Title: The relation between atmospheric composition and fronts
Supervisors: Prof G. Vaughan and Prof D. M. Schultz
External supervisors and institution:
Contact: [email protected]
Is this a CASE studentship? NO
Introduction:
The concept of an atmospheric front as a boundary between two air masses is an old one in
meteorology, but has been largely superseded by the modern picture of a front as a transition
zone between airstreams that move vertically as well as horizontally. One would expect
therefore that a gradual change would be seen in the concentration of trace gases as one
traversed a front. This is not what we observe: sharp gradients in constituents such as ozone
and carbon monoxide are often observed near fronts, as shown in the figure which was
compiled from measurements made on a research aircraft around a warm front. This suggests
that small-scale mixing, which acts to smooth out gradients, is either absent or does not have
enough time to act as the airstreams come together. The problem is relevant to atmospheric
chemistry – there can be chemical consequences of mixing two air masses – and to
atmospheric dynamics, especially in the mixing of stratospheric air into the troposphere in the
vicinity of fronts.
A related question concerns the very sharp vertical gradients in humidity found in descending
airstreams, which show up in VHF radar profiles as multiple frontal bands (Lawson et al 2013).
Project Summary:
This project will explore the creation and maintenance of sharp and multiple gradients of
chemical species (including water vapour) near fronts. To start with, the project will examine
data from the FAAM aircraft in the vicinity of fronts, exploiting a dataset which has not been fully
examined for this aspect. It is likely that this will lead to opportunities to gather further data with
FAAM during future field campaigns.
Alongside the experimental data, the project will use the WRF (Weather Research and
Forecasting) model for simulations of fronts, to determine whether the model is able to
reproduce the observed structure and to use its parameterisations to calculate the degree of
mixing near fronts. Thus, the student will gain experience with analysis of field data and
numerical modeling, as well as tackling an interesting problem in atmospheric physics.
Ozone and CO concentrations, in ppbv, measured by the FAAM aircraft during a study of a warm front.
The FAAM research aircraft
References
S. Bethan, G. Vaughan, C. Gerbig, A. Volz-Thomas, H. Richer and D. A. Tiddeman. Chemical
air mass differences near fronts. J. Geophys. Res., 103, 13413-434, 1998
J. Lawson, D. M. Schultz, G. Vaughan and D. Kirshbaum. Multiple bands near fronts in VHF
wind-profiling radar and radiosonde data. Atmos. Sci. Lett., DOI: 10.1002/asl2.4316 May
2013.