Atmospheric dynamics; Precipitation recycling; Climate system; Water vapor transport; Weather systems; Atmospheric water cycle
Buizert Christo, Sigl Michael, Severi Mirko, Markle Bradley R., Wettstein Justin J., McConnell Joseph R., Pedro Joel B., Sodemann Harald, Goto-Azuma Kumiko, Kawamura Kenji, Fujita Shuji, Motoyama Hideaki, Hirabayashi Motohiro, Uemura Ryu, Stenni Barbara, Parrenin Frédéric, He Feng, Fudge T. J., Steig Eric J. (2018), Abrupt ice-age shifts in southern westerly winds and Antarctic climate forced from the north, in Nature
, 563(7733), 681-685.
Läderach Alexander, Sodemann Harald (2016), A revised picture of the atmospheric moisture residence time, in Geophysical Research Letters
, 43(2), 924-933.
The atmospheric branch of the global water cycle is an important link between the major reservoirs, such as ocean, land, and ice sheets. Water vapour evaporates from the world oceans and land surfaces, is transported through the atmosphere governed by atmospheric dynamics, until it condenses and returns as precipitation to the surface. Variability is a key characteristic of the atmospheric water cycle. Extremes in precipitation variability, such as flooding and drought periods can have severe consequences for human societies. It is the aim of this project to contribute to a better understanding of the processes governing precipitation variability on a global scale through a novel analysis of the linkages between evaporation sources, atmospheric transport, and precipitation processes. One way to characterise the connection between precipitation and the water vapour sources are variables of temporal and spatial scale, such as atmospheric residence time and water vapour transport distance. Previous research has indicated that most of the water vapour converted to precipitation by weather systems had already been present in the atmosphere beforehand. It has however not been studied in detail which processes had lead to the evaporation of that moisture in the first place, over which radius water vapour is typically advected into different weather systems, and which life time of the atmospheric water vapour this implies. While on a global mean an atmospheric life time of water vapour of about 10 days can be derived, several recent studies specifically highlight that substantial variability can exist, ranging between less than two days for mid-latitude heavy precipitation events to about two weeks in polar regions. In order to advance the basic understanding of the atmospheric water cycle, this project proposes to provide a first climatology of the characteristic spatial and temporal scales of linkages in the tropospheric water cycle using the ECMWF ERA-Interim reanalysis data set. To this end, two complementary methods developed by the applicant will be used in the proposed PhD project. The first method is a Lagrangian diagnostic to identify the moisture sources and transport pathways of atmospheric water vapour. This is currently the most advanced method of its kind, and will yield global information on the spatial and temporal scales linking the atmospheric water cycle. Explicitly displaying this information globally will allow to delineate regions by characteristic processes, identify transition regions, and their seasonal and inter-annual variability. Second, a regional numerical weather prediction model equipped with a secondary water cycle for the advection of water vapour tracers will be used to better understand the detailed dynamical and physical processes responsible for setting the identified temporal and spatial scales of water vapour transport in regions identified by the first method. By adapting the Lagrangian diagnostic to output from climate model simulations, it will be possible to assess the representation of the derived water cycle characteristics in climate models, and to build hypotheses on how the simulated water cycle responds to climatic changes. The results from the proposed project will help to guide future research on extremes in the present-day atmospheric water cycle, be relevant for interpreting records of past climate variability, and contribute to a better understanding of our abilities to project changes of the hydrological cycle in a future climate.