New understanding and quantification of the regime dependence of aerosol‐cloud interaction for studying aerosol indirect effects

Chen, J.; Liu, Yangang; Zhang, Minghua; Peng, Yiran

doi:10.1002/2016gl067683

Cited by 75 publications

(113 citation statements)

References 52 publications

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“…Some in situ measurements (Lu et al, ; Zhao et al, ) show unclear signals for the relative dispersion, while many (Lu et al, , ; Miles et al, ; Pawlowska et al, ; Wang et al, ) show an increase in relative dispersion with decrease in number concentration, consistent with the findings presented here. Recent studies by Chen et al, (, , ) suggest that our flight segments could be in an updraft limited regime, and the relative dispersion should depend on the aerosol concentration. Turbulent fluctuations may lead to considerable variability in droplet number concentration thereby increasing the spectral width of the droplet size distribution, consistent with the systems theory approach by (Liu & Hallett, ; Liu et al, ).…”

Section: Discussionmentioning

confidence: 94%

Search for Microphysical Signatures of Stochastic Condensation in Marine Boundary Layer Clouds Using Airborne Digital Holography

et al. 2019

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Droplet growth due to stochastic condensation has been considered as one of the mechanisms to cause broadening of cloud droplet size distributions and jump the bottleneck between droplet growth due to diffusion and collision‐coalescence. Digital in‐line holography is used to measure variations in droplet number concentration and droplet size in marine boundary layer clouds. Distributions of phase relaxation times are quite broad for some clouds. Turbulence correlation times are estimated, and the comparison of these with phase relaxation times suggests that clouds exist in both fast and slow microphysical regimes. Presumed signatures of stochastic condensation, such as increasing relative size dispersion and increasing droplet size with decreasing number density, are observed.

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Section: Discussionmentioning

confidence: 94%

Search for Microphysical Signatures of Stochastic Condensation in Marine Boundary Layer Clouds Using Airborne Digital Holography

et al. 2019

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“…Like N c and LWC, r e exhibits a weaker dependence on aerosol concentration when aerosol concentration is high. These nonlinear relationships reflect the regime dependence of aerosol activation into droplets (Chen et al, 2016;Reutter et al, 2009) and other interactions to be detailed later. Similar nonlinear behaviors have been reported in previous studies.…”

Section: Event-mean Fog Propertiesmentioning

confidence: 88%

“…Note that r e is actually the mean‐volume radius as the monodisperse droplet size distribution is assumed in calculation of r e from LWC and N c . The neglect of the dispersion effect may overestimate or underestimate the change in r e depending on the specific aerosol‐fog interaction regimes (Chen et al, ; Liu & Daum, ). Similar differences exist between the measurements conducted over NCP and Ontario, Canada.…”

Section: Aerosol Effects On Fog Propertiesmentioning

confidence: 99%

Impacts of Anthropogenic Aerosols on Fog in North China Plain

et al. 2019

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Fog poses a severe environmental problem in the North China Plain, China, which has been witnessing increases in anthropogenic emission since the early 1980s. This work first uses the WRF/Chem model coupled with the local anthropogenic emissions to simulate and evaluate a severe fog event occurring in North China Plain. Comparison of the simulations against observations shows that WRF/Chem well reproduces the general features of temporal evolution of PM2.5 mass concentration, fog spatial distribution, visibility, and vertical profiles of temperature, water vapor content, and relative humidity in the planetary boundary layer throughout the whole period of the fog event. Sensitivity studies are then performed with five different levels of anthropogenic emission as model inputs to systematically examine the comprehensive impacts of aerosols on fog microphysical, macrophysical, radiative, and dynamical properties. The results show that as aerosol concentration increases, fog droplet number concentration and liquid water content all increase nonlinearly; but effective radius decreases. Macrophysical properties (fog fraction, fog duration, fog height, and liquid water path) also increase nonlinearly with increasing aerosol concentration, with rates of changes smaller than microphysical properties. Further analysis reveals distinct aerosol effects on thermodynamic and dynamical conditions during different stages of fog evolution: increasing aerosols invigorate fog formation and development by enhancing longwave‐induced instability, fog droplet condensation accompanying latent heat release, and thus turbulence, but delay fog dissipation by reducing surface solar radiation, surface sensible, and latent heat fluxes, and thus suppressing turbulence during the dissipation stage.

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“…In this context, the results presented here certainly provide support for similar stochastic differential equation approaches for cloud microphysics (9,20,28) and perhaps even for macroscopic cloud properties (36). It will be intriguing to investigate exactly how the current turbulence-induced aerosol effect relates to that observed in closed parcel studies that consider wide ranges of aerosol concentrations (37,38).…”

Section: Atmospheric Implicationsmentioning

confidence: 99%

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

Chandrakar

Cantrell

Chang

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

120

215

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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 < τ t ) for high aerosol concentration, and slow microphysics (τc > τ t ) for low aerosol concentration; here, τc is the phase-relaxation time and τ t 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 τ, 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.aerosol indirect effect | cloud-droplet size distribution | cloud-turbulence interactions T he optical properties of warm clouds depend on the droplet size distribution and its moments such as number density and effective radius, which, in turn, are influenced by the aerosol particles that act as nuclei for the formation of cloud droplets (1, 2). Thus, aerosol indirect effects are considered among the largest uncertainties in climate response to changes in radiative forcing (3). This work addresses how the aerosol number concentration affects the cloud-droplet size distribution in a turbulent environment, which is relevant to both the aerosol first and second indirect effects (albedo and lifetime effects). The lifetime effect links the development of precipitation, and thus cloud lifetime, to aerosol number concentration. The logic is that a higher aerosol concentration leads to smaller cloud droplets and narrower size distributions, and therefore suppression of the collision and coalescence of droplets, thereby increasing cloud lifetime and maintaining higher cloud liquid water content (4-7). The microphysical details of the transition from condensation growth to collision growth are not fully understood, however, and it is fair to say that the underlying mechanism of the second indirect effect is still a matter of active research (2, 8). Initiation of precipitation in warm clouds ...

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New understanding and quantification of the regime dependence of aerosol‐cloud interaction for studying aerosol indirect effects

Cited by 75 publications

References 52 publications

Search for Microphysical Signatures of Stochastic Condensation in Marine Boundary Layer Clouds Using Airborne Digital Holography

Search for Microphysical Signatures of Stochastic Condensation in Marine Boundary Layer Clouds Using Airborne Digital Holography

Impacts of Anthropogenic Aerosols on Fog in North China Plain

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

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