Relationship between Turbulence and Drizzle in Continental and Marine Low Stratiform Clouds

Abstract Turbulence and drizzle-rate measurements from a large dataset of marine and continental low stratiform clouds are presented. Turbulence peaks at cloud base over land and near cloud top over the ocean. For both regions, eddy dissipation rate values of 10−5–10−2 m2 s−3 are observed. Surface-based measurements of cloud condensation nuclei number concentration NCCN and liquid water path (LWP) are used to estimate the precipitation susceptibility S0. Results show that positive S0 values are found at low turbulence, consistent with the principle that aerosols suppress precipitation formation, whereas S0 is smaller, and can be negative, in a more turbulent environment. Under similar macrophysical conditions, especially for medium to high LWP, high (low) turbulence is likely to lessen (promote) the suppression effect of high NCCN on precipitation. Overall, the turbulent effect on S0 is stronger in continental than marine stratiform clouds. These observational findings are consistent with recent analytical prediction for a turbulence-broadening effect on cloud droplet size distribution.

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An Observational Study on Cloud Spectral Width in North China

Atmosphere ◽

10.3390/atmos10030109 ◽

2019 ◽

Vol 10 (3) ◽

pp. 109 ◽

Cited By ~ 3

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.

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Aerosol–landscape–cloud interaction: signatures of topography effect on cloud droplet formation

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-7955-2017 ◽

2017 ◽

Vol 17 (12) ◽

pp. 7955-7964 ◽

Cited By ~ 1

Author(s):

Sami Romakkaniemi ◽

Zubair Maalick ◽

Antti Hellsten ◽

Antti Ruuskanen ◽

Olli Väisänen ◽

...

Keyword(s):

Liquid Water ◽

Cloud Condensation Nuclei ◽

Measurement Data ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Liquid Water Content ◽

Droplet Formation ◽

Cloud Base ◽

Topography Effect ◽

The Hill

Abstract. Long-term in situ measurements of aerosol–cloud interactions are usually performed in measurement stations residing on hills, mountains, or high towers. In such conditions, the surface topography of the surrounding area can affect the measured cloud droplet distributions by increasing turbulence or causing orographic flows and thus the observations might not be representative for a larger scale. The objective of this work is to analyse, how the local topography affects the observations at Puijo measurement station, which is located in the 75 m high Puijo tower, which itself stands on a 150 m high hill. The analysis of the measurement data shows that the observed cloud droplet number concentration mainly depends on the cloud condensation nuclei (CCN) concentration. However, when the wind direction aligns with the direction of the steepest slope of the hill, a clear topography effect is observed. This finding was further analysed by simulating 3-D flow fields around the station and by performing trajectory ensemble modelling of aerosol- and wind-dependent cloud droplet formation. The results showed that in typical conditions, with geostrophic winds of about 10 m s−1, the hill can cause updrafts of up to 1 m s−1 in the air parcels arriving at the station. This is enough to produce in-cloud supersaturations (SSs) higher than typically found at the cloud base of ∼  0.2 %), and thus additional cloud droplets may form inside the cloud. In the observations, this is seen in the form of a bimodal cloud droplet size distribution. The effect is strongest with high winds across the steepest slope of the hill and with low liquid water contents, and its relative importance quickly decreases as these conditions are relaxed. We therefore conclude that, after careful screening for wind speed and liquid water content, the observations at Puijo measurement station can be considered representative for clouds in a boreal environment.

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Precipitation effects of giant cloud condensation nuclei artificially introduced into stratocumulus clouds

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-47-2015 ◽

2015 ◽

Vol 15 (1) ◽

pp. 47-76 ◽

Cited By ~ 1

Author(s):

E. Jung ◽

B. A. Albrecht ◽

H. H. Jonsson ◽

Y.-C. Chen ◽

J. H. Seinfeld ◽

...

Keyword(s):

Liquid Water ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Fold Increase ◽

Liquid Water Content ◽

Cloud Base ◽

Condensation Nuclei ◽

Liquid Water Path ◽

Base Level ◽

Stratocumulus Clouds

Abstract. To study the effect of giant cloud condensation nuclei (GCCN) on precipitation processes in stratocumulus clouds, 1–10 μm diameter salt particles (salt powder) were released from an aircraft while flying near cloud top on 3 August 2011 off the central coast of California. The seeded area was subsequently sampled from the aircraft that was equipped with aerosol, cloud, and precipitation probes and an upward-facing cloud radar. During post-seeding sampling, made 30–60 min after seeding, the mean cloud droplet size increased, the droplet number concentration decreased, and large drop (e.g., diameter larger than 10 μm) concentration increased. Average drizzle rates increased from about 0.05 to 0.20 mm h−1, and liquid water path decreased from about 52 to 43 g m−2. Strong radar returns associated with drizzle were observed on the post-seeding cloud-base level-leg flights and were accompanied by a substantial depletion of the cloud liquid water content. The changes were large enough to suggest that the salt particles with concentrations estimated to be 10−2 to 10−4 cm−3 resulted in a four-fold increase in the cloud base rainfall rate and depletion of the cloud water due to rainout. In contrast, a case is shown where the cloud was already precipitating (on 10 August) and the effect of adding GCCN to the cloud was insignificant.

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Precipitation effects of giant cloud condensation nuclei artificially introduced into stratocumulus clouds

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-5645-2015 ◽

2015 ◽

Vol 15 (10) ◽

pp. 5645-5658 ◽

Cited By ~ 13

Author(s):

E. Jung ◽

B. A. Albrecht ◽

H. H. Jonsson ◽

Y.-C. Chen ◽

J. H. Seinfeld ◽

...

Keyword(s):

Liquid Water ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Fold Increase ◽

Liquid Water Content ◽

Cloud Base ◽

Condensation Nuclei ◽

Liquid Water Path ◽

Base Level ◽

Stratocumulus Clouds

Abstract. To study the effect of giant cloud condensation nuclei (GCCN) on precipitation processes in stratocumulus clouds, 1–10 μm diameter salt particles (salt powder) were released from an aircraft while flying near the cloud top on 3 August 2011 off the central coast of California. The seeded area was subsequently sampled from the aircraft that was equipped with aerosol, cloud, and precipitation probes and an upward-facing cloud radar. During post-seeding sampling, made 30–60 min after seeding, the mean cloud droplet size increased, the droplet number concentration decreased, and large drop (e.g., diameter larger than 10 μm) concentration increased. Average drizzle rates increased from about 0.05 to 0.20 mm h−1, and the liquid water path decreased from about 52 to 43 g m−2. Strong radar returns associated with drizzle were observed on the post-seeding cloud-base level-leg flights and were accompanied by a substantial depletion of the cloud liquid water content. The changes were large enough to suggest that the salt particles with concentrations estimated to be 10−2 to 10-4 cm−3 resulted in a four-fold increase in the cloud-base rainfall rate and depletion of the cloud water due to rainout. In contrast, a case is shown where the cloud was already precipitating (on 10 August) and the effect of adding GCCN to the cloud was insignificant.

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Simulation study on the indirect effect of sulfate on the summer climate over the eastern China monsoon region

Scientific Reports ◽

10.1038/s41598-021-87832-5 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Dongdong Wang ◽

Bin Zhu ◽

Hongbo Wang ◽

Li Sun

Keyword(s):

Radiative Forcing ◽

Asian Summer Monsoon ◽

Cloud Condensation Nuclei ◽

Eastern China ◽

Summer Precipitation ◽

Cloud Droplet ◽

Monsoon Region ◽

Liquid Water Path ◽

Surface Cooling ◽

Community Atmosphere Model

AbstractIn this study, we designed a sensitivity test using the half number concentration of sulfate in the nucleation calculation process to study the aerosol-cloud interaction (ACI) of sulfate on clouds, precipitation, and monsoon intensity in the summer over the eastern China monsoon region (ECMR) with the National Center for Atmospheric Research Community Atmosphere Model version 5. Numerical experiments show that the ACI of sulfate led to an approximately 30% and 34% increase in the cloud condensation nuclei and cloud droplet number concentrations, respectively. Cloud droplet effective radius below 850 hPa decreased by approximately 4% in the southern ECMR, while the total liquid water path increased by 11%. The change in the indirect radiative forcing due to sulfate at the top of the atmosphere in the ECMR during summer was − 3.74 W·m−2. The decreased radiative forcing caused a surface cooling of 0.32 K and atmospheric cooling of approximately 0.3 K, as well as a 0.17 hPa increase in sea level pressure. These changes decreased the thermal difference between the land and sea and the gradient of the sea-land pressure, leading to a weakening in the East Asian summer monsoon (EASM) and a decrease in the total precipitation rate in the southern ECMR. The cloud lifetime effect has a relatively weaker contribution to summer precipitation, which is dominated by convection. The results show that the ACI of sulfate was one possible reason for the weakening of the EASM in the late 1970s.

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Broadening of Modeled Cloud Droplet Spectra Using Bin Microphysics in an Eulerian Spatial Domain

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-18-0055.1 ◽

2018 ◽

Vol 75 (11) ◽

pp. 4005-4030 ◽

Cited By ~ 11

Author(s):

Hugh Morrison ◽

Mikael Witte ◽

George H. Bryan ◽

Jerry Y. Harrington ◽

Zachary J. Lebo

Keyword(s):

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Dynamical Models ◽

Mixing Processes ◽

Numerical Diffusion ◽

Vertical Advection ◽

1D Model ◽

Bin Microphysics ◽

Condensational Growth

Abstract This study investigates droplet size distribution (DSD) characteristics from condensational growth and transport in Eulerian dynamical models with bin microphysics. A hierarchy of modeling frameworks is utilized, including parcel, one-dimensional (1D), and three-dimensional large-eddy simulation (LES). The bin DSDs from the 1D model, which includes only vertical advection and condensational growth, are nearly as broad as those from the LES and in line with observed DSD widths for stratocumulus clouds. These DSDs are much broader than those from Lagrangian microphysical calculations within a parcel framework that serve as a numerical benchmark for the 1D tests. In contrast, the bin-modeled DSDs are similar to the Lagrangian microphysical benchmark for a rising parcel in which Eulerian transport is not considered. These results indicate that numerical diffusion associated with vertical advection is a key contributor to broadening DSDs in the 1D model and LES. This DSD broadening from vertical numerical diffusion is unphysical, in contrast to the physical mixing processes that previous studies have indicated broaden DSDs in real clouds. It is proposed that artificial DSD broadening from vertical numerical diffusion compensates for underrepresented horizontal variability and mixing of different droplet populations in typical LES configurations with bin microphysics, or the neglect of other mechanisms that broaden DSDs such as growth of giant cloud condensation nuclei. These results call into question the ability of Eulerian dynamical models with bin microphysics to investigate the physical mechanisms for DSD broadening, even though they may reasonably simulate overall DSD characteristics.

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Demistify: a large-eddy simulation (LES) and single-column model (SCM) intercomparison of radiation fog

Atmospheric Chemistry and Physics ◽

10.5194/acp-22-319-2022 ◽

2022 ◽

Vol 22 (1) ◽

pp. 319-333

Author(s):

Ian Boutle ◽

Wayne Angevine ◽

Jian-Wen Bao ◽

Thierry Bergot ◽

Ritthik Bhattacharya ◽

...

Keyword(s):

Large Eddy Simulation ◽

Weather Prediction ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Radiation Fog ◽

Eddy Simulation ◽

Cloud Droplet Size Distribution ◽

Large Eddy ◽

Single Column ◽

Les Model

Abstract. An intercomparison between 10 single-column (SCM) and 5 large-eddy simulation (LES) models is presented for a radiation fog case study inspired by the Local and Non-local Fog Experiment (LANFEX) field campaign. Seven of the SCMs represent single-column equivalents of operational numerical weather prediction (NWP) models, whilst three are research-grade SCMs designed for fog simulation, and the LESs are designed to reproduce in the best manner currently possible the underlying physical processes governing fog formation. The LES model results are of variable quality and do not provide a consistent baseline against which to compare the NWP models, particularly under high aerosol or cloud droplet number concentration (CDNC) conditions. The main SCM bias appears to be toward the overdevelopment of fog, i.e. fog which is too thick, although the inter-model variability is large. In reality there is a subtle balance between water lost to the surface and water condensed into fog, and the ability of a model to accurately simulate this process strongly determines the quality of its forecast. Some NWP SCMs do not represent fundamental components of this process (e.g. cloud droplet sedimentation) and therefore are naturally hampered in their ability to deliver accurate simulations. Finally, we show that modelled fog development is as sensitive to the shape of the cloud droplet size distribution, a rarely studied or modified part of the microphysical parameterisation, as it is to the underlying aerosol or CDNC.

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Demistify: an LES and SCM intercomparison of radiation fog

10.5194/acp-2021-832 ◽

2021 ◽

Author(s):

Ian Boutle ◽

Wayne Angevine ◽

Jian-Wen Bao ◽

Thierry Bergot ◽

Ritthik Bhattacharya ◽

...

Keyword(s):

Weather Prediction ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Radiation Fog ◽

Eddy Simulation ◽

Cloud Droplet Size Distribution ◽

Single Column ◽

Research Grade ◽

Model Variability ◽

Les Model

Abstract. An intercomparison between 10 single-column (SCM) and 5 large-eddy simulation (LES) models is presented for a radiation fog case study inspired by the LANFEX field campaign. 7 of the SCMs represent single-column equivalents of operational numerical weather prediction (NWP) models, whilst 3 are research-grade SCMs designed for fog simulation, and the LES are designed to reproduce in the best manner currently possible the underlying physical processes governing fog formation. The LES model results are of variable quality, and do not provide a consistent baseline against which to compare the NWP models, particularly under high aerosol or cloud droplet number (CDNC) conditions. The main SCM bias appears to be toward over-development of fog, i.e. fog which is too thick, although the inter-model variability is large. In reality there is a subtle balance between water lost to the surface and water condensed into fog, and the ability of a model to accurately simulate this process strongly determines the quality of its forecast. Some NWP-SCMs do not represent fundamental components of this process (e.g. cloud droplet sedimentation) and therefore are naturally hampered in their ability to deliver accurate simulations. Finally, we show that modelled fog development is as sensitive to the shape of the cloud droplet size distribution, a rarely studied or modified part of the microphysical parametrization, as it is to the underlying aerosol or CDNC.

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Aerosol indirect effect from turbulence-induced broadening of cloud-droplet size distributions

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1612686113 ◽

2016 ◽

Vol 113 (50) ◽

pp. 14243-14248 ◽

Cited By ~ 44

Author(s):

Kamal Kant Chandrakar ◽

Will Cantrell ◽

Kelken Chang ◽

David Ciochetto ◽

Dennis Niedermeier ◽

...

Keyword(s):

Size Distribution ◽

Droplet Size ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Aerosol Concentration ◽

Droplet Radius ◽

Droplet Growth ◽

Moist Convection ◽

Concentration Changes ◽

Precipitation Formation

The influence of aerosol concentration on the cloud-droplet size distribution is investigated in a laboratory chamber that enables turbulent cloud formation through moist convection. The experiments allow steady-state microphysics to be achieved, with aerosol input balanced by cloud-droplet growth and fallout. As aerosol concentration is increased, the cloud-droplet mean diameter decreases, as expected, but the width of the size distribution also decreases sharply. The aerosol input allows for cloud generation in the limiting regimes of fast microphysics (τc<τt) for high aerosol concentration, and slow microphysics (τc>τt) for low aerosol concentration; here, τc is the phase-relaxation time and τt is the turbulence-correlation time. The increase in the width of the droplet size distribution for the low aerosol limit is consistent with larger variability of supersaturation due to the slow microphysical response. A stochastic differential equation for supersaturation predicts that the standard deviation of the squared droplet radius should increase linearly with a system time scale defined as τs−1=τc−1+τt−1, and the measurements are in excellent agreement with this finding. The result underscores the importance of droplet size dispersion for aerosol indirect effects: increasing aerosol concentration changes the albedo and suppresses precipitation formation not only through reduction of the mean droplet diameter but also by narrowing of the droplet size distribution due to reduced supersaturation fluctuations. Supersaturation fluctuations in the low aerosol/slow microphysics limit are likely of leading importance for precipitation formation.

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Aerosol-landscape-cloud interaction: Signatures of topography effect on cloud droplet formation

10.5194/acp-2016-1015 ◽

2016 ◽

Author(s):

Sami Romakkaniemi ◽

Zubair Maalick ◽

Antti Hellsten ◽

Antti Ruuskanen ◽

Olli Väisänen ◽

...

Keyword(s):

Liquid Water ◽

Measurement Data ◽

Cloud Droplet ◽

Droplet Size Distribution ◽

Liquid Water Content ◽

Droplet Formation ◽

Cloud Base ◽

Topography Effect ◽

Boreal Environment ◽

The Hill

Abstract. Long-term in situ measurements of aerosol-cloud interactions are usually performed in measurement stations residing on hills, mountains, or high towers. In such conditions, the surface topography of the surrounding area can affect the measured cloud droplet distributions by increasing turbulence or causing orographic flows and thus the observations might not be representative for a larger scale. The objective of this work is to analyse, how the local topography affects the observations at Puijo measurement station, which is located in the 75 m high Puijo tower, which itself stands on a 150 m high hill. The analysis of the measurement data shows that the observed cloud droplet number concentration mainly depends on the CCN concentration. However, when the wind direction aligns with the direction of the steepest slope of the hill, a clear topography effect is observed. This finding was further analysed by simulating 3D flow fields around the station and by performing trajectory ensemble modelling of aerosol- and wind-dependent cloud droplet formation. The results showed that in typical conditions, with geostrophic winds of about 10 m s−1, the hill can cause updrafts of up to 1 m s−1 in the air parcels arriving at the station. This is enough to produce in-cloud supersaturations higher than typically found at the cloud base (SS of ~ 0.2 %), and thus additional cloud droplets may form inside the cloud. In the observations, this is seen in the form of a bi-modal cloud droplet size distribution. The effect is strongest with high winds across the steepest slope of the hill and with low liquid water contents, and its relative importance quickly decreases as these conditions are relaxed. We therefore conclude that, after careful screening for wind speed and liquid water content, the observations at Puijo measurement station can be considered representative for clouds in a boreal environment.

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