Stratosphere Sub-Project

Summary of 2019 Activities

We have contributed an overview chapter led by Amy Butler to the S2S prediction book “The gap between weather and climate forecasting” on subseasonal predictability and the stratosphere:  https://www.sciencedirect.com/science/article/pii/B9780128117149000115

We have produced two major review papers led by Daniela Domeisen to gather the international community on the topic of predictability of the stratosphere and stratosphere-troposphere coupling on sub-seasonal timescales using the S2S project database. Both studies are published in the JGR special issue on “Bridging Weather and Climate: S2S Prediction”. This was a major milestone for our project.

• Stratospheric predictability: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JD030920
• Stratosphere - troposphere coupling: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JD030923

Another milestone was a joint meeting held with SPARC DynVar in Madrid that brought together a wide range of scientists working on dynamics and predictability, including but not limited to stratosphere topics.

Objectives for 2020

1. Our initial analysis of stratospheric predictability and processes in the S2S prediction systems revealed issues with biases in these models that vary as a function of lead-time and initialization time. We plan to start a new community project on evaluating stratosphere-troposphere coupling biases in S2S prediction systems, and how these biases may influence predictive skill. These efforts will be led by Zachary Lawrence starting in Q1 2020 with plans to result in another community paper.

2. Michael Sigmond has agreed to lead an effort to address the use of different skill scores (in particular the anomaly correlation coefficient) in S2S studies.
There is potential to connect both 1. and 2. with the wider S2S community on this topic.

3. In addition to further exploitation of the S2S database and nurturing our partnership with S2S, recent studies including our review papers have highlighted that key to understanding stratosphere-troposphere coupling in the extra-tropics and S2S predictability more broadly is a greater understanding how the representation of tropospheric eddy-jet feedbacks contribute to this predictability. Similarly, in the tropics, a focus on the links between the QBO and MJO predictability is very important. With this in mind, our next major project is to plan and deliver an experiment in which the stratosphere is damped towards observed stratospheric events, replicating earlier idealised studies in simpler, low- resolution models which helped to develop more detailed theories for how planetary and synoptic scale eddies contribute to coupling between the stratosphere and troposphere. Peter Hitchcock will be the scientific lead. We have already held very fruitful discussions with QBOi about a joint initiative that would explore stratosphere-troposphere coupling in both the extra-tropics and tropics and for both initialised and free-running models using a combined and agreed upon damping framework. This proposal is ambitious and will require significant collaboration with and buy-in from S2S partners. A rough timeline is:

Q2 2020 – submission of paper outlining experimental protocol (with input from modelling centres)
Q4 2020 – begin modelling experiments
Q1 2021 – completion of modelling experiments and transfer of detailed dynamical diagnostics to a shared, open data repository
Q3 2021 – analysis of damped runs and production of 2-3 papers on outcomes