Anyone who is interested in this project is welcome to contact Peter Haynes for further information.
The tropical tropopause layer (TTL) is now recognised as a crucial region of the atmosphere, with processes taking place there still ill-understood, but playing a key role in determining the stratospheric concentrations of water vapour and other chemical species relevant to ozone destruction and production. The subtle mix of convective and non-convective processes and the transition from convective to non-convective regimes over a vertical distance of only two to three km implies that existing chemical transport models and and the meteorological velocity fields used to drive them have significant shortcomings. Coherent and careful use of models and data on chemical species is necessary to assess the strengths and weaknesses of the models.
In late 2005 and early 2006 the ACTIVE consortium will make new measurements of chemical species in the TTL in the Northern Australian region. These measurements will be completed by others in the same region made by the EU-funded SCOUT-O3 project in late 2005 and by a US project in early 2006.
Early models of chemical transport in the tropical tropopause layer (TTL) have tended to emphasise the role of vertical transport, with rapid vertical transport due to convective processes dominating in the lower part of the TTL and slow vertical transport due to non-convective processes dominating the upper part. In this one-dimensional picture the key quantitative uncertainty in the TTL is the partition, as a function of height, horizontal location and season, between convective and non-convective transport.
However the one-dimensional picture is likely to be an oversimplification. There is almost certainly an important role for quasi-horizontal advection, both in redistributing the air injected into the TTL by geographically confined convective events and also in transporting into the TTL air from the extratropical lower stratosphere. Tuck et al. (2004) have recently described observations of rich horizontal structure in chemical species in the TTL. The chemical measurements during the ACTIVE campaign will add significantly to the available data on horizontal variation within the TTL.
The role of horizontal transport and strong geographical variations mean that one-dimensional models of the TTL, which for example, use photochemical calculations plus observed ozone profiles to infer vertical transport rates have limited usefulness. Such models have been used, for example, to infer the role of convective and non-convective processes in vertical transport and in dehydration, and some of the conclusions based on those models therefore need re-examination.
The studentship project will analyse the data on chemical species collected during the ACTIVE campaigns and related campaigns and carry out chemical transport modelling and trajectory modelling necessary to interpret the data, to assess the limitations of the models and to obtain improved quantitative estimates for different transport processes. The role of large-scale horizontal transport in redistributing within the TTL air injected by convective processes and air brought from the extratropics will be a particular focus. The combination of participation in an international observational campaign, data analysis and modelling will provide excellent training experience for a PhD student.
This project would be well suited to a student with an undergraduate degree in mathematics or physics who wishes to exploit their skills and knowledge in research on an important environmental topic that is relevant to understanding ozone-depletion and climate change.
The student will be based in the Department of Applied Mathematics and Theoretical Physics (DAMTP) but will be co-supervised by Peter Haynes (DAMTP) and John Pyle (Department of Chemistry - DoC). The co-supervisors have collaborated successfully on several projects over the last decade and are co-Directors of the Cambridge Centre for Atmospheric Science (which brings together relevant personnel in DAMTP, DoC and Department of Geography).
Bonazzola, M, Haynes, P.H., 2004: A trajectory-based study of the tropical tropopause region. J. Geophys. Res., 109, D20, D20112, 10.1029/2003JD004356.
Esler, J.G., Haynes, P.H., Law, K.S., Barjat, H., Dewey, K., Kent, J., Schmitgen, S., Brough, N., 2002: Transport and Mixing between Airmasses in Cold Frontal Regions during Dynamics and Chemistry of Frontal Zones (DCFZ). J. Geophys. Res., 108, D4, 10.1029/2001JD001494.
Esler, J.G., Tan, D.G.H., Haynes, P.H., Evans, M., Law, K.S., Plantevin, P.-H., Pyle, J.A., 2001: Stratosphere-Troposphere Exchange: chemical sensitivity to mixing. J. Geophys. Res., 106, 4717-4731.
Hadjinicolaou,P., Jrrar, A., Pyle, J.A., Bishop, L., 2002: The dynamically driven long-term trend in stratospheric ozone over northern middle latitudes, Quart. J.R. Met. Soc, 128, 1393-1412.
Haynes, P.H., 1999: Transport, stirring and mixing in the atmosphere. In: Proceedings of the NATO Advanced Study Institute on Mixing: Chaos and Turbulence, Cargese, Corse, France, July 7--20, 1996, ed. H. Chate, E. Villermaux; Dordrecht, Kluwer Academic Publishers, 229-272.
Haynes, P.H., Scinocca J.F., Greenslade, M.D., 2001: Formation and maintenance of the extratropical tropopause by baroclinic eddies. Geophys. Res. Lett., 28, 4179-4182.
Haynes, P.H., Shuckburgh, E.F., 2000: Effective diffusivity as a diagnostic of atmospheric transport. Part II: troposphere and lower stratosphere. J. Geophys. Res., 105, 22795-22810.
Lee, A.M., Jones, R.L., Kilbane-Dawe, I., Pyle, J.A., 2002: Diagnosing ozone loss in the extratropical lower stratosphere, J. Geophys. Res., 107(D11), 4110, doi:10.1029/2001JD000538.
Morgenstern, O., Lee, A.M., Pyle, J.A., 2002: Cumulative mixing inferred from tracer-tracer correlations, J.Geophys.Res108 (D5): 8321, doi:10.1029/2002JD002098,
Tan, D.G.H., Haynes, P.H., MacKenzie, A.R., Pyle, J.A., 1998: Effects of fluid-dynamical stirring and mixing on the deactivation of stratospheric chlorine. J. Geophys. Res., 103, 1585-1605.