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Transport and mixing between airmasses in cold frontal regions during Dynamics and Chemistry of Frontal Zones (DCFZ)

Esler, JG; Haynes, PH; Law, KS; Barjat, H; Dewey, K; Kent, J; Schmitgen, S; (2003) Transport and mixing between airmasses in cold frontal regions during Dynamics and Chemistry of Frontal Zones (DCFZ). Journal of Geophysical Research - Atmospheres , 108 (D4) , Article 4142. 10.1029/2001JD001494. Green open access

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Abstract

The passage of two cold front systems over the United Kingdom are compared and contrasted, using the results of a detailed aircraft and ground-based study. The measurements are interpreted by means of three-dimensional, reverse-domain-filling trajectories using both global models and limited-area mesoscale models. This method provides a three-dimensional picture of the interleaving air-masses in the frontal zone as defined by their Lagrangian histories. The two systems studied differ in that the first is associated with an intense surface low in January and the second is associated with a relatively weak surface low in April. In the intense surface low case the trajectory study suggests that a dry intrusion with stratospheric characteristics penetrated deep into the troposphere along the upper level front. Measurements indeed revealed an unsaturated layer with anomalously high ozone. This layer was intersected at four levels in the troposphere (at 8.5, 7.1, 5.2 and 3.7 km), and the lower the intersection, the lower the measured anomalous ozone and the higher the water vapor content. It is argued that this is best explained by the dry-intrusion layer becoming mixed with background air by three-dimensional turbulence, also encountered by the aircraft, along the upper level front. Evidence for this mixing is apparent on tracer-tracer scatterplots. In the weak surface low case, by contrast, the dry intrusion has a more complex structure, with up to three separate layers of enhanced ozone and low humidity. Strong evidence for mixing was apparent only in the lowest layer. The weaker system may therefore be much more efficient at transporting upper tropospheric/stratospheric ozone to the lower troposphere. The transport of boundary layer air to the upper troposphere in the warm conveyor belt (WCB), however, was found to be around 8 times stronger in the intense system. Sonde measurements suggested that the WCB was ventilated by convection from the surface front in some regions to about 5-6 km, while it was stably stratified in other regions, suggesting layerwise long-range transport.

Type: Article
Title: Transport and mixing between airmasses in cold frontal regions during Dynamics and Chemistry of Frontal Zones (DCFZ)
Open access status: An open access version is available from UCL Discovery
DOI: 10.1029/2001JD001494
Publisher version: http://dx.doi.org/10.1029/2001JD001494
Language: English
Additional information: Copyright 2003 by the American Geophysical Union
Keywords: Frontal zones, Chemistry and mixing, Lagrangian-based analysis, Boundary-layer, Free troposphere, Extratropical cyclones, Lowermost stratosphere, Air, Ozone, Airstreams, Exchange, Nitrogen
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Mathematics
URI: https://discovery.ucl.ac.uk/id/eprint/93588
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