Humidity in the Atmosphere
Atmospheric water vapour is an essential component of the climate system, for example because of its importance for the Earth's radiation budget and the formation of precipitation. A fundamental property of water vapour is the length of time it remains in the atmosphere, i.e. the typical time span between evaporation from the earth's surface and precipitation. Estimates of this time scale, based on fundamental considerations of the moisture budget, amount on average to about 8-10 days (Trenberth, 1998), whereas more recent, more process-oriented estimates result in shorter time scales (Läderach and Sodemann, 2016; see figure below).
In this thesis, a detailed estimation of the atmospheric residence time of water vapour will be carried out using specially designed experiments with a global circulation model (Eckstein et al., 2017). This model version allows water from certain sources to be marked as so-called "tracers" and thus to be tracked separately. Several tracers are used to estimate the length of residence, which mark evaporation in limited periods of time (see Läderach, 2016).
Prerequisites for this work are programming knowledge, interest in working with models and in the atmospheric water cycle. The student should actively participate in the design of the model experiments, which requires some technical work, but also allows an insight into the model structure.
Supervisors: Stephan Pfahl, Ingo Kirchner
- Eckstein, J. et al., 2017: From climatological to small scale applications: Simulating water isotopologues with ICON-ART-iso (version 2.1). Geosci. Model Dev. Discuss., doi:10.5194/gmd-2017-280.
- Läderach, A. and H. Sodemann, 2016: A revised picture of the atmospheric moisture residence time. Geophys. Res. Lett. 43, 924-933, doi:10.1002/2015GL067449.
- Läderach, A., 2016: Characteristic scales of atmospheric moisture transport. Diss. ETH No. 23586, doi:10.3929/ethz-a-010741025.
- Trenberth, K. E., 1998: Atmospheric moisture residence times and cycling: Implications for rainfall rates and climate change. Clim. Change 39, 667-694, doi:10.1023/A:1005319109110.