ASD Seminar Series

  Ernie Lewis, Art Sedlacek, and Mike Jensen, Co-Chairs

The goal of the ASD seminar series is to allow staff and visiting colleagues to present their work in a relaxed, "Gordon Conference"-like atmosphere where a free exchange of ideas can take place. The seminar topics reflect the research interests of the Atmospheric Sciences Division, which include the chemistry, physics and transport of atmospheric substances, and the study of the physical processes that impact clouds and aerosols that ultimately effect the Earth's radiative energy budget and climate (see Research on ASD Homepage. Listed below are past and pending seminars with a brief abstract. If you found a seminar of interest but were unable to attend, you are encouraged to contact the presenter. Seminars are held twice a month on Friday from 11:00 am-12:00 pm in the Bldg. 815E Conference Room (unless otherwise noted).

  [JAN]   [FEB]   [MAR]   [APR]   [MAY]   [JUN]    [JUL]   [AUG]   [SEPT]   [OCT]   [NOV]   [DEC]

Seminar Series Archives:   [2011]   [2010]   [2009]   [2008]   [2007]   [2006]

** Seminars Scheduled for Current Month **

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Fri., July 27,
11:00 am

S. Fred Singer,
Sci & Environ Policy Project (SEPP)

Host: Stephen Schwartz

"Examination of temperature trends over the twentieth century: No evidence for anthropogenic global warming"

- Analysis of observed temperature (from 1979 - 1997) at the surface, in the atmosphere, in the ocean, and from proxies shows increase of surface temperature but not in the other three time series. What does this signify?

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Thurs., July 12,
11:00 am

Gabriel Terejanu,
University of South Carolina

"Towards a Comprehensive Framework for Building Confidence in Predictive Simulations"

- Any reliable prediction of a complex physical system requires not only sophisticated mathematical models of the physical phenomena involved, but also a rigorous assessment of all the uncertainties associated with the predictive simulation. The errors inherent in any simulation are the result of many factors, including model structure inadequacies, uncertainties in model parameters, uncertain initial and boundary conditions, experimental uncertainties, as well as errors due to numerical discretization and sampling schemes. The integration of basic processes such as verification, calibration, validation, uncertainty quantification and data assimilation allows for the management of model prediction accuracy and reliability in the presence of all these potential errors. These processes will serve as the building blocks for an integrated methodology that will allow decision makers to trust model predictions for guiding highly consequential decisions.

In this talk I will describe some of my work on model validation and uncertainty quantification. A newly developed framework for prediction validation in the presence of model error is introduced and applied to an illustrative extrapolation problem involving a misspecified nonlinear oscillator. While model validation is predominantly an off-line endeavor, dynamic data assimilation is mainly associated with real-time applications of conditionally valid models. To address this on-line context, an adaptive Gaussian mixture model is introduced to solve for the state probability density function (pdf) of a stochastic dynamic system. The knowledge about the time evolution of the state pdf is important for data assimilation applications and to quantify the uncertainty in the state at a future time. Several numerical examples are considered to illustrate the efficacy of the Gaussian mixture method.

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Tues., July 10,
11:00 am

Tony Wexler,
University of California, Davis

Host: Jian Wang
"Statistical Thermodynamics of Solutions and Surfaces"

- Atmospheric processes such as urban smog and cloud droplet activation depend on the thermodynamics of small particles. The components of these particles are often highly concentrated and they have a large surface area to volume ratio so surface processes are significant. Over the last couple of years, we have employed surface sorption thermodynamics to successfully model the activities of solute and solvent in solutions over the full range of activities relevant to the atmosphere. But sorption thermodynamics is also ideal for modeling surfaces, so recently we have expended our solution thermodynamics work to both surface tension and surface concentration. The talk will review our progress on solution thermodynamics and introduce the framework that we are using to describe surface phenomena.

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Tues., June 5,
2:00 pm

Mark Miller,
Dept of Environmental Sciences, Rutgers University

Host: Jian Wang

"Cloud Radiative Effects over West Africa using a Top-Down, Bottom-up Approach"

- This seminar will focus on measurements collected in the Sahel region of West Africa and simulations of the region in Global Climate Models (GCMs). The Sahel's location along the tropical margin, its population density, which is roughly equal to that of the northeastern United States, and its economic status combine to increase its vulnerability to climate change. The region exhibits a complex monsoon circulation driven by north-south temperature and moisture gradients that produce all of its rainfall during a short six- to eight-week wet season. Important drivers of the radiation budget and the hydrological cycle were measured during the year 2006 using the Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) and the Geostationary Earth Radiation Budget (GERB) satellite. Continuous measurements of the shortwave (SW) and longwave (LW) radiation fluxes at the surface and the top of the atmosphere were supplemented by continuous, detailed measurements of clouds and other radiative influences within the atmospheric column that modulate these boundary fluxes. This collection of measurements enabled the radiative impacts of clouds upon the atmospheric column itself to be explicitly determined. Predictions in four GCMs used in the Intergovernmental Panel for Climate Change fourth Assessment report (IPCC-AR4) are analyzed to determine if these models are able to simulate the observed structure. Particular emphasis is placed upon the manner in which two of the four GCMs simulate the radiative impacts of cloud cover.

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Thurs., May 24,
11:00 am

Eben Cross,

Host: Ernie Lewis

"Closing the Gap on Organic Carbon Emissions from an Aircraft Engine"

- Low volatility organic compounds (LVOCs) comprise an atmospherically important, largely unmeasured class of organic species in the atmosphere. LVOCs consist of intermediate volatility organic compounds (IVOCs; i.e. C13-C20 n-alkanes) and semi-volatile organic compounds (SVOCs; i.e. C21-C32 n-alkanes). Atmospheric oxidation of gas phase LVOCs results in the formation of secondary organic aerosol (SOA) which in turn has direct implications for climate and human health. The rates and the chemical properties of LVOC emissions and oxidation products (in the gas phase and particle phase) are inadequately characterized and subsequently not yet accurately parameterized in most atmospheric chemistry models.

This seminar will provide an overview of experimental results obtained with a novel technique that provides a volatility-resolved, quantitative measure of LVOCs in the atmosphere. Results from the Alternative Aviation Fuels Experiment (AAFEX-II) conducted at the NASA Dryden Aircraft Operations Facility will be presented. The experiment was designed to characterize the gas phase and particulate emissions from the NASA DC-8 Aircraft as a function of engine power and fuel type. The bulk chemical composition, mass loading and volatility of the LVOC emissions will be discussed in the context of VOC and PM emission profiles.

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Tues., May 22,
11:00 am

Mackenzie Smith,

Host: Ernie Lewis

"Phase Transitions and Miscibility of Mixed Particles of Ammonium Sulfate and Secondary Organic Material"

- The hygroscopic phase transitions of particles composed of laboratory-generated secondary organic material and ammonium sulfate were investigated using a dual arm tandem differential mobility analyzer. Organic material of was generated via isoprene photo-oxidation (oxygen-to-carbon ratio of ~0.7) and α-pinene dark ozonolysis (oxygen-to-carbon ratio of ~0.4).

The DRH and ERH of ammonium sulfate were minimally affected (less than 5% RH from pure ammonium sulfate values) by α-pinene dark ozonolysis products for particles of organic volume fraction up to 0.96. In contrast, we show that the organic material produced by isoprene photo-oxidation exerts a measurable influence on the hygroscopic properties of ammonium sulfate. Compared to an efflorescence relative humidity (ERH) of 30 to 35% for pure ammonium sulfate, efflorescence was eliminated for mixed aqueous particles having organic volume fractions ε of approximately 0.6 and greater. Compared to a deliquescence relative humidity (DRH) of 80% for pure ammonium sulfate, the DRH steadily decreased for increasing ε, approaching a DRH of 40% for ε of 0.9. Parameterizations of DRH(ε) and ERH(ε) and a new account of partial dissolution of ammonium sulfate for RH < DRH (i.e., initial deliquescence) are presented for these mixed particles.

The minimal influence of the α-pinene dark ozonolysis products suggests that the aqueous ammonium sulfate is phase separated from the organic material, while the results for isoprene-derived organic material imply that this organic material is miscible with the aqueous inorganic phase and is therefore able to alter the hygroscopic behavior of ammonium sulfate. In the context of previous work, these overall results show that the influence of secondary organic material on the hygroscopic properties of ammonium sulfate varies with organic composition and confirm that the degree of oxygenation of the organic material, including complex organic materials, is an important variable influencing the hygroscopic properties of mixed organic-inorganic particles.

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Fri., Apr. 27,
11:00 am

Michael P. Jensen,

"Convective cloud life-cycle during the Mid-latitude Continental Convective Clouds Experiment (MC3E)"

- Convective processes play a critical role in the Earth’s energy balance through the redistribution of heat and moisture in the atmosphere and the subsequent impacts on the hydrological cycle. Despite improvements in computing power, current operational weather and global climate models are unable to resolve the natural temporal and spatial scales that are associated with convective processes; therefore, they must turn to parameterization schemes to represent these processes. In turn, the physical basis for these parameterization schemes needs to be evaluated for general application under a variety of atmospheric conditions. Data from field campaigns with appropriate forcing descriptors have been traditionally used by modelers for evaluating and improving parameterization schemes.

The Midlatitude Continental Convective Clouds Experiment (MC3E) took place from 22 April through 6 June 2011 centered at the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Southern Great Plains Central Facility in north-central Oklahoma. This campaign was a joint effort between the ARM and the National Aeronautics and Space Administration's (NASA) Global Precipitation Measurement mission Ground Validation program. During this campaign a comprehensive dataset of surface-, aircraft- and satellite-based observations was collected targeting processes important for the parameterization of convection in large-scale models and the retrieval of precipitation by space-borne sensors over land. This talk will discuss some of the details of the MC3E campaign including preliminary data analysis activities and science results.

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Fri., Apr. 13,
11:00 am

Taro Shinoda,
HyARC-Hydrospheric Atmospheric Research, Japan

Host: Satoshi Endo

"Evaluation of Simulation Results of a Cloud-Resolving Model Using Satellite Data and a Satellite Simulator"

- To confirm the accuracy of the results using a cloud-resolving model, it is useful to compare the simulation results with the satellite observations. Recently, several satellite simulators were developed by Matsui et al. (2009) and Masunaga et al. (2010). This study compares brightness temperature of infrared (TBB-IR) and microwave (TBB-MW) bands and radar reflectivity obtained from the satellite observations with those calculated using Satellite Data Simulator Unit (SDSU: Masunaga et al. 2010) applied to the simulation results by Cloud Resolving Storm Simulator (CReSS: Tsuboki and Sakakibara 2002) around the Taiwan/Okinawa region during the Meiyu/Baiu season in 2008 and 2010.
Daily simulations using CReSS with horizontal grid resolution of 4.0 km are conducted every day for 36 hours from 14 May to 24 June 2008. Those with 2.5 km resolution are carried out from 14 May to 30 June 2010. The sedimentation of cloud ice is additionally included into CReSS in 2010-simulations. Horizontal distributions of TBB-IR, TBB-MW and three-dimensional reflectivity are calculated using SDSU from the simulation results. Satellite data of TBB-IR, 6-bands TBB-MW (from 6.925 to 89.0 GHz), and reflectivity are obtained by Multi-functional Transport Satellite (MTSAT), Advanced Microwave Scanning Radiometer for EOS (AMSR-E) loaded on the Aqua, and TRMM-PR, respectively.

Cloud fraction calculated from TBB-IR is well reproduced in 2010-simulations, although frequency of upper (middle/lower) clouds of the simulation is larger (lesser) than that of the satellite observation. The inclusion of the sedimentation process of cloud ice should contribute to the improvement of the TBB-IR distribution. The excessive existence of solid hydrometeors above the melting level in precipitation systems and less extension of dense stratiform region in the simulation are suggested by TBB-MW (89.0 GHz) and reflectivity distributions. The result shows that there should be points at issue on the microphysical processes in CReSS that are originated by fall speed of solid particles and snow-graupel conversion process.

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Fri., Apr. 6,
11:00 am

Yang Zhang,
North Carolina State Univ.

Host: Yin-Nan Lee

"WRF/Chem Model Development and Application: Urban Pollution, Global Warming, and Earth System Degradation"

- Online-coupled climate-chemistry multiscale atmospheric models provide a powerful tool to accurately simulate urban air pollution, global climate change, and Earth system degradation for integrated air quality control, climate change mitigation, and Earth system management. A unified global-through-urban online-coupled climate-chemistry model has been developed based on NCAR's Global Weather Research and Forecasting (GWRF) model and NOAA's mesoscale WRF with Chemistry (WRF/Chem) (referred to as GU-WRF/Chem hereafter). This seminar will review recent GU-WRF/Chem model development along with several case studies over regional domains such as U.S., Europe, and China as well as nested domains from global to urban scales. The model's capability in representing current atmosphere and projecting its future changes, as well as the model's potential in supporting pollution control and climate change mitigation strategies will be demonstrated. As an extension of GU-WRF/Chem, an Integrated Technology-Driven Earth System Model (ITDEaSM) is being developed built upon NCAR's Community Earth System Model (CESM) to tackle the grand challenges in quantifying the feedbacks among atmosphere, biosphere, hydrosphere, and lithosphere across scales and identifying future technology choices for co-benefits of Earth system management and sustainability. Future research challenges and directions will be discussed in light of coupled air quality/climate studies and their integration into an earth system modeling framework.

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Thurs., Apr. 5,
10:00 am

Binbin Zhou,

Host: Yangang Liu

"Verification of Cloud Forecast from NCEP's Operational Models"

- Clouds have significant impacts on forecast performance of other fields like temperature and precipitation. Verificaiton of cloud forecast provides an objective way to understand the performance of microphysical schemes employed in models. Particularly, with gradual increase in model resolution, more details in model cloud structure can be observed and require to verify. However, objective verification of cloud forecast from operational models at NCEP and other operational weather centers is always challenging and has long been behind those of other regular fields due to lack of an efficient verification tool and appropriate validation cloud data. With availability of global 1-degree satellite cloud detection data and national 4km WSR-88D radar mosaic data recently, substantial efforts have been made in verifcations of cloud, simulated radar reflectivity and echo-top forecasts from both single models and ensemble forecsat systems at NCEP. To faciliate the routine verifications for various operational forecast systems against grid-formatted satellite cloud and mosaic radar reflectivity data, a unified grid-to-grid verification system (g2g) was developed at NCEP, with which a verification becomes more objective and efficient. In this talk, the general verification methods, the unified g2g verification system as well as the verification activities with g2g at NCEP will be briefly introduced at first, and then its application in cloud verification with AFWA and CLAVR satellite data and radar mosaic data for both regional and global models will be described in detail. Time allowed, other issues in grid-to-grid verifications will be discussed.

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Thurs. Mar. 1,
11:00 am

Fan Mei,

"CCN Activation Properties of Organic Aerosol Observed During Recent Field Studies"

- The indirect effects of atmospheric aerosols on the global energy budget remain the most uncertain components in the forcing of climate change over the industrial period. This large uncertainty is, to a large degree, a result of our incomplete understanding of the ability of aerosol particles to form cloud droplets under climatically relevant supersaturations.

During two recent field campaigns, size-resolved cloud condensation nuclei (CCN) spectrum and aerosol chemical composition were characterized at an urban supersite in Pasadena, CA (CalNex-LA, May 16 to June 4, 2010) and an supersite downwind of Sacramento (CARES, June 10 to June 28, 2010). At both sites, aerosol particles were first classified using a differential mobility analyzer at diameters ranging from 25 to 320 nm. The activation efficiency of the classified aerosol, defined as the ratio of its CCN concentration (characterized by a DMT CCN counter) to total CN concentration (measured by a condensation particle counter, TSI 3771), was derived as a function of both particle size and supersaturation, which ranges from ~0.1 to ~0.4%. Aerosol chemical composition was characterized using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS).

At both sites, increases in aerosol mode diameter, organics mass loading, and aerosol organics volume fraction were often observed from ~10:00 AM to 16:00 PM during week days. Particle overall hygroscopicity (κ, Petters and Kreidenweis, 2007, ACP) was derived from the size-resolved CCN measurements and ranged from 0.15 to 0.3 under the measured supersaturations. Based on the particle hygroscopicity and aerosol chemical composition, the hygroscopicity (κorg) of organic species was derived and examined as a function of its oxidation level. The aerosol source, chemical composition, and organic hygroscopicity will be compared and discussed for the two sites.

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Tues. Feb. 21,
11:00 am

Scott Collis,
Argonne National Laboratory

"Weather Radars for Climate Science"

- The ARM Climate Research Facility has a long history of sensing in-situ and in the column however these techniques are unable to capture the kinematic and microphysical nature of precipitating cloud systems. To this end precipitation sensitive scanning radars have been deployed to the ARM fixed sites in Oklahoma, Alaska and on Manus Island, Papua New Guinea. These radars record regular volumes of data that represent the interaction between the radar emitted radiation and the backscattering hydrometeors. This presentation will discuss the processes and challenges involved in retrieving four dimensional geophysical parameters from this remote sensing data. Details of currently available Value Added Products (VAPs) will be presented as well as future plans and directions for the radar products project.

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Fri., Feb. 17,
11:00 am

Paloma Borque,
McGill University

"Preliminary Results on Cumulus Lifecycle during the Midlatitude Continental Convective Clouds Experiment (MC3E)"

- Documenting cloud elements as they transit through different stages of their lifetime (e.g., formation, precipitation onset, dissipation) can provide an improved understanding of the physical processes controlling cloud lifecycle and the scales over which such processes operate. This study capitalizes on the heterogeneous distributed radar network and collocated surface/sounding platforms, deployed during the Midlatitude Continental Convective Clouds Experiment (MC3E). The MC3E campaign emphasized cloud lifecycle studies over the ARM Southern Great Plains facility. The application of a new cloud identification and tracking algorithm for the Ka-band Scanning ARM Cloud Radar (Ka-SACR) will be described with a particular emphasis on the evolution of shallow cumulus clouds.

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Tues., Feb. 14,
9:00 am

Ashish Sharma,
Arizona State University

"Climate Modeling & Downscaling for Semi-Arid Regions"

- The study performs numerical modeling for regional climate, focusing specially on rainfall and circulation patterns of semi-arid regions. The central problem addressed is the feasibility and numerical sensitivity of mesoscale climate simulations as the model resolution approaches the "cloud-resolving scale" of L <10 km. Using the Weather Research and Forecast (WRF) model, a non-hydrostatic geophysical fluid dynamical model with a full suite of physical parameterization, a series of numerical sensitivity experiments are conducted to test how the intensity and spatial/temporal distribution of precipitation change with grid resolution, time step size, and the resolution of lower boundary topography and surface characteristics. Two regions, Arizona/western U.S. and the Aral Sea region in Central Asia, are chosen as the testbeds for the numerical experiments. The former for its complex terrain and the latter for the dramatic man-made changes in its lower boundary conditions (the shrinkage of Aral Sea). The numerical simulations are validated with observation to address the realism of the regional climate model.

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Tues., Jan. 31,
11:00 am

Kostas Tssigaridis,
NASA Goddard Institute for Space Studies

"A multi-model analysis of organic aerosols: global and marine sources"

- Comparisons of individual models with organic aerosol (OA) measurements have shown a large underestimation of the OA component by the models, especially during winter. The formulations used by individual models are very different, since OA simulations have many degrees of freedom due to the missing knowledge on the behavior and fate of both primary OA (POA) and secondary OA (SOA) in the troposphere. On top of that, several assumptions need to be made and are translated to model tuning parameters that vary greatly from one model to the other. Trying to bridge the gap between models and observations, several recent model developments account for SOA, intermediate volatility organics, multiphase chemistry, oceanic fluxes and semi-volatile POA. In addition to the different processes included in various models, the different emission inventories and meteorological fields adopted make a comparison with other models and measurements even more challenging.

The organic aerosol intercomparison AEROCOM exercise aims to evaluate the actual status of global modeling of the OA occurrence in the global troposphere and analyze discrepancies between models as well as between models and observations. More than 30 models participate in this exercise that aims to quantify the uncertainties and attribute them to major contributors. It will also try to identify and analyze potential model systematic biases. The ensemble of the simulations will be used to build an integrated and robust view of organic aerosol sources and sinks in the troposphere. The year 2006 was selected as the base year for the study. Recent results from the intercomparison will be presented together with a compilation of field data that is being used for the validation of the models results. The similarities and differences between models will be highlighted, in an attempt to evaluate and understand the model-measurements comparison.

As a case study, the oceanic source and related uncertainties of oceanic organic aerosols will be analyzed. Marine primary aerosols are traditionally being treated in global models as pure sea-salt. However, sea-spray consists of a mixture of sea-salt and water insoluble organic material. This is expected to affect marine aerosol properties in global models, with probably the most notable change being that the mixed particles have reduced hygroscopicity. This results in an increase of marine aerosol lifetime due to suppressed removal which leads to an increase of the oceanic aerosol burden, as well as in a reduction of their cloud condensation nuclei activity, affecting cloud droplet number concentration and cloud thickness. The importance of the oceanic source of primary organic aerosols will be evaluated and validated against measurements, in conjunction with sea-salt. The importance of the marine organic aerosols on both direct and indirect effects and the potential feedbacks involved will be presented.

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Mon., Jan. 23,
10:00 am

Yu Xie,
Texas A&M University

"Study of Ice Cloud Properties from Synergetic Use of Satellite Observations and Modeling Capabilities"

- It has been commonly recognized that clouds are one of the leading sources of uncertainties in the current General Circulation Models (GCMs). Satellite measurements and retrievals are the only assessment to evaluate global distribution of clouds and their effects on climate change. Our research starts from the optical and microphysical properties of clouds, and covers the simulation of radiative transfer within clouds and evaluating the effect of clouds on global climate change. The single-scattering properties of surface roughened and inhomogeneous ice crystals were investigated using a combination of ray-tracing technique and Monte Carlo method. To investigate the effect of the representation of aggregates on electromagnetic scattering calculations, an algorithm was developed to efficiently specify the geometries of aggregates and to compute their geometric parameters such as the projected area. An aggregate model was determined to provide an accurate and computationally efficient way to represent all aggregates occurring within ice clouds. Collocated Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-angle Imaging SpectroRadiometer (MISR) data were used to determine an appropriate ice cloud model for application to satellite-based retrieval of ice cloud properties. To investigate the global radiative forcing (RF) of contrails, we analyzed the contrail information using the MODIS and Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) data. The MODIS contrail mask was detected by a manually detection algorithm and an automated contrail detection algorithm (CDA). An accurate representation of contrail radiative properties was given to minimize the uncertainties raised by the assumption of a particular contrail model. A parameterization of shortwave and longwave radiative properties of contrails was then developed for global and regional climate model applications.

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Fri., Jan. 13,
11:00 am

Wei Wu,
Atmospheric Sciences Division

"Observational-based Evaluation of NWP Reanalyses in Modeling Cloud Properties over the Southern Great Plains"

- This study evaluates three major Numerical-Weather-Prediction (NWP) reanalyses (ERA-Interim, NCEP/NCAR Reanalysis, and NCEP/DOE Reanalysis) in modeling surface relative shortwave cloud forcing, cloud fraction, and cloud albedo. The observations used for this evaluation are surface-based continuous measurements of the US Atmospheric Radiation Measurement (ARM) program from 03/25/1997 to 12/31/2008 over the Southern Great Plains (SGP) site. These cloud properties from the reanalyses are evaluated at multiple temporal scales. Like the observations, all the reanalyses show a strong annual cycle, and relatively weak diurnal or inter-annual variations of the cloud properties. The reanalyses exhibit significant underestimation on the cloud properties, and the model biases of the cloud properties are linearly linked to one another. Further analysis reveals that the model biases of the cloud properties exhibit quasi-linear relationships to the model biases of near-surface relative humidity (and temperature for ERA-Interim). A combined statistical analysis indicates that ERA-Interim (NCEP/NCAR Reanalysis) has the best (worst) overall performance among the three reanalyses.

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Weds., Jan. 4,
11:00 am

Stephen E. Schwartz,
Atmospheric Sciences Division

"An Ecological Approach to Climate and Climate Change"

- An "ecological" approach to the study of Earth's climate system is presented. This approach, consists of identifying the major compartments of the climate system and quantifying their couplings. It is motivated by the ecological approach to the study of Earth's biosphere, which has led to major advances in understanding through examination of flows of energy and materials among major compartments and by identification and quantification of the conservation laws that govern an ecosystem as a whole, as opposed to an approach that catalogs individual species and their properties: numbers, birth rate, development, death rate, transport, use and release of energy and specific chemical substances, and the multiple interactions of all the individual species. A similar approach to examination of Earth's climate system may likewise advance understanding of the climate system and its responses to perturbations.

A primary objective of research on Earth's climate system has been determination of climate response to perturbations generally and, in particular, the so-called equilibrium climate sensitivity, the normalized change in global mean surface temperature (GMST) that would ultimately result from a given sustained forcing. This equilibrium sensitivity has served as a basis for assessing the amount of carbon dioxide that might be added to the atmosphere consistent with a given allowable increase in global temperature. As Earth's climate sensitivity depends strongly on feedbacks -- changes in atmospheric composition and structure (e.g., water vapor, clouds, lapse rate) that would result from a change in GMST -- much current research focuses on determining the processes controlling these elements of the climate system and representing them in increasingly complicated climate models.

An alternative, "ecological" approach to the study of Earth's climate system tries to infer sensitivity of Earth's climate to perturbations from examination of the properties of major compartments of the climate system and the changes in these compartments over the industrial period. Important "ecological" variables of Earth's climate system are GMST itself, absorbed and emitted radiative fluxes, and the flow of energy between the upper compartment of the climate system, which is radiatively coupled to space, and the deep ocean, which is the major contributor to global heat capacity on century-to-millennium time scales. Representation of the climate system as a two-compartment model yields simple expressions relating response time constants, heat capacities, heat exchange coefficients, and transient and equilibrium sensitivities. Determination of the pertinent variables from observations of fluctuations of the climate system and response to perturbations over the past century is an alternative approach to providing information about Earth's climate system that can usefully inform policymaking regarding allowable carbon dioxide emissions and energy policy.

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[REV. 07/09/12]