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

---

General circulation models simulate negative liquid water path–droplet number correlations, but anthropogenic aerosols still increase simulated liquid water path

Atmospheric chemistry and physics, Journal Year: 2024, Volume and Issue: 24(12), P. 7331 - 7345

Published: June 27, 2024

Abstract. General circulation models' (GCMs) estimates of the liquid water path adjustment to anthropogenic aerosol emissions differ in sign from other lines evidence. This reduces confidence effective radiative forcing climate by aerosol–cloud interactions (ERFaci). The discrepancy is thought stem part GCMs' inability represent turbulence–microphysics cloud-top entrainment, a mechanism that leads reduction response an increase aerosols. In real atmosphere, enhanced entrainment be dominant for path, weakening overall ERFaci. We show latest generation GCMs includes models produce negative correlation between present-day cloud droplet number and key piece observational evidence supporting aerosols one earlier-generation could not reproduce. However, even with this correlation, preindustrial values still simulated due parameterized precipitation suppression mechanism. adds correlations are necessarily causal. investigate sources confounding explain noncausal number. These results reminder assessments parameters based on multiple must carefully consider complementary strengths different when disagree.

Language: Английский

---

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

---

Process-evaluation of forest aerosol-cloud-climate feedback shows clear evidence from observations and large uncertainty in models

Nature Communications, Journal Year: 2024, Volume and Issue: 15(1)

Published: Feb. 7, 2024

Abstract Natural aerosol feedbacks are expected to become more important in the future, as anthropogenic emissions decrease due air quality policy. One such feedback is initiated by increase biogenic volatile organic compound (BVOC) with higher temperatures, leading secondary (SOA) production and a cooling of surface via impacts on cloud radiative properties. Motivated considerable spread strength Earth System Models (ESMs), we here use two long-term observational datasets from boreal tropical forests, together satellite data, for process-based evaluation BVOC-aerosol-cloud four ESMs. The model shows that weakest modelled estimates can likely be excluded, but highlights compensating errors making it difficult draw conclusions strongest estimates. Overall, method evaluating along process chains promise pin-pointing sources uncertainty constraining feedbacks.

Language: Английский

---

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

---

Constraining effects of aerosol-cloud interaction by accounting for coupling between cloud and land surface

Science Advances, Journal Year: 2024, Volume and Issue: 10(21)

Published: May 23, 2024

Aerosol-cloud interactions (ACIs) are vital for regulating Earth’s climate by influencing energy and water cycles. Yet, effects of ACI bear large uncertainties, evidenced systematic discrepancies between observed modeled estimates. This study quantifies a major bias in determinations, stemming from conventional surface or space measurements that fail to capture aerosol at the cloud level unless is coupled with land surface. We introduce an advanced approach determine radiative forcing accounting cloud-surface coupling. By integrating field observations, satellite data, model simulations, this reveals drastic alteration vertical transport caused In regimes, aerosols enhance droplet number concentration across boundary layer more homogeneously than decoupled conditions, under which free atmosphere predominantly affect properties, leading marked cooling effects. Our findings spotlight coupling as key factor quantification, hinting potential underassessments traditional

Language: Английский

---

Frontiers in Satellite‐Based Estimates of Cloud‐Mediated Aerosol Forcing

Reviews of Geophysics, Journal Year: 2023, Volume and Issue: 61(4)

Published: Oct. 18, 2023

Abstract Atmospheric aerosols affect the Earth's climate in many ways, including acting as seeds on which cloud droplets form. Since a large fraction of these particles is anthropogenic, clouds' microphysical and radiative characteristics are influenced by human activity global scale leading to important climatic effects. The respective change energy budget at top atmosphere defined effective forcing due aerosol‐cloud interaction (ERF aci ). It estimated that ERF offsets presently nearly 1/4 greenhouse‐induced warming, but uncertainty within factor two. A common method calculate multiplication susceptibility effect changes anthropogenic aerosol concentration. This has be done integrating it over all regimes. Here we review various methods estimation. Global measurements require satellites' coverage. challenge quantifying amounts cloudy atmospheres met with rapid development novel methodologies reviewed here. can retrieved from space based their optical properties, polarization. concentrations serve drop condensation nuclei also impact satellite‐retrieved number concentrations. These observations critical for reducing calculated models (GCMs), further required allow GCMs properly simulate benefit observables.

Language: Английский

---

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

---

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

---

Impacts of Mesoscale Cloud Organization on Aerosol‐Induced Cloud Water Adjustment and Cloud Brightness

Geophysical Research Letters, Journal Year: 2023, Volume and Issue: 50(13)

Published: July 6, 2023

Abstract The role of mesoscale cellular convection (MCC) in regulating aerosol‐induced cloud brightness remains unaddressed. Using 7 years satellite‐based observations water adjustment to perturbations for closed MCCs across different sizes (8, 16, 32, and 64 km) over the North Atlantic Ocean, we show that MCC cell‐size plays a nontrivial via adjustment. In cells are primarily non‐precipitating, small‐scale can be 10 times more negative than large‐scale MCCs, consistent with stronger evaporation top entrainment. Consequently, response is significantly MCCs. We also find notable intra‐cell co‐variability between liquid path (LWP) drop concentration ( N d ) within varies cell size. Erroneously considering such as LWP lead significant positive bias, especially small scale

Language: Английский

---