Abstract
Abstract. The Hygrosonde-2 campaign took place on 16 December 2001 at Esrange/Sweden (68° N, 21° E) with the aim to investigate the small scale distribution of water vapour in the middle atmosphere in the vicinity of the Arctic polar vortex. In situ balloon and rocket-borne measurements of water vapour were performed by means of OH fluorescence hygrometry. The combined measurements yielded a high resolution water vapour profile up to an altitude of 75 km. Using the characteristic of water vapour being a dynamical tracer it was possible to directly relate the water vapour data to the location of the polar vortex edge, which separates air masses of different character inside and outside the polar vortex. The measurements probed extra-vortex air in the altitude range between 45 km and 60 km and vortex air elsewhere. Transitions between vortex and extra-vortex usually coincided with wind shears caused by gravity waves which advect air masses with different water vapour volume mixing ratios. From the combination of the results from the Hygrosonde-2 campaign and the first flight of the optical hygrometer in 1994 (Hygrosonde-1) a clear picture of the characteristic water vapour distribution inside and outside the polar vortex can be drawn. Systematic differences in the water vapour concentration between the inside and outside of the polar vortex can be observed all the way up into the mesosphere. It is also evident that in situ measurements with high spatial resolution are needed to fully account for the small-scale exchange processes in the polar winter middle atmosphere.
Highlights
Water vapour plays a major role in the radiative budget and chemistry of the Earth’s atmosphere
Recent research on middle atmospheric water vapour has focused on global trends in the stratosphere (e.g. Oltmans et al, 2000; Rosenlof et al, 2001; Nedoluha et al, 2003; Randel et al, 2004; Scherer et al, 2008; Rosenlof and Reid, 2008) and their impacts on the ozone destruction by polar stratospheric clouds (PSC) in the polar vortex (e.g. Rex et al, 2004), tropospherestratosphere exchange (e.g. SPARC, 2000; Sherwood and Dessler, 2000; Bonazzola and Haynes, 2004; Engel et al, 2006; Lelieveld et al, 2006; Fueglistaler et al, 2009), and the water budget in the summer mesopause region
The observations exhibit three distinct maxima in the water vapour concentration at about 32 km, 52 km and 57 km. We suggest that this aspect reflects measurements probing both vortex and extra-vortex air in different altitude ranges
Summary
Water vapour plays a major role in the radiative budget and chemistry of the Earth’s atmosphere. Water vapour enters the middle atmosphere primarily by vertical transport through the tropical tropopause transition layer (TTL) (e.g. Holton et al, 1995; Fueglistaler et al, 2009). The tropical tropopause works as a cold trap where freeze-drying of water vapour and subsequent sedimentation of ice particles strongly reduces the amount of water vapour entering the stratosphere (Brewer, 1949). Besides the transport from the troposphere the only water vapour source in the stratosphere is the oxidation of methane. This production process, outweighs the main sink process of water vapour in the stratosphere, i.e. the reaction with O(1D).
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