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Causes of Ocean Surface temperature Changes in Atlantic andPacific Topical Cyclogenesis Regions

Description: Previous research has identified links between changes in sea surface temperature (SST) and hurricane intensity. We use climate models to study the possible causes of SST changes in Atlantic and Pacific tropical cyclogenesis regions. The observed SST increases in these regions range from 0.32 to 0.67 C over the 20th century. The 22 climate models examined here suggest that century-timescale SST changes of this magnitude cannot be explained solely by unforced variability of the climate system, even under conservative assumptions regarding the magnitude of this variability. Model simulations that include external forcing by combined anthropogenic and natural factors are generally capable of replicating observed SST changes in both tropical cyclogenesis regions.
Date: January 31, 2006
Creator: Santer, B.D.; Wigley, T.M.L.; Gleckler, P.J.; Bonfils, C.; Wehner, M.F.; AchutaRao, K. et al.
Partner: UNT Libraries Government Documents Department

Formulation of Moist Dynamics and Physics for Future Climate Models

Description: In this project, one of our goals is to develop atmospheric models, in which innovative ideas on improving the quality of moisture predictions can be tested. Our other goal is to develop an explicit time integration scheme based on the multi-point differencing that does the same job as an implicit trapezoidal scheme but uses information only from limited number of grid points.
Date: April 30, 2008
Creator: Arakwa, Celal S. Konor and Akio
Partner: UNT Libraries Government Documents Department

Amplification of surface temperature trends and variability in thetropical atmosphere

Description: The month-to-month variability of tropical temperatures is larger in the troposphere than at the Earth's surface. This amplification behavior is similar in a range of observations and climate model simulations, and is consistent with basic theory. On multi-decadal timescales, tropospheric amplification of surface warming is a robust feature of model simulations, but occurs in only one observational dataset. Other observations show weak or even negative amplification. These results suggest that either different physical mechanisms control amplification processes on monthly and decadal timescales, and models fail to capture such behavior, or (more plausibly) that residual errors in several observational datasets used here affect their representation of long-term trends.
Date: August 11, 2005
Creator: Santer, B.D.; Wigley, T.M.L.; Mears, C.; Wentz, F.J.; Klein,S.A.; Seidel, D.J. et al.
Partner: UNT Libraries Government Documents Department

ESG-CET Final Progress Title

Description: Drawing to a close after five years of funding from DOE's ASCR and BER program offices, the SciDAC-2 project called the Earth System Grid (ESG) Center for Enabling Technologies has successfully established a new capability for serving data from distributed centers. The system enables users to access, analyze, and visualize data using a globally federated collection of networks, computers and software. The ESG software - now known as the Earth System Grid Federation (ESGF) - has attracted a broad developer base and has been widely adopted so that it is now being utilized in serving the most comprehensive multi-model climate data sets in the world. The system is used to support international climate model intercomparison activities as well as high profile U.S. DOE, NOAA, NASA, and NSF projects. It currently provides more than 25,000 users access to more than half a petabyte of climate data (from models and from observations) and has enabled over a 1,000 scientific publications.
Date: October 6, 2011
Creator: Middleton, Don
Partner: UNT Libraries Government Documents Department

Detection of anthropogenic climate change: a modeling study

Description: This project involved two related areas of research: (1) simulating natural climate variability using a global climate model, and (2) using the computer resources of the Accelerated Strategic Computing Initiative (ASCI) Blue computer for specific problems in atmospheric science and climate. Although originally scheduled to last two years, this ER project ended after one year; the work is begin continued under a larger (Strategic Initiative) project which started in FY99.
Date: February 17, 1998
Creator: Duffy, P B & Eltgroth, P G
Partner: UNT Libraries Government Documents Department

Interannual Variations in Simulated and Observed MSU-2 Temperatures

Description: Microwave Sounding Unit (MSU) channel 2 temperatures are computed for three sets of model experiments and their interannual variation is compared to that of the observed. The models used are: (1) an ensemble of ten integrations of the NCAR CCM3 using prescribed SSTs for 1979 t o 1995, (2) A 300 year integration of the NCAR/DOE Parallel Climate Model (which has the CCM3 as the atmospheric model) and (3) a 300 year integration of the ECHAM4/OPYC coupled model at the Max Planck Institute for Meteorology. In addition Nino34 and AO indices were computed from SST and MSLP of each data set. The observed data spanned the period of 1979 to 1998. The CCM3 integrations used the observed SSTs from 1979 to 1995. The 300 year coupled runs were divided into non-overlapping 20 year segments and each segment was processed independently. The EOFs of the zonally averaged, monthly mean MSU-2 anomalies were computed. An SVD analysis of the covariance of the tropical (30S-30N) precipitation and MSU-2 was carried out. The first and second mode of the observations are related to the ENSO variations and the Arctic Oscillation, respectively. The Nino34 index leads the ENSO mode by 5 months in the observations. For the nine realizations of the CCM3, all have the ENSO as the leading mode but one does not have the AO as the second. The lag between the Nino34 and leading EOF decreases to about 3 months.The fourteen PCM 20 year segments show a similar variation to the CCM3, but the lag is decreased to 2 months. All fourteen of the ECHAM segments have the ENSO and AO as the leading and second modes. The fourteen ECHAM data sets evince smaller variations between segments than the PCM and even the CCM3 realizations. The lag between the ECHAM Nino34 and ...
Date: August 16, 2000
Creator: Boyle, J.
Partner: UNT Libraries Government Documents Department

General support for integrated assessment research. Final report

Description: The climate change problem spans an extraordinarily large number of disciplines from earth sciences to social and political sciences. The interaction of processes described by these different fields is why climate change is such a complex issue. Keeping track of these interactions and bringing coherence to the assumptions underlying each disciplinary insight on the climate problem is a massive undertaking. Integrated assessment is an interdisciplinary approach designed to provide systematic evaluations of technically complex problems such as the analysis of environmental change challenges facing humanity. Ph.D. theses stemming from this application are summarized. Then some aspects of Integrated Climate Assessment Models are described.
Date: March 1, 2001
Creator: Dowlatabadi, Hadi
Partner: UNT Libraries Government Documents Department

Comparison of Convection Characteristics at the Tropical Western Pacific Darwin Site Between Observation and Global Climate Models Simulations

Description: One of the scientific objectives of the ARM Tropical Warm Pool International Cloud Experiment (TWPICE) planned for early 2006 at Darwin, Australia is to describe convection characteristics and its interaction with the large-scale fields. In view of the short duration of the experiment, it is important to determine the long-term statistics of convection and its associated clouds from the observations and global climate models (GCM) so as to put the experiment results in proper climate perspective. For this purpose, we examine several important fields associated with the characteristics of convection and the relationships between convection and clouds using GCM simulations and available satellite and surface observations. These include the seasonal variation of convection, the relationships between convection and the upper-level cloud amount, cloud ice water content and cloud radiative forcing. One major goal of the ARM program is to improve GCM cloud and convection parameterizations. Using NCAR Community Atmosphere Model (CAM3), we demonstrate that GCM simulations in the tropical western Pacific including Darwin can be significantly improved by improving convection parameterization.
Date: March 14, 2005
Creator: Zhang, G. J.
Partner: UNT Libraries Government Documents Department

Retrieval of Cloud Ice Water Content Profiles from Advanced Microwave Sounding Unit-B Brightness Temperatures Near the Atmospheric Radiation Measurement Southern Great Plains Site

Description: One of the Atmospheric Radiation Measurement (ARM) Program important goals is to develop and test radiation and cloud parameterizations of climate models using single column modeling (SCMs) (Randall et al. 1996). As forcing terms, SCMs need advection tendency of cloud condensates besides the tendencies of temperature, moisture and momentum. To compute the tendency terms of cloud condensates, 3D distribution of cloud condensates over a scale much larger than the climate model's grid scale is needed. Since they can cover a large area within a short time period, satellite measurements are useful utilities to provide advection tendency of cloud condensates for SCMs. However, so far, most satellite retrieval algorithms only retrieve vertically integrated quantities, for example, in the case of cloud ice, ice water path (IWP). To fulfill the requirement of 3D ice water content field for computing ice water advection, in this study, we develop an ice water content profile retrieval algorithm by combining the vertical distribution characteristics obtained from long-term surface radar observations and satellite high-frequency microwave observations that cover a large area. The algorithm is based on the Bayesian theorem using a priori database derived from analyzing cloud radar observations at the Southern Great Plains (SGP) site. The end product of the algorithm is a 3D ice water content covering 10{sup o} x 10{sup o} surrounding the SGP site during the passage of the satellite. This 3D ice water content, together with wind field analysis, can be used to compute the advection tendency of ice water for SCMs.
Date: March 18, 2005
Creator: Seo, E-K. & Liu, G.
Partner: UNT Libraries Government Documents Department

Impact of Light-Duty Vehicle Emissions on 21st Century Carbon Dioxide Concentrations

Description: The impact of light-duty passenger vehicle emissions on global carbon dioxide concentrations was estimated using the MAGICC reduced-form climate model combined with the PNNL contribution to the CCSP scenarios product. Our central estimate is that tailpipe light duty vehicle emissions of carbon-dioxide over the 21st century will increase global carbon dioxide concentrations by slightly over 12 ppmv by 2100.
Date: August 4, 2007
Creator: Smith, Steven J. & Kyle, G. Page
Partner: UNT Libraries Government Documents Department

California Wintertime Precipitation in Regional and Global Climate Models

Description: In this paper, wintertime precipitation from a variety of observational datasets, regional climate models (RCMs), and general circulation models (GCMs) is averaged over the state of California (CA) and compared. Several averaging methodologies are considered and all are found to give similar values when model grid spacing is less than 3{sup o}. This suggests that CA is a reasonable size for regional intercomparisons using modern GCMs. Results show that reanalysis-forced RCMs tend to significantly overpredict CA precipitation. This appears to be due mainly to overprediction of extreme events; RCM precipitation frequency is generally underpredicted. Overprediction is also reflected in wintertime precipitation variability, which tends to be too high for RCMs on both daily and interannual scales. Wintertime precipitation in most (but not all) GCMs is underestimated. This is in contrast to previous studies based on global blended gauge/satellite observations which are shown here to underestimate precipitation relative to higher-resolution gauge-only datasets. Several GCMs provide reasonable daily precipitation distributions, a trait which doesn't seem tied to model resolution. GCM daily and interannual variability is generally underpredicted.
Date: April 27, 2009
Creator: Caldwell, P M
Partner: UNT Libraries Government Documents Department

Uncertainty quantification for large-scale ocean circulation predictions.

Description: Uncertainty quantificatio in climate models is challenged by the sparsity of the available climate data due to the high computational cost of the model runs. Another feature that prevents classical uncertainty analyses from being easily applicable is the bifurcative behavior in the climate data with respect to certain parameters. A typical example is the Meridional Overturning Circulation in the Atlantic Ocean. The maximum overturning stream function exhibits discontinuity across a curve in the space of two uncertain parameters, namely climate sensitivity and CO{sub 2} forcing. We develop a methodology that performs uncertainty quantificatio in the presence of limited data that have discontinuous character. Our approach is two-fold. First we detect the discontinuity location with a Bayesian inference, thus obtaining a probabilistic representation of the discontinuity curve location in presence of arbitrarily distributed input parameter values. Furthermore, we developed a spectral approach that relies on Polynomial Chaos (PC) expansions on each sides of the discontinuity curve leading to an averaged-PC representation of the forward model that allows efficient uncertainty quantification and propagation. The methodology is tested on synthetic examples of discontinuous data with adjustable sharpness and structure.
Date: September 1, 2010
Creator: Safta, Cosmin; Debusschere, Bert J.; Najm, Habib N. & Sargsyan, Khachik
Partner: UNT Libraries Government Documents Department

Fast Physics Testbed for the FASTER Project

Description: This poster describes the Fast Physics Testbed for the new FAst-physics System Testbed and Research (FASTER) project. The overall objective is to provide a convenient and comprehensive platform for fast turn-around model evaluation against ARM observations and to facilitate development of parameterizations for cloud-related fast processes represented in global climate models. The testbed features three major components: a single column model (SCM) testbed, an NWP-Testbed, and high-resolution modeling (HRM). The web-based SCM-Testbed features multiple SCMs from major climate modeling centers and aims to maximize the potential of SCM approach to enhance and accelerate the evaluation and improvement of fast physics parameterizations through continuous evaluation of existing and evolving models against historical as well as new/improved ARM and other complementary measurements. The NWP-Testbed aims to capitalize on the large pool of operational numerical weather prediction products. Continuous evaluations of NWP forecasts against observations at ARM sites are carried out to systematically identify the biases and skills of physical parameterizations under all weather conditions. The highresolution modeling (HRM) activities aim to simulate the fast processes at high resolution to aid in the understanding of the fast processes and their parameterizations. A four-tier HRM framework is established to augment the SCM- and NWP-Testbeds towards eventual improvement of the parameterizations.
Date: March 15, 2010
Creator: Lin, W.; Liu, Y.; Hogan, R.; Neggers, R.; Jensen, M.; Fridlind, A. et al.
Partner: UNT Libraries Government Documents Department

FASTER: A new DOE effort to bridge ESM and ASR sciences

Description: In order to better use the long-term ARM measurements to evaluate parameterizations of fast processes used in global climate models --- mainly those related to clouds, precipitation and aerosols, the DOE Earth System Modeling (ESM) program funds a new multi-institution project led by the Brookhaven National Laboratory, FAst -physics System Testbed and Research (FASTER). This poster will present an overview of this new project and its scientific relationships to the ASR sciences and ARM measurements.
Date: March 15, 2010
Creator: Liu, Y.
Partner: UNT Libraries Government Documents Department

Interannual/decadal variability in MJO activity as diagnosed in the 40-year NCEP/NCAR reanalysis and simulated in an ensemble of GISST integrations

Description: The Madden-Julian Oscillation (MJO) is the dominant mode of tropical variability at intraseasonal timescales. It displays substantial interannual variability in intensity which may have important implications for the predictability of the coupled system. The reasons for this interannual variability are not understood. The interannual behaviour of the MJO has been diagnosed initially in the 40-year NCEP/NCAR Reanalysis by calculating the variance of the 20-100 day filtered zonal mean zonal wind (10 o N-10 o S averaged) in a 100- day moving window. The results suggest that prior to the mid-1970s the activity of the MJO was consistently lower than during the latter part of the record. This may be related to either inadequacies in the data coverage, particularly over the tropical Indian Ocean prior to the introduction of satellite observations, or to the real effects of a decadal timescale warming in the tropical SSTs. This interdecadal trend is captured by the dominant EOF (explaining 28% of the variance) of the monthly mean SSTs (after removal of the mean seasonal cycle), as used in the NCEP/NCAR Reanalysis for the region of the tropics where the MJO is convectively active (i.e., 60 o E-180 o E, 20 o S-20 o N). During the latter part of 1970�s there was an abrupt change from a predominantly negative PC1 (i.e. colder Indian Ocean) to a positive PC1 (i.e. warmer Indian Ocean), indicative of a general warming of the tropical Indian Ocean by at least 0.5 o K over the last 40 years. However, on interannual timescales, the teleconnection patterns between MJO activity and SST show only a weak, barely significant, influence of El Niño in which the MJO is more active during the cold phase. As well as the NCEP/NCAR Reanalysis, a 4-member ensemble of 45 year integrations with the Hadley Centre climate model ...
Date: April 21, 1999
Creator: Nortley, F; Rowell, D P; Slingo, J M & Sperber, K R
Partner: UNT Libraries Government Documents Department

Inference of the potential predictability of seasonal land-surface climate from AMIP ensemble integrations

Description: A number of recent studies of the potential predictability of seasonal climate have utilized AGCM ensemble integrations--i.e., experiments where the atmospheric model is driven by the same ocean boundary conditions and radiative forcings, but is started from different initial states. However, only a few variables of direct relevance to the climate of the land surface have been examined. In this study, the authors infer the potential predictability of 11 climate variables that are indicative of the energetics, dynamics, and hydrology of the land surface. They used a T42Ll9 ECMWF (cycle 36) AGCM having a land-surface scheme with prognostic temperature and moisture of 2 layers occupying the topmost 0.50 meters of soil, but with monthly climatological values of these fields prescribed below. Six model realizations of decadal climate (for the period 1979--1988) were considered. In each experiment, the SSTs and sea ice extents were those specified for the Atmospheric Model Intercomparison Project (AMIP), and some radiative parameters were prescribed as well. However, the initial conditions of the model atmosphere and land surface were different: the first two simulations were initialized from ECMWF analyses, while the initial states of subsequent realizations were assigned values that were the same as those at the last time step of the preceding integration.
Date: December 1, 1995
Creator: Phillips, T.J. & Santer, B.D.
Partner: UNT Libraries Government Documents Department

Scale Interaction in a California precipitation event

Description: Heavy rains and severe flooding frequently plaque California. The heavy rains are most often associated with large scale cyclonic and frontal systems, where large scale dynamics and large moisture influx from the tropical Pacific interact. however, the complex topography along the west coast also interacts with the large scale influences, producing local areas with heavier precipitation. In this paper, we look at some of the local interactions with the large scale.
Date: September 1, 1997
Creator: Leach, M. J., LLNL
Partner: UNT Libraries Government Documents Department

Comparison of the 200 hPa circulation in CSM and CCM3 simulations and NCEP and ERA reanalysis: principal and common principa

Description: In this paper the interannual variation of monthly mean vorticity and divergence at 200 hPa are compared from four data sources: The NCEP/NCAR reanalyses 1958 through 1994, the ECMWF (ERA) reanalyses, 1979 through 1994, a NCAR CCM3 integration using prescribed SSTs from 1979 through 1993, and the NCAR CSM 300 year integration. Four twenty year periods were taken from the 300 year simulation for analysis. The NCEP, ERA and CCM3 all provide data for the period 1979 through1993. The techniques used are principal and common principal component analyses on the fields transformed to spherical harmonics. The seasonal cycle is removed. For the common time period, 1979 through 1994, the ERA, NCEP and CCM3 display a close correspondence for the leading PC of the 200 hPa vorticity.This mode is closely related to the ENSO variations of the period but the agreement extends to the extratropics. All four CSM periods have similar leading modes which are dominated by a PNA type pattern and lack any Equatorial Pacific ENSO patterns. The agreement between the leading PC for the 200 hPa divergence was somewhat less than that of the vorticity. The CCM3 and ERA indicate a larger magnitude center in the Equatorial Pacific about the dateline than NCEP. The CSM has an intense center a 150E. There are indications in the vorticity and divergence fields that this center is at the source for waves propagating to the midlatitudes. Two twenty year periods of the 1958 to 1996 NCEP reanalyses show a distinct difference between the two periods. The variations are comparable in magnitude if not nature to the variations seen amongst the time sections of the CSM run examined. A CPC analysis of the NCEP, ERA and CCM3 show a common ENS0 type response as the leading common component. The models depart from the ...
Date: October 20, 1998
Creator: Boyle, J. S.
Partner: UNT Libraries Government Documents Department

Predicted 21st century changes in seasonal extreme precipitation events in the parallel climate model

Description: Twenty-year return value of annual and seasonal maxima of daily precipitation are calculated from a set of transiently forced coupled general circulation model simulations. The magnitude and pattern of return values are found to be highly dependent on the seasonal cycle. A similar dependence is found for projected future changes in return values. The correlation between the spatial pattern of return value changes and mean precipitation changes is found to be low. Hence, the changes in mean precipitation do not provide significant information about changes in precipitation extreme values.
Date: June 7, 2004
Creator: Wehner, Michael F.
Partner: UNT Libraries Government Documents Department