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Ernie Lewis, Art Sedlacek, and Mike Jensen, Co-Chairs
[JAN] [FEB] [MAR] [APR] [MAY] [JUN] [JUL] [AUG] [SEPT] [OCT] [NOV] [DEC] ** Seminars Scheduled for Current Month ** |
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| Fri., July 27, 11:00 am |
Sci & Environ Policy Project (SEPP) Host: Stephen Schwartz |
- 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? [Return to top] |
| Thurs., July 12, 11:00 am |
University of South Carolina |
- 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.
[Return to top] |
| Tues., July 10, 11:00 am |
University of California, Davis Host: Jian Wang |
- 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.
[Return to top] |
| Tues., June 5, 2:00 pm |
Dept of Environmental Sciences, Rutgers University Host: Jian Wang |
- 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.
[Return to top] |
| Thurs., May 24, 11:00 am |
M.I.T. Host: Ernie Lewis |
- 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.
[Return to top] |
| Tues., May 22, 11:00 am |
Harvard Host: Ernie Lewis |
- 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).
[Return to top] |
| Fri., Apr. 27, 11:00 am |
ASD |
- 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.
[Return to top] |
| Fri., Apr. 13, 11:00 am |
HyARC-Hydrospheric Atmospheric Research, Japan Host: Satoshi Endo |
- 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. [Return to top] |
| Fri., Apr. 6, 11:00 am |
North Carolina State Univ. Host: Yin-Nan Lee |
- 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.
[Return to top] |
| Thurs., Apr. 5, 10:00 am |
NOAA/NCEP Host: Yangang Liu |
- 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.
[Return to top] |
| Thurs. Mar. 1, 11:00 am |
ASD |
- 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.
[Return to top] |
| Tues. Feb. 21, 11:00 am |
Argonne National Laboratory |
- 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.
[Return to top] |
| Fri., Feb. 17, 11:00 am |
McGill University |
- 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.
[Return to top] |
| Tues., Feb. 14, 9:00 am |
Arizona State University |
- 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.
[Return to top] |
| Tues., Jan. 31, 11:00 am |
NASA Goddard Institute for Space Studies |
- 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.
[Return to top] |
| Mon., Jan. 23, 10:00 am |
Texas A&M University |
- 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. [Return to top] |
| Fri., Jan. 13, 11:00 am |
Atmospheric Sciences Division |
- 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. [Return to top] |
| Weds., Jan. 4, 11:00 am |
Atmospheric Sciences Division |
- 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.
[Return to top] |
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[Return to top] [REV. 07/09/12] |
