Evaluation of long-term changes of upper tropospheric and lower stratospheric water vapour and ice supersaturated regions in different altitudes and geographical regions derived from MOZAIC and IAGOS routine in-situ observations

Water vapour is the most important greenhouse gas in the Earth’s atmosphere, both, due to radiative forcing and the formation of clouds. The upper troposphere and lowermost stratosphere (UTLS) region is an especially sensitive region for climate radiative forcing. In the UTLS the air is cold with a large spatial and temporal variability of water vapour.  With the MOZAIC (Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft) data it was recently shown that in the extratropical UT close to the tropopause the air is nearly saturated with respect to ice and contains a significant fraction of ice-supersaturated regions (ISSRs) (Petzold et al., ACP, 2020, doi.org/10.5194/acp-20-8157-2020).

In the present study we investigate the long-term changes of water vapour in the tropopause region using the combined time series of MOZAIC and IAGOS (In-Service Aircraft for a Global Observing System; www.iagos.org). Their observation systems are deployed on a fleet of commercial aircraft and aim at the provision of long-term, regular, and spatially resolved in situ observations of the atmospheric composition on a global scale. The combined water vapour and relative humidity time series spans now more than 27 years and is comprised of nearly 65000 flights. This makes the data set well-suited for long-term characterization of the water vapour distribution in the extratropical UTLS, namely at mid-latitudes with highest flight densities.

 We will present analyses of the time series from 1996 to 2020 for long-term changes of absolute humidity, temperature, relative humidity with respect to ice (RHice) and occurrence of ISSRs. Our focus lies on different altitude levels in the UTLS at northern mid-latitudes over the regions Eastern North America, North Atlantic and Europe.