Remote sensing measurements of the atmospheric boundary layer
Supervised by Prof Geraint Vaughan of the School of Earth, Atmospheric and Environmental Sciences
The atmospheric boundary layer is the region of the atmosphere in direct contact with the ground – this is where air pollution has its greatest impact and where heat and moisture from the Earth’s surface enters the atmosphere. It is a layer characterised by turbulence, where good measurements are required to understand the processes involved. It is becoming increasingly apparent that measurements from the ground, or on towers, are insufficient to constrain models of the boundary layer, and that novel techniques for remote sensing are required.
The Centre for Atmospheric Sciences is a leading group in the development and use of active remote sensing – radar and lidar (like radar but using lasers) – see http://tinyurl.com/77h9u2. We have mobile lidars and a mobile radar wind profiler, and have powerful fixed lidars at the Capel Dewi field site near Aberystwyth in mid-Wales (http://tinyurl.com/a4kjtm) when the UK’s most powerful radar wind profiler is located.
The project has a number of strands which can be adapted to suit the aptitude and interest of potential students:
- developing a new lidar to measure temperature profiles over a city, and using this to investigate the night-time boundary layer over the city of Manchester. The group has a special laboratory for lidar development, with a roof hatch to view the atmosphere. Rotational Raman scattering is a technique we have used in the past to measure temperature and is ideal for this project. The night-time boundary layer is of interest for two reasons: it is scientifically interesting, because the lower atmosphere decouples from the surface layer; and this decoupling leads to an accumulation of pollutants near the surface, which has obvious implications for human health.
- Use of aerosol lidars to study the structure of the boundary layer near the coast, and the effect of sea breezes. We have access to a site on the sea-shore in Norfolk (Weybourne) and the Aberystwyth site is also near the coast. The venting of pollutants from the boundary layer into the free troposphere at the coast is poorly understood, and is an important element in the long-range transport of pollutants.
- Developing new humidity measurements using Raman lidar. The group already has a water vapour lidar at Capel Dewi, and is planning to develop a mobile lidar for use on field campaigns. This is a vital measurement for understanding cloud formation in the atmosphere.
Allied to these measurements will modelling work using a range of meteorological models available under the aegis of the National Centre for Atmospheric Sciences.
- G. Vaughan, D. P. Wareing, S. J. Pepler, L. Thomas, V. Mitev. Atmospheric temperature measurements by rotational Raman scattering. Applied Optics, 32, 2758-64, 1993.
- E. G. Norton, G. Vaughan, J. Methven, H. Coe, B. Brooks, M. Gallagher and I. Longley. Boundary layer structure and decoupling from synoptic scale flow during NAMBLEX. Atmos. Chem. Phys. 6, 433-445, 2006.
- D. N. Whiteman Examination of the Traditional Raman Lidar Technique. II. Evaluating the Ratios for Water Vapor and Aerosols. Applied Optics, 42, 2593-2608, 2003.