Opportunistic experiments to constrain aerosol effective radiative forcing

Atmospheric chemistry and physics, Journal Year: 2022, Volume and Issue: 22(1), P. 641 - 674

Published: Jan. 17, 2022

Aerosol-cloud interactions (ACIs) are considered to be the most uncertain driver of present-day radiative forcing due human activities. The nonlinearity cloud-state changes aerosol perturbations make it challenging attribute causality in observed relationships forcing. Using correlations infer can when meteorological variability also drives both and cloud independently. Natural anthropogenic from well-defined sources provide "opportunistic experiments" (also known as natural experiments) investigate ACI cases where may more confidently inferred. These cover a wide range locations spatiotemporal scales, including point such volcanic eruptions or industrial sources, plumes biomass burning forest fires, tracks individual ships shipping corridors. We review different experimental conditions conduct synthesis available satellite datasets field campaigns place these opportunistic experiments on common footing, facilitating new insights clearer understanding key uncertainties Cloud albedo strongly sensitive background conditions. Strong liquid water path increases largely ruled out by averaging across experiments. Opportunistic have significantly improved process-level ACI, but remains unclear how reliably found scaled global level, thus demonstrating need for deeper investigation order improve assessments climate change.

Language: Английский

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Machine learning reveals climate forcing from aerosols is dominated by increased cloud cover

Nature Geoscience, Journal Year: 2022, Volume and Issue: 15(8), P. 609 - 614

Published: Aug. 1, 2022

Language: Английский

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Robust evidence for reversal of the trend in aerosol effective climate forcing

Atmospheric chemistry and physics, Journal Year: 2022, Volume and Issue: 22(18), P. 12221 - 12239

Published: Sept. 21, 2022

Abstract. Anthropogenic aerosols exert a cooling influence that offsets part of the greenhouse gas warming. Due to their short tropospheric lifetime only several days, aerosol forcing responds quickly emissions. Here, we present and discuss evolution since 2000. There are multiple lines evidence allow us robustly conclude anthropogenic effective radiative (ERF) – both aerosol–radiation interactions (ERFari) aerosol–cloud (ERFaci) has become less negative globally, i.e. trend in changed sign from positive. Bottom-up inventories show primary precursor emissions declined most regions world; observations related burden declining trends, particular fine-mode particles make up aerosols; satellite retrievals cloud droplet numbers trends with declines consistent these sign, as do top-of-atmosphere radiation. Climate model results, including revised set is constrained by ocean heat content magnitude for positive relative year 2000 due reduced effects. This reduction leads an acceleration climate change, increase 0.1 0.3 W m−2, 12 % total 2019 compared 1750 according Intergovernmental Panel on Change (IPCC).

Language: Английский

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Physical science research needed to evaluate the viability and risks of marine cloud brightening

Science Advances, Journal Year: 2024, Volume and Issue: 10(12)

Published: March 20, 2024

Marine cloud brightening (MCB) is the deliberate injection of aerosol particles into shallow marine clouds to increase their reflection solar radiation and reduce amount energy absorbed by climate system. From physical science perspective, consensus a broad international group scientists that viability MCB will ultimately depend on whether observations models can robustly assess scale-up local-to-global in today's identify strategies ensure an equitable geographical distribution benefits risks associated with projected regional changes temperature precipitation. To address knowledge gaps required societal implications MCB, we propose substantial targeted program research-field laboratory experiments, monitoring, numerical modeling across range scales.

Language: Английский

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Substantial cooling effect from aerosol-induced increase in tropical marine cloud cover

Nature Geoscience, Journal Year: 2024, Volume and Issue: 17(5), P. 404 - 410

Published: April 11, 2024

Abstract With global warming currently standing at approximately +1.2 °C since pre-industrial times, climate change is a pressing issue. Marine cloud brightening one proposed method to tackle through injecting aerosols into marine clouds enhance their reflectivity and thereby planetary albedo. However, because it unclear how influence clouds, especially cover, both projections the effectiveness of remain uncertain. Here we use satellite observations volcanic eruptions in Hawaii quantify aerosol fingerprint on tropical clouds. We observe large enhancement reflected sunlight, mainly due an aerosol-induced increase cover. This observed strong negative forcing suggests that current level driven by weaker net radiative than previously thought, arising from competing effects greenhouse gases aerosols. implies greater sensitivity Earth’s therefore larger response rising gas concentrations reductions atmospheric air quality measures. our findings also indicate mitigation via plausible most effective humid stable conditions tropics where solar radiation strong.

Language: Английский

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ARMTRAJ: a set of multipurpose trajectory datasets augmenting the Atmospheric Radiation Measurement (ARM) user facility measurements

Earth system science data, Journal Year: 2025, Volume and Issue: 17(1), P. 29 - 42

Published: Jan. 8, 2025

Abstract. Ground-based instruments offer unique capabilities such as detailed atmospheric, thermodynamic, cloud, and aerosol profiling at a high temporal sampling rate. The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) user facility provides comprehensive datasets from key locations around the globe, facilitating long-term characterization process-level understanding clouds, aerosol, aerosol–cloud interactions. However, with other ground-based datasets, fixed (Eulerian) nature these measurements often introduces knowledge gap in relating those observations air-mass hysteresis. Here, we describe ARMTRAJ (https://doi.org/10.5439/2309851, Silber, 2024a; https://doi.org/10.5439/2309849, 2024b; https://doi.org/10.5439/2309850, 2024c; https://doi.org/10.5439/2309848, 2024d), set multipurpose trajectory that helps close this ARM deployments. Each dataset targets different aspect atmospheric research, including analysis surface, planetary boundary layer, distinct liquid-bearing cloud layers, (primary) decks. Trajectories are calculated using Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model informed by European Centre for Medium-Range Weather Forecasts ERA5 reanalysis its highest spatial resolution (0.25°) initialized datasets. include information about coordinates state variables extracted before after site overpass. Ensemble runs generated each initialization enhance consistency, while ensemble variability serves valuable uncertainty metric reported variables. Following description processing structure, demonstrate applications to case study few bulk analyses collected during ARM's Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) field deployment. will soon become near real-time product accompanying new deployments an augmenting ongoing previous deployments, promoting reaching science goals research relying on observations.

Language: Английский

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Constraining the Twomey effect from satellite observations: issues and perspectives

Atmospheric chemistry and physics, Journal Year: 2020, Volume and Issue: 20(23), P. 15079 - 15099

Published: Dec. 4, 2020

Abstract. The Twomey effect describes the radiative forcing associated with a change in cloud albedo due to an increase anthropogenic aerosol emissions. It is driven by perturbation droplet number concentration (ΔNd, ant) liquid-water clouds and currently understood exert cooling on climate. key driver effective aerosol–cloud interactions, but rapid adjustments also contribute. These are essentially responses of fraction liquid water path ΔNd, ant thus scale approximately it. While fundamental physics influence added particles (Nd) well described established theory at particle (micrometres), how this relationship expressed large-scale (hundreds kilometres) perturbation, ant, remains uncertain. discrepancy between process understanding insufficient quantification climate-relevant large caused co-variability updraught velocity sink processes. operate scales order tens metres which only localised observations available no approach yet exists quantify perturbation. Different atmospheric models suggest diverse magnitudes even when applying same emission Thus, observational data needed constrain effect. At global scale, means satellite data. There four uncertainties determining namely (i) cloud-active – condensation nuclei (CCN) concentrations or above base, (ii) Nd, (iii) statistical for inferring sensitivity Nd from (iv) uncertainty CCN concentrations, not easily accessible This review discusses deficiencies current approaches different aspects problem proposes several ways forward: terms CCN, retrievals optical quantities such as depth suffer lack vertical resolution, size hygroscopicity information, non-direct relation aerosols, difficulty it within below clouds, low addition retrieval errors. A future forward can include utilising co-located polarimeter lidar instruments, ideally including high-spectral-resolution capability two wavelengths maximise vertically resolved distribution information content. In operational quantity inaccuracy especially broken-cloud regimes. As Nd-to-CCN sensitivity, issues distributions role processes, empirical assessments specific regimes best solutions. considerations point conclusion that past studies using existing have likely underestimated true and, thus,

Language: Английский

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Albedo susceptibility of northeastern Pacific stratocumulus: the role of covarying meteorological conditions

Atmospheric chemistry and physics, Journal Year: 2022, Volume and Issue: 22(2), P. 861 - 880

Published: Jan. 19, 2022

Abstract. Quantification of the radiative adjustment marine low clouds to aerosol perturbations, regionally and globally, remains largest source uncertainty in assessing current future climate. One important steps towards quantifying role modifying cloud properties is quantify susceptibility albedo liquid water path (LWP) perturbations droplet number concentration (Nd). We use 10 years spaceborne observations from polar-orbiting Aqua satellite Nd over northeast (NE) Pacific stratocumulus (Sc) region. Mutual information analysis reveals a dominating control state (e.g., LWP Nd) on low-cloud susceptibility, relative meteorological states that drive these states. Through LWP–Nd space decomposition susceptibilities, we show clear separation among regimes (brightening or darkening), consistent with previously established mechanisms through which modulates properties. These include (i) thin non-precipitating (LWP < 55 g m−2) exhibit brightening (occurring 37 % time), corresponding Twomey effect; (ii) thicker clouds, entrainment-driven negative adjustments manifest as darkening regime (36 time); (iii) another (22 time) consisting mostly precipitating precipitation-suppression positive adjustments. Overall, find an annual-mean regional potential 20.8±2.68 W m−2 ln(Nd)−1, despite overall for stratocumulus, owing high occurrence Twomey–brightening regime. Over NE Pacific, seasonal covariabilities factors related large-scale circulation are found play grouping conditions favorable each When considering covarying conditions, our results indicate northeastern strongest occur most frequently within shallow boundary layers cool ocean surface stable atmosphere dry free troposphere above. Clouds associated deep atmospheric instability not strong warm enough produce frequent precipitation. Cloud warm-rain suppression preferably either under unstable humid free-tropospheric co-occur surface.

Language: Английский

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Observational evidence of strong forcing from aerosol effect on low cloud coverage

Science Advances, Journal Year: 2023, Volume and Issue: 9(45)

Published: Nov. 8, 2023

Aerosols cool Earth's climate indirectly by increasing low cloud brightness and their coverage (Cf), constituting the aerosol indirect forcing (AIF). The partially offsets greenhouse warming positively correlates with sensitivity. However, it remains highly uncertain. Here, we show direct observational evidence for strong from Cf adjustment to increased aerosols weak liquid water path adjustment. We estimate that drives between 52% 300% of additional Twomey effect over ocean a total AIF -1.1 ± 0.8 W m-2. follows power law as function background droplet number concentration, Nd. It thus depends on time location is stronger when Nd low. only increases substantially clouds start drizzle, suggesting role aerosol-precipitation interactions. Our findings highlight key process reducing uncertainty future projections.

Language: Английский

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Diurnal Patterns in the Observed Cloud Liquid Water Path Response to Droplet Number Perturbations

Geophysical Research Letters, Journal Year: 2024, Volume and Issue: 51(4)

Published: Feb. 10, 2024

Abstract A key uncertainty in Aerosol‐cloud interactions is the cloud liquid water path (LWP) response to increased aerosols ( λ ). LWP can either increase due precipitation suppression or decrease entrainment‐drying. Previous research suggests that dominates thick clouds, while entrainment‐drying prevails thin clouds. The time scales of two competing effects are vastly different, requiring temporally resolved observations. We analyze 3‐day Lagrangian trajectories stratocumulus clouds over southeast Pacific using 2019–2021 geostationary data. find with a exceeding 200 g m −2 exhibit positive response, lower show negative response. observe significant diurnal cycle , indicating more strongly daytime adjustment driven by In contrast, at night, occasionally fully counteract mechanism. Overall, appears weaker than previously suggested studies do not account for cycle.

Language: Английский

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