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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 4
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Book Description
Observation-based studies have shown that the aerosol cloud lifetime effect or the increase of cloud liquid water path (LWP) with increased aerosol loading may have been overestimated in climate models. Here, we simulate shallow warm clouds on 05/27/2011 at the Southern Great Plains (SGP) measurement site established by Department of Energy's Atmospheric Radiation Measurement (ARM) Program using a single column version of a global climate model (Community Atmosphere Model or CAM) and a cloud resolving model (CRM). The LWP simulated by CAM increases substantially with aerosol loading while that in the CRM does not. The increase of LWP in CAM is caused by a large decrease of the autoconversion rate when cloud droplet number increases. In the CRM, the autoconversion rate is also reduced, but this is offset or even outweighed by the increased evaporation of cloud droplets near cloud top, resulting in an overall decrease in LWP. Our results suggest that climate models need to include the dependence of cloud top growth and the evaporation/condensation process on cloud droplet number concentrations.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 4
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Book Description
Observation-based studies have shown that the aerosol cloud lifetime effect or the increase of cloud liquid water path (LWP) with increased aerosol loading may have been overestimated in climate models. Here, we simulate shallow warm clouds on 05/27/2011 at the Southern Great Plains (SGP) measurement site established by Department of Energy's Atmospheric Radiation Measurement (ARM) Program using a single column version of a global climate model (Community Atmosphere Model or CAM) and a cloud resolving model (CRM). The LWP simulated by CAM increases substantially with aerosol loading while that in the CRM does not. The increase of LWP in CAM is caused by a large decrease of the autoconversion rate when cloud droplet number increases. In the CRM, the autoconversion rate is also reduced, but this is offset or even outweighed by the increased evaporation of cloud droplets near cloud top, resulting in an overall decrease in LWP. Our results suggest that climate models need to include the dependence of cloud top growth and the evaporation/condensation process on cloud droplet number concentrations.
Author: Yuan Wang
Publisher: Springer
ISBN: 3662471752
Category : Science
Languages : en
Pages : 100
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Book Description
The studies in this dissertation aim at advancing our scientific understandings about physical processes involved in the aerosol-cloud-precipitation interaction and quantitatively assessing the impacts of aerosols on the cloud systems with diverse scales over the globe on the basis of the observational data analysis and various modeling studies. As recognized in the Fifth Assessment Report by the Inter-government Panel on Climate Change, the magnitude of radiative forcing by atmospheric aerosols is highly uncertain, representing the largest uncertainty in projections of future climate by anthropogenic activities. By using a newly implemented cloud microphysical scheme in the cloud-resolving model, the thesis assesses aerosol-cloud interaction for distinct weather systems, ranging from individual cumulus to mesoscale convective systems. This thesis also introduces a novel hierarchical modeling approach that solves a long outstanding mismatch between simulations by regional weather models and global climate models in the climate modeling community. More importantly, the thesis provides key scientific solutions to several challenging questions in climate science, including the global impacts of the Asian pollution. As scientists wrestle with the complexities of climate change in response to varied anthropogenic forcing, perhaps no problem is more challenging than the understanding of the impacts of atmospheric aerosols from air pollution on clouds and the global circulation.
Author: Constantin Andronache
Publisher: Elsevier
ISBN: 012810550X
Category : Science
Languages : en
Pages : 302
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Book Description
Mixed-Phase Clouds: Observations and Modeling presents advanced research topics on mixed-phase clouds. As the societal impacts of extreme weather and its forecasting grow, there is a continuous need to refine atmospheric observations, techniques and numerical models. Understanding the role of clouds in the atmosphere is increasingly vital for current applications, such as prediction and prevention of aircraft icing, weather modification, and the assessment of the effects of cloud phase partition in climate models. This book provides the essential information needed to address these problems with a focus on current observations, simulations and applications. - Provides in-depth knowledge and simulation of mixed-phase clouds over many regions of Earth, explaining their role in weather and climate - Features current research examples and case studies, including those on advanced research methods from authors with experience in both academia and the industry - Discusses the latest advances in this subject area, providing the reader with access to best practices for remote sensing and numerical modeling
Author: Wei-Kuo Tao
Publisher:
ISBN:
Category :
Languages : en
Pages : 62
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Book Description
Aerosols are a critical factor in the atmospheric hydrological cycle and radiation budget. As a major agent for clouds to form and a significant attenuator of solar radiation, aerosols affect climate in several ways. Current research suggests that aerosol effects on clouds could further extend to precipitation, both through the formation of cloud particles and by exerting persistent radiative forcing on the climate system that disturbs dynamics. However, the various mechanisms behind these effects, in particular, the ones connected to precipitation, are not yet well understood. The atmospheric and climate communities have long been working to gain a better grasp of these critical effects and hence to reduce the significant uncertainties in climate prediction resulting from such a lack of adequate knowledge. Here we review past efforts and summarize our current understanding of the effect of aerosols on convective precipitation processes from theoretical analysis of microphysics, observational evidence, and a range of numerical model simulations. In addition, the discrepancies between results simulated by models, as well as those between simulations and observations, are presented. Specifically, this paper addresses the following topics: (1) fundamental theories of aerosol effects on microphysics and precipitation processes, (2) observational evidence of the effect of aerosols on precipitation processes, (3) signatures of the aerosol impact on precipitation from large-scale analyses, (4) results from cloud-resolving model simulations, and (5) results from large-scale numerical model simulations. Finally, several future research directions for gaining a better understanding of aerosol-cloud-precipitation interactions are suggested.
Author: Partha Sarathi Bhattacharjee
Publisher:
ISBN:
Category : Atmospheric aerosols
Languages : en
Pages : 0
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Book Description
Increasing human population and rapid urbanization in the last two decades have caused a sharp rise in anthropogenic aerosols particularly over South and East Asia. Numerous studies have shown that aerosols play an important role in climate change through their interaction with the global water and energy cycles. Thus Aerosol-cloud-radiation-monsoon interaction related droughts and floods are two of the most serious environmental hazards confronting more than 60% of the population of the world living in the Asian monsoon countries. General circulation models (GCMs) are an important tool for understanding the climate response to changes in the amounts and composition of aerosols due to evolving use of fossil and biomass fuels. This dissertation attempt to get an insight into the aerosol-cloud interaction and study impacts of aerosol forcing, with particular emphasis on the interaction of aerosol with monsoon water cycle. NASA Goddard Earth Observing System (GEOS) version 4 General Circulation Model (called GEOS4-GCM) with moist convection of Relaxed Arakawa-Schubert Scheme (McRAS) clouds and state-of-the-art parameterization of cloud microphysical process is used this study. A Single Column version (SCM) of the model is used to evaluate various parameterization schemes by comparing against in-situ and satellite observations. The model simulated realistic annual mean and annual cycles of cloud water, cloud optical thickness, cloud drop number concentration and effective radius without showing any systematic biases. GCM version of the model is used to study aerosol induced anomalies during summer months (June-August) particularly focusing over Indian monsoon. The individual aerosol effects (direct and indirect) and their combination show different impacts on radiation as well as on cloud microphysics, precipitation and circulation. However, complexities of nucleation of ice clouds in the model result not enough aerosols were acting as ice nuclei, which led to incomplete understanding of indirect effect in the atmosphere.
Author: Julian A.L. Mann
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: National Academies of Sciences, Engineering, and Medicine
Publisher: National Academies Press
ISBN: 0309443458
Category : Science
Languages : en
Pages : 53
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Book Description
One of the most significant and uncertain aspects of climate change projections is the impact of aerosols on the climate system. Aerosols influence the climate indirectly by interacting with nearby clouds leading to small changes in cloud cover, thickness, and altitude, which significantly affect Earth's radiative balance. Advancements have been made in recent years on understanding the complex processes and atmospheric interactions involved when aerosols interact with surrounding clouds, but further progress has been hindered by limited observations. The National Academies of Sciences, Engineering, and Medicine organized a workshop to discuss the usefulness of the classified observing systems in advancing understanding of cloud and aerosol interactions. Because these systems were not developed with weather and climate modeling as a primary mission objective, many participants said it is necessary for scientists to find creative ways to utilize the data. The data from these systems have the potential to be useful in advancing understanding of cloud and aerosol interactions. This publication summarizes the presentations and discussions from the workshop.
Author: Huilin Huang
Publisher:
ISBN:
Category :
Languages : en
Pages : 61
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Book Description
Aerosols come from both natural and anthropogenic sources and contribute large uncertainties to estimates of the Earth's changing energy budget. It is thus of great importance to understand the mechanism through which aerosols play a role on global climate. In this thesis, we investigate the direct and indirect effect of aerosols on global and regional climate variability (e.g. West Africa, South Asia and East Asia) using an atmospheric general circulation model, GFS (Global Forecast System) coupled with SSiB2 (the second version of Si mplified Simple Biosphere Model). The three-dimensional aerosol data from the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model has been adopted in this study. We first analyze the direct effect of aerosols, especially absorption aerosols, on global and regional energy budget, precipitation, and surface temperature and the mechanism involved. For instance, we find the dust aerosol in North Africa produces a heating in the atmosphere, which generates a cyclonic circulation in middle layer over Sahel region, which further brings about upward motion in the lower level and results in precipitation increase by 0.96 mm/day in June-July-August. We also examine the impact of aerosols on ice clouds effective radius by applying an advanced ice cloud parameterization in the GCM. We find that increased aerosol loading reduces ice crystal size due to aerosol first indirect effect, with the maxima occurs in South Asia and North Indian Ocean. Ice clouds with smaller crystal sizes can absorb both shortwave and longwave radiation, thus resulting in less downward solar flux and less outgoing longwave on top of atmosphere (TOA). Global mean net radiation change on TOA is about 0.5W/m2 and its sign is largely dependent on the relative magnitude of shortwave and longwave change and precipitation changes primarily respond to cooling/warming of the atmosphere. Lastly, we use sulfate data in both pre-industrial and present-day case to test the impact of aerosols on liquid cloud effective radius. We find aerosols can act as cloud condensation nuclei, and hence change the shortwave optical properties of liquid clouds. Radiative cooling occurs globally because smaller droplets size leads to increased cloud albedo. The mean value is about 2.5W/m2. Moreover, most radiative cooling occurs in North Hemisphere, where anthropogenic sulfate aerosols locate, such as East Asia and North America. We also compare the radiative forcing of aerosol direct and indirect effect on both ice clouds and liquid clouds on global as well as the three monsoon regions. All aerosol effects result in radiative cooling on global scale. However, surface net radiation changes are different in West Africa, East and South Asia, which relates to local atmospheric conditions such as cloud cover and convection. Aerosol direct effect and aerosol indirect effect for liquid clouds have comparable impact on surface net radiation change (more than -3 W/m2), while aerosol indirect effects for ice cloud are smaller (~1 W/m2) because of the negative feedback from cloud cover. Decreased land surface temperature can be found over North Hemisphere continent in all three effects, especially over higher latitude, with varied magnitude. The precipitation changes are less predictable. Aerosol indirect effects on averaged global precipitations are close to zero because the precipitation changes are different or even opposite in different regions. The effect of aerosol on precipitations can be influenced by convection strength, topography, and even the relative location of aerosols and monsoon system.
Author: PRUPPACHER
Publisher: Birkhäuser
ISBN:
Category : Juvenile Nonfiction
Languages : en
Pages : 386
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Evidence of aerosol-cloud interactions are evaluated using satellite data from MODIS, CERES, AMSR-E, reanalysis data from NCEP and data from the NASA Goddard Institute for Space Studies climate model. We evaluate a series of model simulations: (1) Exp N- aerosol direct radiative effects; (2) Exp C- Like Exp N but with aerosol effects on liquid-phase cumulus and stratus clouds; (3) Exp CN- Like Exp C but with model wind fields nudged to reanalysis data. Comparison between satellite-retrieved data and model simulations for June to August 2002, over the Atlantic Ocean indicate the following: a negative correlation between aerosol optical thickness (AOT) and cloud droplet effective radius (R{sub eff}) for all cases and satellite data, except for Exp N; a weak but negative correlation between liquid water path (LWP) and AOT for MODIS and CERES; and a robust increase in cloud cover with AOT for both MODIS and CERES. In all simulations, there is a positive correlation between AOT and both cloud cover and LWP (except in the case of LWP-AOT for Exp CN). The largest slopes are obtained for Exp N, implying that meteorological variability may be an important factor. The main fields associated with AOT variability in NCEP/MODIS data are warmer temperatures and increased subsidence for less clean cases, not well captured by the model. Simulated cloud fields compared with an enhanced data product from MODIS and AMSR-E indicate that model cloud thickness is over-predicted and cloud droplet number is within retrieval uncertainties. Since LWP fields are comparable this implies an under-prediction of R{sub eff} and thus an over-prediction of the indirect effect.
