The impact of vertical downdraft on rain attenuation estimation from rain rate measurements has been studied. The rain rate ( R ) and specific attenuation (γ) are derived from rain drop size ...distributions (DSD) by considering the widely accepted Gunn-Kinzer (G-K) relationship between drop size and drop fall velocity that is valid for stagnant air. In the real atmosphere, drops are carried with the vertical wind draft, and the actual fall velocity of the raindrops deviates from the G-K formulation. The ITU-R estimated rain attenuation values, based on DSDs, which are mostly valid for temperate regions, can deviate from actual rain attenuation measurements in tropical regions, especially at higher rain rates when downdraft is prominent. The present study uses disdrometer measurements of DSD, optical rain gauge measurements of rain rates, and Ku-band rain attenuation data over an earth-space path at a tropical location Kolkata (22°34′ N, 88°29′ E) to show that vertical downdrafts impact the rain attenuation estimation from rain rate measurements. At the present location, an overall representative vertical downdraft of 2 m/s needs to be considered to match the experimental attenuation measurements with the estimated values using the modified γ- R relationship in the ITU-R model.
•Mixing/separation was studied in stirred tank with oil volume fractions 0.1-0.9.•The working temperatures were varied from 20 °C to 80 °C.•Temperature has minor impact on drop sizes but significant ...effect on separation.•Henschke model predicted well at high dispersed phase fractions and temperatures.
Drop size distributions and phase separation were determined in a batch stirred tank with water/paraffin oil using optical measurement techniques. Temperature was varied from 20 °C to 80 °C and dispersed phase fractions up to 0.7, resulting in a phase inversion from oil-in-water to water-in-oil emulsions. Higher temperatures only increase Sauter mean diameters by 9.9%, but reduce phase separation time up to 67.4%. Higher dispersed phase fractions lead to bigger drop sizes and longer separation time. The interplay between drop size distribution characteristics and the phase separation process is investigated in detail. The performance of an existing phase separation model which considers physical properties and the initial Sauter mean diameter was evaluated, showing quite satisfying predictive power. Its predictive power might be further increased by including more information about the whole drop size distribution in future studies.
Abstract
This study aimed to reveal the seasonal climatic variations in the microphysical properties of precipitation over the Asian monsoon region. We used the Dual-Frequency Precipitation Radar ...satellite product aboard the Global Precipitation Measurement Mission
Core Observatory
for 8 years from 2014 to 2021 to statistically analyze the mass-weighted mean diameter (
D
m
) and frequency of heavy ice precipitation (graupel and hail). The results showed statistically significant seasonal changes. The microphysical characteristics of large
D
m
and frequent heavy ice precipitation were observed over the Indian subcontinent and Indochina Peninsula in the premonsoon season and over the western Himalayan region in the mature-monsoon season, which can be related to the intense and deeply developed precipitation systems. The relationship between precipitation rate and
D
m
was also examined. The results indicated that changes in
D
m
were not caused only by changes in precipitation rate but were probably induced by changes in precipitation characteristics. In terms of the relationship between the microphysical properties, heavy ice precipitation particles in the upper atmosphere above the melting layer were observed more frequently as
D
m
near the surface increased. We also studied lower-atmospheric instability by investigating the vertical gradients of the dry and moist static energies. The results indicated that instability properties were different; dry and wet instabilities were dominant in the premonsoon and monsoon seasons, respectively, consistent with the results of the precipitation characteristics.
Significance Statement
The purpose of this study was to reveal seasonal variations in precipitation microphysical characteristics, such as precipitation particle size and the existence of graupel and hail in the upper atmosphere, by climatological analysis over the Asian monsoon region. In previous studies, microphysical characteristics have mainly been addressed using ground-based observations. However, more sampling is needed to expand our understanding of climatological perspectives; therefore, we used recently available satellite observations. As a result, we found that precipitation particles at the surface were larger, and more graupel and hail existed in clouds in the premonsoon season when less precipitation was observed, compared to the mature-monsoon season when precipitation amount and frequency were abundant.
Commonly used disdrometers tend not to accurately measure concentrations of very small drops in the raindrop size distribution (DSD), either through truncation of the DSD at the small-drop end or ...because of large uncertainties on these measurements. Recent studies have shown that, as a result of these inaccuracies, many if not most ground-based disdrometers do not capture the “drizzle mode” of precipitation, which consists of large concentrations of small drops and is often separated from the main part of the DSD by a shoulder region. We present a technique for reconstructing the drizzle mode of the DSD from “incomplete” measurements in which the drizzle mode is not present. Two statistical moments of the DSD that are well measured by standard disdrometers are identified and used with a double-moment normalized DSD function that describes the DSD shape. A model representing the double-moment normalized DSD is trained using measurements of DSD spectra that contain the drizzle mode obtained using collocated Meteorological Particle Spectrometer and 2D video disdrometer instruments. The best-fitting model is shown to depend on temporal resolution. The result is a method to estimate, from truncated or uncertain measurements of the DSD, a more complete DSD that includes the drizzle mode. The technique reduces bias on low-order moments of the DSD that influence important bulk variables such as the total drop concentration and mass-weighted mean drop diameter. The reconstruction is flexible and often produces better rain-rate estimations than a previous DSD correction routine, particularly for light rain.
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•The average distribution of droplet sizes is independent of lubricant viscosity.•Droplet sizes at onset of droplet sliding are almost twice as large as predicted.•Sweeping rates do ...not influence the steady-state distribution of droplet sizes.•Heat transfer rates are nearly constant along large vertical plates.•Heat transfer rates can be 10–15 times higher than for filmwise condensation.
Condensation is a ubiquitous phenomenon in nature and industry. Heat transfer rates during dropwise condensation on non-wetting substrates can be 6-8X higher than heat transfer rates during traditional filmwise condensation on wetting substrates. Dropwise condensation on lubricant-infused surfaces (LIS, or SLIPS) is particularly interesting due to high droplet mobility on these surfaces. To accurately predict heat transfer rates during dropwise condensation, the distribution of droplet sizes must be known. Here we present condensation studies of water on aluminum-based lubricant-infused surfaces with a wide range of lubricant viscosities (12–2717cSt) to determine droplet size distributions. Through optical imaging and microscopy, we show that the distribution of droplet sizes on LIS is independent of lubricant viscosity, and agrees well with the model developed by Rose for the distribution of droplet sizes on hydrophobic surfaces, especially in the range 10<r<100µm. Using artificial sweeping experiments and numerical modeling, we investigate the dependence of sweeping rates on the distribution of droplet sizes and on average heat transfer rates. The maximum size to which droplets grow before being swept decreases rapidly with only a modest decrease in sweeping period, from 750 to 62µm. Yet, the distribution of droplet sizes and heat transfer rates are nearly unaffected by the change in sweeping period, due to a relative insensitivity of heat transfer to droplets with radii r>100µm due to a high conduction resistance within these droplets. Our work provides an experimental and analytical framework to predict heat transfer and sweeping rates for water condensation on a vertical plate coated with a LIS or SLIPS surface.
Abstract
Total ice water content (IWC) derived from an isokinetic evaporator probe and ice crystal particle size distributions (PSDs) measured by a two-dimensional stereo probe and precipitation ...imaging probe installed on an aircraft during the 2014 European High Altitude Ice Crystals–North American High IWC field campaign (HAIC/HIWC) were used to characterize regions of high IWC consisting mainly of small ice crystals (HIWC_S) with IWC ≥ 1.0 g m
−3
and median mass diameter (MMD) < 0.5 mm. A novel fitting routine developed to automatically determine whether a unimodal, bimodal, or trimodal gamma distribution best fits a PSD was used to compare characteristics of HIWC_S and other PSDs (e.g., multimodality, gamma fit parameters) for HIWC_S simulations. The variation of these characteristics and bulk properties (MMD, IWC) was regressed with temperature, IWC, and vertical velocity. HIWC_S regions were most pronounced in updraft cores. The three modes of the PSD reveal different dominant processes contributing to ice growth: nucleation for maximum dimension
D
< 0.15 mm, diffusion for 0.15 <
D
< 1.0 mm, and aggregation for
D
> 1.0 mm. The frequency of trimodal distributions increased with temperature. The volumes of equally plausible parameters derived in the phase space of gamma fit parameters increased with temperature for unimodal distributions and, for temperatures less than −27°C, for multimodal distributions. Bimodal distributions with 0.4 mm in the larger mode were most common in updraft cores and HIWC_S regions; bimodal distributions with 0.4 mm in the smaller mode were least common in convective cores.
Solid/oil separation is widely used in various industrial fields. Conventional methods can effectively separate solids with large particle sizes from oil media; however, removing fine solids using ...these methods remains challenging. Researchers have attempted to remove fine particles by applying wettability modification, interface capture, and sedimentation, but these methods have several disadvantages and exhibit low efficiency. The relationship between wettability, solid removal rate, and drop size distribution variation of particle-laden droplets remains unclear. Herein, we propose the application of a centrifugal field to enhance the water-based “forth flotation” and investigate its separation characteristics experimentally. Separation experiments under gravity and centrifugal conditions were performed, and the sedimentation of particle-laden droplets dispersed in oil was conducted. The effects of wettability and initial water moisture on separation efficiency were explored, and the solid/oil separation mechanism was analyzed. The variation in the drop size distribution under different conditions was evaluated, and a mathematical relation for predicting the initial average drop size of particle-laden droplets was fitted. In addition, the fitted mathematical expression can be utilized to predict the initial average drop size of particle-laden droplets.
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In this paper, precipitation rate retrieval algorithms for the Global Precipitation Measurement mission's Dual-frequency Precipitation Radar (DPR) are developed. The DPR consists of a Ku-band radar ...(KuPR; 13.6 GHz) and a Ka-band radar (KaPR; 35.5 GHz). For the KuPR, an algorithm similar to the Tropical Rainfall Measuring Mission's Precipitation Radar algorithm is developed, with the relation between precipitation rate R and massweighted mean diameter Dm (R−Dm relation) replacing the relation between the specific attenuation k and effective radar reflectivity factor Ze. The R−Dm relation can also be applied to the KaPR and dual-frequency algorithms. In both the single-frequency and dual-frequency algorithms, the forward retrieval method is applied with an assumed adjustment factor for the R−Dm relation (ε) and the results are evaluated to select the best value of ε. The advantages of the dual-frequency algorithm are the availability of the dual-frequency surface reference technique and the ZfKa method, which is a method to use the attenuation-corrected radar reflectivity factor Zf of KaPR, to select ε as well as the possibility to selectively use measurements from KuPR or KaPR. This paper also describes the derivation of the scattering table and the R−Dm relation as well as the procedure for non-uniform beam filling correction in detail. The outputs are then statistically analyzed to demonstrate algorithm performance.
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