Cloud microphysical structure analysis based on high-resolution insitu measurements

AbstractThis study investigates the microphysical parameters and shapes of droplet size distributions (DSDs) along three aircraft traverses of developing convective clouds during Cloud Aerosol Interactions and Precipitation Enhancement EXperiment (CAIPEEX) 2015 at a sampling frequency of 25 Hz. The droplet number concentration (Nc, cm−3), and liquid water content (LWC, gm−3) present steep gradients within a few tens of meters’ zones near the cloud edges and relatively gentle gradients in the strong updraft zones. Sometimes, the horizontal LWC distribution resembles a trapezoid-like shape with steep LWC and Nc gradients near the cloud edges. The LWC maximums (LWCmax) are lower than the adiabatic LWC, but the high adiabatic fractions in the cloud core indicate low dilution. High LWC/LWCmax, largest droplets, and narrow and similarly-shaped DSDs are found in the regions of high updrafts. Zones of low LWC/LWCmax are found close to the cloud edges, where DSDs are highly diverse, containing both large and small droplets. Finally, we analyze the mixing diagrams.Significant in-phase turbulent fluctuations in LWC and Nc were found. The effective radii change slightly across cloud updraft zones but decrease at the low LWC/LWCmax ratio zone close to cloud edges. The spectra of LWC and Nc obey Kolmogorov -5/3 turbulence law. The radii of the correlation of LWC and Nc in updraft zones are of several tens of meters. Filaments up to 120-175 m in size are also noticed.

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-9255-2016 ◽

2016 ◽

Vol 16 (14) ◽

pp. 9255-9272 ◽

Cited By ~ 20

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.

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Impact of entrainment-mixing and turbulent fluctuations on droplet size distributions in a cumulus cloud: An investigation using Lagrangian microphysics with a sub-grid-scale model

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0281.1 ◽

2021 ◽

Author(s):

Kamal Kant Chandrakar ◽

Wojciech W. Grabowski ◽

Hugh Morrison ◽

George H. Bryan

Keyword(s):

Droplet Size ◽

Cloud Droplet ◽

Relative Dispersion ◽

Size Distributions ◽

Modeling Framework ◽

Turbulent Fluctuations ◽

Droplet Activation ◽

Droplet Size Distributions ◽

Entrainment Mixing ◽

Grid Length

AbstractEntrainment-mixing and turbulent fluctuations critically impact cloud droplet size distributions (DSDs) in cumulus clouds. This problem is investigated via a new sophisticated modeling framework using the CM1 LES model and a Lagrangian cloud microphysics scheme – the “super-droplet method” (SDM) – coupled with sub-grid-scale (SGS) schemes for particle transport and supersaturation fluctuations. This modeling framework is used to simulate a cumulus congestus cloud. Average DSDs in different cloud regions show broadening from entrainment and secondary cloud droplet activation (activation above the cloud base). DSD width increases with increasing entrainment-induced dilution as expected from past work, except in the most diluted cloud regions. The new modeling framework with SGS transport and supersaturation fluctuations allows a more sophisticated treatment of secondary activation compared to previous studies. In these simulations, it contributes about 25%of the cloud droplet population and impacts DSDs in two contrastingways: narrowing in extremely diluted regions and broadening in relatively less diluted. SGS supersaturation fluctuations contribute significantly to an increase in DSD width via condensation growth and evaporation. Mixing of super-droplets from SGS velocity fluctuations also broadens DSDs. The relative dispersion (ratio of DSD dispersion and mean radius) negatively correlates with grid-scale vertical velocity in updrafts, but is positively correlated in downdrafts. The latter is from droplet activation driven by positive SGS supersaturation fluctuations in grid-mean subsaturated conditions. Finally, the sensitivity to model grid length is evaluated. The SGS schemes have greater influence as the grid length is increased, and they partially compensate for the reduced model resolution.

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Theoretical study of mixing in liquid clouds – Part 1: Classical concept

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-30211-2015 ◽

2015 ◽

Vol 15 (21) ◽

pp. 30211-30267 ◽

Cited By ~ 5

Author(s):

A. Korolev ◽

A. Khain ◽

M. Pinsky ◽

J. French

Keyword(s):

Theoretical Study ◽

Response Times ◽

Liquid Water Content ◽

Convective Clouds ◽

Droplet Concentration ◽

Microphysical Parameters ◽

In Situ Observations ◽

Different Response ◽

Analytical Expressions

Abstract. Relationships between basic microphysical parameters are studied within the framework of homogeneous and extreme inhomogeneous mixing. Analytical expressions and numerical simulations of relationships between droplet concentration, extinction coefficient, liquid water content, and mean volume droplet size, formed at the final stage of mixing are presented. The expressions are used to identify type of mixing for in-situ observations obtained in convective clouds. The analysis suggests that for the set of observations investigated here, the interaction between cloudy and entrained environments is dominated by inhomogeneous mixing. Lastly, an analysis of different response times of the cloud environment undergoing mixing is presented. Comparisons of different characteristic times suggest that within the same mixing environment depending on mixing fraction some volumes may be dominated by homogeneous mixing whereas others by inhomogeneous mixing.

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Examination of Aerosol-Induced Convective Invigoration Using Idealized Simulations

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0023.1 ◽

2021 ◽

Vol 78 (1) ◽

pp. 287-298

Author(s):

William R. Cotton ◽

Robert Walko

Keyword(s):

Atmospheric Chemistry ◽

Convective Cloud ◽

Liquid Water Content ◽

South Florida ◽

Relative Role ◽

Anthropogenic Aerosol ◽

Convective Clouds ◽

Large Eddy ◽

Precipitation Enhancement

AbstractIdealized large-eddy simulations (LESs) are performed of deep convective clouds over south Florida to examine the relative role of aerosol-induced condensational versus mixed-phase invigoration to convective intensity and rainfall. Aerosol concentrations and chemistry are represented by using output from the GEOS-Chem global atmospheric chemistry model run with and without anthropogenic aerosol sources. The results clearly show that higher aerosol concentrations result in enhanced precipitation, larger amounts of cloud liquid water content, enhanced updraft velocities during the latter part of the simulation, and a modest enhancement of the latent heating of condensation. Overall, our results are consistent with the concept that convective cloud invigoration is mainly due to condensational invigoration and not primarily to mixed-phase invigoration. Furthermore, our results suggest that condensational invigoration can result in appreciable precipitation enhancement of ordinary warm-based convective clouds such as are common in locations like south Florida.

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

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-30269-2015 ◽

2015 ◽

Vol 15 (21) ◽

pp. 30269-30320 ◽

Cited By ~ 5

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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Microphysics of Premonsoon and Monsoon Clouds as Seen from In Situ Measurements during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX)

Journal of the Atmospheric Sciences ◽

10.1175/2011jas3707.1 ◽

2011 ◽

Vol 68 (9) ◽

pp. 1882-1901 ◽

Cited By ~ 78

Author(s):

Thara V. Prabha ◽

A. Khain ◽

R. S. Maheshkumar ◽

G. Pandithurai ◽

J. R. Kulkarni ◽

...

Keyword(s):

Numerical Models ◽

In Situ Measurements ◽

Cloud Base ◽

Cloud Droplets ◽

Convective Clouds ◽

Deep Convective Clouds ◽

Droplet Size Distributions ◽

Small Cloud ◽

Precipitation Enhancement

Abstract Analysis of the microphysical structure of deep convective clouds using in situ measurements during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) over the Indian peninsular region is presented. It is shown that droplet size distributions (DSDs) in highly polluted premonsoon clouds are substantially narrower than DSDs in less polluted monsoon clouds. High values of DSD dispersion (0.3–0.6) and its vertical variation in the transient and monsoon clouds are related largely to the existence of small cloud droplets with diameters less than 10 μm, which were found at nearly all levels. This finding indicates the existence of a continuous generation of the smallest droplets at different heights. In some cases this generation of small droplets leads to the formation of bimodal and even multimodal DSDs. The formation of bimodal DSDs is especially pronounced in monsoon clouds. Observational evidence is presented to suggest that in-cloud nucleation at elevated layers is a fundamental mechanism for producing multimodal drop size distribution in monsoon clouds as well as in most deep convective clouds. These findings indicate that inclusion of continued nucleation away from the cloud base into numerical models should be considered to predict microphysics and precipitation of clouds in monsoons and other cloud-related phenomena.

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