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  • Keywords: Civil engineering ; Climate change management
    Notes: This book demystifies the models we use to simulate present and future climates, allowing readers to better understand how to use climate model results. In order to predict the future trajectory of the Earth’s climate, climate-system simulation models are necessary. When and how do we trust climate model predictions? The book offers a framework for answering this question. It provides readers with a basic primer on climate and climate change, and offers non-technical explanations for how climate models are constructed, why they are uncertain, and what level of confidence we should place in them. It presents current results and the key uncertainties concerning them. Uncertainty is not a weakness but understanding uncertainty is a strength and a key part of using any model, including climate models. Case studies of how climate model output has been used and how it might be used in the future are provided. The ultimate goal of this book is to promote a better understanding of the structure and uncertainties of climate models among users, including scientists, engineers and policymakers. | Contents: Basic Principles and the Problem of Climate Forecasts --- Key Concepts in Climate Modeling / Andrew Gettelman, Richard B. Rood / Pages 3-12 --- Components of the Climate System / Andrew Gettelman, Richard B. Rood / Pages 13-22 --- Climate Change and Global Warming / Andrew Gettelman, Richard B. Rood / Pages 23-35 --- Essence of a Climate Model / Andrew Gettelman, Richard B. Rood / Pages 37-58 --- Model Mechanics --- Simulating the Atmosphere / Andrew Gettelman, Richard B. Rood / Pages 61-85 --- Simulating the Ocean and Sea Ice / Andrew Gettelman, Richard B. Rood / Pages 87-108 --- Simulating Terrestrial Systems / Andrew Gettelman, Richard B. Rood / Pages 109-137 --- Bringing the System Together: Coupling and Complexity / Andrew Gettelman, Richard B. Rood / Pages 139-158 --- Using Models --- Model Evaluation / Andrew Gettelman, Richard B. Rood / Pages 161-176 --- Predictability / Andrew Gettelman, Richard B. Rood / Pages 177-197 --- Results of Current Models / Andrew Gettelman, Richard B. Rood / Pages 199-220 --- Usability of Climate Model Projections by Practitioners / Andrew Gettelman, Richard B. Rood / Pages 221-236 --- Summary and Final Thoughts / Andrew Gettelman, Richard B. Rood / Pages 237-253
    Pages: XVII, 274 S., 4 schwarz-weiß Abbildungen, 58 Farbabbildungen
    ISBN: 978-3-662-48957-4
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  • Publication Date: 2015-01-12
    Description: This work presents the development of a two-moment cloud microphysics scheme within the version 5 of the NASA Goddard Earth Observing System (GEOS-5). The scheme includes the implementation of a comprehensive stratiform microphysics module, a new cloud coverage scheme that allows ice supersaturation and a new microphysics module embedded within the moist convection parameterization of GEOS-5. Comprehensive physically-based descriptions of ice nucleation, including homogeneous and heterogeneous freezing, and liquid droplet activation are implemented to describe the formation of cloud particles in stratiform clouds and convective cumulus. The effect of preexisting ice crystals on the formation of cirrus clouds is also accounted for. A new parameterization of the subgrid scale vertical velocity distribution accounting for turbulence and gravity wave motion is developed. The implementation of the new microphysics significantly improves the representation of liquid water and ice in GEOS-5. Evaluation of the model shows agreement of the simulated droplet and ice crystal effective and volumetric radius with satellite retrievals and in situ observations. The simulated global distribution of supersaturation is also in agreement with observations. It was found that when using the new microphysics the fraction of condensate that remains as liquid follows a sigmoidal increase with temperature which differs from the linear increase assumed in most models and is in better agreement with available observations. The performance of the new microphysics in reproducing the observed total cloud fraction, longwave and shortwave cloud forcing, and total precipitation is similar to the operational version of GEOS-5 and in agreement with satellite retrievals. However the new microphysics tends to underestimate the coverage of persistent low level stratocumulus. Sensitivity studies showed that the simulated cloud properties are robust to moderate variation in cloud microphysical parameters. However significant sensitivity in ice cloud properties was found to variation in the dispersion of the ice crystal size distribution and the critical size for ice autoconversion. The implementation of the new microphysics leads to a more realistic representation of cloud processes in GEOS-5 and allows the linkage of cloud properties to aerosol emissions.
    Keywords: Geosciences (General)
    Type: GSFC-E-DAA-TN11166
    Format: application/pdf
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  • Publication Date: 2014-03-09
    Description: Several different ice nucleation parameterizations in two different General Circulation Models (GCMs) are used to understand the effects of ice nucleation on the mean climate state, and the Aerosol Indirect Effects (AIE) of cirrus clouds on climate. Simulations have a range of ice microphysical states that are consistent with the spread of observations, but many simulations have higher present-day ice crystal number concentrations than in-situ observations. These different states result from different parameterizations of ice cloud nucleation processes, and feature different balances of homogeneous and heterogeneous nucleation. Black carbon aerosols have a small (0.06 Wm(exp-2) and not statistically significant AIE when included as ice nuclei, for nucleation efficiencies within the range of laboratory measurements. Indirect effects of anthropogenic aerosols on cirrus clouds occur as a consequence of increasing anthropogenic sulfur emissions with different mechanisms important in different models. In one model this is due to increases in homogeneous nucleation fraction, and in the other due to increases in heterogeneous nucleation with coated dust. The magnitude of the effect is the same however. The resulting ice AIE does not seem strongly dependent on the balance between homogeneous and heterogeneous ice nucleation. Regional effects can reach several Wm2. Indirect effects are slightly larger for those states with less homogeneous nucleation and lower ice number concentration in the base state. The total ice AIE is estimated at 0.27 +/- 0.10 Wm(exp-2) (1 sigma uncertainty). This represents a 20% offset of the simulated total shortwave AIE for ice and liquid clouds of 1.6 Wm(sup-2).
    Keywords: Meteorology and Climatology
    Type: GSFC-E-DAA-TN8104 , Journal of Geophysical Research; Volume 112; Issue D20, 27
    Format: application/pdf
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  • Publication Date: 2014-03-09
    Description: In this study the effect of dust aerosol on upper tropospheric cirrus clouds through heterogeneous ice nucleation is investigated in the Community Atmospheric Model version 5 (CAM5) with two ice nucleation parameterizations. Both parameterizations consider homogeneous and heterogeneous nucleation and the competition between the two mechanisms in cirrus clouds, but differ significantly in the number concentration of heterogeneous ice nuclei (IN) from dust. Heterogeneous nucleation on dust aerosol reduces the occurrence frequency of homogeneous nucleation and thus the ice crystal number concentration in the Northern Hemisphere (NH) cirrus clouds compared to simulations with pure homogeneous nucleation. Global and annual mean shortwave and longwave cloud forcing are reduced by up to 2.0+/-0.1Wm (sup2) (1 uncertainty) and 2.4+/-0.1Wm (sup2), respectively due to the presence of dust IN, with the net cloud forcing change of 0.40+/-0.20W m(sup2). Comparison of model simulations with in situ aircraft data obtained in NH mid-latitudes suggests that homogeneous ice nucleation may play an important role in the ice nucleation at these regions with temperatures of 205-230 K. However, simulations overestimate observed ice crystal number concentrations in the tropical tropopause regions with temperatures of 190- 205 K, and overestimate the frequency of occurrence of high ice crystal number concentration (greater than 200 L(sup-1) and underestimate the frequency of low ice crystal number concentration (less than 30 L(sup-1) at NH mid-latitudes. These results highlight the importance of quantifying the number concentrations and properties of heterogeneous IN (including dust aerosol) in the upper troposphere from the global perspective.
    Keywords: Geophysics
    Type: GSFC-E-DAA-TN8100 , Atmospheric Chemistry and Physics; Volume 12; 12061-12079
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  • Publication Date: 2011-11-08
    Description: The motivation for this work is to better characterize the controls on the tropical upper tropospheric/lower stratospheric (UTLS) temperature and humidity.
    Keywords: Meteorology and Climatology
    Type: American Geophysical Union Fall Meeting; 17 Dec. 2010; San Francisco, CA; United States
    Format: text
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  • Publication Date: 2011-11-08
    Description: The motivation for this study was to better characterize the controls on the tropical upper tropospheric/lower stratospheric (UTLS) temperature and humidity.
    Keywords: Meteorology and Climatology
    Type: A-Train Symposium; 27 Oct. 2010; New Orleans, LA; United States
    Format: text
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  • ISSN: 1573-1480
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A Local Climate Model (LCM) is described that can provide a high-resolution (10 km) simulation of climate resulting from a doubling of atmospheric CO2 concentrations. A canonicalregression function is used to compute the monthly temperature (mean of daily-maximum-temperature) and precipitation for any point, given a set of predictor variables. Predictor variables represent the influence of terrain, sea-surface temperature (SST), windfields, CO2 concentration, and solar radiation on climate. The canonical-regression function is calibrated and validated using empirical windfield, SST, and climate data from stations in the western U.S. To illustrate an application of the LCM, the climate of northern and central California is simulated for a doubled CO2 (600 ppmv) and a control scenario (300 ppmv CO2). Windfields and SSTs used to compute predictor variables are taken from general circulation model simulations for these two scenarios. LCM solutions indicate that doubling CO2 will result in a 3 C° increase in January temperature, a 2 C° increase in July temperature, a 16 mm (37%) increase in January precipitation, and a 3 mm (46%) increase in July precipitation.
    Type of Medium: Electronic Resource
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  • Publication Date: 2017-09-29
    Description: Aerosols have a potentially large effect on climate, particularly through their interactions with clouds, but the magnitude of this effect is highly uncertain. Large volcanic eruptions produce sulfur dioxide, which in turn produces aerosols; these eruptions thus represent a natural experiment through which to quantify aerosol-cloud interactions. Here we show that the massive 2014-2015 fissure eruption in Holuhraun, Iceland, reduced the size of liquid cloud droplets - consistent with expectations - but had no discernible effect on other cloud properties. The reduction in droplet size led to cloud brightening and global-mean radiative forcing of around minus 0.2 watts per square metre for September to October 2014. Changes in cloud amount or cloud liquid water path, however, were undetectable, indicating that these indirect effects, and cloud systems in general, are well buffered against aerosol changes. This result will reduce uncertainties in future climate projections, because we are now able to reject results from climate models with an excessive liquid-water-path response.
    Keywords: Meteorology and Climatology
    Type: GSFC-E-DAA-TN46440 , Nature (ISSN 0028-0836; e-ISSN 1476-4687); Volume 546; Issue 7659; 485-491
    Format: text
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