between 4.5 and 3.21 K km−1. Each experimental run was performed at a constant relative humidity that was varied between 12% and 92% from one experiment to the other. From the image processing of video recordings, variations in minimum and maximum dimension, volume, aspect ratio, density, volume equivalent radius, and ice core radius were obtained. New parameterizations of the terminal velocity prior to melting and during melting were developed. It was found that mass and heat transfer in the dry stage is 2 times as high as that of liquid drops at the same Reynolds number. Based on the experimental results, a model was develo...
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Abstract An experimental study was carried out to investigate the processes which occur during drop-to-particle conversion in atmospheric clouds whose drops are evaporating. The experiment was carried out in the Mainz vertical wind tunnel... more
Abstract An experimental study was carried out to investigate the processes which occur during drop-to-particle conversion in atmospheric clouds whose drops are evaporating. The experiment was carried out in the Mainz vertical wind tunnel and in a 4-m high fall shaft. Drops consisting of aqueous solutions of NaCl, (NH 4 ) 2 SO 4 , and salts of artificial and natural ocean water, containing various kinds of solid, water-insoluble particles such as clays, were studied. The aerosol particles produced by the evaporation of drops had diameters in the range 0.1–1 μm, 5–20 μm, 40–80 μm and 100–300 μm. The shape and fall mode of these particles are discussed. It was found that the aerosol particles formed did not break up or splinter during the evaporation of drops. This led to the conclusion that, in evaporating atmospheric clouds, each evaporating drop produces by drop-to-particle conversion one aerosol particle of mass and chemistry given by the mass and chemistry of the foreign material present in the drop.
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Page 1. ERAD 2008 - THE FIFTH EUROPEAN CONFERENCE ON RADAR IN METEOROLOGY AND HYDROLOGY A Wind Tunnel Study On The Oscillation of Freely Falling Raindrops Miklós Szakáll1 , Karoline Diehl1, Subir ...
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From measurements it is known that the air motion inside clouds is turbulent. Energy dissipation rates (ϵ) varying between 0.001 and 0.1 m 2 s −3 have been observed, depending on the type and age of the clouds. Figure 1 shows observed... more
From measurements it is known that the air motion inside clouds is turbulent. Energy dissipation rates (ϵ) varying between 0.001 and 0.1 m 2 s −3 have been observed, depending on the type and age of the clouds. Figure 1 shows observed values of the turbulent spectral energy ...
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Page 1. Part III Experiments and Observations in Campaigns and Independent Separate Projects Dynamics and Chemistry of Hydrometeors. Deutsche Forschungsgemeinschaft (DFG) Copyright © 2001 WILEY-VCH Verlag GmbH, Weinheim ISBN:... more
Page 1. Part III Experiments and Observations in Campaigns and Independent Separate Projects Dynamics and Chemistry of Hydrometeors. Deutsche Forschungsgemeinschaft (DFG) Copyright © 2001 WILEY-VCH Verlag GmbH, Weinheim ISBN: 978-3-527-27727-8 Page 2. ...
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Precipitation prediction using weather radars requires detailed knowledge of the shape parameters of raindrops falling at their terminal velocities in air. Because the raindrops undergo oscillation, the most important shape parameters... more
Precipitation prediction using weather radars requires detailed knowledge of the shape parameters of raindrops falling at their terminal velocities in air. Because the raindrops undergo oscillation, the most important shape parameters from the radar prediction point of view are the equilibrium drop shape, the time-averaged axis ratio, and the oscillation frequency. These parameters for individual water drops with equivalent diameter from 2.5 to 7.5 mm were investigated in a vertical wind tunnel using high-speed video imaging. A very good agreement was found between the measured and the theoretically determined raindrop shape calculated by a force balance model. A new method was developed to determine the equivalent drop diameter with the help of the oscillation frequency. The drop size determination by means of the frequency method was found to be three times more precise than by volumetric methods. The time-averaged axis ratio was found to be equal to the equilibrium axis ratio in ...
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Laboratory experiments were conducted in the Mainz vertical wind tunnel to study the effects of pollutants dissolved or suspended in cloud droplets on the droplet size measurements of a Forward Scattering Spectrometer Probe (FSSP). The... more
Laboratory experiments were conducted in the Mainz vertical wind tunnel to study the effects of pollutants dissolved or suspended in cloud droplets on the droplet size measurements of a Forward Scattering Spectrometer Probe (FSSP). The FSSP is a widely used instrument to derive microphysical properties of atmospheric clouds. Individual droplets of different well-defined sizes were freely falling at their terminal velocities in the wind tunnel while the intensity of radiation emitted by the He–Ne laser of the FSSP and scattered by the droplets was measured. For this purpose, the FSSP was adapted and mounted to the wind tunnel. The intensity of radiation scattered by the droplets in the FSSP measurement is principally used to derive the droplet size. The droplets contained soluble ammonium sulfate or suspended absorbent graphite particles as pollutants in concentrations that were higher than usually found in atmospheric cloud droplets. The results of the measurements and corresponding...
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Comparisons of drop shapes between measurements made using 2D video disdrometer (2DVD) and wind-tunnel experiments are presented. Comparisons are made in terms of the mean drop shapes and the axis ratio distributions. Very close agreement... more
Comparisons of drop shapes between measurements made using 2D video disdrometer (2DVD) and wind-tunnel experiments are presented. Comparisons are made in terms of the mean drop shapes and the axis ratio distributions. Very close agreement of the mean shapes is seen between the two sets of measurements; the same applies to the mean axis ratio versus drop diameter. Also, in both sets of measurements, an increase in the oscillation amplitudes with increasing drop diameter is observed. In the case of the 2DVD, a small increase in the skewness was also detected. Given that the two sets of measurements were conducted in very different conditions, the agreement between the two sets of data implies a certain “robustness” in the mean shape of oscillating drops that may be extended to natural raindrop oscillations, at least in steady rainfall and above the surface layer.
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ABSTRACT Important characteristics of raindrops pertinent to fields in atmospheric sciences such as weather radar or pollution scavenging are drop shape, oscillation frequency and amplitude, as well as the internal circulation.... more
ABSTRACT Important characteristics of raindrops pertinent to fields in atmospheric sciences such as weather radar or pollution scavenging are drop shape, oscillation frequency and amplitude, as well as the internal circulation. Atmospheric raindrops are never pure water drops but contain additional components like aerosol particles and dissolved species. Surface active substances, when present, reduce the surface tension of raindrops and, thus, increase the drop deformation which in turn affects breakup and coalescence, pollutant scavenging, and, finally, the formation of precipitation. Experiments were performed at the Mainz vertical wind tunnel with raindrops freely suspended at their terminal velocities in a vertical air stream. Drops with various reduced surface tensions and sizes between 3.5 and 7.5mm equivalent diameter were investigated. The most relevant microphysical parameters of the drops, i.e. terminal velocity, shape, mean axis ratio, oscillation modes, frequencies and amplitudes, and the internal circulation were measured and compared to those of pure water drops. The experimental data were also compared to the results of a theoretical drop shape model which indicated that the model is applicable to atmospheric drops with reduced surface tensions. From a novel frequency analyzing method it was found that the oscillation modes cover not only the (2,0) and (2,1) but also the (2,2) modes. Depending on the existence of a surfactant film on the drop surface, drops with the same surface tension can show presence or absence of internal circulation.
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Research Interests: Environmental Engineering, Chemistry, Atmospheric Science, Crystal Growth, Adsorption, and 15 moreAtmospheric sciences, Hydrocarbon, Gas Chromatography, Specific surface area, Field Study, Analytical Method, Gas Chromatography/mass Spectrometry, Solid Phase Micro Extraction, Benzene, Flow Rate, Toluene, Aromatic Hydrocarbon, Organic Compound, Atmospheric Environment, and ice crystals
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Title: Shape and oscillation measurements of pure and polluted raindrops in the Mainz vertical wind tunnel. Authors: Szakáll, Miklós; Mitra, Subir K.; Müller, Stefan; Diehl, Karoline; Borrmann, Stephan. Affiliation: AA(Institute for ...
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Page 1. Quart. JR Met. SOC. (1977), 103, pp. 511-517 551.521.321 Transmission function for infrared radiative transfer in an inhomogeneous atmosphere* By JACOB G. KURIYAN, ZVI SHIPPONY and SUBIR K. MITRA DepartmPnt of Atmospheric. ...
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ABSTRACT The Curtis-Godson (1953) method, when applied to the 9.6-micron ozone band, yields large errors. Kuriyan et al. (1977) suggested a method improving this result and yet retaining the analytic simplicity of the transmission... more
ABSTRACT The Curtis-Godson (1953) method, when applied to the 9.6-micron ozone band, yields large errors. Kuriyan et al. (1977) suggested a method improving this result and yet retaining the analytic simplicity of the transmission function. In this paper, the analytic form of the derivative of the transmission function is obtained and then the heating rates are calculated with the new approximation. The errors in this case are negligibly small. Algebraic manipulation enables the reduction of this approximation to a form similar to that proposed by Goody (1964). This procedure permits interpretation of the boundary conditions in physical terms.
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ABSTRACT The effects due to the passage of IR radiation through clouds are predominantly due to the window-region spectrum (between 8 and 13 microns). An approximation scheme is used to identify those parameters in the cloud model that... more
ABSTRACT The effects due to the passage of IR radiation through clouds are predominantly due to the window-region spectrum (between 8 and 13 microns). An approximation scheme is used to identify those parameters in the cloud model that determine the heating and cooling effects and the sensitivity of these effects to the variations in the parameters. The results show that the anomalously large heating/cooling effects predicted by the exact calculations are actually a consequence of the choice of a homogeneous liquid-water-content profile and that an adjustment in this profile results in a lessening of these effects. The radiative effects are also found to be dependent on the size distribution in a nontrivial fashion. In particular, it is found that the use of bimodal distributions, a characteristic feature of clouds with entrainment, results in a lowering of the heating and cooling effects, even with a homogeneous vertical profile, to values more realistic than those obtained with monomodal distributions.
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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 μm while they were freely floated... more
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 μm while they were freely floated in a laminar flow containing a cloud of supercooled droplets with radii between 10 and 20 μm. The experiments were performed in a temperature range between −8 and −12°C, where riming proceeds in the atmosphere, and with cloud liquid water contents lying between 0.9 and 1.6 g m−3 (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 cm3 s−1 depending on their collector momenta (mass ×...