Evaluation of the SKYHI general circulation model usingaircraft N2O measurements 2. Tracer variability and diabatic meridional circulation S.E. $trahan 1 Atmospheric and OceanicSciences Program,Princeton University,Princeton,New Jersey

Winterpolarstratospheric nitrousoxide(N20) measurements madeduringtwo NASA polaraircraftfieldcampaigns providea uniqueopportunity to evaluatetheperformance of the1ølatituderesolution versionof theGeophysical FluidDynamicsLaboratory 's"SKYI-H" generalcirculationmodel.Thishigh-resolution modelhasbeenintegrated20 months, producing oneAntarcticandtwoArcticwinters.Powerspectra of thedynamically controlled tracerN20 areusedasa diagnostic of waveactivity.Comparison of thespectra of SKYHI and theobservations showsthattheSKYHI Arcticwinterlowerstratosphere is dynamicallyactive enoughto generaterealisticmesoscale tracervariabilitybutthattheSKYHI Antarctichas deficientvariabilityat scalesof 220-3000km. Low-passfilteringis appliedto a newtypeof analysis thatattempts to discriminate betweendifferentsources of atmospheric variability,to theextentthatdifferentsources arecharacterized by differenttimescales. The goalis to diagnose mesoscale sources of tracervariabilityin themodelandin theobservations andthen to assess whetherSKYH• generates variabilityfor thefightphysicalreasons. This analysis showsthatvariabilityfrom"slow"processes suchasplanetary wavebreakingdominates andis generated in realisticamountsin theSKYHI Arcticwinters.The SKYHI Antarcticvortex showsinsufficient "debris"fromplanetarywavebreakingat scalesbelow700 km. Thebalance betweendiabaticdescentinsidethevortexandwavebreakingin the"surfzone"generates N20 gradients at thevortexedgein themodelandtherealatmosphere. Becausethediabatic circulationis drivenby waveactivity,thestrengthof modelwaveactivitydiagnosed by the spectral analysis andthemeanN20 gradients canbeusedto evaluateSKYHI'sdiabatic circulation andnettracertransport. In theArctic,SKYHI temperatures, spectralresults,and realisticN20 gradients at thevortexedgesuggest a reasonablediabaticmeridional circulation andtransport. Antarcticspectral results,low vortextemperatures, andflatterN20 gradients at theedgeall supporttheconclusion thatthediabaticcirculation andwaveactivityin themodel southern hemisphere is too weak.