Analyzing Signatures of Aerosol-cloud Interactions from Satelliteretrievals and the GISS GCM to Constrain the Aerosol Indirecteffect PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Analyzing Signatures of Aerosol-cloud Interactions from Satelliteretrievals and the GISS GCM to Constrain the Aerosol Indirecteffect PDF full book. Access full book title Analyzing Signatures of Aerosol-cloud Interactions from Satelliteretrievals and the GISS GCM to Constrain the Aerosol Indirecteffect by . Download full books in PDF and EPUB format.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
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.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
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.
Author: Mian Chin
Publisher: DIANE Publishing
ISBN: 1437912613
Category : Science
Languages : en
Pages : 128
Get Book Here
Book Description
This Synthesis and Assessment Product (SAP) critically reviews current knowledge about global distributions and properties of atmospheric aerosols, as they relate to aerosol impacts on climate. It assesses possible next steps aimed at substantially reducing uncertainties in aerosol radiative forcing estimates. Current measurement techniques and modeling approaches are summarized, providing context. The objectives of this report are: (1) to promote a consensus about the knowledge base for climate change decision support; and (2) to provide a synthesis and integration of the current knowledge of the climate-relevant impacts of anthropogenic aerosols. Illustrations.
Author:
Publisher:
ISBN:
Category : Atmospheric ozone
Languages : en
Pages : 128
Get Book Here
Book Description
Author: Ghassem R. Asrar
Publisher: Springer Science & Business Media
ISBN: 9400766920
Category : Science
Languages : en
Pages : 506
Get Book Here
Book Description
This volume offers a comprehensive survey and a close analysis of efforts to develop actionable climate information in support of vital decisions for climate adaptation, risk management and policy. Arising from submissions and discussion at the 2011 Open Science Conference (OSC) of the World Climate Research Program (WCRP), the book addresses research and intellectual challenges which span the full range of Program activities.
Author: Alyson Douglas
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Get Book Here
Book Description
When aerosols enter the atmosphere through anthropogenic and natural activities, they interact with clouds in the atmosphere in what is termed aerosol-cloud interactions (ACI). ACI alter the cloud's radiative properties by acting as cloud condensation nuclei within the cloud, thereby reducing the mean drop size and increasing the cloud's albedo and cooling the earth by reflecting incoming shortwave radiation in what is termed the first indirect effect. By reducing the mean drop size throughout the cloud, aerosol also act to delay precipitation formation, leading to larger, longer lived clouds and further cooling the earth in a process known as the second indirect effect. Using four years of satellite observations, the overall impact of aerosols on warm cloud radiative effect is evaluated. Warm clouds are defined as clouds with cloud top temperatures below freezing level. The estimates are constrained within regimes of stability, relative humidity of the free atmosphere, and by the scene liquid water path to control for how meteorology modulates the strength and sign of ACI. The sum of the first and second indirect effect, estimates of how aerosols alter the warm cloud shortwave effect and cloud fraction, are compared to an estimate of the full indirect effect, which includes all changes to the warm cloud shortwave radiative effect. The decomposed, or summative, indirect effect (-0.26 +/- .15 Wm2) is less than the full indirect effect (-0.32 +/- .16 Wm2), though they lie within each other's uncertainty estimates. When the decomposed indirect effect is further constrained by precipitation, the estimate decreases to .21 +/- .15 Wm2. The difference between the full indirect effect forcing and the decomposed forcings may be secondary indirect effects not included in our decomposition. The second indirect effect includes not only the cloud extent broadening, but the cloud depth increasing. This deepening response may increase warming due to a larger longwave cloud radiative effect. The longwave indirect effect susceptibility is decomposed to determine how large it may potentially be and whether it could offset any cooling due to the shortwave indirect effect. We find the longwave indirect effect does have the potential to offset cooling through cloud deepening in regions where the shortwave indirect effect is extremely small, however the magnitude of the longwave component is sensitive to the diurnal cycle. Cloud deepening signals clouds may be invigorated, or experiencing a state where precipitation formation and turbulence increase due to ACI. The effects of aerosol on precipitation formation and vertical motion are investigated using WALRUS, an algorithm of latent heating within the cloud determined using CloudSat radar returns. The LWP is constrained to thicker clouds 150 gm2
Author: National Academies of Sciences, Engineering, and Medicine
Publisher: National Academies Press
ISBN: 0309443458
Category : Science
Languages : en
Pages : 53
Get Book Here
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:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Aerosol indirect effects continue to constitute one of the most important uncertainties for anthropogenic climate perturbations. Within the international AEROCOM initiative, the representation of aerosol-cloud-radiation interactions in ten different general circulation models (GCMs) is evaluated using three satellite datasets. The focus is on stratiform liquid water clouds since most GCMs do not include ice nucleation effects, and none of the model explicitly parameterizes aerosol effects on convective clouds. We compute statistical relationships between aerosol optical depth (Ta) and various cloud and radiation quantities in a manner that is consistent between the models and the satellite data. It is found that the model-simulated influence of aerosols on cloud droplet number concentration (Nd) compares relatively well to the satellite data at least over the ocean. The relationship between Ta and liquid water path is simulated much too strongly by the models. It is shown that this is partly related to the representation of the second aerosol indirect effect in terms of autoconversion. A positive relationship between total cloud fraction (fcld) and Ta as found in the satellite data is simulated by the majority of the models, albeit less strongly than that in the satellite data in most of them. In a discussion of the hypotheses proposed in the literature to explain the satellite-derived strong fcld - Ta relationship, our results indicate that none can be identified as unique explanation. Relationships similar to the ones found in satellite data between Ta and cloud top temperature or outgoing long-wave radiation (OLR) are simulated by only a few GCMs. The GCMs that simulate a negative OLR - Ta relationship show a strong positive correlation between Ta and fcld The short-wave total aerosol radiative forcing as simulated by the GCMs is strongly influenced by the simulated anthropogenic fraction of Ta, and parameterisation assumptions such as a lower bound on Nd. Nevertheless, the strengths of the statistical relationships are good predictors for the aerosol forcings in the models. An estimate of the total short-wave aerosol forcing inferred from the combination of these predictors for the modelled forcings with the satellite-derived statistical relationships yields a global annual mean value of -1.5+-0.5 Wm-2. An alternative estimate obtained by scaling the simulated clear- and cloudy-sky forcings with estimates of anthropogenic Ta and satellite-retrieved Nd - Ta regression slopes, respectively, yields a global annual mean clear-sky (aerosol direct effect) estimate of -0.4+-0.2 Wm-2 and a cloudy-sky (aerosol indirect effect) estimate of -0.7+-0.5 Wm-2, with a total estimate of -1.2+-0.4 Wm-2.
Author: Benjamin Stephen Grandey
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Microphysical and dynamical interactions between aerosols and clouds are associated with some of the largest uncertainties in projections of future climate. Many possible aerosol effects on clouds have been suggested, but large uncertainties remain. In order to improve model projections of fu- ture climate, it is essential that we improve our quantitative understanding of anthropogenic aerosol effects. Several studies investigating interactions between satellite-observed aerosol and cloud prop- erties have been published in recent years. However, the observed relationships are not necessarily due to aerosol effects on clouds. They may be due to cloud and precipitation effects on aerosol, me- teorological covariation, observational data errors or methodological errors. An analysis of method- ological errors arising through climatological spatial gradients is performed. For region sizes larger than 40 x 40, commonly used in the literature, spurious spatial variations in retrieved cloud and aerosol properties are found to introduce widespread significant errors to calculations of aerosol- cloud relationships. Small scale analysis prior to error-weighted aggregation to larger region sizes is recommended. Appropriate ways of quantifying relationships between aerosol optical depth (T) and cloud properties are considered, and results are presented for three satellite datasets. There is much disagreement in observed relationships between T and liquid cloud droplet number concentration and between T and liquid cloud droplet effective radius, particularly over land. However, all three satellite datasets are in agreement about strong positive relationships between T and cloud top height and between T and cloud fraction (fc). Using reanalysis T data, which are less affected by retrieval artifacts, it is suggested that a large part of the observed Ie-r signal may fc-T be due to cloud contamination of T. General circulation model simulations further demonstrate that positive fc-T relationships may primarily arise due to covariation with relative humidity, and that negative fc-T relationships may arise due to scavenging of aerosol by precipitation. A new method of investigating the contribu- tion of meteorological covariation to the observed relationships is introduced. Extratropical cyclone storm-centric composites of retrieved aerosol and cloud properties are investigated. A storm-centric description of the synoptics is found to be capable of explaining spurious fc-T relationships, although the spurious relationships explained are considerably smaller than observed relationships.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 759
Get Book Here
Book Description
Author: C. Chuang
Publisher:
ISBN:
Category :
Languages : en
Pages : 9
Get Book Here
Book Description
While considerable advances in the understanding of atmospheric processes and feedbacks in the climate system have led to a better representation of these mechanisms in general circulation models (GCMs), the greatest uncertainty in predictability of future climate arises from clouds and their interactions with radiation. To explore this uncertainty, cloud resolving model has been evolved as one of the main tools for understanding and testing cloud feedback processes in climate models, whereas the indirect effects of aerosols are closely linked with cloud feedback processes. In this study we incorporated an existing parameterization of cloud drop concentration (Chuang et al., 2002a) together with aerosol prediction from a global chemistry/aerosol model (IMPACT) (Rotman et al., 2004; Chuang et al., 2002b; Chuang et al., 2005) into LLNL cloud resolving model (Chin, 1994; Chin et al., 1995; Chin and Wilhelmson, 1998) to investigate the effects of aerosols on cloud/precipitation properties and the resulting radiation fields over the Southern Great Plains.
