Aerosol effects on clouds are concealed by natural cloud heterogeneity and satellite retrieval errors

Nature Communications, Journal Year: 2022, Volume and Issue: 13(1)

Published: Nov. 30, 2022

One major source of uncertainty in the cloud-mediated aerosol forcing arises from magnitude cloud liquid water path (LWP) adjustment to aerosol-cloud interactions, which is poorly constrained by observations. Many recent satellite-based studies have observed a decreasing LWP as function droplet number concentration (CDNC) dominating behavior. Estimating response CDNC changes complex task since various confounding factors need be isolated. However, an important aspect has not been sufficiently considered: propagation natural spatial variability and errors satellite retrievals optical depth effective radius estimates LWP. Here we use simulated measurements demonstrate that, because this propagation, even positive likely misinterpreted negative. This biasing effect therefore leads underestimate aerosol-cloud-climate cooling must properly considered future studies.

Language: Английский

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Distinct regional meteorological influences on low-cloud albedo susceptibility over global marine stratocumulus regions

Atmospheric chemistry and physics, Journal Year: 2023, Volume and Issue: 23(2), P. 1073 - 1090

Published: Jan. 20, 2023

Abstract. Marine stratocumuli cool the Earth effectively due to their high reflectance of incoming solar radiation and persistent occurrence. The susceptibility cloud albedo droplet number concentration perturbations depends strongly on large-scale meteorological conditions. Studies focused dependence adjustments often overlook covariability among factors geographical temporal variability. We use 8 years satellite observations sorted by day location show global distribution marine low-cloud susceptibility. find an overall brightening potential for most warm clouds, which is more pronounced over subtropical coastal regions. A weak darkening in annual mean evident remote SE Pacific Atlantic. that fields from ERA5 reanalysis data, including lower-tropospheric stability, free-tropospheric relative humidity, sea surface temperature, boundary layer depth, have distinct covariabilities each eastern ocean basins where prevail. This leads a markedly different cycle basin. Moreover, we basin-specific regional relationships between key susceptibilities are absent analysis. Our results stress importance considering distinctiveness when scaling up local-to-global response aerosol perturbations.

Language: Английский

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Stratocumulus adjustments to aerosol perturbations disentangled with a causal approach

npj Climate and Atmospheric Science, Journal Year: 2023, Volume and Issue: 6(1)

Published: Aug. 29, 2023

Abstract A large fraction of the uncertainty around future global warming is due to cooling effect aerosol-liquid cloud interactions, and in particular elusive sign liquid water path (LWP) adjustments aerosol perturbations. To quantify this adjustment, we propose a causal approach that combines physical knowledge form graph with geostationary satellite observations stratocumulus clouds. This allows us remove confounding influences from large-scale meteorology disentangle counteracting processes (cloud-top entrainment enhancement precipitation suppression perturbations) on different timescales. results weak LWP are time-dependent (first positive then negative) meteorological regime-dependent. More importantly, reveals failing account for covariations droplet sizes depth, which are, respectively, mediator confounder influences, leads an overly negative aerosol-induced response. would result underestimation influence aerosol-cloud interactions.

Language: Английский

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Microphysical, macrophysical, and radiative responses of subtropical marine clouds to aerosol injections

Atmospheric chemistry and physics, Journal Year: 2023, Volume and Issue: 23(2), P. 1345 - 1368

Published: Jan. 25, 2023

Abstract. Ship tracks in subtropical marine low clouds are simulated and investigated using large-eddy simulations. Five variants of a shallow stratocumulus-topped boundary layer (MBL) chosen to span range background aerosol concentrations variations free-tropospheric moisture. Idealized time-invariant meteorological forcings approximately steady-state constitute the conditions. We investigate processes controlling cloud microphysical, macrophysical, radiative responses injections. For analysis, we use novel methods decompose liquid water path (LWP) adjustment into changes boundary-layer properties effect (CRE) contributions from macro- microphysics. The key results that (a) cloud-top entrainment rate increases all cases, with stronger for thicker than thinner clouds; (b) drying warming induced by increased is offset differing degrees corresponding surface fluxes, precipitation, radiation; (c) MBL turbulence responds caused perturbation, this significantly affects macrophysics; (d) across 2 d simulation, were brightened cases. In pristine MBL, significant drizzle suppression injections not only greater retention but also intensification, leading increase amount. case, Twomey brightening strongly augmented an thickness cover. addition, reduction loss through coalescence scavenging more offsets dilution. This interplay precludes estimation lifetime perturbation. combined microphysics lead 10–100 times effective these cases relative those non-precipitating moderate polluted MBLs, enhancement makes drier, warmer, stratified, decrease thickness. LWP response greatest fraction moderately moist free troposphere. finding differs previous studies found larger drier troposphere, it initially clouds, so offsetting effects weaker. injected MBLs estimated be 2–3 d, which much longer estimates typical ship track lifetimes satellite images.

Language: Английский

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Environmental and Internal Controls on Lagrangian Transitions from Closed Cell Mesoscale Cellular Convection over Subtropical Oceans

Journal of the Atmospheric Sciences, Journal Year: 2021, Volume and Issue: 78(8), P. 2367 - 2383

Published: June 9, 2021

Abstract Classifications of mesoscale cellular convection (MCC) for marine boundary layer clouds are produced using a supervised neural network algorithm applied to MODIS daytime liquid water path data. The classifier, used in prior studies, distinguishes closed, open, and but disorganized MCC. This work uses trajectories four eastern subtropical ocean basins compare meteorological variables the structures layers that begin as closed cells evolve into either open or remain over one afternoon–afternoon cycle. Results show contrasts between trajectory sets: Trajectories MCC more frequently observed nearer coasts, whereas break farther offshore. frequency at which transition is seasonally invariant. fraction stay varies throughout year opposition those cells, so their annual cycles 180° out phase. cell austral spring boreal summer when trade inversion stronger. closed–disorganized breakup associated with weaker subsidence, inversion, drier free troposphere, enhanced nighttime deepening, consistent warming–drying mechanism. closed–open occurs conditions similar closed–closed trajectories. However, transition, exhibit stronger surface winds lower cloud droplet concentrations rain heavily overnight. suggest multiple, independent mechanisms drive changes amount morphology.

Language: Английский

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Objectively combining climate sensitivity evidence

Climate Dynamics, Journal Year: 2022, Volume and Issue: 60(9-10), P. 3139 - 3165

Published: Sept. 19, 2022

Abstract Recent assessments of climate sensitivity per doubling atmospheric CO 2 concentration have combined likelihoods derived from multiple lines evidence. These were very influential in the Intergovernmental Panel on Climate Change Sixth Assessment Report (AR6) assessment equilibrium sensitivity, likely range lower limit which was raised to 2.5 °C (from 1.5 previously). This study evaluates methodology and results a particularly that evidence, Sherwood et al. (Rev Geophys 58(4):e2019RG000678, 2020). That used subjective Bayesian statistical method, with an investigator-selected prior distribution. estimates using Objective method computed, mathematical priors, since methods may produce uncertainty ranges poorly match confidence intervals. Identical model equations and, initially, identical input values those are used. corrects al.'s likelihood estimation, producing three agree closely each other, but differ they derived. Finally, selection is revisited, where appropriate adopting based more recent evidence or otherwise appear better justified. The resulting long-term much constrained (median 2.16 °C, 17–83% 1.75–2.7 5–95% 1.55–3.2 °C) than AR6 (central value 3 2.0–5.0 °C). assumptions employed implies remains difficult ascertain, between quite plausible.

Language: Английский

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The Radiative and Cloud Responses to Sea Salt Aerosol Engineering in GFDL Models

Geophysical Research Letters, Journal Year: 2023, Volume and Issue: 50(2)

Published: Jan. 18, 2023

Abstract Marine cloud brightening is a proposal to counteract global warming by increasing sea salt aerosol emissions. In theory, this increases the droplet number concentration of subtropical marine stratocumulus decks, brightness and longevity. However, theoretical progression remains uncertain in coupled climate models, especially response liquid water path fraction seeding. We use GFDL CM4 model simulate following published G4sea‐salt protocol, which emissions are uniformly increased over 30 S–30 N addition standard forcings from SSP2‐4.5 future scenario. The perturbed radiative responses temporally stable though spatially heterogeneous, direct scattering added predominates changes reflectance. fact, feedbacks simulation lead net warming, rather than cooling, clouds.

Language: Английский

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Global observations of aerosol indirect effects from marine liquid clouds

Atmospheric chemistry and physics, Journal Year: 2023, Volume and Issue: 23(20), P. 13125 - 13141

Published: Oct. 18, 2023

Abstract. Interactions between aerosols and liquid clouds are one of the largest sources uncertainty in historical radiative forcing climate. One widely shared goal to reduce this is decompose anomalies arising from aerosol–cloud interactions into components associated with changes cloud-droplet number concentration (Twomey effect), liquid-water-path adjustments, cloud-fraction adjustments. However, there has not been a quantitative foundation for simultaneously estimating these global satellite observations. Here we present method assessing shortwave flux Twomey effect cloud adjustments over ocean 55∘ S N. We find that larger aerosol concentrations widespread brightening effect, positive adjustment decreasing water path subtropical stratocumulus regions, negative increasing fraction subtropics midlatitudes. The total have contributed −0.77 ± 0.25 −1.02 0.43 W m−2, respectively, effective since 1850 domain (95 % confidence). Our findings suggest make contribution than commonly believed.

Language: Английский

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Cloud water adjustments to aerosol perturbations are buffered by solar heating in non-precipitating marine stratocumuli

Atmospheric chemistry and physics, Journal Year: 2024, Volume and Issue: 24(18), P. 10425 - 10440

Published: Sept. 19, 2024

Abstract. Marine low-level clouds are key to the Earth's energy budget due their expansive coverage over global oceans and high reflectance of incoming solar radiation. Their responses anthropogenic aerosol perturbations remain largest source uncertainty in estimating radiative forcing climate. A major challenge is quantification cloud water response perturbations. In particular, presence feedbacks through microphysical, dynamical, thermodynamical pathways at various spatial temporal scales could augment or weaken response. Central this problem evolution adjustment, governed by entangled feedback mechanisms. We apply an innovative conditional Monte Carlo subsampling approach a large ensemble diurnal large-eddy simulation non-precipitating marine stratocumulus study role heating governing relationship between droplet number water. find persistent negative trend night, confirming that microphysically enhanced cloud-top entrainment. After sunrise, appears buffered converges ∼-0.2 late afternoon. This buffering effect attributed strong dependence cloud-layer shortwave absorption on liquid path. These cycle characteristics further demonstrate tight connection brightening potential which has implications for impact timing advertent

Language: Английский

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Daytime variation in the aerosol indirect effect for warm marine boundary layer clouds in the eastern North Atlantic

Atmospheric chemistry and physics, Journal Year: 2024, Volume and Issue: 24(5), P. 2913 - 2935

Published: March 6, 2024

Abstract. Warm boundary layer clouds in the eastern North Atlantic region exhibit significant diurnal variations cloud properties. However, cycle of aerosol indirect effect (AIE) for these remains poorly understood. This study takes advantage recent advancements spatial resolution geostationary satellites to explore daytime variation AIE by estimating susceptibilities changes droplet number concentration (Nd). Cloud retrievals month July over 4 years (2018–2021) from Spinning Enhanced Visible and Infrared Imager (SEVIRI) on Meteosat-11 this are analyzed. Our results reveal a “U-shaped” liquid water path (LWP), albedo, fraction. Clouds found be more susceptible Nd perturbations at noon less morning evening. The magnitude sign depend heavily state defined LWP precipitation conditions. Non-precipitating thin account 44 % all warm July, they contribute most observed variation. thick least frequent (10 %), negative albedo compared clouds. Precipitating dominant (46 but their show minimal throughout day. We find evidence that non-precipitating is influenced combination transition between “lagged” responses perturbations. fraction susceptibility can attributed morphology (e.g., overcast or broken). dissipation development do not adequately explain susceptibilities. Additionally, primarily driven intensity response rather than frequency occurrence states. imply polar-orbiting with an overpass time 13:30 LT underestimate mean values susceptibility, as observe daily minima region.

Language: Английский

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