Confronting the Challenge of Modeling Cloud and Precipitation Microphysics

Journal of Advances in Modeling Earth Systems, Journal Year: 2020, Volume and Issue: 12(8)

Published: May 11, 2020

In the atmosphere, microphysics refers to microscale processes that affect cloud and precipitation particles is a key linkage among various components of Earth's atmospheric water energy cycles. The representation microphysical in models continues pose major challenge leading uncertainty numerical weather forecasts climate simulations. this paper, problem treating divided into two parts: (i) how represent population particles, given impossibility simulating all individually within cloud, (ii) uncertainties process rates owing fundamental gaps knowledge physics. recently developed Lagrangian particle-based method advocated as way address several conceptual practical challenges representing particle populations using traditional bulk bin parameterization schemes. For addressing critical physics knowledge, sustained investment for observational advances from laboratory experiments, new probe development, next-generation instruments space needed. Greater emphasis on work, which has apparently declined over past decades relative other areas research, argued be an essential ingredient improving process-level understanding. More systematic use natural observations constrain schemes also advocated. Because it generally difficult quantify individual these directly, presents inverse can viewed standpoint Bayesian statistics. Following idea, probabilistic framework proposed combines elements statistical physical modeling. Besides providing rigorous constraint schemes, there added benefit quantifying systematically. Finally, broader hierarchical approach accelerate improvements leveraging described paper related modeling (using schemes), experimentation, observations, methods.

Language: Английский

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Remote Sensing of Droplet Number Concentration in Warm Clouds: A Review of the Current State of Knowledge and Perspectives

Reviews of Geophysics, Journal Year: 2018, Volume and Issue: 56(2), P. 409 - 453

Published: April 17, 2018

The cloud droplet number concentration (N d) is of central interest to improve the understanding physics and for quantifying effective radiative forcing by aerosol-cloud interactions. Current standard satellite retrievals do not operationally provide N d, but it can be inferred from optical depth (τ c) radius (r e) top temperature. This review summarizes issues with this approach quantifies uncertainties. A total relative uncertainty 78% pixel-level relatively homogeneous, optically thick unobscured stratiform clouds favorable viewing geometry. even greater if these conditions are met. For averages over 1° ×1° regions reduced 54% assuming random errors instrument In contrast, few evaluation studies against reference in situ observations suggest much better accuracy little variability bias. More such required a error characterization. d dominated r e, therefore, improvements e would greatly quality retrievals. Recommendations made how might achieved. Some existing data sets compared discussed, best practices use current passive instruments (e.g., filtering criteria) recommended. Emerging alternative estimates also considered. First, new ideas additional information upcoming spaceborne second, approaches using high-quality ground-based examined.

Language: Английский

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Bounding global aerosol radiative forcing of climate change

Published: March 9, 2020

<p>Aerosol radiative forcing plays an important role in the attribution of past climate changes, estimates future allowable carbon emissions, and assessment potential geoengineering solutions. Substantial progress made over 40 years observing, understanding, modelling aerosol processes helped quantify forcing, but uncertainties remain large.</p><p>In spring 2018, under auspices World Climate Research Programme's Grand Science Challenge on Clouds, Circulation Sensitivity, thirty-six experts gathered to take a fresh comprehensive look at present understanding identify prospects for some most pressing open questions. The outcome that meeting is review paper, Bellouin et al. (2019), accepted publication Reviews Geophysics. This provides new range industrial era based multiple, traceable arguable lines evidence, including approaches, theoretical considerations, observations. A substantial achievement focus evidence rather than survey results or expert judgement, make questions much more specific.</p><p>This talk will key messages arguments work show promise improving quantification forcing.</p>

Language: Английский

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Aerosols enhance cloud lifetime and brightness along the stratus-to-cumulus transition

Proceedings of the National Academy of Sciences, Journal Year: 2020, Volume and Issue: 117(30), P. 17591 - 17598

Published: July 13, 2020

Significance All cloud droplets on Earth form from tiny airborne particles known as aerosols. Additional aerosols anthropogenic activity have produced more but at smaller sizes. The smaller, numerous in clouds do not collide effectively, therefore resulting less precipitation. Using a combination of time-lapse satellite imagery and air mass trajectory modeling, we show that can enhance fraction extend the lifetime overcast fields primarily under stable atmospheric conditions typically found off west coasts subtropical stratocumulus-dominated regions. Longer-lived stronger cooling influence climate therefore, need to be correctly parameterized models so accurate projections change achieved.

Language: Английский

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Improved Aerosol Processes and Effective Radiative Forcing in HadGEM3 and UKESM1

Journal of Advances in Modeling Earth Systems, Journal Year: 2018, Volume and Issue: 10(11), P. 2786 - 2805

Published: Oct. 15, 2018

Abstract Aerosol processes and, in particular, aerosol‐cloud interactions cut across the traditional physical‐Earth system boundary of coupled Earth models and remain one key uncertainties estimating anthropogenic radiative forcing climate. Here we calculate historical aerosol effective (ERF) HadGEM3‐GA7 climate model order to assess suitability this for inclusion UK model, UKESM1. The ERF, calculated year 2000 relative 1850, is large negative standard GA7 leading an unrealistic total over twentieth century. We show how underlying assumptions missing both physical parameterizations lead ERF. A number improvements are investigated their impact on These include improved representation cloud droplet spectral dispersion, updates activation scheme, black carbon optical properties. One largest contributors uncertainty insufficient knowledge preindustrial evaluate contribution natural marine emissions dimethyl sulfide organic combination derived from these studies weakens ERF by up 50% original value leads a more line with assessed values.

Language: Английский

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Weak average liquid-cloud-water response to anthropogenic aerosols

Nature, Journal Year: 2019, Volume and Issue: 572(7767), P. 51 - 55

Published: July 31, 2019

Language: Английский

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Constraining the aerosol influence on cloud liquid water path

Atmospheric chemistry and physics, Journal Year: 2019, Volume and Issue: 19(8), P. 5331 - 5347

Published: April 18, 2019

Abstract. The impact of aerosols on cloud properties is one the largest uncertainties in anthropogenic radiative forcing climate. Significant progress has been made constraining this using observations, but uncertainty remains, particularly magnitude rapid adjustments to aerosol perturbations. Cloud liquid water path (LWP) leading control liquid-cloud albedo, making it important observationally constrain LWP. Previous modelling and observational studies have shown that multiple processes play a role determining LWP response perturbations, effect can be difficult isolate. Following previous mediating variables, work investigates use relationship between droplet number concentration (Nd) for aerosols. Using joint-probability histograms account non-linear relationship, finds broadly consistent with studies. There significant geographical variation partly due meteorological factors (particularly relative humidity). Nd–LWP negative majority regions, suggesting aerosol-induced reductions could offset fraction instantaneous from aerosol–cloud interactions (RFaci). However, variations volcanic shipping perturbations indicate overestimates causal Nd confounding factors. weaker reduction implied by these “natural experiments” means provides an upper bound changes

Language: Английский

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Description and evaluation of aerosol in UKESM1 and HadGEM3-GC3.1 CMIP6 historical simulations

Geoscientific model development, Journal Year: 2020, Volume and Issue: 13(12), P. 6383 - 6423

Published: Dec. 21, 2020

Abstract. We document and evaluate the aerosol schemes as implemented in physical Earth system models, Global Coupled 3.1 configuration of Hadley Centre Environment Model version 3 (HadGEM3-GC3.1) United Kingdom System (UKESM1), which are contributing to sixth Intercomparison Project (CMIP6). The simulation aerosols present-day period historical ensemble these models is evaluated against a range observations. Updates microphysics scheme documented well differences representation between configurations. additional interactions included UKESM1 lead emissions natural sources such dimethyl sulfide, mineral dust organic subsequent evolution species model. also includes stratospheric–tropospheric chemistry fully coupled scheme, while GC3.1 employs simplified mechanism driven by prescribed monthly climatologies relevant oxidants. Overall, simulated speciated mass concentrations compare reasonably with Both capture negative trend sulfate over Europe eastern States America (US) although tend underestimate both regions. Interactive biogenic volatile compounds an improved agreement US. Simulated burdens similar despite 2-fold difference emissions. Aerosol optical depth biased low source outflow regions but performs other compared number satellite ground-based retrievals depth. generally within factor 2 observations, tending overestimate remote ocean regions, apart from at high latitudes, Northern Hemisphere continents. Finally, new primary marine for first time. impact this evaluated. Over pristine Southern Ocean, it found improve seasonal cycle cloud droplet relative underestimations remain. This paper provides useful characterisation climatology will facilitate understanding numerous aerosol–climate interaction studies that be conducted part CMIP6 beyond.

Language: Английский

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Strong Dependence of Atmospheric Feedbacks on Mixed‐Phase Microphysics and Aerosol‐Cloud Interactions in HadGEM3

Journal of Advances in Modeling Earth Systems, Journal Year: 2019, Volume and Issue: 11(6), P. 1735 - 1758

Published: May 17, 2019

Abstract We analyze the atmospheric processes that explain large changes in radiative feedbacks between two latest climate configurations of Hadley Centre Global Environmental model. use a set atmosphere‐only change simulations ( amip and amip‐p4K ) to separate contributions differences feedback parameter from all model developments configurations. show are mostly driven by shortwave cloud midlatitudes, mainly over Southern Ocean. Two new schemes most differences: introduction aerosol scheme development mixed‐phase scheme. Both reduce strength preexisting negative midlatitudes. The dampens strong aerosol‐cloud interaction, it also suppresses clear‐sky feedback. increases amount liquid water path (LWP) present day reduces increase LWP with warming. contribute reducing warmer climate. enhances strong, preexisting, positive fraction assess realism comparing present‐day against observations discuss avenues could help constrain relevant processes.

Language: Английский

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The hemispheric contrast in cloud microphysical properties constrains aerosol forcing

Proceedings of the National Academy of Sciences, Journal Year: 2020, Volume and Issue: 117(32), P. 18998 - 19006

Published: July 27, 2020

Significance Enhancement of aerosol that can nucleate cloud droplets increases the droplet number concentration and albedo clouds. This amount sunlight reflected to space. Uncertainty in how aerosol−cloud interactions over industrial period have increased planetary by this mechanism leads significant uncertainty climate projections. Our work presents a method for observationally constraining change due anthropogenic emissions: hemispheric difference remotely sensed between pristine Southern Ocean (a preindustrial proxy) polluted Northern Hemisphere. Application constraint models reduces range estimated since industrialization suggests current underpredict era.

Language: Английский

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