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J T Kiehl - One of the best experts on this subject based on the ideXlab platform.
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a description of the global sulfur cycle and its controlling processes in the national center for atmospheric Research Community climate model version 3
Journal of Geophysical Research, 2000Co-Authors: Philip J Rasch, J T Kiehl, Mary C Barth, Stephen E Schwartz, Carmen M BenkovitzAbstract:We examine the balance between processes that contribute to the global and regional distributions of sulfate aerosol in the Earth's atmosphere using a set of simulations from the National Center for Atmospheric Research Community Climate Model, Version 3. The analysis suggests that the seasonal cycle of SO2 and SO42− are controlled by a complex interplay between transport, chemistry and deposition processes. The seasonal cycle of these species is not strongly controlled by temporal variations in emissions but by seasonal variations in volume of air processed by clouds, mass of liquid water serving as a site for aqueous chemistry, amount of oxidant available for the conversion from SO2 to SO42−, vertical transport processes, and deposition. A tagging of the sulfate by emission region (Europe, North America, Asia, and rest of world [ROW]), chemical pathway (gaseous versus in-cloud), and type of emissions (anthropogenic versus biogenic) is used to differentiate the balance of processes controlling the production and loading from this material. Significant differences exist in the destiny of SO2 molecules emitted from the several regions. An SO2 molecule emitted from the ROW source region has a much greater potential to form sulfate than one emitted from, for example, Europe. A greater fraction of the SO2 molecules is oxidized that originate from ROW compared with other areas, and once formed, the sulfate has a longer residence time (that is, it is not readily scavenged). The yield of sulfate from ROW sources of SO2 is a factor of 4 higher than that of Europe. A substantially higher fraction of the SO2 emitted over Europe is oxidized to sulfate through the ozone pathway compared to other regions. The analysis suggests that there are significant differences in the vertical distribution, and horizontal extent, of the propagation of sulfate emitted from the several source regions. Sulfate from Asian source regions reaches the farthest from its point of origin and makes a significant contribution to burdens in both hemispheres, primarily from plumes reaching out in the upper troposphere. Sulfate from other source regions tends to remain trapped in their hemisphere of origin.
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the national center for atmospheric Research Community climate model ccm3
Journal of Climate, 1998Co-Authors: J T Kiehl, Byron A Boville, David L Williamson, Gordon B Bonan, James J. Hack, Philip J RaschAbstract:The latest version of the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM3) is described. The changes in both physical and dynamical formulation from CCM2 to CCM3 are presented. The major differences in CCM3 compared to CCM2 include changes to the parameterization of cloud properties, clear sky longwave radiation, deep convection, boundary layer processes, and land surface processes. A brief description of each of these parameterization changes is provided. These modifications to model physics have led to dramatic improvements in the simulated climate of the CCM. In particular, the top of atmosphere cloud radiative forcing is now in good agreement with observations, the Northern Hemisphere winter dynamical simulation has significantly improved, biases in surface land temperatures and precipitation have been substantially reduced, and the implied ocean heat transport is in very good agreement with recent observational estimates. The improvement in implied ocean heat transport is among the more important attributes of the CCM3 since it is used as the atmospheric component of the NCAR Climate System Model. Future improvements to the CCM3 are also discussed.
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the simulated earth radiation budget of the national center for atmospheric Research Community climate model ccm2 and comparisons with the earth radiation budget experiment erbe
Journal of Geophysical Research, 1994Co-Authors: J T Kiehl, James J. Hack, Bruce P BrieglebAbstract:This study documents the Earth radiation budget as simulated by the latest version of the National Center for Atmospheric Research Community climate model (CCM2). The validation of the simulated Earth radiation budget is carried out through comparison with Earth Radiation Budget Experiment (ERBE) data. The study also documents the new cloud parameterization employed by CCM2. In general, the radiation budget of CCM2 is in better agreement with the ERBE data than previous versions of the CCM. In particular, the latitudinal structure of cloud radiative forcing is much improved over CCM1. The phase of the simulated seasonal cycle in top of atmosphere radiation quantities is well represented. In the tropics the magnitude is in good agreement with the observations from ERBE. In the northern hemisphere summer the model radiative properties contain a bias. In the shortwave spectral region the clouds reflect an insufficient amount of solar radiation, while in the longwave, too much radiation is emitted to space. These biases are associated with deficiencies in the cloud optical properties, namely, cloud liquid water path and cloud effective radius specification.
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Climate statistics from the National Center for Atmospheric Research Community climate model CCM2
Journal of Geophysical Research, 1994Co-Authors: James J. Hack, Byron A Boville, J T Kiehl, Philip J Rasch, David L WilliamsonAbstract:Climatological statistics are shown from a 20-year simulation conducted with the National Center for Atmospheric Research (NCAR) Community Climate Model, version 2 (CCM2), using an annually repeating prescribed sea surface temperature climatology. In most regards, the simulated climate is significantly improved over earlier versions of the CCM, particularly with respect to mean climatological biases. The tropospheric thermodynamic cold and dry bias that has historically plagued the CCM is largely eliminated. Additionally, several aspects of the large-scale circulation are more faithfully reproduced, with significant improvements in the southern hemisphere circulation. Although most aspects of the CCM2 simulation are improved over those of previous model releases, there are some important elements of the climatology where the simulation is no better than, or in some cases degraded from, the earlier versions. The problem of a cold polar tropopause, although slightly improved, continues to be a major weakness of the simulation. Another more serious deficiency in the simulation is a warm bias in the northern hemisphere summer circulation, which affects the lower tropospheric and surface climate, as well as the top-of-atmosphere radiation budget. An aspect of the simulation that degrades certain characteristics of the midlatitude winter circulation when compared to the CCM1 is anmore » anomalous southwestward displacement of diabatic heating in the western Pacific. A large component of the northern hemisphere summer warm bias and the shift in western Pacific deep convection are related to limitations in the CCM2 diagnosis of cloud optical properties. Unrealistic nonlinear interactions between moist convection and atmospheric boundary layer processes also play a role in tropical precipitation distribution deficiencies.« less
Philip J Rasch - One of the best experts on this subject based on the ideXlab platform.
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a description of the global sulfur cycle and its controlling processes in the national center for atmospheric Research Community climate model version 3
Journal of Geophysical Research, 2000Co-Authors: Philip J Rasch, J T Kiehl, Mary C Barth, Stephen E Schwartz, Carmen M BenkovitzAbstract:We examine the balance between processes that contribute to the global and regional distributions of sulfate aerosol in the Earth's atmosphere using a set of simulations from the National Center for Atmospheric Research Community Climate Model, Version 3. The analysis suggests that the seasonal cycle of SO2 and SO42− are controlled by a complex interplay between transport, chemistry and deposition processes. The seasonal cycle of these species is not strongly controlled by temporal variations in emissions but by seasonal variations in volume of air processed by clouds, mass of liquid water serving as a site for aqueous chemistry, amount of oxidant available for the conversion from SO2 to SO42−, vertical transport processes, and deposition. A tagging of the sulfate by emission region (Europe, North America, Asia, and rest of world [ROW]), chemical pathway (gaseous versus in-cloud), and type of emissions (anthropogenic versus biogenic) is used to differentiate the balance of processes controlling the production and loading from this material. Significant differences exist in the destiny of SO2 molecules emitted from the several regions. An SO2 molecule emitted from the ROW source region has a much greater potential to form sulfate than one emitted from, for example, Europe. A greater fraction of the SO2 molecules is oxidized that originate from ROW compared with other areas, and once formed, the sulfate has a longer residence time (that is, it is not readily scavenged). The yield of sulfate from ROW sources of SO2 is a factor of 4 higher than that of Europe. A substantially higher fraction of the SO2 emitted over Europe is oxidized to sulfate through the ozone pathway compared to other regions. The analysis suggests that there are significant differences in the vertical distribution, and horizontal extent, of the propagation of sulfate emitted from the several source regions. Sulfate from Asian source regions reaches the farthest from its point of origin and makes a significant contribution to burdens in both hemispheres, primarily from plumes reaching out in the upper troposphere. Sulfate from other source regions tends to remain trapped in their hemisphere of origin.
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the national center for atmospheric Research Community climate model ccm3
Journal of Climate, 1998Co-Authors: J T Kiehl, Byron A Boville, David L Williamson, Gordon B Bonan, James J. Hack, Philip J RaschAbstract:The latest version of the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM3) is described. The changes in both physical and dynamical formulation from CCM2 to CCM3 are presented. The major differences in CCM3 compared to CCM2 include changes to the parameterization of cloud properties, clear sky longwave radiation, deep convection, boundary layer processes, and land surface processes. A brief description of each of these parameterization changes is provided. These modifications to model physics have led to dramatic improvements in the simulated climate of the CCM. In particular, the top of atmosphere cloud radiative forcing is now in good agreement with observations, the Northern Hemisphere winter dynamical simulation has significantly improved, biases in surface land temperatures and precipitation have been substantially reduced, and the implied ocean heat transport is in very good agreement with recent observational estimates. The improvement in implied ocean heat transport is among the more important attributes of the CCM3 since it is used as the atmospheric component of the NCAR Climate System Model. Future improvements to the CCM3 are also discussed.
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Climate statistics from the National Center for Atmospheric Research Community climate model CCM2
Journal of Geophysical Research, 1994Co-Authors: James J. Hack, Byron A Boville, J T Kiehl, Philip J Rasch, David L WilliamsonAbstract:Climatological statistics are shown from a 20-year simulation conducted with the National Center for Atmospheric Research (NCAR) Community Climate Model, version 2 (CCM2), using an annually repeating prescribed sea surface temperature climatology. In most regards, the simulated climate is significantly improved over earlier versions of the CCM, particularly with respect to mean climatological biases. The tropospheric thermodynamic cold and dry bias that has historically plagued the CCM is largely eliminated. Additionally, several aspects of the large-scale circulation are more faithfully reproduced, with significant improvements in the southern hemisphere circulation. Although most aspects of the CCM2 simulation are improved over those of previous model releases, there are some important elements of the climatology where the simulation is no better than, or in some cases degraded from, the earlier versions. The problem of a cold polar tropopause, although slightly improved, continues to be a major weakness of the simulation. Another more serious deficiency in the simulation is a warm bias in the northern hemisphere summer circulation, which affects the lower tropospheric and surface climate, as well as the top-of-atmosphere radiation budget. An aspect of the simulation that degrades certain characteristics of the midlatitude winter circulation when compared to the CCM1 is anmore » anomalous southwestward displacement of diabatic heating in the western Pacific. A large component of the northern hemisphere summer warm bias and the shift in western Pacific deep convection are related to limitations in the CCM2 diagnosis of cloud optical properties. Unrealistic nonlinear interactions between moist convection and atmospheric boundary layer processes also play a role in tropical precipitation distribution deficiencies.« less
James J. Hack - One of the best experts on this subject based on the ideXlab platform.
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the national center for atmospheric Research Community climate model ccm3
Journal of Climate, 1998Co-Authors: J T Kiehl, Byron A Boville, David L Williamson, Gordon B Bonan, James J. Hack, Philip J RaschAbstract:The latest version of the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM3) is described. The changes in both physical and dynamical formulation from CCM2 to CCM3 are presented. The major differences in CCM3 compared to CCM2 include changes to the parameterization of cloud properties, clear sky longwave radiation, deep convection, boundary layer processes, and land surface processes. A brief description of each of these parameterization changes is provided. These modifications to model physics have led to dramatic improvements in the simulated climate of the CCM. In particular, the top of atmosphere cloud radiative forcing is now in good agreement with observations, the Northern Hemisphere winter dynamical simulation has significantly improved, biases in surface land temperatures and precipitation have been substantially reduced, and the implied ocean heat transport is in very good agreement with recent observational estimates. The improvement in implied ocean heat transport is among the more important attributes of the CCM3 since it is used as the atmospheric component of the NCAR Climate System Model. Future improvements to the CCM3 are also discussed.
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the simulated earth radiation budget of the national center for atmospheric Research Community climate model ccm2 and comparisons with the earth radiation budget experiment erbe
Journal of Geophysical Research, 1994Co-Authors: J T Kiehl, James J. Hack, Bruce P BrieglebAbstract:This study documents the Earth radiation budget as simulated by the latest version of the National Center for Atmospheric Research Community climate model (CCM2). The validation of the simulated Earth radiation budget is carried out through comparison with Earth Radiation Budget Experiment (ERBE) data. The study also documents the new cloud parameterization employed by CCM2. In general, the radiation budget of CCM2 is in better agreement with the ERBE data than previous versions of the CCM. In particular, the latitudinal structure of cloud radiative forcing is much improved over CCM1. The phase of the simulated seasonal cycle in top of atmosphere radiation quantities is well represented. In the tropics the magnitude is in good agreement with the observations from ERBE. In the northern hemisphere summer the model radiative properties contain a bias. In the shortwave spectral region the clouds reflect an insufficient amount of solar radiation, while in the longwave, too much radiation is emitted to space. These biases are associated with deficiencies in the cloud optical properties, namely, cloud liquid water path and cloud effective radius specification.
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Climate statistics from the National Center for Atmospheric Research Community climate model CCM2
Journal of Geophysical Research, 1994Co-Authors: James J. Hack, Byron A Boville, J T Kiehl, Philip J Rasch, David L WilliamsonAbstract:Climatological statistics are shown from a 20-year simulation conducted with the National Center for Atmospheric Research (NCAR) Community Climate Model, version 2 (CCM2), using an annually repeating prescribed sea surface temperature climatology. In most regards, the simulated climate is significantly improved over earlier versions of the CCM, particularly with respect to mean climatological biases. The tropospheric thermodynamic cold and dry bias that has historically plagued the CCM is largely eliminated. Additionally, several aspects of the large-scale circulation are more faithfully reproduced, with significant improvements in the southern hemisphere circulation. Although most aspects of the CCM2 simulation are improved over those of previous model releases, there are some important elements of the climatology where the simulation is no better than, or in some cases degraded from, the earlier versions. The problem of a cold polar tropopause, although slightly improved, continues to be a major weakness of the simulation. Another more serious deficiency in the simulation is a warm bias in the northern hemisphere summer circulation, which affects the lower tropospheric and surface climate, as well as the top-of-atmosphere radiation budget. An aspect of the simulation that degrades certain characteristics of the midlatitude winter circulation when compared to the CCM1 is anmore » anomalous southwestward displacement of diabatic heating in the western Pacific. A large component of the northern hemisphere summer warm bias and the shift in western Pacific deep convection are related to limitations in the CCM2 diagnosis of cloud optical properties. Unrealistic nonlinear interactions between moist convection and atmospheric boundary layer processes also play a role in tropical precipitation distribution deficiencies.« less
Heber Macmahon - One of the best experts on this subject based on the ideXlab platform.
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lung image database consortium developing a resource for the medical imaging Research Community
Radiology, 2004Co-Authors: Samuel G Armato, Geoffrey Mclennan, Michael F Mcnittgray, Charles R Meyer, David F Yankelevitz, Denise R Aberle, Claudia I Henschke, Eric A Hoffman, Ella A Kazerooni, Heber MacmahonAbstract:To stimulate the advancement of computer-aided diagnostic (CAD) Research for lung nodules in thoracic computed tomography (CT), the National Cancer Institute launched a cooperative effort known as the Lung Image Database Consortium (LIDC). The LIDC is composed of five academic institutions from across the United States that are working together to develop an image database that will serve as an international Research resource for the development, training, and evaluation of CAD methods in the detection of lung nodules on CT scans. Prior to the collection of CT images and associated patient data, the LIDC has been engaged in a consensus process to identify, address, and resolve a host of challenging technical and clinical issues to provide a solid foundation for a scientifically robust database. These issues include the establishment of (a) a governing mission statement, (b) criteria to determine whether a CT scan is eligible for inclusion in the database, (c) an appropriate definition of the term qualifyi...
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lung image database consortium developing a resource for the medical imaging Research Community
Radiology, 2004Co-Authors: Samuel G Armato, Geoffrey Mclennan, Michael F Mcnittgray, Charles R Meyer, David F Yankelevitz, Denise R Aberle, Claudia I Henschke, Eric A Hoffman, Ella A Kazerooni, Heber MacmahonAbstract:To stimulate the advancement of computer-aided diagnostic (CAD) Research for lung nodules in thoracic computed tomography (CT), the National Cancer Institute launched a cooperative effort known as the Lung Image Database Consortium (LIDC). The LIDC is composed of five academic institutions from across the United States that are working together to develop an image database that will serve as an international Research resource for the development, training, and evaluation of CAD methods in the detection of lung nodules on CT scans. Prior to the collection of CT images and associated patient data, the LIDC has been engaged in a consensus process to identify, address, and resolve a host of challenging technical and clinical issues to provide a solid foundation for a scientifically robust database. These issues include the establishment of (a) a governing mission statement, (b) criteria to determine whether a CT scan is eligible for inclusion in the database, (c) an appropriate definition of the term qualifying nodule, (d) an appropriate definition of "truth" requirements, (e) a process model through which the database will be populated, and (f) a statistical framework to guide the application of assessment methods by users of the database. Through a consensus process in which careful planning and proper consideration of fundamental issues have been emphasized, the LIDC database is expected to provide a powerful resource for the medical imaging Research Community. This article is intended to share with the Community the breadth and depth of these key issues.
David L Williamson - One of the best experts on this subject based on the ideXlab platform.
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the national center for atmospheric Research Community climate model ccm3
Journal of Climate, 1998Co-Authors: J T Kiehl, Byron A Boville, David L Williamson, Gordon B Bonan, James J. Hack, Philip J RaschAbstract:The latest version of the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM3) is described. The changes in both physical and dynamical formulation from CCM2 to CCM3 are presented. The major differences in CCM3 compared to CCM2 include changes to the parameterization of cloud properties, clear sky longwave radiation, deep convection, boundary layer processes, and land surface processes. A brief description of each of these parameterization changes is provided. These modifications to model physics have led to dramatic improvements in the simulated climate of the CCM. In particular, the top of atmosphere cloud radiative forcing is now in good agreement with observations, the Northern Hemisphere winter dynamical simulation has significantly improved, biases in surface land temperatures and precipitation have been substantially reduced, and the implied ocean heat transport is in very good agreement with recent observational estimates. The improvement in implied ocean heat transport is among the more important attributes of the CCM3 since it is used as the atmospheric component of the NCAR Climate System Model. Future improvements to the CCM3 are also discussed.
-
Climate statistics from the National Center for Atmospheric Research Community climate model CCM2
Journal of Geophysical Research, 1994Co-Authors: James J. Hack, Byron A Boville, J T Kiehl, Philip J Rasch, David L WilliamsonAbstract:Climatological statistics are shown from a 20-year simulation conducted with the National Center for Atmospheric Research (NCAR) Community Climate Model, version 2 (CCM2), using an annually repeating prescribed sea surface temperature climatology. In most regards, the simulated climate is significantly improved over earlier versions of the CCM, particularly with respect to mean climatological biases. The tropospheric thermodynamic cold and dry bias that has historically plagued the CCM is largely eliminated. Additionally, several aspects of the large-scale circulation are more faithfully reproduced, with significant improvements in the southern hemisphere circulation. Although most aspects of the CCM2 simulation are improved over those of previous model releases, there are some important elements of the climatology where the simulation is no better than, or in some cases degraded from, the earlier versions. The problem of a cold polar tropopause, although slightly improved, continues to be a major weakness of the simulation. Another more serious deficiency in the simulation is a warm bias in the northern hemisphere summer circulation, which affects the lower tropospheric and surface climate, as well as the top-of-atmosphere radiation budget. An aspect of the simulation that degrades certain characteristics of the midlatitude winter circulation when compared to the CCM1 is anmore » anomalous southwestward displacement of diabatic heating in the western Pacific. A large component of the northern hemisphere summer warm bias and the shift in western Pacific deep convection are related to limitations in the CCM2 diagnosis of cloud optical properties. Unrealistic nonlinear interactions between moist convection and atmospheric boundary layer processes also play a role in tropical precipitation distribution deficiencies.« less
