Aerosol Indirect Effects on the Predicted Precipitation in a Global Weather Forecasting Model

Aerosol indirect effects on precipitation were investigated in this study using a Global/Regional Integrated Model system (GRIMs) linked with a chemistry package devised for reducing the heavy computational burden occurring in common atmosphere–chemistry coupling models. The chemistry package was based on the Goddard Chemistry Aerosol Radiation and Transport scheme of Weather Research and Forecasting with Chemistry (WRF-Chem), and five tracers that are relatively important for cloud condensation nuclei (CCN) formation were treated as prognostic variables. For coupling with the cloud physics processes in the GRIMs, the CCN number concentrations derived from the simplified chemistry package were utilized in the cumulus parameterization scheme (CPS) and the microphysics scheme (MPS). The simulated CCN number concentrations were higher than those used in original cloud physics schemes and, overall, the amount of incoming shortwave radiation reaching the ground was indirectly reduced by an increase in clouds owing to a high CCN. The amount of heavier precipitation increased over the tropics owing to the inclusion of enhanced riming effects under deep precipitating convection. The trend regarding the changes in non-convective precipitation was mixed depending on the atmospheric conditions. The increase in small-size cloud water owing to a suppressed autoconversion led to a reduction in precipitation. More precipitation can occur when ice particles fall under high CCN conditions owing to the accretion of cloud water by snow and graupel, along with their melting.

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Sensitivity of precipitation and structure of Typhoon Hato to bulk and explicit spectral bin microphysics schemes

10.5194/egusphere-egu2020-3788 ◽

2020 ◽

Author(s):

xiaodian shen ◽

qimin cao ◽

baolin jiang ◽

wenshi lin ◽

lan zhang

Keyword(s):

Water Vapor ◽

Cloud Condensation Nuclei ◽

Grid Point ◽

Cloud Water ◽

Convective Precipitation ◽

Dynamical Structure ◽

Time Step ◽

Microphysics Scheme ◽

Typhoon Structure ◽

Simulated Precipitation

<p>This study simulated the evolution of Typhoon Hato (2017) with the Weather Research and Forecasting model using three bulk schemes and one bin scheme. It was found that the track of the typhoon was insensitive to the microphysics scheme, whereas the degree of correspondence between the simulated precipitation and cloud structure of the typhoon was closest to the observations when using the bin scheme. The different microphysical structure of the bin and three bulk schemes was reflected mainly in the cloud water and snow content. The three bulk schemes were found to produce more cloud water because the application of saturation adjustment condensed all the water vapor at the end of each time step. The production of more snow by the bin scheme could be attributed to several causes: (1) the calculations of cloud condensation nuclei size distributions and supersaturation at every grid point that cause small droplets to form at high levels, (2) different fall velocities of different sizes of particles that mean small particles remain at a significant height, (3) sufficient water vapor at high levels, and (4) smaller amounts of cloud water that reduce the rates of riming and conversion of snow to graupel. The distribution of hydrometeors affects the thermal and dynamical structure of the typhoon. The saturation adjustment hypothesis in the bulk schemes overestimates the condensate mass. Thus, the additional latent heat makes the typhoon structure warmer, which increases vertical velocity and enhances convective precipitation in the eyewall region.</p>

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Incorporation of advanced aerosol activation treatments into CESM/CAM5: model evaluation and impacts on aerosol indirect effects

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-32291-2013 ◽

2013 ◽

Vol 13 (12) ◽

pp. 32291-32325

Author(s):

B. Gantt ◽

J. He ◽

X. Zhang ◽

Y. Zhang ◽

A. Nenes

Keyword(s):

Indirect Effects ◽

Cloud Condensation Nuclei ◽

Shortwave Radiation ◽

Condensation Nuclei ◽

Liquid Water Path ◽

Near Surface ◽

Aerosol Indirect Effects ◽

Model Version ◽

Cloud Properties ◽

Aerosol Activation

Abstract. One of the greatest sources of uncertainty in the science of anthropogenic climate change is from aerosol-cloud interactions. The activation of aerosols into cloud droplets is a direct microphysical link between aerosols and clouds; parameterizations of this process realistically link aerosol with cloud condensation nuclei (CCN) and the resulting indirect effects. Small differences between parameterizations can have a large impact on the spatiotemporal distributions of activated aerosols and the resulting cloud properties. In this work, we incorporate a series of aerosol activation schemes into the Community Atmosphere Model version 5.1.1 within the Community Earth System Model version 1.0.5 (CESM/CAM5), which include factors such as insoluble aerosol adsorption, giant cloud condensation nuclei (CCN) activation kinetics, and entrainment to understand their individual impacts on global scale cloud droplet number concentrations (CDNCs). Compared to the existing simple activation scheme in CESM/CAM5, this series of schemes predict CDNCs that are typically in better agreement with satellite-derived and observed values. The largest changes in predicted CDNCs occur over desert and oceanic regions, owing to the enhanced activation of dust from insoluble aerosol adsorption and reductions in cloud supersaturation from the intense absorption of water vapor in regions of strong giant CCN emissions (e.g., sea-salt). Comparison of CESM/CAM5 against satellite-derived cloud optical thickness and liquid water path shows that the updated activation schemes improve the low biases in their predictions. Globally, the incorporation of all updated schemes leads to an average increase in column CDNCs of 155%, an increase in shortwave cloud forcing of 13%, and a decrease in surface shortwave radiation of 4%. In terms of meteorological impacts, these updated aerosol activation schemes result in a slight decrease in near-surface temperature of 0.9 °C and precipitation of 0.04 mm day−1, respectively. With the improvement of model-predicted CDNCs and better agreement with most satellite-derived cloud properties, the inclusion of these aerosol activation processes should result in better predictions of the aerosol indirect effects.

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Numerical Simulation of the Effect of Cloud Condensation Nuclei Concentration on the Microphysical Processes in Typhoon Usagi

Advances in Meteorology ◽

10.1155/2019/8293062 ◽

2019 ◽

Vol 2019 ◽

pp. 1-9 ◽

Cited By ~ 1

Author(s):

Xiying Ye ◽

Qimin Cao ◽

Baolin Jiang ◽

Wenshi Lin

Keyword(s):

Latent Heat ◽

Cloud Condensation Nuclei ◽

Cloud Water ◽

Weather Research And Forecasting ◽

Forecasting Model ◽

Condensation Nuclei ◽

Microphysics Scheme ◽

Sensitivity Tests ◽

Microphysical Processes ◽

Heat Released

The Weather Research and Forecasting model version 3.2.1 with the Lin microphysics scheme was used herein to simulate super typhoon Usagi, which occurred in 2013. To investigate the effect of the concentration of cloud condensation nuclei (CCN) on the development of typhoon Usagi, a control simulation was performed with a CCN concentration of 100 cm−3, together with two sensitivity tests: C10 and C1000, having CCN concentrations of 10 cm−3 and 1000 cm−3, respectively. The path, intensity, precipitation, microphysical processes, and the release of latent heat resulting from the typhoon in all three simulations were analyzed to show that an increase in CCN concentration leads to decreases in intensity and precipitation, an increase of the cloudless area in the eye of the typhoon, a more disordered cloud system, and less latent heat released through microphysical processes, especially the automatic conversion of cloud water into rainwater. Overall, an increase in CCN concentration reduces the total latent heat released during the typhoon suggesting that typhoon modification by aerosol injection may be optimized using numerical simulations to ensure the strongest release of latent heat within the typhoon.

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Cancellation of Aerosol Indirect Effects in Marine Stratocumulus through Cloud Thinning

Journal of the Atmospheric Sciences ◽

10.1175/jas3942.1 ◽

2007 ◽

Vol 64 (7) ◽

pp. 2657-2669 ◽

Cited By ~ 129

Author(s):

Robert Wood

Keyword(s):

Time Scales ◽

Environmental Conditions ◽

Indirect Effects ◽

Marine Boundary Layer ◽

Cloud Condensation Nuclei ◽

Cloud Droplet ◽

Cloud Base ◽

Aerosol Indirect Effects ◽

Surface Precipitation ◽

Cloud Thickness

Abstract Applying perturbation theory within a mixed layer framework, the response of the marine boundary layer (MBL) cloud thickness h to imposed increases of the cloud droplet concentration Nd as a surrogate for increases in cloud condensation nuclei (CCN) concentrations is examined. An analytical formulation is used to quantify the response and demonstrate theoretically that for the range of environmental conditions found over the subtropical eastern oceans, on time scales of less than a day, the cloud thickness feedback response is largely determined by a balance between the moistening/cooling of the MBL resulting from the suppression of surface precipitation, and the drying/warming resulting from enhanced entrainment resulting from increased turbulent kinetic energy. Quantifying the transient cloud response as a ratio of the second to the first indirect effects demonstrates that the nature of the feedback is critically dependent upon the nature of the unperturbed state, with the cloud-base height zcb being the single most important determinant. For zcb < 400 m, increasing Nd leads to cloud thickening in accordance with the Albrecht hypothesis. However, for zcb > 400 m, cloud thinning occurs, which results in a feedback effect that increasingly cancels the Twomey effect as zcb increases. The environmental conditions favoring an elevated cloud base are relatively weak lower-tropospheric stability and a dry free troposphere, although the former is probably more important over the subtropical eastern oceans. On longer time scales an invariable thickening response is found, and thus accurate quantification of the aerosol indirect effects will require a good understanding of the processes that control the time scale over which aerosol perturbations are modified.

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Aerosol indirect forcing in a global model with particle nucleation

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-239-2009 ◽

2009 ◽

Vol 9 (1) ◽

pp. 239-260 ◽

Cited By ~ 218

Author(s):

M. Wang ◽

J. E. Penner

Keyword(s):

Boundary Layer ◽

Indirect Effects ◽

Global Climate ◽

Cloud Condensation Nuclei ◽

Particle Formation ◽

Particle Nucleation ◽

So2 Emissions ◽

Aerosol Indirect Effects ◽

Aerosol Model ◽

Indirect Forcing

Abstract. The number concentration of cloud condensation nuclei (CCN) formed as a result of anthropogenic emissions is a key uncertainty in the study of aerosol indirect forcing and global climate change. Here, we use a global aerosol model that includes an empirical boundary layer nucleation mechanism, the use of primary-emitted sulfate particles to represent sub-grid scale nucleation, as well as binary homogeneous nucleation to explore how nucleation affects the CCN concentration and the first aerosol indirect effect (AIE). The inclusion of the boundary layer nucleation scheme increases the global average CCN concentrations in the boundary layer by 31.4% when no primary-emitted sulfate particles are included and by 5.3% when they are included. Particle formation with the boundary layer nucleation scheme decreases the first indirect forcing over ocean, and increases the first indirect forcing over land when primary sulfate particles are included. This suggests that whether particle formation from aerosol nucleation increases or decreases aerosol indirect effects largely depends on the relative change of primary particles and SO2 emissions from the preindustrial to the present day atmosphere. Including primary-emitted sulfate particle significantly increases both the anthropogenic fraction of CCN concentrations and the first aerosol indirect forcing. The forcing from various treatments of aerosol nucleation ranges from −1.22 to −2.03 w/m2. This large variation shows the importance of better quantifying aerosol nucleation mechanisms for the prediction of CCN concentrations and aerosol indirect effects.

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Aerosol impacts on warm-cloud microphysics and drizzle in a moderately polluted environment

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-4487-2021 ◽

2021 ◽

Vol 21 (6) ◽

pp. 4487-4502

Author(s):

Ying-Chieh Chen ◽

Sheng-Hsiang Wang ◽

Qilong Min ◽

Sarah Lu ◽

Pay-Liam Lin ◽

...

Keyword(s):

Size Distribution ◽

Indirect Effects ◽

Cloud Microphysics ◽

Cloud Water ◽

Aerosol Indirect Effects ◽

Low Level ◽

Warm Cloud ◽

Raindrop Size Distribution ◽

Raindrop Size ◽

Northern Taiwan

Abstract. Climate is critically affected by aerosols, which alter cloud lifecycles and precipitation distribution through radiative and microphysical effects. In this study, aerosol and cloud property datasets from MODIS (Moderate Resolution Imaging Spectroradiometer), onboard the Aqua satellite, and surface observations, including aerosol concentrations, raindrop size distribution, and meteorological parameters, were used to statistically quantify the effects of aerosols on low-level warm-cloud microphysics and drizzle over northern Taiwan during multiple fall seasons (from 15 October to 30 November of 2005–2017). Our results indicated that northwestern Taiwan, which has several densely populated cities, is dominated by low-level clouds (e.g., warm, thin, and broken clouds) during the fall season. The observed effects of aerosols on warm clouds indicated aerosol indirect effects (i.e., increased aerosol loading caused a decrease in cloud effective radius (CER)), an increase in cloud optical thickness, an increase in cloud fraction, and a decrease in cloud-top temperature under a fixed cloud water path. Quantitatively, aerosol–cloud interactions (ACI=-∂ln⁡CER∂ln⁡α|CWP, changes in CER relative to changes in aerosol amounts) were 0.07 for our research domain and varied between 0.09 and 0.06 in the surrounding remote (i.e., ocean) and polluted (i.e., land) areas, respectively, indicating aerosol indirect effects were stronger in the remote area. From the raindrop size distribution analysis, high aerosol loading resulted in a decreased frequency of drizzle events, redistribution of cloud water to more numerous and smaller droplets, and reduced collision–coalescence rates. However, during light rain (≤1 mm h−1), high aerosol concentrations drove raindrops towards smaller droplet sizes and increased the appearance of drizzle drops. This study used long-term surface and satellite data to determine aerosol variations in northern Taiwan, effects on clouds and precipitation, and observational strategies for future research on aerosol–cloud–precipitation interactions.

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Aerosol indirect forcing in a global model with particle nucleation

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-13943-2008 ◽

2008 ◽

Vol 8 (4) ◽

pp. 13943-13998 ◽

Cited By ~ 1

Author(s):

M. Wang ◽

J. E. Penner

Keyword(s):

Boundary Layer ◽

Indirect Effects ◽

Global Climate ◽

Cloud Condensation Nuclei ◽

Particle Formation ◽

Particle Nucleation ◽

So2 Emissions ◽

Aerosol Indirect Effects ◽

Aerosol Model ◽

Indirect Forcing

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Aerosol impacts on warm-cloud microphysics and drizzle in a moderately polluted environment

10.5194/acp-2020-692 ◽

2020 ◽

Author(s):

Ying-Chieh Chen ◽

Sheng-Hsiang Wang ◽

Qilong Min ◽

Sarah Lu ◽

Pay-Liam Lin ◽

...

Keyword(s):

Size Distribution ◽

Indirect Effects ◽

Cloud Microphysics ◽

Cloud Water ◽

Aerosol Indirect Effects ◽

Low Level ◽

Warm Cloud ◽

Raindrop Size Distribution ◽

Raindrop Size ◽

Northern Taiwan

Abstract. Climate is critically affected by aerosols, which can alter cloud lifecycles and precipitation distribution through radiative and microphysical effects. In this study, aerosol and cloud properties datasets from MODIS onboard Aqua satellite and surface observations, including aerosol concentrations, raindrop size distribution, and meteorological parameters, were used to statistically quantify the effects of aerosols on low-level warm cloud microphysics and drizzle over northern Taiwan during fall seasons (from October 15 to November 30 of 2005–2017). Results indicated that clouds in northwestern Taiwan, which with active human activity is dominated by low-level clouds (e.g. warm, thin, and broken clouds). The observed effects of aerosols on warm clouds indicated aerosol indirect effects; increasing aerosol loading caused a decrease in cloud effective radius (CER), an increase in cloud optical thickness, an increase in cloud fraction, and a decrease in cloud top temperature under a fixed cloud water path. A quantitative value of aerosol–cloud interactions (ACI = (δ ln⁡ CER)/(δ ln⁡ α), changes in CER depend on changes in aerosols) were calculated to be 0.07 for our research domain. ACI values varied between 0.09 and 0.06 in surrounding clean and heavily polluted areas, respectively, which indicated that aerosol indirect effects were more sensitive in the clean area. Analysis of raindrop size distribution observations during high aerosol loading resulted in a decreased frequency of drizzle events, redistributed cloud water to more numerous and smaller droplets, and reduced collision–coalescence rates. However, in the scenario of light precipitation (&leq; 1 mm h−1), high aerosol concentrations drive raindrops towards smaller droplet sizes and increase the appearance of drizzle drops. This study used long-term surface and satellite data to determine aerosol variations in northern Taiwan, effects on the clouds and precipitations, and applications to observational strategy planning for future research on aerosol–cloud–precipitation interactions.

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WRF Precipitation Performance and Predictability for Systematically Varied Parameterizations over Complex Terrain

Weather and Forecasting ◽

10.1175/waf-d-20-0195.1 ◽

2021 ◽

Author(s):

Julia Jeworrek ◽

Gregory West ◽

Roland Stull

Keyword(s):

Complex Terrain ◽

Wrf Model ◽

Precipitation Intensity ◽

Cumulus Parameterization ◽

Precipitation Forecast ◽

Convective Precipitation ◽

Microphysics Scheme ◽

Forecast Performance ◽

Relative Standard ◽

Spatial Differences

AbstractPhysics parameterizations in the Weather Research and Forecasting (WRF) model are systematically varied to investigate precipitation forecast performance over the complex terrain of southwest British Columbia (BC). Comparing a full year of modelling data from over 100 WRF configurations to station observations reveals sensitivities of precipitation intensity, season, location, grid resolution, and accumulation window. The choice of cumulus and microphysics parameterizations is most important. The WSM5 microphysics scheme yields competitive verification scores when compared to more sophisticated and computationally expensive parameterizations. Although the cale-aware Grell-Freitas cumulus parameterization performs better for summertime convective precipitation, the conventional Kain-Fritsch parameterization better simulates wintertime frontal precipitation, which contributes to the majority of the annual precipitation in southwest BC. Finer grid spacings have lower relative biases and a more realistic spread in precipitation intensity distribution, yet higher relative standard deviations of their errors — they produce finer spatial differences and local extrema. Finer resolutions produce the best fraction of correct-to-incorrect forecasts across all precipitation intensities, whereas the coarser 27-km domain yields the highest hit rates and equitable threat scores. Verification metrics improve greatly with longer accumulation windows — hourly precipitation values are prone to double-penalty issues, while longer accumulation windows compensate for timing errors but lose information about short-term precipitation intensities. This study provides insights regarding WRF precipitation performance in complex terrain across a wide variety of configurations, using metrics important to a range of end users.

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Reply to “Comments on ‘Do Ultrafine Cloud Condensation Nuclei Invigorate Deep Convection?’”

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0315.1 ◽

2021 ◽

Vol 78 (1) ◽

pp. 341-350

Author(s):

Wojciech W. Grabowski ◽

Hugh Morrison

Keyword(s):

Negative Impact ◽

Cloud Condensation Nuclei ◽

Deep Convection ◽

Diagnostic Technique ◽

Cloud Water ◽

Latent Heating ◽

Condensation Nuclei ◽

Modeling Framework ◽

Microphysics Scheme ◽

The Impact

AbstractThis is a rebuttal of Fan and Khain’s comments (hereafter FK21) on a 2020 paper by Grabowski and Morrison (hereafter GM20) that questions the impact of ultrafine cloud condensation nuclei (CCN) on deep convection. GM20 argues that “cold invigoration,” an increase of the updraft speed from lofting and freezing of additional cloud water in polluted environments, is unlikely because the latent heating from freezing of this cloud water approximately recovers the negative impact on the buoyancy from the weight of this water. FK21 suggest a variety of processes that could invalidate our claim. We maintain that our argument is valid and invite the authors to compare their microphysics scheme with ours in the same simplified modeling framework. However, pollution does affect the partitioning of latent heating within the column and likely leads to convection changes beyond a single diurnal cycle through larger-scale circulation changes. This argument explains impacts seen in our idealized mesoscale simulations and in convective–radiative equilibrium simulations by others. We agree with FK21 on the existence of a “warm invigoration” mechanism but question its interpretation. Consistent with the simulations in GM20, we argue that changes in the buoyancy can be explained by the response of the supersaturation to droplet microphysical changes induced by pollution. The buoyancy change is determined by supersaturation differences between pristine and polluted conditions, while condensation rate responds to these supersaturation changes. Finally, we agree with FK21 that the piggybacking modeling technique cannot prove or disprove invigoration; rather, it is a diagnostic technique that can be used to understand mechanisms driving simulation differences.

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