Frontal zones are regions where are descending from the upper troposphere and lower stratosphere comes in close proximity to rising air of recent boundary-layer origin. Such zones are often strongly sheared and subject to shearing instability and mixing.

The aim of the UTLS-DCFZ project was to investigate the nature and effect of the mixing of the two airmasses which may be characterised by very different chemical compositions. In particular, the experimental campaign helped answer questions concerning:

The distribution of chemical species around fronts.
The role of frontal systems in transporting chemical species from the boundary layer and the stratosphere into the troposphere.
The extent and rate of mixing between the differing air-masses in the vicinity of fronts.
The effect of this mixing on the photochemistry of OH and ozone.
The effect of this mixing on the dynamical structure of the front, which will feed back through 1. and 2. above.

Five flights were carried out between January and April 1999, two of which were in the period which overlapped with MAXOX. These flights sampled a range of frontal situations, so the main improvement which could be made to the dataset would be to sample more fronts in a similar way, to improve the statistical basis for any analysis. Aircraft measurements of the chemical (e.g. CO, O3, NOx as well as MAXOX measureables during some of the flights), thermodynamic, physical (e.g. liquid water content, CCN etc.) and dynamical characteristics of a number of frontal situations were made. Chilbolton radar images are also available.