Directorate

• Contents
• EXECUTIVE SUMMARY
• 1. SCOPE OF THE PROGRAM
• 2. IMPROVING OUR UNDERSTANDING OF EARTH-SYSTEM PROCESSES
• 2.1 Scale Interactions Associated with Precipitating Convective Systems
• 2.2 Understanding the Dynamics and Predictability of Weather Systems on Time Scales of 0-48 h
• 2.3 Fundamental Research on Precipitation Processes, with an Emphasis on their Improved Representation in Numerical Models
• 2.4 Understanding the Dynamics, Physics and Chemistry of Multi-Scale Atmospheric Chemical Constituent and Particulate Transport, Dispersion and Transformations
• 2.5 Fundamental Research in Boundary Layers and their Interfacial Interactions
• 3. ADVANCING THE SCIENCE OF ATMOSPHERIC PREDICTION
• 3.1 Advancing Short-Range Weather Prediction
• 3.2Advancing Data Assimilation Research
• 3.3 Improving Forecasting of Pollutants and Hazardous Materials
• 4. ADVANCED COMMUNITY RESEARCH TOOLS
• 4.1 WRF Community Model
• 4.2 Community Data Assimilation Techniques
• 4.3 Nested Community Climate Model
• 5. SUMMARY
• Acronym List
• Print Version
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Mesoscale & Microscale Meteorology Division Science Plan:

2.4 Understanding the Dynamics, Physics and Chemistry of Multi-Scale Atmospheric Chemical Constituent and Particulate Transport, Dispersion and Transformations

Goal: To develop a deeper understanding of the underlying dynamics, physics and chemistry involved in transport, dispersion and transformation of atmospheric pollutants, particulates and chemical constituents.

Atmospheric chemical and particulate transport, dispersion and transformation depend on accurate specification of the dynamics and physics across a wide range of scales, from microscale to mesoscale. Important processes include:

• Surface-atmosphere interactions;
• Boundary layer turbulence transport and dynamics;
• Exchange between the boundary layer and free troposphere; and,
• Boundary layer venting via convective transport, rainout, and chemistry.

This research is focused on fundamental boundary layer and moist-convective processes that affect air quality through the interactions that modify distributions of atmospheric constituents. Our work in this area will include close collaboration with ACD and EOL, with the biogeosciences initiative under TIMES, and with several universities.

Understanding the fundamental processes in the boundary layer that affect the distribution of constituent concentrations is of paramount importance. A major tool in this research is the Large Eddy Simulation (LES) model, which is a three-dimensional numerical simulation of turbulent flow in which large eddies (with scales smaller than the overall dimension of the problem in question) are explicitly resolved and the effects of smaller-scale eddies are parameterized. The simulation is based on a numerical integration of the time-dependent Navier-Stokes equations that extends down to scales in the inertial subrange, where Kolmogorov theory is commonly used to parameterize the unresolved eddies.

The processes that contribute to chemical constituent transport in complex terrain are being addressed using the results of recent biocomplexity field experiments: CME (Carbon in the Mountain Experiment) and its airborne counterpart, ACME. Our goal is to test our level of understanding of tracer transport in complex terrain by conducting LES of CO2 transport in the CME area. In addition we are planning a field experiment to measure for the first time the sub-grid variability of trace gases within and above forest canopies. This will advance our knowledge of sub-grid transport within the LES domain.

Wildland fires expose the public to extremely high short-term fine particulate concentrations, producing the highest particulate concentrations ever recorded in certain states and elevating pollution levels thousands of kilometers downstream through long range transport, subsequent downward mixing, and chemical transformations. In collaborative work with the Wildland Fire Program and ACD, we are conducting studies to understand the air quality impacts of fires, both the direct emissions and indirect impacts through modification of land cover. These studies involve studying the complex interactions between meteorology, fire behavior, vegetation characteristics, smoke transport and dispersion, and atmospheric chemical reactions.

Studies of the effect of boundary layer dynamics and clouds on chemical species concentrations and distributions are also being examined with LES. Transport and turbulent dispersion of scalars emitted from surface and elevated sources, or fumigated into the boundary layer, are being investigated with a Lagrangian particle dispersion model coupled with the LES. Understanding the importance of boundary layer clouds on chemical species, and investigating the interactions between the biosphere, hydrosphere, and atmosphere on gas-phase and aerosol-phase constituent concentrations will lead to quantification of methods of improving their prediction.

Mesoscale transport and transformation are important for understanding the impact of pollutants downwind of urban centers and the redistribution of chemical species by deep convection. In and around deep convection, several processes affect the concentration of chemical species, including: vertical transport, cloud microphysics, lightning, solar radiation, cloud chemistry, and rainout. These processes are systematically being investigated using WRF coupled with gas and aqueous chemistry modules. Simulations are being evaluated using observations from field experiments such as STERAO. This work has highlighted the need for measurements of the soluble, reactive species that are key to ozone formation. We are collaborating with scientists in ACD and EOL, and in the university community in planning a field experiment designed to provide these data.

A specific initiative is our participation in the MIRAGE initiative to investigate the prediction of chemical species transport from Mexico City. The WRF model is being used to simulate tracers in a region of complex terrain without the strong dynamical forcing that can occur from, for example, the mid-latitude jet.

It is also important to recognize that some atmospheric constituents, such as hygroscopic aerosols, can modify cloud properties. Studies of the role of anthropogenic aerosols on perturbing ice concentrations and sizes in cirrus formed from convective outflow over the Indian Ocean are being pursued as part of this study.

Next section: Fundamental Research in Boundary Layers and their Interfacial Interactions

 

 

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