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

2018 ◽  
Author(s):  
Hailing Jia ◽  
Xiaoyan Ma ◽  
Yangang Liu
Keyword(s):  
Vertical Velocity ◽  
Cloud Droplet ◽  
Liquid Water Content ◽  
Relative Dispersion ◽  
Aircraft Measurements ◽  
Cloud Droplets ◽  
Aerosol Cloud ◽  
Microphysical Properties ◽  
Entrainment Zone ◽  
The Difference

Abstract. In situ aircraft measurements during the VAMOS Ocean–Cloud–Atmosphere–Land Study-Regional Experiment (VOCALS-REx) field campaign are employed to study the interaction between aerosol and stratocumulus over the southeast Pacific Ocean, as well as entrainment process near the top of stratocumulus and its possible impacts on aerosol–cloud interaction. Our analysis suggest that the increase of liquid water content (LWC) is mainly contributed by cloud droplet number concentration (Nd) instead of effective radius of cloud droplets in the polluted case, in which more droplets form with smaller size, while the opposite is true in the clean case. By looking into the influences of dynamical conditions and aerosol microphysical properties on the cloud droplet formation, it is confirmed that cloud droplets are more easily to form under the conditions with large vertical velocity and aerosol size. An increase in aerosol concentration tends to increase both 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, positive correlation between ϵ and Nd become stronger, implying that perturbations of w could weaken the influence of aerosol on ϵ, and hence may result in an underestimation of aerosol dispersion effect. The difference of cloud microphysical properties between entrainment and non-entrainment zones confirms that the entrainment-mixing mechanism is predominantly extreme inhomogeneous in the stratocumulus that capped by a sharp inversion, namely the entrainment reduces Nd and LWC by 28.9 % and 24.8 % on average, respectively, while the size of droplets is relatively unaffected. In entrainment zone, smaller aerosols and drier air entrained from the top induce less cloud droplet with respect to total in-cloud particles (0.56 ± 0.22) than the case in non-entrainment zone (0.73 ± .0.13) by inhibiting aerosol activation and promoting cloud droplets evaporation.

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 Monte Carlo-based subgrid parameterization of vertical velocity and stratiform cloud microphysics in ECHAM5.5-HAM2

2013 ◽  
Vol 13 (2) ◽  
pp. 5477-5507
Author(s):  
J. Tonttila ◽  
P. Räisänen ◽  
H. Järvinen
Keyword(s):  
Monte Carlo ◽  
Vertical Velocity ◽  
Cloud Droplet ◽  
Cloud Microphysics ◽  
Radiative Effects ◽  
Cloud Droplets ◽  
Microphysical Properties ◽  
Cloud Radiative Effects ◽  
Cloud Activation ◽  
The Impact

Abstract. A new method for parameterizing the subgrid variations of vertical velocity and cloud droplet number concentration (CDNC) is presented for GCMs. These parameterizations build on top of existing parameterizations that create stochastic subgrid cloud columns inside the GCM grid-cells, which can be employed by the Monte Carlo independent column approximation approach for radiative transfer. The new model version adds a description for vertical velocity in individual subgrid columns, which can be used to compute cloud activation and the subgrid distribution of the number of cloud droplets explicitly. This provides a consistent way for simulating the cloud radiative effects with two-moment cloud microphysical properties defined in subgrid-scale. The primary impact of the new parameterizations is to decrease the CDNC over polluted continents, while over the oceans the impact is smaller. This promotes changes in the global distribution of the cloud radiative effects and might thus have implications on model estimation of the indirect radiative effect of aerosols.

Aircraft measurements of aerosol, cloud droplets and drizzle in stratiform clouds over the northwest Atlantic ocean

2013 ◽  
Author(s):  
Stéphanie Gagné ◽  
Landan MacDonald ◽  
Michael Earle ◽  
W. Richard Leaitch ◽  
Jeffrey R. Pierce
Keyword(s):  
Atlantic Ocean ◽  
Aircraft Measurements ◽  
Cloud Droplets ◽  
Northwest Atlantic ◽  
Aerosol Cloud ◽  
Stratiform Clouds

scholarly journals The evolution of cloud microphysics upon aerosol interaction at the summit of Mt. Tai, China

2019 ◽  
Author(s):  
Jiarong Li ◽  
Chao Zhu ◽  
Hui Chen ◽  
Defeng Zhao ◽  
Likun Xue ◽  
...  
Keyword(s):  
Climate Models ◽  
Cloud Condensation Nuclei ◽  
Liquid Water Content ◽  
Cloud Microphysics ◽  
Life Cycles ◽  
Cloud Droplets ◽  
Climate Effect ◽  
Local Climate ◽  
The North ◽  
Microphysical Properties

Abstract. The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and behaviour of clouds and their influence on climate. In an attempt to understand better the microphysical properties of cloud droplets, the aerosol-cloud interactions, and the corresponding climate effect during cloud life cycles in the North China Plain, an intensive observation took place from 17 June to 30 July 2018 at the summit of Mt. Tai. Cloud microphysical parameters were monitored simultaneously with number concentrations of cloud condensation nuclei (NCCN) at different supersaturations, PM2.5 mass concentrations, particle size distributions and meteorological parameters. Number concentrations of cloud droplets (NC), liquid water content (LWC) and effective radius of cloud droplets (reff) show large variations among 40 cloud events observed during the campaign. Perturbations of aerosols will significantly increase the NC of cloud droplets and shift cloud droplets toward smaller size ranges. Clouds in clean days are more susceptible to the change in concentrations of particle number (NP). LWC shows positive correlation with reff. As NC increases, reff changes from a trimodal distribution to a unimodal distribution. By assuming a cloud thickness of 100 m, we find that the albedo can increase 36.4 % if the cloud gets to be disturbed by aerosols. This may induce a cooling effect on the local climate system. Our results contribute more information about regional cloud microphysics and will help to reduce the uncertainties in climate models when predicting climate responses to cloud-aerosol interactions.

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 Aerosol–Cloud Interaction in Deep Convective Clouds over the Indian Peninsula Using Spectral (Bin) Microphysics

2017 ◽  
Vol 74 (10) ◽  
pp. 3145-3166 ◽  
Author(s):  
K. Gayatri ◽  
S. Patade ◽  
T. V. Prabha
Keyword(s):  
Size Distribution ◽  
Cloud Condensation Nuclei ◽  
Wrf Model ◽  
Cloud Droplet ◽  
Liquid Water Content ◽  
Cloud Microphysics ◽  
Large Area ◽  
Surface Precipitation ◽  
Aerosol Cloud ◽  
Bin Microphysics

Abstract The Weather Research and Forecasting (WRF) Model coupled with a spectral bin microphysics (SBM) scheme is used to investigate aerosol effects on cloud microphysics and precipitation over the Indian peninsular region. The main emphasis of the study is in comparing simulated cloud microphysical structure with in situ aircraft observations from the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX). Aerosol–cloud interaction over the rain-shadow region is investigated with observed and simulated size distribution spectra of cloud droplets and ice particles in monsoon clouds. It is shown that size distributions as well as other microphysical characteristics obtained from simulations such as liquid water content, cloud droplet effective radius, cloud droplet number concentration, and thermodynamic parameters are in good agreement with the observations. It is seen that in clouds with high cloud condensation nuclei (CCN) concentrations, snow and graupel size distribution spectra were broader compared to clouds with low concentrations of CCN, mainly because of enhanced riming in the presence of a large number of droplets with a diameter of 10–30 μm. The Hallett–Mossop ice multiplication process is illustrated to have an impact on snow and graupel mass. The changes in CCN concentrations have a strong effect on cloud properties over the domain, amounts of cloud water, and the glaciation of the clouds, but the effects on surface precipitation are small when averaged over a large area. Overall enhancement of cold-phase cloud processes in the high-CCN case contributed to slight enhancement (5%) in domain-averaged surface precipitation.

scholarly journals The Route to Raindrop Formation in a Shallow Cumulus Cloud Simulated by a Lagrangian Cloud Model

2017 ◽  
Vol 74 (7) ◽  
pp. 2125-2142 ◽  
Author(s):  
Fabian Hoffmann ◽  
Yign Noh ◽  
Siegfried Raasch
Keyword(s):  
Drop Size ◽  
Cloud Model ◽  
Cloud Droplet ◽  
Liquid Water Content ◽  
Cumulus Cloud ◽  
Turbulent Environments ◽  
Shallow Cumulus ◽  
History Of ◽  
The Difference ◽  
Single Droplets

Abstract The mechanism of raindrop formation in a shallow cumulus cloud is investigated using a Lagrangian cloud model (LCM). The analysis is focused on how and under which conditions a cloud droplet grows to a raindrop by tracking the history of individual Lagrangian droplets. It is found that the rapid collisional growth, leading to raindrop formation, is triggered when single droplets with a radius of 20 μm appear in the region near the cloud top, characterized by large liquid water content, strong turbulence, large mean droplet size, broad drop size distribution (DSD), and high supersaturations. Raindrop formation easily occurs when turbulence-induced collision enhancement (TICE) is considered, with or without any extra broadening of the DSD by another mechanism (such as entrainment and mixing). In contrast, when TICE is not considered, raindrop formation is severely delayed if no other broadening mechanism is active. The reason for the difference is clarified by the additional analysis of idealized box simulations of the collisional growth process for different DSDs in varied turbulent environments. It is found that TICE does not accelerate the timing of the raindrop formation for individual droplets, but it enhances the collisional growth rate significantly afterward by providing a greater number of large droplets for collision. Higher droplet concentrations increase the time for raindrop formation and decrease precipitation but intensify the effect of TICE.

scholarly journals The importance of vertical velocity variability for estimates of the indirect aerosol effects

2013 ◽  
Vol 13 (10) ◽  
pp. 27053-27113 ◽  
Author(s):  
R. E. L. West ◽  
P. Stier ◽  
A. Jones ◽  
C. E. Johnson ◽  
G. W. Mann ◽  
...  
Keyword(s):  
Vertical Velocity ◽  
Cloud Droplet ◽  
Detailed Examination ◽  
Radiative Flux ◽  
Cloud Droplets ◽  
Anthropogenic Aerosol ◽  
Aerosol Forcing ◽  
Hadley Centre ◽  
The Uk ◽  
Aerosol Effects

Abstract. The activation of aerosols to form cloud droplets is dependent upon vertical velocities whose local variability is not typically resolved at the GCM grid scale. Consequently, it is necessary to represent the sub-grid-scale variability of vertical velocity in the calculation of cloud droplet number concentration. This study uses the UK Chemistry and Aerosols community model (UKCA) within the Hadley Centre Global Environmental Model (HadGEM3), coupled for the first time to an explicit aerosol activation parameterisation, and hence known as UKCA-Activate. We explore the range of uncertainty in estimates of the indirect aerosol effects attributable to the choice of parameterisation of the sub-grid-scale variability of vertical velocity in HadGEM-UKCA. Results of simulations demonstrate that the use of a characteristic vertical velocity cannot replicate results derived with a distribution of vertical velocities, and is to be discouraged in GCMs. This study focuses on the effect of the variance (σw2) of a Gaussian pdf of vertical velocity. Fixed values of σw2 (spanning the range measured in situ by nine flight campaigns found in the literature) and a configuration in which σw2 depends on turbulent kinetic energy are tested. Results from the mid-range fixed σw2 and TKE-based configurations both compare well with observed vertical velocity distributions and cloud droplet number concentrations. The radiative flux perturbation due to the total effects of anthropogenic aerosol is estimated at −1.4 W m−2 with σw2 = 0.1 m s−1, −1.7 W m−2 with σw2 derived from TKE, −1.9 W m−2 with σw = 0.4 m s−1 and −2.0 W m−2 with σw = 0.7 m s−1. The breadth of this range (0.6 W m−2) corresponds to almost a third of the total estimate of −1.9 W m−2, obtained with the mid-range value of σw = 0.4 m s−1, and is comparable to the total diversity of current aerosol forcing estimates. Reducing the uncertainty in the parameterisation of σw would therefore be an important step towards reducing the uncertainty in estimates of the indirect aerosol effects. Detailed examination of regional radiative flux perturbations reveals that aerosol microphysics can be responsible for some climate-relevant radiative effects, highlighting the importance of including microphysical aerosol processes in GCMs.

scholarly journals Aerosol concentration and size distribution measured below, in, and above cloud from the DOE G-1 during VOCALS-REx

2011 ◽  
Vol 11 (6) ◽  
pp. 17289-17336 ◽  
Author(s):  
L. I. Kleinman ◽  
P. H. Daum ◽  
Y.-N. Lee ◽  
E. R. Lewis ◽  
A. J. Sedlacek ◽  
...  
Keyword(s):  
Power Plants ◽  
Marine Boundary Layer ◽  
Cloud Droplet ◽  
Pollution Source ◽  
Number Concentration ◽  
Dew Point ◽  
Cloud Droplets ◽  
The North ◽  
Stratocumulus Clouds ◽  
The Difference

Abstract. During the VOCALS Regional Experiment, the DOE G-1 aircraft was used to sample a varying aerosol environment pertinent to properties of stratocumulus clouds over a longitude band extending 800 km west from the Chilean coast at Arica. Trace gas and aerosol measurements are presented as a function of longitude, altitude, and dew point in this study. Spatial distributions are consistent with an upper atmospheric source for O3 and South American coastal sources for marine boundary layer (MBL) CO and aerosol, most of which is acidic sulfate in agreement with the dominant pollution source being SO2 from Cu smelters and power plants. Pollutant layers in the free troposphere (FT) can be a result of emissions to the north in Peru or long range transport from the west. At a given altitude in the FT (up to 3 km), dew point varies by 40 °C with dry air descending from the upper atmospheric and moist air having a BL contribution. Ascent of BL air to a cold high altitude results in the condensation and precipitation removal of all but a few percent of BL water along with aerosol that served as CCN. Thus, aerosol volume decreases with dew point in the FT. Aerosol size spectra have a bimodal structure in the MBL and an intermediate diameter unimodal distribution in the FT. Comparing cloud droplet number concentration (CDNC) and pre-cloud aerosol (Dp > 100 nm) gives a linear relation up to a number concentration of ~150 cm−3, followed by a less than proportional increase in CDNC at higher aerosol number concentration. A number balance between below cloud aerosol and cloud droplets indicates that ~25 % of aerosol in the PCASP size range are interstitial (not activated). One hundred and two constant altitude cloud transects were identified and used to determine properties of interstitial aerosol. One transect is examined in detail as a case study. Approximately 25 to 50 % of aerosol with Dp > 110 nm were not activated, the difference between the two approaches possibly representing shattered cloud droplets or unknown artifact. CDNC and interstitial aerosol were anti-correlated in all cloud transects, consistent with the occurrence of dry in-cloud areas due to entrainment or circulation mixing.

scholarly journals Why do GCMs overestimate the aerosol cloud lifetime effect? A comparison of CAM5 and a CRM

2016 ◽  
Author(s):  
Cheng Zhou ◽  
Joyce E. Penner
Keyword(s):  
Great Plains ◽  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Cloud Droplet ◽  
Condensation Process ◽  
Cloud Droplets ◽  
Aerosol Cloud ◽  
Aerosol Loading

Abstract. Observation-based studies have shown that the aerosol cloud lifetime effect or the increase of cloud liquid water (LWP) with increased aerosol loading may have been overestimated in climate models. Here, we simulate shallow warm clouds on 05/27/2011 at the Southern Great Plains (SGP) measurement site established by Department of Energy's Atmospheric Radiation Measurement (ARM) Program using a single column version of a global climate model (CAM5.3) and a cloud resolving model (CRM). The LWP simulated by CAM increases substantially with aerosol loading while that in the CRM does not. The increase of LWP in CAM is caused by a large decrease of the autoconversion rate when cloud droplet number increases. In the CRM, the autoconversion rate is also reduced, but this is offset or even outweighed by the increased evaporation of cloud droplets near cloud top, resulting in an overall decrease in LWP. Our results suggest that climate models need to include the dependence of cloud top growth and the evaporation/condensation process on cloud droplet number concentrations.

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