An underestimated negative cloud feedback from cloud lifetime changes

Nature Climate Change, Journal Year: 2021, Volume and Issue: 11(6), P. 508 - 513

Published: June 1, 2021

Language: Английский

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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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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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Influences of Recent Particle Formation on Southern Ocean Aerosol Variability and Low Cloud Properties

Journal of Geophysical Research Atmospheres, Journal Year: 2021, Volume and Issue: 126(8)

Published: March 26, 2021

Abstract Controls on pristine aerosol over the Southern Ocean (SO) are critical for constraining strength of global indirect forcing. Observations summertime SO clouds and aerosols in synoptically varied conditions during 2018 SOCRATES aircraft campaign reveal novel mechanisms influencing aerosol‐cloud interactions. The free troposphere (3–6 km) is characterized by widespread, frequent new particle formation events contributing to much larger concentrations (≥1,000 mg −1 ) condensation nuclei (diameters > 0.01 μm) than typical sub‐tropical regions. Synoptic‐scale uplift warm conveyor belts sub‐polar vortices lifts marine biogenic sulfur‐containing gases free‐tropospheric environments favorable generating Aitken‐mode particles (0.01–0.1 μm). Free‐tropospheric Aitken subside into boundary layer, where they grow size dominate sulfur‐based cloud (CCN) driving droplet number ( N d ∼ 60–100 cm −3 ). Evidence presented a hypothesized ‐ buffering mechanism which maintains persistently high against precipitation removal through CCN replenishment from activation growth layer particles. Nudged hindcasts Community Atmosphere Model (CAM6) found underpredict accumulation mode , impacting brightness interactions indicating incomplete representations associated with ocean biology.

Language: Английский

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Large uncertainty in future warming due to aerosol forcing

Nature Climate Change, Journal Year: 2022, Volume and Issue: 12(12), P. 1111 - 1113

Published: Nov. 14, 2022

Language: Английский

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Assessing effective radiative forcing from aerosol–cloud interactions over the global ocean

Proceedings of the National Academy of Sciences, Journal Year: 2022, Volume and Issue: 119(46)

Published: Nov. 7, 2022

How clouds respond to anthropogenic sulfate aerosols is one of the largest sources uncertainty in radiative forcing climate over industrial era. This limits our ability predict equilibrium sensitivity (ECS)-the global warming following a doubling atmospheric CO2. Here, we use satellite observations quantify relationships between and low-level while carefully controlling for meteorology. We then combine with estimates change concentration since about 1850 constrain associated forcing. estimate that cloud-mediated from [Formula: see text] W m-2 ocean (95% confidence). constraint implies ECS likely 2.9 4.5 K (66% Our results indicate aerosol less uncertain probably larger than ranges proposed by recent assessments.

Language: Английский

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The impact of sampling strategy on the cloud droplet number concentration estimated from satellite data

Atmospheric measurement techniques, Journal Year: 2022, Volume and Issue: 15(12), P. 3875 - 3892

Published: July 1, 2022

Abstract. Cloud droplet number concentration (Nd) is of central importance to observation-based estimates aerosol indirect effects, being used quantify both the cloud sensitivity and base state cloud. However, derivation Nd from satellite data depends on a assumptions about accuracy retrievals properties which it derived, making prone systematic biases. A sampling strategies have been proposed address these biases by selecting most accurate in data. This work compares impact retrieved Nd, using selection situ measurements. In stratocumulus regions, MODIS retrieval able achieve high precision (r2 0.5–0.8). lower other regimes but can be increased appropriate choices. Although significant effects climatology, produces only 20 % variation implied radiative forcing aerosol–cloud interactions, with choice proxy driving overall uncertainty. The results are summarised into recommendations for products sampling.

Language: Английский

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Iodine oxoacids enhance nucleation of sulfuric acid particles in the atmosphere

Science, Journal Year: 2023, Volume and Issue: 382(6676), P. 1308 - 1314

Published: Dec. 14, 2023

The main nucleating vapor in the atmosphere is thought to be sulfuric acid (H2SO4), stabilized by ammonia (NH3). However, marine and polar regions, NH3 generally low, H2SO4 frequently found together with iodine oxoacids [HIOx, i.e., iodic (HIO3) iodous (HIO2)]. In experiments performed CERN CLOUD (Cosmics Leaving OUtdoor Droplets) chamber, we investigated interplay of HIOx during atmospheric particle nucleation. We that greatly enhances H2SO4(-NH3) nucleation through two different interactions. First, HIO3 strongly binds charged clusters so they drive synergistically. Second, HIO2 substitutes for NH3, forming bound H2SO4-HIO2 acid-base pairs molecular clusters. Global observations imply enhancing rates 10- 10,000-fold regions.

Language: Английский

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Southern Ocean Cloud Properties Derived From CAPRICORN and MARCUS Data

Journal of Geophysical Research Atmospheres, Journal Year: 2020, Volume and Issue: 126(4)

Published: Dec. 30, 2020

Abstract The properties of Southern Ocean (SO) liquid phase non precipitating clouds (hereafter clouds) are examined using shipborne data collected during the Measurements Aerosols, Radiation and Clouds over Aerosols Precipitation atmospheric Composition Over SoutheRN ocean I II campaigns that took place south Australia Autumn 2016 Summer 2017–2018. Cloud derived from W‐band radars, lidars, microwave radiometers an optimal estimation algorithm. SO tended to have larger water paths (LWP, 115 ± 117 g m −2 ), smaller effective radii ( r e , 8.7 3 μm), higher number concentrations N d 90 107 cm −3 ) than typical values eastern basin stratocumulus. demonstrated a tendency for LWP increase with presumably due precipitation suppression up approximately 100 when mean decreased increasing . Due optical depth, cloud albedos were less susceptible changes in compared subtropical highest latitude datasets, observed along near Antarctic coast, presented distinctly bimodal character. One mode had marine further north. other occurred aerosol environment characterized by high condensation nuclei elevated sulfate without obvious continental markers. These regions suggesting sensitivity seasonal biogenic production SO.

Language: Английский

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The value of remote marine aerosol measurements for constraining radiative forcing uncertainty

Atmospheric chemistry and physics, Journal Year: 2020, Volume and Issue: 20(16), P. 10063 - 10072

Published: Aug. 28, 2020

Abstract. Aerosol measurements over the Southern Ocean are used to constrain aerosol–cloud interaction radiative forcing (RFaci) uncertainty in a global climate model. Forcing is quantified using 1 million model variants that sample nearly 30 parameters. Measurements of cloud condensation nuclei and other aerosol properties from an Antarctic circumnavigation expedition strongly natural emissions: default sea spray emissions need be increased by around factor 3 consistent with measurements. reduced 7 % this set several hundred measurements, which comparable 8 reduction achieved diverse extensive 9000 predominantly Northern Hemisphere When combined, RFaci 21 %, strongest 20 values ruled out as implausible. In combined constraint, observationally plausible 0.17 W m−2 weaker (less negative) 95 credible ranging −2.51 −1.17 (standard deviation −2.18 −1.46 m−2). The measurement datasets complementary because they different processes. These results highlight value remote marine

Language: Английский

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