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Abstract

A case study of aircraft measurements in the vicinity of a warm front over the North Sea is presented. Measurements of ozone, carbon monoxide and meteorological parameters were recorded at several altitudes behind a dissipating warm front by the U. K. Met. Office's C130 aircraft, operated by the Meteorological Research Flight on 3rd October 1997. The aim of the study was to investigate the composition of the warm conveyor belt (WCB), the main air flow associated with mid-latitude cyclones, which has the potential to transport boundary layer air containing ozone and its precursors into the free troposphere. Three distinct air masses were identified by changes in the parameters measured. Trajectory analyses together with synoptic charts showed that these air masses corresponded to a WCB and air ahead and behind it, and that the WCB consisted of marine air from the boundary layer and lower free-troposphere. The WCB was clearly identifiable as a distinct chemical air mass that retained its integrity even after the warm front began to dissipate; it contained lower ozone than the surrounding free tropospheric air due to its remote marine origin.