Water vapour is one of the most important variables for weather prediction and climate
20 research. Particularly, the interaction between the water vapour in the UT/LS (upper
troposphere and lowermost stratosphere) and tropopause dynamics is not well understood.
Thus, in the latest IPCC report (Stocker et al., 2013), it is stated that the knowledge
about potential trends and climate feedback mechanisms of upper tropospheric
water vapour is low because of the lack of long data records of high quality in this
25 specific region of the global atmosphere. Neither the global radiosondes network nor
satellites can provide measurements of the required spatial and temporal resolution,
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