DOPPLER LIDAR STUDIES OF FLOW AND VERTICAL MIXING IN A MOUNTAIN BASIN
Robert M. Banta and Lisa S. Darby NOAA/Environmental Technology Laboratory
ABSTRACT
We propose to deploy ETL's Doppler lidar system (TEACO2) to the Salt Lake City basin during VTMX's field phases to study vertical transport and mixing under stable, cold-pool conditions. The emphasis in this effort will be on buildup and destruction processes in the cold pool, exchange and dilution of cold-pool air (often polluted) with ambient air, and transport and mixing processes within the cold pool. The lidar will be able to cover the entire basin with its 20-km routine range. The range resolution of 300 m means that the lidar will be able to probe layers and atmospheric structures ranging from a few hundred meters to basin scale. Structures would include gravity waves, Kelvin-Helmholtz waves, turbulent bursts, canyon outflow jets, slope flows, and sloshing of the cold pool (seiche effects). Vertical resolution depends on scanning speed, but tens of meters has been achieved in previous experiments. Given the small-scale measurement needs under stable conditions, the Doppler lidar's capabilities match the program requirements very well. We are requesting 4 years of funding to obtain and analyze the lidar data and perform coordinated data analysis with other researchers.
The Lidar
The NOAA/ETL TEACO2 lidar is a scanning remote sensing system that maps out the Doppler velocity and aerosol backscatter fields in 2-D or 3-D as it scans. On several field projects over the past decade, it has proven its ability to reveal over a wide area, horizontal and vertical structure that can be missed by more conventional instrumentation arrays and that is often smoothed out or otherwise not-well-represented by numerical models. Accurate representation of many of these features and structures will most likely be necessary to the success of VTMX program objectives pertaining to the nature and effects of transport and mixing mechanisms.
Objectives
The objectives of this proposal are to use Doppler lidar data, both in conjunction with the other available VTMX datasets and in conjunction with relevant modeling studies, to increase our understanding of vertical transport and mixing processes in an urban basin atmosphere. These objectives are more specifically:
To better understand processes responsible for the formation and destruction of cold pools in a mountain basin, including synoptic cold and warm advection aloft, radiation, drainage (slope and valley outflow) flows, surface heating, turbulent erosion, and others, and to better understand their relative importance and roles under different meteorological conditions.
To better understand processes of transport and mixing within a mountain basin, and their roles in regulating surface concentrations of atmospheric contaminants or surface values of other quantities, such as temperature, moisture, and fluxes.
To understand the role of dilution and processes involved in export of air from the basin cold pool in the overall basin budgets of heat and trace species.
To use Doppler lidar data in conjunction with data from the other VTMX sources to test the hypotheses given in this proposal.
To provide a comprehensive dataset of case studies at fine detail for numerical modeling investigations designed to demonstrate model capabilities in simulating cold pool evolution and small-scale features of the stable cold-air layer, and for improving model parameterizations.
Questions to be Addressed
What is the nature of the interaction of terrain induced flows (e.g., drainage winds at night, upslope winds during the day, and waves) with cold air pools in basins, and how do such flows affect the formation and erosion of those pools and the dispersion of pollutants in them?
What are the fundamental processes that control vertical transport for stable and transition boundary layers? What measurements are required to identify and quantify these processes and how can they be made?
How do traveling weather systems remove stable stagnant air out of a basin, and under what conditions do these removal mechanisms fail?
How do pollutants move through residual layers above a stable or convective surface layer and to what extent can pollutants penetrate stable and residual layers aloft? How rapidly will an elevated layer of pollutants mix downwards to the ground in a stable cold pool trapped within a basin?
How well can remote and in situ sensors measure winds, temperature, turbulence, and pollutants in the lowest few kilometers of the atmosphere? What improvements are needed and practical?
