The water vapour distribution in the Arctic lowermost stratosphere during the LAUTLOS campaign and related transport processes including stratosphere-troposphere exchange

摘要

Balloon-borne water vapour measurements during January and February 2004,which were obtained as part of the LAUTLOS campaign at Sodankylä,Finland, 67° N, were used to analyse the water vapour distribution in thewintertime Arctic lowermost stratosphere. A 2.5 km thick layer (or 30 K inthe potential temperature scale) above the tropopause is characterized by asignificant water vapour variability on a synoptic timescale with valuesbetween stratospheric and tropospheric, which is in good agreement withpreviously reported measurements. A cross-correlation analysis of ozone andwater vapour confirms that this layer contains a mixture of stratosphericand tropospheric air masses. Some of the flights sampled laminae of enhancedwater vapour above the tropopause. Meteorological analyses and backwardtrajectory calculations show that these features were related to filamentsthat had developed along the flanks of cut-off anticyclones, which had beenactive at this time over the Northern Atlantic. The role of the filamentswas however not to transport water vapour from the troposphere to thestratosphere but rather to transport it within the stratosphere away fromregions where intensive two-way stratosphere-troposphere exchange (STE) wasidentified. Intensive STE occurred around cut-off anticyclones in regions ofstrong winds, where calculations suggest the presence of clear-airturbulence (CAT). Evidences that CAT contributes to thetroposphere-to-stratosphere transport (TST) are presented. However,statistically, relation between TST and CAT during the studied period isweak.