The January 2006 low ozone event over the UK

[摘要] In this paper we present a case study of a record low ozone event observedover the UK in January 2006. We focus on the dynamical processes thatcause this event. This is done by examining the observations, meteorologicalanalyses and back trajectories calculated by the NAME III atmospheric dispersionmodel. We show that this model, hitherto only used for troposphericpollution studies, can be an important and effective tool for theexamination of transport in the upper troposphere/lower stratosphere (UTLS)and mid-stratosphere regions.

A record low total ozone column of 177 DU was observed at Reading, UK, on19 January 2006. Low ozone values were also recorded at other stations inNorthwest Europe around this date. Ozonesonde measurements indicate thedepletion is occurring in two distinct vertical regions, with around a thirdof the reduction in total ozone column values originating from themid-stratosphere and the rest from the UTLS region. Evidence suggests thatair inside the stratospheric polar vortex was poor in ozone prior to19 January and the occurrence of a major stratospheric warming shifted thisair over Northwest Europe. In addition we show that moderateozone depletion, related to the lifting of the tropopause and divergencein the lower stratosphere associated with the presence of an anticyclone,is also a plausible mechanism for the record low ozone column that is observed.

In order to confirm that both mid-stratosphere and UTLS transport processes areresponsible for the record low ozone values, we perform turbulent backtrajectory calculations using the Met Office NAME III model. The results showthat air parcels in the mid-stratosphere that arrive over the British Isleson 19 January originate in the polar vortex, and furthermore that airparcels near the tropopause arrive from low latitudes and are transportedanticyclonically. Therefore this strongly suggests that the record low ozonevalues are due to a combination of a raised tropopause with increased divergencein the lower stratosphere and the presence of low ozone stratospheric air aloft.

[学科分类] 大气科学