Comment on “Cloud droplet spectral width relationship to CCN spectra and vertical velocity” by Hudson et al.

2014 ◽  
Vol 119 (4) ◽  
pp. 1874-1877 ◽  
Author(s):  
Yangang Liu ◽  
Peter H. Daum ◽  
Chunsong Lu
Keyword(s):  
Vertical Velocity ◽  
Cloud Droplet ◽  
Spectral Width

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 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.

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 Biomass burning aerosol as a modulator of the droplet number in the southeast Atlantic region

2020 ◽  
Vol 20 (5) ◽  
pp. 3029-3040 ◽  
Author(s):  
Mary Kacarab ◽  
K. Lee Thornhill ◽  
Amie Dobracki ◽  
Steven G. Howell ◽  
Joseph R. O'Brien ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Biomass Burning ◽  
Vertical Velocity ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Droplet Formation ◽  
Aerosol Concentration ◽  
Aerosol Size Distribution ◽  
Small Shift ◽  
Significant Difference

Abstract. The southeastern Atlantic (SEA) and its associated cloud deck, off the west coast of central Africa, is an area where aerosol–cloud interactions can have a strong radiative impact. Seasonally, extensive biomass burning (BB) aerosol plumes from southern Africa reach this area. The NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) study focused on quantitatively understanding these interactions and their importance. Here we present measurements of cloud condensation nuclei (CCN) concentration, aerosol size distribution, and characteristic vertical updraft velocity (w∗) in and around the marine boundary layer (MBL) collected by the NASA P-3B aircraft during the August 2017 ORACLES deployment. BB aerosol levels vary considerably but systematically with time; high aerosol concentrations were observed in the MBL (800–1000 cm−3) early on, decreasing midcampaign to concentrations between 500 and 800 cm−3. By late August and early September, relatively clean MBL conditions were sampled (<500 cm−3). These data then drive a state-of-the-art droplet formation parameterization from which the predicted cloud droplet number and its sensitivity to aerosol and dynamical parameters are derived. Droplet closure was achieved to within 20 %. Droplet formation sensitivity to aerosol concentration, w∗, and the hygroscopicity parameter, κ, vary and contribute to the total droplet response in the MBL clouds. When aerosol concentrations exceed ∼900 cm−3 and maximum supersaturation approaches 0.1 %, droplet formation in the MBL enters a velocity-limited droplet activation regime, where the cloud droplet number responds weakly to CCN concentration increases. Below ∼500 cm−3, in a clean MBL, droplet formation is much more sensitive to changes in aerosol concentration than to changes in vertical updraft. In the competitive regime, where the MBL has intermediate pollution (500–800 cm−3), droplet formation becomes much more sensitive to hygroscopicity (κ) variations than it does in clean and polluted conditions. Higher concentrations increase the sensitivity to vertical velocity by more than 10-fold. We also find that characteristic vertical velocity plays a very important role in driving droplet formation in a more polluted MBL regime, in which even a small shift in w∗ may make a significant difference in droplet concentrations. Identifying regimes where droplet number variability is driven primarily by updraft velocity and not by aerosol concentration is key for interpreting aerosol indirect effects, especially with remote sensing. The droplet number responds proportionally to changes in characteristic velocity, offering the possibility of remote sensing of w∗ under velocity-limited conditions.

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 On the drivers of droplet variability in Alpine mixed-phase clouds

2020 ◽  
Author(s):  
Paraskevi Georgakaki ◽  
Aikaterini Bougiatioti ◽  
Jörg Wieder ◽  
Claudia Mignani ◽  
Fabiola Ramelli ◽  
...  
Keyword(s):  
Vertical Velocity ◽  
Anthropogenic Activities ◽  
Cloud Condensation Nuclei ◽  
Ultrafine Particle ◽  
Cloud Droplet ◽  
Atmospheric Model ◽  
Droplet Formation ◽  
Mixed Phase ◽  
Velocity Variations ◽  
Mixed Phase Clouds

Abstract. Droplet formation provides a direct microphysical link between aerosols and clouds (liquid or mixed phase), and its adequate description poses a major challenge for any atmospheric model. Observations are critical for evaluating and constraining the process. Towards this, aerosol size distributions, cloud condensation nuclei, hygroscopicity and lidar-derived vertical velocities were observed in Alpine mixed-phase clouds during the Role of Aerosols and Clouds Enhanced by Topography on Snow (RACLETS) field campaign in the Davos, Switzerland region during February and March 2019. Data from the mountain-top site of Weissfluhjoch (WFJ) and the valley site of Davos Wolfgang are studied. These observations are coupled with a state-of-the art droplet activation parameterization to investigate the aerosol-cloud droplet link in mixed-phase clouds. The mean CCN-derived hygroscopicity parameter, κ, at WFJ ranges between 0.2–0.3, consistent with expectations for continental aerosol. κ tends to decrease with size, possibly from an enrichment in organic material associated with the vertical transport of fresh ultrafine particle emissions (likely from biomass burning) from the valley floor in Davos. The parameterization provides droplet number that agrees with observations to within ~25 %. We also find that the susceptibility of droplet formation to aerosol concentration and vertical velocity variations can be appropriately described as a function of the standard deviation of the distribution of updraft velocities, σw, as the droplet number never exceeds a characteristic limit, termed limiting droplet number, of ~150–550 cm−3, which depends solely on σw. We also show that high aerosol levels in the valley, most likely from anthropogenic activities, increase cloud droplet number, reduce cloud supersaturation (<0.1 %) and shift the clouds to a state that is less susceptible to aerosol and become very sensitive to vertical velocity variations. The transition from aerosol to velocity-limited regime depends on the ratio of cloud droplet number to the limiting droplet number, as droplet formation becomes velocity-limited when this ratio exceeds 0.5. Under such conditions, droplet size tends to be minimal, reducing the likelihood that large drops are present that promote glaciation through rime splintering and droplet shattering. Identifying regimes where droplet number variability is dominated by dynamical – rather than aerosol – changes is key for interpreting and constraining when and which types of aerosol effects on clouds are active.

The Growth of Cloud Drops by Condensation. I. General Characteristics

1952 ◽  
Vol 5 (1) ◽  
pp. 59 ◽  
Author(s):  
P Squires
Keyword(s):  
Vertical Velocity ◽  
Cloud Droplet ◽  
Condensation Nucleus ◽  
Threshold Effect ◽  
Condensation Nuclei ◽  
Final Size ◽  
Definition Of ◽  
Precise Interpretation

Condensation in 'cloud is studied to demonstrate certain general characteristics, without special assumptions about the condensation nuclei or the vertical velocity. The equation of growth of a droplet is constructed, taking account of ventilation due to its falling velocity. Lifting is assumed to occur adiabatically. An approximate value is found for the supersaturation of cloud air, which under certain conditions can be computed from observable quantities-the cloud droplet spectrum and the vertical velocity. Growth of drops at small sizes is very rapid : at constant supersaturation, in a period of a few seconds, a drop in general either grows beyond r= 1μ, or else comes so close to equilibrium at some smaller size that growth practically ceases. When the supersaturation is moderate or large, a threshold effect appears : the size of the condensation nucleus determines whether or not the drop shall grow, but, if it does, has little influence on its final size. The definition of the size of a small condensation nucleus is reviewed and a more precise interpretation is suggested.

scholarly journals Large Eddy Simulation of Microphysics and Influencing Factors in Shallow Convective Clouds

Atmosphere ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 485
Author(s):  
Zhuangzhuang Zhou ◽  
Chongzhi Yin ◽  
Chunsong Lu ◽  
Xingcan Jia ◽  
Fang Ye ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Influencing Factors ◽  
Vertical Velocity ◽  
Large Scale ◽  
Cloud Droplet ◽  
Relative Dispersion ◽  
Cloud Base ◽  
Convective Clouds ◽  
Eddy Simulation ◽  
Large Eddy

A flight of shallow convective clouds during the SCMS95 (Small Cumulus Microphysics Study 1995) observation project is simulated by the large eddy simulation (LES) version of the Weather Research and Forecasting Model (WRF-LES) with spectral bin microphysics (SBM). This study focuses on relative dispersion of cloud droplet size distributions, since its influencing factors are still unclear. After validation of the simulation by aircraft observations, the factors affecting relative dispersion are analyzed. It is found that the relationships between relative dispersion and vertical velocity, and between relative dispersion and adiabatic fraction are both negative. Furthermore, the negative relationships are relatively weak near the cloud base, strengthen with the increasing height first and then weaken again, which is related to the interplays among activation, condensation and evaporation for different vertical velocity and entrainment conditions. The results will be helpful to improve parameterizations related to relative dispersion (e.g., autoconversion and effective radius) in large-scale models.

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