How is the coupling of the stratosphere and troposphere affected by climate change, and how strong is the feedback on climate?

Ulrike Langematz (PI), Martin Dameris, Hauke Schmidt, Christoph Brühl, Ulrich Cubasch

Phase I:

The focus of SHARP-STC is to determine the role of the interaction between the stratosphere and troposphere in a changing climate, in particular to assess the impact of a changing stratosphere on the troposphere-surface system. Observations and model studies have shown that the troposphere and stratosphere influence each other on different time scales, but the mechanisms responsible are not well understood. The project addresses the questions if the importance of the coupling between the stratosphere and the troposphere will change in a changing climate and what the consequences will be for surface climate and weather. Transient simulations of the past and future as well as complementary sensitivity simulations with state-of-the-art Chemistry-Climate Models are performed and analysed to study how well current models are able to reproduce the observed coupling, to understand the responsible mechanisms, and to predict its future evolution.

 

Anomalies of the Northern Annular Mode (NAM) index after weak stratospheric vortex events between 1970 and 2010, simulated with a Chemistry-Climate Model. Stratospheric circulation anomalies influence the troposphere with a time lag of up to 2 months.

 

Phase II

The focus of SHARP-STC is to determine the role of the interaction between the stratosphere and troposphere in a changing climate, in particular to assess the impact of a changing stratosphere on the troposphere-surface system. Observations and model studies have shown that the troposphere and stratosphere influence each other on different time scales, but the mechanisms responsible are not well understood. Questions that will be addressed also in Phase II of this project are if the importance of the coupling between the stratosphere and the troposphere will change in a changing climate and what the consequences will be for surface climate and weather. Transient simulations of the past and future as well as complementary sensitivity simulations with state-of-the-art Chemistry-Climate models (CCMs) will be performed and analyzed to study how well current models are able to reproduce the observed coupling, to understand the responsible mechanisms, and to predict its future evolution.

New aspects in Phase II are the extension of our studies to the effects of radiative and chemical coupling processes on the troposphere-surface system. The relevance of additional climate feedback processes associated with ocean coupling will be addressed by applying a CCM with an interactive ocean model. The role of the representation of stratospheric processes for stratosphere-troposphere coupling will be studied in simulations with an Earth System Model (ESM) with different spatial resolutions.

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