scholarly journals Parameterizations of Entrainment‐Mixing Mechanisms and Their Effects on Cloud Droplet Spectral Width Based on Numerical Simulations

2020 ◽  
Vol 125 (22) ◽  
Author(s):  
Shi Luo ◽  
Chunsong Lu ◽  
Yangang Liu ◽  
Jianchun Bian ◽  
Wenhua Gao ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Cloud Droplet ◽  
Spectral Width ◽  
Entrainment Mixing

DROPLET FEEDBACK ON VAPOR IN A WARM CLOUD

2009 ◽  
Vol 23 (28n29) ◽  
pp. 5434-5443 ◽  
Author(s):  
ANTONIO CELANI ◽  
ANDREA MAZZINO ◽  
MARCO TIZZI
Keyword(s):  
Numerical Simulations ◽  
Droplet Size ◽  
Cloud Droplet ◽  
Direct Numerical Simulations ◽  
Cloud Droplets ◽  
Size Spectra ◽  
New Model ◽  
Warm Cloud ◽  
Local Reduction ◽  
The One

A new model to study the effect of turbulence on the cloud droplets in the condensation phase is proposed and its behavior investigated by direct numerical simulations. The model is a generalization of the one by Celani, Mazzino, Tizzi, New J. Phys.10, 075021 (2008), where the droplet feedback on vapor is now explicitly taken into account. Physically, it amounts to considering the fact that when a cloud droplet increases its size, vapor is subtracted from the ambient with the net result of a local reduction in the supersaturation field. It is shown how this effect plays to reduce the broadening of droplet size spectra in the condensation stage and thus to produce results in closer agreement with observations.

scholarly journals An Observational Study on Cloud Spectral Width in North China

Atmosphere ◽  
2019 ◽  
Vol 10 (3) ◽  
pp. 109 ◽  
Author(s):  
Yuan Wang ◽  
Shengjie Niu ◽  
Chunsong Lu ◽  
Yangang Liu ◽  
Jingyi Chen ◽  
...  
Keyword(s):  
Size Range ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Spectral Width ◽  
Relative Dispersion ◽  
Cloud Base ◽  
Cloud Droplets ◽  
Factors Affecting ◽  
Cloud Droplet Size Distribution ◽  
Stratiform Clouds

Cloud droplet size distribution (CDSD) is a critical characteristic for a number of processes related to clouds, considering that cloud droplets are formed in different sizes above the cloud-base. This paper analyzes the in-situ aircraft measurements of CDSDs and aerosol concentration ( N a ) performed in stratiform clouds in Hebei, China, in 2015 to reveal the characteristics of cloud spectral width, commonly known as relative dispersion ( ε , ratio of standard deviation (σ) to mean radius (r) of the CDSD). A new algorithm is developed to calculate the contributions of droplets of different sizes to ε . It is found that small droplets with the size range of 1 to 5.5 μm and medium droplets with the size range of 5.5 to 10 μm are the major contributors to ε, and the medium droplets generally dominate the change of ε. The variation of ε with N a can be well explained by comparing the normalized changes of σ and r ( k σ / σ and k r / r ), rather than k σ and k r only ( k σ is Δσ/Δ N a and k r is Δr/Δ N a ). From the perspective of external factors affecting ε change, the effects of N a and condensation are examined. It is found that ε increases initially and decreases afterward as N a increases, and “condensational broadening” occurs up to 1 km above cloud-base, potentially providing observational evidence for recent numerical simulations in the literature.

scholarly journals Exploring aerosol–cloud interaction using VOCALS-REx aircraft measurements

2019 ◽  
Vol 19 (12) ◽  
pp. 7955-7971 ◽  
Author(s):  
Hailing Jia ◽  
Xiaoyan Ma ◽  
Yangang Liu
Keyword(s):  
Climate Models ◽  
Global Climate ◽  
Cloud Droplet ◽  
Global Climate Models ◽  
Relative Dispersion ◽  
Aircraft Measurements ◽  
Aerosol Cloud ◽  
Dispersion Effects ◽  
Entrainment Zone ◽  
Entrainment Mixing

Abstract. In situ aircraft measurements obtained during the VAMOS (Variability of the American Monsoons) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) field campaign are analyzed to study the aerosol–cloud interactions in the stratocumulus clouds over the southeastern Pacific Ocean (SEP), with a focus on three understudied topics (separation of aerosol effects from dynamic effects, dispersion effects, and turbulent entrainment-mixing processes). Our analysis suggests that an increase in aerosol concentration tends to simultaneously increase both cloud droplet number concentration (Nd) and relative dispersion (ε), while an increase in vertical velocity (w) often increases Nd but decreases ε. After constraining the differences of cloud dynamics, the positive correlation between ε and Nd becomes stronger, implying that perturbations of w could weaken the aerosol influence on ε and hence result in an underestimation of dispersion effect. A comparative analysis of the difference of cloud microphysical properties between the entrainment and non-entrainment zones suggests that the entrainment-mixing mechanism is predominantly extremely inhomogeneous in the stratocumulus that capped by a sharp inversion, whereby the variation in liquid water content (25 %) is similar to that of Nd (29 %) and the droplet size remains approximately constant. In entrainment zone, drier air entrained from the top induces fewer cloud droplets with respect to total in-cloud particles (0.56±0.22) than the case in the non-entrainment zone (0.73±0.13) by promoting cloud droplet evaporation. This study is helpful in reducing uncertainties in dispersion effects and entrainment mixing for stratocumulus, and the results of this study may benefit cloud parameterizations in global climate models to more accurately assess aerosol indirect effects.

scholarly journals Conditions for super-adiabatic droplet growth after entrainment mixing

2016 ◽  
Vol 16 (14) ◽  
pp. 9421-9433 ◽  
Author(s):  
Fan Yang ◽  
Raymond Shaw ◽  
Huiwen Xue
Keyword(s):  
Cloud Model ◽  
Cloud Droplet ◽  
Droplet Radius ◽  
Droplet Growth ◽  
Critical Height ◽  
Growth Region ◽  
Cloud Droplets ◽  
Environmental Air ◽  
Bin Microphysics ◽  
Entrainment Mixing

Abstract. Cloud droplet response to entrainment and mixing between a cloud and its environment is considered, accounting for subsequent droplet growth during adiabatic ascent following a mixing event. The vertical profile for liquid water mixing ratio after a mixing event is derived analytically, allowing the reduction to be predicted from the mixing fraction and from the temperature and humidity for both the cloud and environment. It is derived for the limit of homogeneous mixing. The expression leads to a critical height above the mixing level: at the critical height the cloud droplet radius is the same for both mixed and unmixed parcels, and the critical height is independent of the updraft velocity and mixing fraction. Cloud droplets in a mixed parcel are larger than in an unmixed parcel above the critical height, which we refer to as the “super-adiabatic” growth region. Analytical results are confirmed with a bin microphysics cloud model. Using the model, we explore the effects of updraft velocity, aerosol source in the environmental air, and polydisperse cloud droplets. Results show that the mixed parcel is more likely to reach the super-adiabatic growth region when the environmental air is humid and clean. It is also confirmed that the analytical predictions are matched by the volume-mean cloud droplet radius for polydisperse size distributions. The findings have implications for the origin of large cloud droplets that may contribute to onset of collision–coalescence in warm clouds.

scholarly journals Analysis of Cloud Seeding Experiment by Aircraft: A Case Study of an International Joint Experiment in 2019

2020 ◽  
Vol 20 (6) ◽  
pp. 67-78
Author(s):  
Jung Mo Ku ◽  
A-Reum Ko ◽  
Sanghee Chae ◽  
Hyun Jun Hwang ◽  
Yonghun Ro ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Water Concentration ◽  
Cloud Droplet ◽  
Observation Data ◽  
Cloud Seeding ◽  
Aircraft Observation ◽  
Imaging Probe ◽  
International Joint ◽  
Average Water ◽  
Weather Control

In this study, an international joint cloud seeding experiment (International Joint Cloud Observation and Weather Control Experiment 2019, IJCO-WCE 2019) by aircraft was analyzed using numerical simulations, ground observation data, and aircraft observation data. As a result of numerical simulations, it was found that the seeding material was diffused in a direction consistent with the wind direction observed by the aircraft. Further, aircraft observation data showed an increase in average water concentration of clouds and precipitation particles after seeding rather than during seeding. The average water concentration of clouds observed by the Cloud Droplet Probe (CDP) increased by about 59% after seeding than during seeding, and that observed by the Cloud Imaging Probe (CIP) increased by about 82%. In addition, precipitation particles observed by the Precipitation Imaging Probe (PIP) were hardly noticed during seeding, but appeared after seeding.

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

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.

scholarly journals Cloud droplet spectral width relationship to CCN spectra and vertical velocity

2012 ◽  
Vol 117 (D11) ◽  
pp. n/a-n/a ◽  
Author(s):  
James G. Hudson ◽  
Stephen Noble ◽  
Vandana Jha
Keyword(s):  
Vertical Velocity ◽  
Cloud Droplet ◽  
Spectral Width

scholarly journals Distinct Impacts of Increased Aerosols on Cloud Droplet Number Concentration of Stratus/Stratocumulus and Cumulus

2020 ◽  
Author(s):  
Hailing Jia ◽  
Xiaoyan Ma ◽  
Fangqun Yu ◽  
Yangang Liu ◽  
Yan Yin
Keyword(s):  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Number Concentration ◽  
New Approach ◽  
Cloud Dynamics ◽  
Cloud Droplet Number Concentration ◽  
Aerosol Effects ◽  
Cloud Regimes ◽  
Entrainment Mixing

<p>In situ aircraft measurements obtained during the RACORO field campaign are analyzed to study the aerosol effects on different cloud regimes. The results show that with increasing cloud condensation nuclei (CCN), cloud droplet number concentration (N<sub>d</sub>) significantly increases in stratocumulus (Sc) while remains almost unchanged in cumulus (Cu). By using a new approach to strictly constrain the dynamics in Cu, we found that neither simultaneously changing cloud dynamics nor dilution of cloud water induced by entrainment-mixing can explain the observed insensitivity of N<sub>d</sub>. The different degree of reduction in cloud supersaturation caused by increasing aerosols might be responsible for the observed different aerosol indirect effect between Sc and Cu.</p>

Spectral width of seeded and ASE XUV lasers: experiment and numerical simulations

2011 ◽  
Author(s):  
A. Klisnick ◽  
L. M. Meng ◽  
D. Alessi ◽  
O. Guilbaud ◽  
Y. Wang ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Spectral Width
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