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Centre for Atmospheric Science

Research grants awarded

15 Jan 2010

Scientists from the Centre for Atmospheric Science have recently been awarded three grants in the latest NERC funding round. The grants awarded have a combined value of over £1,000,000.

The projects funded include studies of convection processes, atmospheric soot and urban pollution. Details of the individual projects are listed below.


Tropopause folding, stratospheric intrusions and deep convection (G. Vaughan, A. Russell, D. Schultz)

Deep convection brings heavy rain, flooding, strong winds and fire risk from lightning. Forecasting these events accurately is therefore a priority for meteorologists. Deep convective storms have many causes, some of which are relatively easy to predict, but others of which are more subtle and not well understood. One example of the latter is the effect of stratospheric intrusions and layers of stratospheric air on the development of convection. The processes by which weather systems form involves distortions of the tropopause, bringing stratospheric air to altitudes normally found in the troposphere. It has long been known that these intrusions promote convection, essentially by introducing cold air aloft, but recent research has suggested a more complex picture is possible, with convection in some cases being suppressed. The picture gets even more complex when the evolution of these stratospheric intrusions is considered - layers of stratospheric air flow into the troposphere and become detached from their parent trough, travelling many thousands of miles before dissipating. In most cases such layers inhibit convection but in certain circumstances they appear to initiate lines of thunderstorms. This proposal seeks to clarify the overall impact of stratospheric intrusions and layers on convection. The proposal will use a combination of statistical studies using past data, dedicated case studies and numerical modelling. Two novel datasets not applied to convection research previously will be exploited in the statistical studies - the database of European ozonesonde profiles gathered since 1990 and the NERC MST radar which has operated continuously since 1996. From the ozonesondes we will learn how frequently layers which can affect convection and are of stratospheric origin are measured, and from the radar the vertical structure of tropopause-level disturbances and their associated convection. These will provide context for the next stage of the project, which is to conduct a series of case studies (5-6 cases), using the MST radar together with lidars to measure ozone and water vapour. We will seek cases which span the continuum from tropopause-level disturbances through tropopause folds to detached layers, where convection has occurred and where it has not. Satellite data and rain radar data from the Met Office (available from BADC) will provide the observations of convection for these case studies. Measurements will be compared with ECMWF and UM analyses to determine how well the convection was represented in the models. The case studies will be used to guide a series of numerical modelling experiments based on the WRF model, to pinpoint the physical processes involved in the interaction between stratospheric intrusions and layers on the one hand and convection on the other. Questions to be addressed will include the mechanism whereby bands of showers form at the leading edge of stratospheric layers (is this merely a coincidence?), the initiation of convection by stratospheric intrusions (is this just a misnomer?) and the transition between convective initiation and suppression as a layer evolves. By changing the initial conditions in the model and rerunning the model, we will be able to understand the sensitivity of the resulting convection to the stratospheric layers. The results from the project will inform weather forecasters of the importance of representing stratospheric features correctly for convection forecasting, and bring a rather disparate area of the scientific literature to a focus.


Multiscale Chemical Composition of Carbonaceous particles and Coatings (MC4) (J. Allan, H. Coe, M. Flynn, G. McMeeking, P. Williams)

Schematic of SP-AMS
Schematic of the SP-AMS instrument which will be further developed and used to characterise atmospheric soot particles and their coatings during the MC4 project.

Black carbon (BC) particles are an important and highly relevant area of study in atmospheric science. These are produced in large quantities by human activities in the form of soot from fires and transport emissions. Concentrations of BC in the atmosphere have increased since pre-industrial times and the effect on global climate has been one of warming, as these particles can absorb incident radiation. In addition, these particles have the ability to alter regional climate and weather patterns through localised warming of the atmosphere. However, the exact effects of BC on the atmosphere are hard to predict, as the exact light-absorbing properties vary according to the exact source of the particles. In addition, atmospheric processes can cause the particles to become mixed with others and obtain coatings from gas phase reactions. These effects substantially change the absorption properties of the aerosol but are hard to predict. The study of these effects has traditionally been hampered by the lack of suitable instrumentation that can directly measure the chemical composition of BC and any coatings on the particles. To address these needs, the Soot Particle Aerosol Mass Spectrometer (SP-AMS) is being developed through a partnership between Aerodyne Research Inc., Droplet Measurement Technologies and the University of Manchester. This uses a near infra red laser to vaporise particles containing BC before the resultant vapours are analysed using mass spectrometry. Because particles that do not contain BC do not absorb the laser light, these are not detected. In this manner, the SP-AMS selectively measures only BC particles and their coatings, so therefore this instrument can be used to study the mixing state and the chemical composition of their coatings selectively. Multiscale Chemical Composition of Carbonaceous particles and Coatings (MC4) will use this novel instrument in conjunction with a suite of other measurements to study the sources and evolution of BC particles in the atmosphere, which will in turn lead to better model treatments and more accurate predictions of BC's climatic impacts. In addition, development work will take place in the laboratory to improve instrument sensitivity and data quality, accurately determine detection limits and formulate an operational protocol. This will maximise the effectiveness of subsequent experimental work. Measurements will take place in Los Angeles, Manchester and the Weybourne Atmospheric Observatory on the north Norfolk coast. A wide variety of sites is needed to characterise a broad range of aerosols. The measurements of coating and mixing will be compared with optical absorption measurements from automated filter-based methods. These will compared with estimates of the amount of chemical processing that the aerosol has undergone since emission based on gas phase VOC measurements. Different sources and types of BC particles will be identified and characterised using numerical factor analysis. The results from these studies will drive parameterisations that will be of use to the modelling community. This will allow the more accurate evaluation of the climatic impacts of BC particles over the course of their atmospheric lifetimes and lead to more accurate regional and global climate predictions in general.


ClearfLo: Clean Air for London (M. Gallagher, G. Vaughan)

Poor air quality, particularly in urban areas, has a demonstrable effect on human health, but the processes responsible for producing the main pollutants, namely particulate matter, ozone, nitrogen dioxide and heat are not well understood and are poorly predicted. The ambition of ClearfLo is to provide integrated measurements of the meteorology, composition and particulate loading of London's urban atmosphere, made at street level and at elevated sites, complemented by modelling, to improve predictive capability for air quality. This ambition will be addressed by establishing new measurement capabilities in London, which will be used for long-term measurements and intensive observation periods, and by analysis and modelling of the measurements to establish key processes.

This project also involves researchers from University of Reading, CEH Edinburgh, University of East Anglia, University of Hertfordshire, University of Leicester, University of Salford, University of York, Kings College London, University of Birmingham and University of Leeds and has a total budget of over £2,700,000.