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Bodo Ahrens - One of the best experts on this subject based on the ideXlab platform.
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the radiation budget in a regional Climate Model
Climate Dynamics, 2011Co-Authors: Steffen Kothe, Andreas Dobler, Alexander Beck, Bodo AhrensAbstract:The long- and short-wave components of the radiation budget are among the most important quantities in Climate Modelling. In this study, we evaluated the radiation budget at the earth’s surface and at the top of atmosphere over Europe as simulated by the regional Climate Model CLM. This was done by comparisons with radiation budgets as computed by the GEWEX/SRB satellite-based product and as realised in the ECMWF re-analysis ERA40. Our comparisons show that CLM has a tendency to underestimate solar radiation at the surface and the energy loss by thermal emission. We found a clear statistical dependence of radiation budget imprecision on cloud cover and surface albedo uncertainties in the solar spectrum. In contrast to cloud fraction errors, surface temperature errors have a minor impact on radiation budget uncertainties in the long-wave spectrum. We also evaluated the impact of the number of atmospheric layers used in CLM simulations. CLM simulations with 32 layers perform better than do those with 20 layers in terms of the surface radiation budget components but not in terms of the outgoing long-wave radiation and of radiation divergence. Application of the evaluation approach to similar simulations with two additional regional Climate Models confirmed the results and showed the usefulness of the approach.
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analysis of the indian summer monsoon system in the regional Climate Model cosmo clm
Journal of Geophysical Research, 2010Co-Authors: Andreas Dobler, Bodo AhrensAbstract:[1] The Indian summer monsoon (ISM) influences daily lives and economies in many countries in the South Asian region. This study analyzes the representation of the ISM system in the regional Climate Model COSMO-CLM. Simulations driven by ERA-40 reanalysis and present-day (1960–2000) data from the global Climate Model ECHAM5 are investigated. The ability of COSMO-CLM to reproduce the ISM better than the coarser-grid driving Models is tested using a set of well-established, complementary monsoon indices: the all-India monsoon rainfall, vertical wind shear indices, and an outgoing longwave radiation (OLR) index. The results show that regarding these large-scale indices the COSMO-CLM simulations are not more accurate than the driving Models. Considering the spatial distribution of rainfall, the ERA-40–driven COSMO-CLM simulations show major overestimations (about 100%) for the west coast of India and underestimations (about 50%) for the Himalayan foothills. Large biases occur in the OLR data over the Arabian Sea and the Bay of Bengal where COSMO-CLM shows high convective activity (OLR < 180 W m−2) at about 3 times as many days as observed in the monsoon season. In the ECHAM5-driven simulation, underestimations of rainfall also appear at the Himalayan foothills. Nevertheless, the application of COSMO-CLM to ECHAM5 improves the temporal correlations of the Modeled ISM indices, and the spatial patterns are better simulated in COSMO-CLM with 0.44° horizontal grid spacing than in the large-scale ECHAM5 data.
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Analysis of the Indian summer monsoon system in the regional Climate Model COSMO‐CLM
Journal of Geophysical Research, 2010Co-Authors: Andreas Dobler, Bodo AhrensAbstract:[1] The Indian summer monsoon (ISM) influences daily lives and economies in many countries in the South Asian region. This study analyzes the representation of the ISM system in the regional Climate Model COSMO-CLM. Simulations driven by ERA-40 reanalysis and present-day (1960–2000) data from the global Climate Model ECHAM5 are investigated. The ability of COSMO-CLM to reproduce the ISM better than the coarser-grid driving Models is tested using a set of well-established, complementary monsoon indices: the all-India monsoon rainfall, vertical wind shear indices, and an outgoing longwave radiation (OLR) index. The results show that regarding these large-scale indices the COSMO-CLM simulations are not more accurate than the driving Models. Considering the spatial distribution of rainfall, the ERA-40–driven COSMO-CLM simulations show major overestimations (about 100%) for the west coast of India and underestimations (about 50%) for the Himalayan foothills. Large biases occur in the OLR data over the Arabian Sea and the Bay of Bengal where COSMO-CLM shows high convective activity (OLR < 180 W m−2) at about 3 times as many days as observed in the monsoon season. In the ECHAM5-driven simulation, underestimations of rainfall also appear at the Himalayan foothills. Nevertheless, the application of COSMO-CLM to ECHAM5 improves the temporal correlations of the Modeled ISM indices, and the spatial patterns are better simulated in COSMO-CLM with 0.44° horizontal grid spacing than in the large-scale ECHAM5 data.
Andreas Dobler - One of the best experts on this subject based on the ideXlab platform.
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the radiation budget in a regional Climate Model
Climate Dynamics, 2011Co-Authors: Steffen Kothe, Andreas Dobler, Alexander Beck, Bodo AhrensAbstract:The long- and short-wave components of the radiation budget are among the most important quantities in Climate Modelling. In this study, we evaluated the radiation budget at the earth’s surface and at the top of atmosphere over Europe as simulated by the regional Climate Model CLM. This was done by comparisons with radiation budgets as computed by the GEWEX/SRB satellite-based product and as realised in the ECMWF re-analysis ERA40. Our comparisons show that CLM has a tendency to underestimate solar radiation at the surface and the energy loss by thermal emission. We found a clear statistical dependence of radiation budget imprecision on cloud cover and surface albedo uncertainties in the solar spectrum. In contrast to cloud fraction errors, surface temperature errors have a minor impact on radiation budget uncertainties in the long-wave spectrum. We also evaluated the impact of the number of atmospheric layers used in CLM simulations. CLM simulations with 32 layers perform better than do those with 20 layers in terms of the surface radiation budget components but not in terms of the outgoing long-wave radiation and of radiation divergence. Application of the evaluation approach to similar simulations with two additional regional Climate Models confirmed the results and showed the usefulness of the approach.
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analysis of the indian summer monsoon system in the regional Climate Model cosmo clm
Journal of Geophysical Research, 2010Co-Authors: Andreas Dobler, Bodo AhrensAbstract:[1] The Indian summer monsoon (ISM) influences daily lives and economies in many countries in the South Asian region. This study analyzes the representation of the ISM system in the regional Climate Model COSMO-CLM. Simulations driven by ERA-40 reanalysis and present-day (1960–2000) data from the global Climate Model ECHAM5 are investigated. The ability of COSMO-CLM to reproduce the ISM better than the coarser-grid driving Models is tested using a set of well-established, complementary monsoon indices: the all-India monsoon rainfall, vertical wind shear indices, and an outgoing longwave radiation (OLR) index. The results show that regarding these large-scale indices the COSMO-CLM simulations are not more accurate than the driving Models. Considering the spatial distribution of rainfall, the ERA-40–driven COSMO-CLM simulations show major overestimations (about 100%) for the west coast of India and underestimations (about 50%) for the Himalayan foothills. Large biases occur in the OLR data over the Arabian Sea and the Bay of Bengal where COSMO-CLM shows high convective activity (OLR < 180 W m−2) at about 3 times as many days as observed in the monsoon season. In the ECHAM5-driven simulation, underestimations of rainfall also appear at the Himalayan foothills. Nevertheless, the application of COSMO-CLM to ECHAM5 improves the temporal correlations of the Modeled ISM indices, and the spatial patterns are better simulated in COSMO-CLM with 0.44° horizontal grid spacing than in the large-scale ECHAM5 data.
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Analysis of the Indian summer monsoon system in the regional Climate Model COSMO‐CLM
Journal of Geophysical Research, 2010Co-Authors: Andreas Dobler, Bodo AhrensAbstract:[1] The Indian summer monsoon (ISM) influences daily lives and economies in many countries in the South Asian region. This study analyzes the representation of the ISM system in the regional Climate Model COSMO-CLM. Simulations driven by ERA-40 reanalysis and present-day (1960–2000) data from the global Climate Model ECHAM5 are investigated. The ability of COSMO-CLM to reproduce the ISM better than the coarser-grid driving Models is tested using a set of well-established, complementary monsoon indices: the all-India monsoon rainfall, vertical wind shear indices, and an outgoing longwave radiation (OLR) index. The results show that regarding these large-scale indices the COSMO-CLM simulations are not more accurate than the driving Models. Considering the spatial distribution of rainfall, the ERA-40–driven COSMO-CLM simulations show major overestimations (about 100%) for the west coast of India and underestimations (about 50%) for the Himalayan foothills. Large biases occur in the OLR data over the Arabian Sea and the Bay of Bengal where COSMO-CLM shows high convective activity (OLR < 180 W m−2) at about 3 times as many days as observed in the monsoon season. In the ECHAM5-driven simulation, underestimations of rainfall also appear at the Himalayan foothills. Nevertheless, the application of COSMO-CLM to ECHAM5 improves the temporal correlations of the Modeled ISM indices, and the spatial patterns are better simulated in COSMO-CLM with 0.44° horizontal grid spacing than in the large-scale ECHAM5 data.
Jan Seibert - One of the best experts on this subject based on the ideXlab platform.
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bias correction of regional Climate Model simulations for hydrological Climate change impact studies review and evaluation of different methods
Journal of Hydrology, 2012Co-Authors: Claudia Teutschbein, Jan SeibertAbstract:Despite the increasing use of regional Climate Model (RCM) simulations in hydrological Climate-change impact studies, their application is challenging due to the risk of considerable biases. To dea ...
Filippo Giorgi - One of the best experts on this subject based on the ideXlab platform.
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assessing the contribution of different factors in regional Climate Model projections using the factor separation method
Atmospheric Science Letters, 2014Co-Authors: Csaba Torma, Filippo GiorgiAbstract:This study applies the factor separation (FS) method to investigate the contributions of different factors, along with their synergy, on a set of regional Climate Model (RCM) projections for the Mediterranean region. The FS method is applied to six projections for the period 1970–2100 performed with the regional Model RegCM4 over the Med-CORDEX domain. Two different sets of factors are intercompared, namely the driving global Climate Model (GCM) boundary conditions against two Model physics settings (convection scheme and irrigation). We demonstrate the usefulness of the FS method to assess different sources of uncertainty in RCM-based regional Climate projections.
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An atmosphere–ocean regional Climate Model for the Mediterranean area: assessment of a present Climate simulation
Climate Dynamics, 2010Co-Authors: Vincenzo Artale, Sandro Calmanti, Marine Herrmann, Paolo M. Ruti, Alessandro Dell’aquila, Giovanna Pisacane, Gianmaria Sannino, A. Carillo, Maria Vittoria Struglia, Filippo GiorgiAbstract:We present an atmosphere–ocean regional Climate Model for the Mediterranean basin, called the PROTHEUS system, composed by the regional Climate Model RegCM3 as the atmospheric component and by a regional configuration of the MITgcm Model as the oceanic component. The Model is applied to an area encompassing the Mediterranean Sea and compared to a stand-alone version of its atmospheric component. An assessment of the Model performances is done by using available observational datasets. Despite a persistent bias, the PROTHEUS system is able to capture the inter-annual variability of seasonal sea surface temperature (SST) and also the fine scale spatio-temporal evolution of observed SST anomalies, with spatial correlation as high as 0.7 during summer. The close inspection of a 10-day strong wind event during the summer of 2000 proves the capability of the PROTHEUS system to correctly describe the daily evolution of SST under strong air–sea interaction conditions. As a consequence of the Model’s skill in reproducing observed SST and wind fields, we expect a reliable estimation of air–sea fluxes. The Model skill in reproducing climatological land surface fields is in line with that of state of the art regional Climate Models.
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an atmosphere ocean regional Climate Model for the mediterranean area assessment of a present Climate simulation
Climate Dynamics, 2010Co-Authors: Vincenzo Artale, Sandro Calmanti, Marine Herrmann, Paolo M. Ruti, Giovanna Pisacane, Gianmaria Sannino, A. Carillo, Maria Vittoria Struglia, Alessandro Dellaquila, Filippo GiorgiAbstract:We present an atmosphere–ocean regional Climate Model for the Mediterranean basin, called the PROTHEUS system, composed by the regional Climate Model RegCM3 as the atmospheric component and by a regional configuration of the MITgcm Model as the oceanic component. The Model is applied to an area encompassing the Mediterranean Sea and compared to a stand-alone version of its atmospheric component. An assessment of the Model performances is done by using available observational datasets. Despite a persistent bias, the PROTHEUS system is able to capture the inter-annual variability of seasonal sea surface temperature (SST) and also the fine scale spatio-temporal evolution of observed SST anomalies, with spatial correlation as high as 0.7 during summer. The close inspection of a 10-day strong wind event during the summer of 2000 proves the capability of the PROTHEUS system to correctly describe the daily evolution of SST under strong air–sea interaction conditions. As a consequence of the Model’s skill in reproducing observed SST and wind fields, we expect a reliable estimation of air–sea fluxes. The Model skill in reproducing climatological land surface fields is in line with that of state of the art regional Climate Models.
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development of a second generation regional Climate Model regcm2 part i boundary layer and radiative transfer processes
Monthly Weather Review, 1993Co-Authors: Filippo Giorgi, Maria Rosaria Marinucci, Gary T BatesAbstract:Abstract During the last few years the development of a second-generation regional Climate Modeling system (RegCM2) has been completed at the National Center for Atmospheric Research (NCAR). Based upon the National Center for Atmospheric Research-Pennsylvania State University Mesoscale Model (MM4), RegCM2 includes improved formulations of boundary layer, radiative transfer, surface physics, cumulus convection, and time integration technique, which make it more physically comprehensive and more computationally efficient than the previous regional Climate Model version. This paper discusses a number of month-long simulations over the European region that were conducted to test the new RegCM2 boundary-layer parameterization (the scheme developed by Holtsag et al.) and radiative transfer formulation [the package developed for the NCAR Community Climate Model 2 (CCM 2)]. Both schemes significantly affect the Model precipitation, temperature, moisture, and cloudiness climatology, leading to overall more realist...
D. E. Kinnison - One of the best experts on this subject based on the ideXlab platform.
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The global impact of supersaturation in a coupled chemistry-Climate Model
Atmospheric Chemistry and Physics, 2007Co-Authors: A. Gettelman, D. E. KinnisonAbstract:Ice supersaturation is important for understanding condensation in the upper troposphere. Many general circulation Models however do not permit supersaturation. In this study, a coupled chemistry Climate Model, the Whole Atmosphere Community Climate Model (WACCM), is modified to include supersaturation for the ice phase. Rather than a study of a detailed parameterization of supersaturation, the study is intended as a sensitivity experiment, to understand the potential impact of supersaturation, and of expected changes to stratospheric water vapor, on Climate and chemistry. High clouds decrease and water vapor in the stratosphere increases at a similar rate to the prescribed supersaturation (20% supersaturation increases water vapor by nearly 20%). The stratospheric Brewer-Dobson circulation slows at high southern latitudes, consistent with slight changes in temperature likely induced by changes to cloud radiative forcing. The cloud changes also cause an increase in the seasonal cycle of near tropopause temperatures, increasing them in boreal summer over boreal winter. There are also impacts on chemistry, with small increases in ozone in the tropical lower stratosphere driven by enhanced production. The radiative impact of changing water vapor is dominated by the reduction in cloud forcing associated with fewer clouds (~+0.6 Wm?2) with a small component likely from the radiative effect (greenhouse trapping) of the extra water vapor (~+0.2 Wm?2), consistent with previous work. Representing supersaturation is thus important, and changes to supersaturation resulting from changes in aerosol loading for example, might have a modest impact on global radiative forcing, mostly through changes to clouds. There is no evidence of a strong impact of water vapor on tropical tropopause temperatures.
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The global impact of supersaturation in a coupled chemistry-Climate Model
Atmospheric Chemistry and Physics Discussions, 2006Co-Authors: A. Gettelman, D. E. KinnisonAbstract:Ice supersaturation is important for understanding condensation in the upper troposphere. Most general circulation Models however do not permit supersaturation. In this study, a coupled chemistry Climate Model, the Whole Atmosphere Community Climate Model (WACCM), is modified to include supersaturation for the ice phase. The study is intended as a sensitivity experiment, to understand the potential impact of supersaturation, and of expected changes to stratospheric water vapor, on Climate and chemistry. Results indicate that high clouds decrease and water vapor in the stratosphere increases nearly linearly with supersaturation (20% supersaturation increases water vapor by nearly 20%). The stratospheric Brewer-Dobson circulation slows at high southern latitudes, consistent with slight changes in temperature likely induced by changes to cloud radiative forcing. The cloud changes also cause an increase in the seasonal cycle of near tropopause temperatures, increasing them in boreal summer over boreal winter. There are also impacts on chemistry, with small increases in ozone in the tropical lower stratosphere driven by enhanced production. The radiative impact of changing water vapor is dominated by the reduction in cloud forcing associated with fewer clouds (~+0.6 Wm?2) with a small component likely from radiative effect (greenhouse trapping) of the extra water vapor (~+0.2 Wm?2), consistent with previous work. Representing supersaturation is thus important, and changes to supersaturation resulting from changes in aerosol loading for example, might have a modest impact on global radiative forcing, mostly through changes to clouds. We do not see evidence of a strong impact of water vapor on tropical tropopause temperatures.
