Project B09:
The role of UTLS moisture for the extra-tropical mean circulation

Brief Summary

The synoptic- to climate-scale distribution and variability of moisture in the UTLS is poorly represented in state-of-the-art numerical models. Moisture and clouds in the UTLS couple to the dynamics by radiation and thereby impact on the prevailing, climatological mean wind. In particular, the impact on the mean winds in the extra-tropics – the midlatitude jet stream – is not yet well understood. Importantly, the location and strength of the jet exhibit a crucial link to regional surface climate. The midlatitude jet is shaped by the cyclonic and anticyclonic weather systems that occur preferentially in the so-called storm tracks, e.g., in the North Atlantic. The project aims at improving our fundamental understanding of how weather systems in the storm tracks mediate the impact of UTLS moisture on the jet. To this end, we will perform numerical experiments of idealized storm tracks, analyze the moisture and cloud structure in these experiments, and apply diagnostics to quantify the individual contributions to changes of the jet. We will thereby link transient, weather-scale processes to the large-scale winds. Eventually, this project will thus contribute to assess more reliably the robustness of regional surface climate projections in the extra-tropics.

Formation of modified jet stream (colours) by the action of weather systems in idealized numerical experiments similar to the ones that will be performed in this project (by Dr. I. Orlanski at Princton, USA, published in 2003). Time increases from left to right. The contour lines depict a metric for weather-system activity. In the beginning of the experiment, the jet is located at 40N. The development of weather systems first weakens the jet and then re-forms a strong jet further polewards (around 50°N).

Project Poster

Evaluation Poster Phase I in 2025

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