One-third of Southern Ocean productivity is supported by dust deposition

Nature, Journal Year: 2024, Volume and Issue: 629(8012), P. 603 - 608

Published: May 15, 2024

Language: Английский

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Clouds Are Crucial to Capture Antarctic Sea Ice Variability

Geophysical Research Letters, Journal Year: 2025, Volume and Issue: 52(3)

Published: Feb. 4, 2025

Abstract Models from the Coupled Model Intercomparison Project phase 6 (CMIP6) typically struggle to reproduce observed Antarctic sea ice trends, a bias that is substantially alleviated when constraining winds. We use wind‐nudged simulations two CMIP models investigate influence of clouds on area (SIA). find nudging model winds in coupled toward reanalysis, addition improving SIA variability, crucial realistic anomalies cloud radiative effect (CRE) and cover. Biases variability properties at edge—characterized by CRE anomalies—help explain remaining discrepancies between simulated SIA; 1 anomaly corresponds negative 0.43 anomaly. Finally, we most CMIP6 show positive trends biases, which should contribute enhanced decline, long‐standing models.

Language: Английский

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Using Machine Learning to Generate a GISS ModelE Calibrated Physics Ensemble (CPE)

Journal of Advances in Modeling Earth Systems, Journal Year: 2025, Volume and Issue: 17(4)

Published: April 1, 2025

Abstract A neural network (NN) surrogate of the NASA GISS ModelE atmosphere (version E3) is trained on a perturbed parameter ensemble (PPE) spanning 45 physics parameters and 36 outputs. The NN leveraged in Markov Chain Monte Carlo (MCMC) Bayesian inference framework to generate second posterior constrained coined “calibrated ensemble,” or CPE. CPE members are characterized by diverse combinations are, definition, close top‐of‐atmosphere radiative balance, must broadly agree with numerous hydrologic, energy cycle forcing metrics simultaneously. Global observations cloud, environment, radiation properties (provided global satellite products) crucial for generation. explicitly accounts discrepancies (or biases) products during We demonstrate that product strongly impact calibration important model settings (e.g., convective plume entrainment rates; fall speed cloud ice). Structural improvements new E3 retained across stratocumulus simulation). Notably, improved simulation shallow cumulus Amazon rainfall while not degrading fields, an upgrade neither default nor Latin Hypercube searching achieved. Analyses initial PPE suggested several were unimportant output variation. However, many “unimportant” needed generation, result brings forefront how importance should be determined PPEs. From CPE, two 45‐dimensional configurations radiatively‐balanced, auto‐tuned atmospheres used submissions CMIP6.

Language: Английский

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Wet deposition in shallow convection over the Southern Ocean

npj Climate and Atmospheric Science, Journal Year: 2024, Volume and Issue: 7(1)

Published: March 22, 2024

Abstract Southern Ocean (SO) air is amongst the most pristine on Earth, particularly during winter. Historically, there has been a focus biogenic sources as an explanation for seasonal cycle in cloud condensation nuclei concentrations ( N CCN ). also sensitive to strength of sink terms, although magnitude this term varies considerably. Wet deposition, process encompassing coalescence scavenging (drizzle formation), one such that may be especially relevant over SO. Using boundary layer climatology, and precipitation observations from Kennaook/Cape Grim Observatory (CGO), we find statistically significant difference between when upwind meteorology dominated by open mesoscale cellular convection (MCC) closed MCC. When MCC dominant, lower median (69 cm −3 ) found compared (89 dominant. Open precipitate more heavily (1.72 mm day −1 frequently (16.7% time) than (0.29 , 4.5%). These relationships are observed hold across with maximum minimum Austral summer (DJF). Furthermore, morphology strongly depends meteorological conditions. The relationship can further examined diurnal season. Although was again negative out phase cycle, leading it ~3 hours, suggesting other factors, specifically play primary role influencing precipitation.

Language: Английский

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Marine emissions of methanethiol increase aerosol cooling in the Southern Ocean

Science Advances, Journal Year: 2024, Volume and Issue: 10(48)

Published: Nov. 27, 2024

Ocean-emitted dimethyl sulfide (DMS) is a major source of climate-cooling aerosols. However, most the marine biogenic sulfur cycling not routed to DMS but methanethiol (MeSH), another volatile whose reactivity has hitherto hampered measurements. Therefore, global emissions and climate impact MeSH remain unexplored. We compiled database seawater concentrations, identified their statistical predictors, produced monthly fields adding emissions. Implemented into chemistry-climate model, increase sulfate aerosol burden by 30 70% over Southern Ocean enhance cooling effect while depleting atmospheric oxidants increasing lifetime transport. Accounting for reduces radiative bias current models in this climatically relevant region.

Language: Английский

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Marine Boundary Layer Cloud Condensation Nuclei Bias Over the Southern Ocean: Comparisons Between the Community Atmosphere Model 6 and Field Observations

Journal of Geophysical Research Atmospheres, Journal Year: 2025, Volume and Issue: 130(8)

Published: April 19, 2025

Abstract Marine boundary layer (MBL) clouds play a crucial role in regulating radiative balance the atmosphere. Previous studies identified that MBL cloud droplet number concentration (Nd) is underestimated by factor of 2 over summertime Southern Ocean (SO) close to Antarctic coast many models. Here, comparisons between condensation nuclei (CCN) observations from field campaigns during 2017–2018 Austral summer Australasian sector SO and simulated CCN Community Atmospheric Model 6 (CAM6) are presented. Modeled (N ) underestimated, 100% at latitudes south 55°S with N bias (a) largest Plateau summer, implying biased type has seasonal latitudinal variation and, (b) three times larger sea ice than open water, spray better compared secondary CCN. Assessments aerosol size distributions indicate an underestimation accumulation‐mode‐aerosols (Ac) diameters 70 nm < D 100 nm. supersaturation spectra observed had lower hygroscopicity CCN, differences chemical composition. With aerosols including sulfate being less hygroscopic salt activation ratio derived using bulk kappa Abdul‐Razzak function leads critical 62°S. The biases reported here highlight important shortfalls can be well‐documented d Earth System Models, key feature uncertainty pre‐industrial conditions.

Language: Английский

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Simulating Mixed‐Phase Clouds Over Coastal Antarctica During a Significant Snowfall Event in a High‐Resolution Regional Model

Journal of Geophysical Research Atmospheres, Journal Year: 2025, Volume and Issue: 130(10)

Published: May 13, 2025

Abstract Global climate models and reanalysis products have revealed large, persistent downwelling shortwave radiation biases over the Southern Ocean coastal Antarctica, likely caused by incapability of to accurately simulate frequent low‐level mixed‐phase clouds in these regions. In this study, we use ground‐based observations collected at Davis, Antarctica during Precipitation Land The field campaign austral summer 2019 assess capability high‐resolution regional Unified Model (UM) reproduce precipitating off Antarctica. We test new UM RAL3 (Regional Atmosphere 3) configuration with double‐moment Cloud AeroSol Interacting Microphysics scheme bimodal cloud fraction scheme, running spatial resolution 1.5‐km. compare it previous RA2M a single‐moment microphysics unimodal scheme. exhibits marginally degraded meteorological conditions relative compared observations. For properties, can generally phase, vertical structure timing events sublimation precipitation periods. Nevertheless, overestimated ice water path potentially underestimated liquid (LWP) contribute positive surface negative longwave biases. simulates more LWP, though suggest for wrong reasons due its nucleating parameterization. Our results that combined parameterizations, while having reduced performance some respects, has large potential better represent mixed phase region.

Language: Английский

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Earth-system-model evaluation of cloud and precipitation occurrence for supercooled and warm clouds over the Southern Ocean's Macquarie Island

Atmospheric chemistry and physics, Journal Year: 2023, Volume and Issue: 23(16), P. 9037 - 9069

Published: Aug. 17, 2023

Abstract. Over the remote Southern Ocean (SO), cloud feedbacks contribute substantially to Earth system model (ESM) radiative biases. The evolution of low clouds (cloud-top heights < ∼ 3 km) is strongly modulated by precipitation and/or evaporation, which act as primary sink condensate. Constraining processes in ESMs requires robust observations suitable for process-level evaluations. A year-long subset (April 2016–March 2017) ground-based profiling instrumentation deployed during Macquarie Island Cloud and Radiation Experiment (MICRE) field campaign (54.5∘ S, 158.9∘ E) combines a 95 GHz (W-band) Doppler radar, two lidar ceilometers, balloon-borne soundings quantify occurrence frequency from liquid-phase base. Liquid-based at precipitate 70 % time, with deeper colder precipitating more frequently higher intensity compared thinner warmer clouds. Supercooled layers readily than cloud-top temperatures > 0 ∘C, regardless geometric thickness layer, also evaporate frequently. We further demonstrate an approach employ these observational constraints evaluation 9-year GISS-ModelE3 ESM simulation. Model output processed through Column Collaboratory (EMC2) radar instrument simulator same specifications those MICRE, therefore accounting sensitivities ensuring coherent comparison. Relative MICRE observations, produces smaller frequency, greater sub-cloud evaporation. lower relative contrasts numerous studies that suggest ubiquitous bias too over SO when satellite-based likely owing sensitivity limitations spaceborne different sampling methodologies ground- versus space-based observations. Despite deficiencies, reproduces observed tendency intensity. specific regimes, including near-surface account 25 liquid-based optically thin, non-precipitating 27 bases 250 m. demonstrated framework, merges appropriately constrained output, valuable evaluate responsible ESMs.

Language: Английский

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Addressing Complexity in Global Aerosol Climate Model Cloud Microphysics

Journal of Advances in Modeling Earth Systems, Journal Year: 2023, Volume and Issue: 15(5)

Published: April 29, 2023

Abstract In a quest to represent the Earth system, climate models have become more and complex. This generates problems, for example, hindering model interpretability. study contributes regain of understanding proposes simplifications decrease scheme complexity. We reflect on reasons complexity problems it or deepens, connecting perspectives from atmospheric science philosophy science. Using an emulated perturbed parameter ensemble cloud microphysics (CMP) process efficiencies, we investigate sensitivity perturbations. The analysis characterizes behavior, contrasting physical as well alternative CMP formulation (comparing 2M (Lohmann et al., 2007, https://doi.org/10.5194/acp-7-3425-2007 ) P3 (Morrison & Milbrandt, 2015, https://doi.org/10.1175/JAS-D-14-0065.1 ; Dietlicher 2018, https://doi.org/10.5194/gmd-11-1557-2018 )). For scheme, ice crystal autoconversion dominates in phase. removes this artificial thus shows balanced sensitivities. Model behavior sometimes aligns with understanding, but many sensitivities are masked by other dominant processes finally responds differently due adjustments. identify that is not sensitive test their simplification. heterogeneous freezing secondary production drastically simplifiable. Depending one's modeling vision one may interpret study's findings pointing simplification potential need representation improvements where does tally our understanding.

Language: Английский

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Southern Ocean Low Cloud and Precipitation Phase Observed During the Macquarie Island Cloud and Radiation Experiment (MICRE)

Journal of Geophysical Research Atmospheres, Journal Year: 2023, Volume and Issue: 128(17)

Published: Aug. 29, 2023

Abstract Shallow cloud decks residing in or near the boundary layer cover a large fraction of Southern Ocean (SO) and play major role determining amount shortwave radiation reflected back to space from this region. In article, we examine macrophysical characteristics thermodynamic phase low clouds (tops <3 km) precipitation using ground‐based ceilometer, depolarization lidar vertically‐pointing W‐band radar measurements collected during Macquarie Island Cloud Radiation Experiment (MICRE) April 2016 March 2017. During MICRE, occurred ∼65% time on average (slightly more often austral winter than summer). About 2/3 were cold‐topped (temperatures ≤0°C). These thicker had higher bases warm‐topped clouds. 83%–88% liquid at base (depending season). The majority vertical range 150–250 m below base, significant which did not reach surface. Phase characterization is limited period between November 2016. Small‐particle (low‐radar‐reflectivity) (which dominates occurrence) was mostly below‐cloud, while large‐particle total accumulation) predominantly mixed/ambiguous ice phase. Approximately 40% (with droplets base). Below‐cloud with reflectivity factors about −10 dBZ liquid, above 0 ice.

Language: Английский

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