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October 2006 saw renewed interest in theclimate change debate, particularly with therecent publication of the Stern Review on theEconomics of Climate Change. The issue ofclimate change was also addressed by theRoyal Meteorological Society (RMetS) at aWednesday meeting held jointly with theUpper Troposphere Lower StratosphereOzone Programme (UTLS Ozone) on 18October. The meeting, entitled ‘The UTLSRegion: Improvements in Understanding’,was aimed at providing an overview of thecontribution of UTLS Ozone research to thescientific debate.

UTLS Ozone is a Natural EnvironmentResearch Council thematic programmewhich has carried out research on thechemical composition and structure of theupper troposphere and lower stratosphereat mid-latitudes. The main scientific objec-tives, which were reflected in the meeting,were to further our understanding of thecauses for observed mid-latitude ozonechanges in the past and our expectations forthe future. The multidisciplinary approachto tackling the scientific issues was demon-strated in the diversity of research interestsof the speakers and attendees. The speakerscovered the areas of field campaign obser-vations, long-term measurements overmulti-annual timescales, theoretical studiesincluding numerical modelling and dataanalysis, laboratory studies, and thedevelopment of novel instrumentation.

Mr Jonathan Shanklin (British AntarcticSurvey) presented an overview of TheAntarctic ozone hole from discovery to pres-ent day. The existence of the ozone layerwas discovered by astronomers in the nine-teenth century. By the mid-twentieth centu-ry the basic mechanism for its creation wasunderstood and chemicals that coulddestroy it had begun to be fabricated. A fewdecades later ozone levels over Antarcticahad declined by a detectable amount. TheMontreal Protocol and its extensions havestopped the increase of ozone-destroyingsubstances in the atmosphere; nevertheless2006 has seen a record-breaking ozone hole.

A Lagrangian perspective of thetropopause and the ventilation of the lower-most stratosphere was given by Dr GavinEsler (University College London).Trajectories driven by large-scale analysedwind fields are used to investigate tropo-sphere to stratosphere transport in thetropopause region, with particular emphasison the barrier to mixing associated with thetropopause. A quantitative comparison ofthe seasonal evolution of the tropopausebarrier to transport, as well as its variation

with height was shown. The ultimatesources for the transport of air to the lower-most stratosphere, defined in terms of thelocations where each trajectory last left theatmospheric boundary layer, were alsoinvestigated.

In an overview of laboratory studies of thechemistry and photochemistry of the UTLS,Prof. Andrew Orr-Ewing (University of Bristol)described how our understanding of thechemical composition of regions of theEarth’s atmosphere, such as the uppertroposphere or lower stratosphere, isderived from a combination of in situmeasurements, computer models, andlaboratory experiments. Emphasis was

given to the contributions made by labora-tory studies, with examples drawn fromrecent work on the photochemistry oforganic molecules, rates of reactions of per-oxy and hydroxyl radicals, mechanisms ofoxidation of organic compounds, and het-erogeneous chemistry on aerosol particles.Such measurements provide data on reac-tion rates in the gas phase and at surfaces,and values for photochemical quantumyields and cross sections. The impact of newlaboratory measurements on predictedabundances of key atmospheric con-stituents, such as ozone in the UTLS region,was also illustrated.

Results from recent field campaigns

Meeting report The Upper Troposphere/Lower Stratosphere

Figure 1. Top: Met Office C130 flight path across a tropopause fold on 19 May 2000 during the UTLS Ozone‘Atmospheric Chemistry and Transport of Ozone (ACTO)’ campaign. The structure observed in ozone is wellrepresented by high-resolution models. Middle: Observed ozone (black) compared with a simulation by aLagrangian (trajectory) model (red). Bottom: Observed ozone (black) compared with a simulation by a high-resolution Eulerian model (red).

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(Top) Methven J, Arnold SR, O’Connor FM, Barjat H, Dewey K, Kent J, Brough N. Estimating photo-chemically produced ozone throughout a domain using flight data and a Lagrangian model, Journal ofGeophysical Research, 108, pp. 4271. 2003. © 2003 American Geophysical Union. Reproduced/modifiedby permission of American Geophysical Union.

(Middle and Bottom) O’Connor FM, Carver GD, Savage NH, Pyle JA, Methven J, Arnold SR, Kent J.Comparison and visualisation of high-resolution transport modelling with aircraft measurements.Atmospheric Science Letters, 6, pp. 164–170. 2005. © 2005 Royal Meteorological Society. Reproduced bypermission of John Wiley & Sons Ltd on behalf of RMetS.

funded by the UTLS Ozone programme andother sources during the past eight yearswere presented by Prof. Geraint Vaughan(University of Manchester). This has been aperiod when considerable attention hasbeen paid to the UTLS region and wheresignificant advances in our understandinghave been made with regard to the forma-tion of filaments and layers in the UTLS bybreaking Rossby waves, the extent of turbu-lence and mixing in the mid-latitude UTLS,and the importance of convection on theTropical Tropopause Layer (Figure 1).

Tropospheric ozone is a key secondary airpollutant; it is also the third-largest contrib-utor to radiative forcing of climate change,with its forcing dominated by upper tropo-sphere changes. With a lifetime of days toweeks, tropospheric ozone has a hetero-geneous global distribution, strongly in-fluenced by synoptic meteorology,challenging both observers and modellers.Dr David Stevenson (University of Edinburgh)reviewed the current state of globalmodelling efforts in a talk entitled ‘Globalmodelling of UTLS ozone’. Focus was given

to future predictions of upper troposphericO3 which requires knowledge of several keyprocesses, many of which will be influencedby climate change, such as the distributionof convection and lightning, surface emis-sions (including biogenic sources), and thestrength of the Brewer-Dobson circulation.

After briefly reviewing the surface climateeffects of a range of externally forcedchanges in the UTLS, Dr Nathan Gillett(University of East Anglia) focused on theeffects of ozone depletion on SouthernHemisphere climate. The influence of long-term changes in the UTLS on surface climatewas examined with simulations of theresponse to Antarctic stratospheric ozonedepletion showing a strengthening of thezonal circulation from the stratosphere tothe troposphere and an accompanyingsummer cooling over Antarctica, consistentwith observed changes. These resultsprompted discussion over whether ozonedepletion in the mid-stratosphere or in theUTLS has been dominant in forcingobserved surface climate changes. Theresults of a recent modelling study in which

ozone depletion was prescribed only in thelowermost stratosphere indicate thattropospheric climate changes have beenforced mainly by ozone depletion above thelowermost stratosphere.

Overall it was agreed that the meeting,whilst providing an insight into recentimprovements in our understanding of theupper troposphere and lower stratosphere,also raised new questions regarding theimpact of future climate change on thecomposition, structure and meteorology ofthe atmosphere.

Helen Rogers

University of Cambridge

Correspondence to: Helen Rogerse-mail: helen.rogers@atm.ch.cam.ac.uk

© Royal Meteorological Society, 2007

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Lenticular cloud over Gustav Adolf Land on the Island of Nordaustlandet, in the archipelago of Svalbard in the Arctic Ocean to the north of Norway, 2130 local time,15 August 2006 (© K. Tomlinson).