scholarly journals Theoretical analysis of mixing in liquid clouds. Part IV: DSD evolution and mixing diagrams

2017 ◽  
Author(s):  
Mark Pinsky ◽  
Alexander Khain
Keyword(s):  
Droplet Size Distribution ◽  
Liquid Water Content ◽  
Droplet Evaporation ◽  
Cloud Fraction ◽  
Effective Radius ◽  
Time Dependent ◽  
Droplet Concentration ◽  
The Difference ◽  
Mixing Diagrams ◽  
Dependent Processes

Abstract. Evolution of droplet size distribution (DSD) due to mixing between cloudy and dry volumes is investigated for different values of the cloud fraction and different initial DSD shapes. The analysis is performed using a diffusion-evaporation model which describes time-dependent processes of turbulent diffusion and droplet evaporation within a mixing volume. Time evolution of the DSD characteristics such as droplet concentration, liquid water content, mean volume and the effective radii is analyzed. The mixing diagrams are plotted for the final mixing stages. It is shown that the difference between the mixing diagrams for homogeneous and inhomogeneous mixing is insignificant and decreases with an increase in the DSD width. The dependencies of normalized cube of the effective radius on the cloud fraction were compared with those on normalized droplet concentration and found to be quite different. In case the normalized droplet concentration is used, mixing diagrams do not show any significant dependency on relative humidity in the dry volume. The main conclusion of the study is that traditional mixing diagrams cannot serve as a reliable tool in analysis of mixing type.

scholarly journals Theoretical analysis of mixing in liquid clouds – Part IV: DSD evolution and mixing diagrams

2018 ◽  
Vol 18 (5) ◽  
pp. 3659-3676 ◽  
Author(s):  
Mark Pinsky ◽  
Alexander Khain
Keyword(s):  
Relative Humidity ◽  
Droplet Size Distribution ◽  
Droplet Evaporation ◽  
Cloud Fraction ◽  
Time Dependent ◽  
Droplet Concentration ◽  
The Mean ◽  
The Difference ◽  
Mixing Diagrams ◽  
Dependent Processes

Abstract. Evolution of droplet size distribution (DSD) due to mixing between cloudy and dry volumes is investigated for different values of the cloud fraction and for different initial DSD shapes. The analysis is performed using a diffusion–evaporation model which describes time-dependent processes of turbulent diffusion and droplet evaporation within a mixing volume. Time evolution of the DSD characteristics such as droplet concentration, LWC and mean volume radii is analyzed. The mixing diagrams are plotted for the final mixing stages. It is shown that the difference between the mixing diagrams for homogeneous and inhomogeneous mixing is insignificant and decreases with an increase in the DSD width. The dependencies of the normalized cube of the mean volume radius on the cloud fraction were compared with those on normalized droplet concentration and found to be quite different. If the normalized droplet concentration is used, mixing diagrams do not show any significant dependence on relative humidity in the dry volume. The main conclusion of the study is that traditional mixing diagrams cannot serve as a reliable tool for analysis of mixing type.

scholarly journals Investigation of aerosol indirect effects on monsoon clouds using ground-based measurements over a high-altitude site in Western Ghats

2016 ◽  
Author(s):  
V. Anil Kumar ◽  
G. Pandithurai ◽  
P. P. Leena ◽  
K. K. Dani ◽  
P. Murugavel ◽  
...  
Keyword(s):  
High Altitude ◽  
Indirect Effects ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Liquid Water Content ◽  
Number Concentration ◽  
Effective Radius ◽  
Aerosol Indirect Effects ◽  
Cloud Droplet Number Concentration ◽  
Aerosol Effects

Abstract. The effect of aerosols on cloud droplet number concentration and droplet effective radius are investigated from ground-based measurements over a high-altitude site where in clouds pass over the surface. First aerosol indirect effect AIE estimates were made using i) relative changes in cloud droplet number concentration (AIEn) and ii) relative changes in droplet effective radius (AIEs) with relative changes in aerosol for different LWC values. AIE estimates from two different methods reveal that there is systematic overestimation in AIEn as compared to that of AIEs. Aerosol indirect effects (AIEn and AIEs) and Dispersion effect (DE) at different liquid water content (LWC) regimes ranging from 0.05 to 0.50 gm-3 were estimated. The analysis demonstrates that there is overestimation of AIEn as compared to AIEs which is mainly due to DE. Aerosol effects on spectral dispersion in droplet size distribution plays an important role in altering Twomey’s cooling effect and thereby changes in climate. This study shows that the higher DE in the medium LWC regime which offsets the AIE by 30%.

scholarly journals Theoretical investigation of mixing in warm clouds – Part 2: Homogeneous mixing

2016 ◽  
Vol 16 (14) ◽  
pp. 9255-9272 ◽  
Author(s):  
Mark Pinsky ◽  
Alexander Khain ◽  
Alexei Korolev ◽  
Leehi Magaritz-Ronen
Keyword(s):  
Liquid Water ◽  
Liquid Water Content ◽  
Time Dependent ◽  
Size Distributions ◽  
Conceptual Scheme ◽  
Dimensional Parameter ◽  
Droplet Concentration ◽  
Droplet Sizes ◽  
Droplet Size Distributions ◽  
Analytical Expressions

Abstract. Evolution of monodisperse and polydisperse droplet size distributions (DSD) during homogeneous mixing is analyzed. Time-dependent universal analytical expressions for supersaturation and liquid water content are derived. For an initial monodisperse DSD, these quantities are shown to depend on a sole non-dimensional parameter. The evolution of moments and moment-related functions in the course of homogeneous evaporation of polydisperse DSD is analyzed using a parcel model.It is shown that the classic conceptual scheme, according to which homogeneous mixing leads to a decrease in droplet mass at constant droplet concentration, is valid only in cases of monodisperse or initially very narrow polydisperse DSD. In cases of wide polydisperse DSD, mixing and successive evaporation lead to a decrease of both mass and concentration, so the characteristic droplet sizes remain nearly constant. As this feature is typically associated with inhomogeneous mixing, we conclude that in cases of an initially wide DSD at cloud top, homogeneous mixing is nearly indistinguishable from inhomogeneous mixing.

scholarly journals The influence of cloud structure and droplet concentration on the reflectance of shortwave radiation

1996 ◽  
Vol 14 (8) ◽  
pp. 845-852 ◽  
Author(s):  
P. F. Coley ◽  
P. R. Jonas
Keyword(s):  
Solar Radiation ◽  
Monte Carlo Model ◽  
Liquid Water Content ◽  
Cloud Fraction ◽  
Cloud Layer ◽  
Shortwave Radiation ◽  
Transmission Properties ◽  
Droplet Concentration ◽  
The Impact ◽  
Side Illumination

Abstract. The effects of cloud shadowing, channelling, cloud side illumination and droplet concentration are investigated with regard to the reflection of shortwave solar radiation. Using simple geometric clouds, coupled with a Monte Carlo model the transmission properties of idealized cloud layers are found. The clouds are illuminated with direct solar radiation from above. The main conclusion reached is that the distribution of the cloud has a very large influence on the reflectivity of a cloud layer. In particular, if the cloud contains vertical gaps through the cloud layer in which the liquid water content is zero, then, smaller more numerous gaps are more influential on the radiation than fewer, larger gaps with equal cloud fraction. At very low solar zenith angles channelling of the radiation reduces the reflection expected on the basis of the percentage cloud cover. At high solar zenith angles the illumination of the cloud edges significantly increases the reflection despite the shadowing of one cloud by another when the width of the gaps is small. The impact of droplet concentration upon the reflection of cloud layers is also investigated. It is found that at low solar zenith angles where channelling is important, the lower concentrations increase the transmission. Conversely, when cloud edge illumination is dominant the cloud distribution is found to be more important for the higher concentrations.

scholarly journals Stratocumulus Liquid Water Content from Dual-Wavelength Radar

2005 ◽  
Vol 22 (8) ◽  
pp. 1207-1218 ◽  
Author(s):  
Robin J. Hogan ◽  
Nicolas Gaussiat ◽  
Anthony J. Illingworth
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Wave Attenuation ◽  
Droplet Size Distribution ◽  
Liquid Water Content ◽  
Radar Signal ◽  
Cloud Base ◽  
Liquid Water Path ◽  
Atmospheric Radiation Measurement ◽  
The Difference

Abstract A technique is described to retrieve stratocumulus liquid water content (LWC) using the differential attenuation measured by vertically pointing radars at 35 and 94 GHz. Millimeter-wave attenuation is proportional to LWC and increases with frequency, so LWC can be derived without the need to make any assumptions on the nature of the droplet size distribution. There is also no need for the radars to be well calibrated. A significant advantage over many radar techniques in stratocumulus is that the presence of drizzle drops (those with a diameter larger than around 50 μm) does not affect the retrieval, even though such drops may dominate the radar signal. It is important, however, that there are not significant numbers of drops larger than 600 μm, which scatter outside of the Rayleigh regime at 94 GHz. A lidar ceilometer is used to locate the cloud base in the presence of drizzle falling below the cloud. An accuracy of around 0.04 g m−3 is achievable with averaging over 1 min and 150 m (two range gates), but for the previously suggested frequency pair of 10 and 35 GHz, the corresponding accuracy would be considerably worse at 0.34 g m−3. First, the retrieval of LWC is simulated using aircraft-measured size spectra taken from a profile through marine stratocumulus. Results are then presented from two case studies—one using two cloud radars at Chilbolton in southern United Kingdom, and another using the Cloud Profiling Radar System at the Atmospheric Radiation Measurement site in Oklahoma. The liquid water path from the technique was found to be in good agreement with the values that were obtained from microwave radiometers, with the difference between the two being close to the accuracy of the radiometer retrieval. In the case of well-mixed stratocumulus, the profiles were close to adiabatic.

scholarly journals Parameterization of the Autoconversion Process. Part II: Generalization of Sundqvist-Type Parameterizations

2006 ◽  
Vol 63 (3) ◽  
pp. 1103-1109 ◽  
Author(s):  
Yangang Liu ◽  
Peter H. Daum ◽  
R. McGraw ◽  
R. Wood
Keyword(s):  
Critical Radius ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Liquid Water Content ◽  
Smooth Transition ◽  
Relative Dispersion ◽  
Droplet Concentration ◽  
Single Function ◽  
Cloud Droplet Size Distribution ◽  
Part Structure

Abstract Existing Sundqvist-type parameterizations, which only consider dependence of the autoconversion rate on cloud liquid water content, are generalized to explicitly account for the droplet concentration and relative dispersion of the cloud droplet size distribution as well. The generalized Sundqvist-type parameterization includes the more commonly used Kessler-type parameterization as a special case, unifying the two different types of parameterizations for the autoconversion rate. The generalized Sundqvist-type parameterization is identical with the Kessler-type parameterization presented in Part I beyond the autoconversion threshold, but exhibits a more realistic, smooth transition in the vicinity of the autoconversion threshold (threshold behavior) in contrast to the discontinuously abrupt transition embodied in the Kessler-type parameterization. A new Sundqvist-type parameterization is further derived by applying the expression for the critical radius derived from the kinetic potential theory to the generalized Sundqvist-type parameterization. The new parameterization eliminates the need for defining the driving radius and for prescribing the critical radius associated with Kessler-type parameterizations. The two-part structure of the autoconversion process raises questions regarding model-based empirical parameterizations obtained by fitting simulation results from detailed collection models with a single function.

scholarly journals The relative dispersion of cloud droplets: its robustness with respect to key cloud properties

2015 ◽  
Vol 15 (4) ◽  
pp. 2009-2017 ◽  
Author(s):  
E. Tas ◽  
A. Teller ◽  
O. Altaratz ◽  
D. Axisa ◽  
R. Bruintjes ◽  
...  
Keyword(s):  
Size Distribution ◽  
Droplet Size ◽  
Measurement Data ◽  
Thermodynamic Characteristics ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Liquid Water Content ◽  
Relative Dispersion ◽  
Droplet Concentration ◽  
Cloud Droplet Size Distribution

Abstract. Flight data measured in warm convective clouds near Istanbul in June 2008 were used to investigate the relative dispersion of cloud droplet size distribution. The relative dispersion (ϵ), defined as the ratio between the standard deviation (σ) of the cloud droplet size distribution and cloud droplet average radius (⟨r⟩), is a key factor in regional and global models. The relationship between ε and the clouds' microphysical and thermodynamic characteristics is examined. The results show that ε is constrained with average values in the range of ~0.25–0.35. ε is shown not to be correlated with cloud droplet concentration or liquid water content (LWC). However, ε variance is shown to be sensitive to droplet concentration and LWC, suggesting smaller variability of ϵ in the clouds' most adiabatic regions. A criterion for use of in situ airborne measurement data for calculations of statistical moments (used in bulk microphysical schemes), based on the evaluation of ϵ, is suggested.

scholarly journals Parameterization of Vertical Profiles of Governing Microphysical Parameters of Shallow Cumulus Cloud Ensembles Using LES with Bin Microphysics

2019 ◽  
Vol 76 (2) ◽  
pp. 533-560 ◽  
Author(s):  
Pavel Khain ◽  
Reuven Heiblum ◽  
Ulrich Blahak ◽  
Yoav Levi ◽  
Harel Muskatel ◽  
...  
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Liquid Water Content ◽  
Effective Radius ◽  
Cloud Base ◽  
Vertical Profiles ◽  
Droplet Concentration ◽  
Radiation Properties ◽  
Microphysical Parameters ◽  
Bin Microphysics

Abstract Shallow convection is a subgrid process in cloud-resolving models for which their grid box is larger than the size of small cumulus clouds (Cu). At the same time such Cu substantially affect radiation properties and thermodynamic parameters of the low atmosphere. The main microphysical parameters used for calculation of radiative properties of Cu in cloud-resolving models are liquid water content (LWC), effective droplet radius, and cloud fraction (CF). In this study, these parameters of fields of small, warm Cu are calculated using large-eddy simulations (LESs) performed using the System for Atmospheric Modeling (SAM) with spectral bin microphysics. Despite the complexity of microphysical processes, several fundamental properties of Cu were found. First, despite the high variability of LWC and droplet concentration within clouds and between different clouds, the volume mean and effective radii per specific level vary only slightly. Second, the values of effective radius are close to those forming during adiabatic ascent of air parcels from cloud base. These findings allow for characterization of a cloud field by specific vertical profiles of effective radius and of mean liquid water content, which can be calculated using the theoretical profile of adiabatic liquid water content and the droplet concentration at cloud base. Using the results of these LESs, a simple parameterization of cloud-field-averaged vertical profiles of effective radius and of liquid water content is proposed for different aerosol and thermodynamic conditions. These profiles can be used for calculation of radiation properties of Cu fields in large-scale models. The role of adiabatic processes in the formation of microstructure of Cu is discussed.

scholarly journals Theoretical investigation of mixing in warm clouds – Part 2: Homogeneous mixing

2015 ◽  
Vol 15 (21) ◽  
pp. 30269-30320 ◽  
Author(s):  
M. Pinsky ◽  
A. Khain ◽  
A. Korolev ◽  
L. Magaritz-Ronen
Keyword(s):  
Liquid Water ◽  
Liquid Water Content ◽  
Time Dependent ◽  
Size Distributions ◽  
Conceptual Scheme ◽  
Dimensional Parameter ◽  
Droplet Concentration ◽  
Droplet Sizes ◽  
Analytical Relations ◽  
Droplet Size Distributions

Abstract. The evolution of monodisperse and polydisperse droplet size distributions (DSDs) during homogeneous mixing is analyzed. Time-dependent universal analytical relations of supersaturation and liquid water content, which depend on a sole non-dimensional parameter, are obtained for a monodisperse DSD. The evolution of moments and moment-relation functions in the course of the homogeneous evaporation of polydisperse DSDs is analyzed using a parcel model. It is shown that the classic conceptual scheme, according to which homogeneous mixing leads to a decrease in the droplet mass under constant droplet concentration, is valid only in cases of monodisperse or initially very narrow polydisperse DSDs. In cases of wide polydisperse DSDs, mixing and successive evaporation lead to a decrease of both mass and concentration such that the characteristic droplet sizes remain nearly constant. As this feature is typically associated with inhomogeneous mixing, we conclude that in cases of an initially wide DSD at cloud top, homogeneous mixing is nearly indistinguishable from inhomogeneous mixing.

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