DynVar: Modelling Stratosphere-Troposphere Dynamics and Variability

1. DynVar is an international group on the modelling of the dynamics and variability of the stratosphere-troposphere system. Co-Chairs: Edwin Gerber (New York University) Elisa Manzini (Max-Planck-Institut, Hamburg) http://www.sparcdynvar.org/ Email list: sparcdynvar

2. DynVar strated in 2007 (Kushner et al) Mission: To understand and predict the 2-way stratosphere troposphere dynamical couplings and their linkages to atmospheric variability and change. To achieve its mission, DynVar promotes the development and use of coupled atmosphere-ocean-seaice general circulation models, with the atmospheric component extending to above the stratopause.

3. Later on: • Link to CMIP5 and SHFP (from 2010) • DynVarMIP, CMIP6 endorsed MIP (now) • DynVar works by calling for participation to CMIP (with “high top” models) and for analysis of CMIP model outputs, by means of workshops (4, in total)

4. DynVarMIP, CMIP6 endorsed MIP: • Gerber and Manzini, The Dynamics and Variability Model Intercomparison Project (DynVarMIP) for CMIP6: assessing the stratosphere–troposphere system, Geosci. Model Dev., 9, 3413-3425, 2016, http://www.geosci-model-dev.net/9/3413/2016/ • Approximately 10 model centers have committed to providing extended diagnostics of the atmospheric circulation.

5. MIP • Key questions: • How do dynamical processes contribute to persistent model biases in the mean state and variability of the atmosphere? • What is the role of atmospheric momentum and heat transport in shaping the climate response to global warming and ozone depletion? • How does the stratosphere affect climate variability at intra-seasonal, inter-annual and decadal timescales?

6. Proposal for a new focusof the SPARC DynVar initiative:Variability and Predictabilityof Surface Impacts and Extremes Daniela Domeisen, Alexey Karpechko, Olivia Martius, Edwin Gerber, Elisa Manzini

7. PROPOSED TOPIC We propose a new activity focussed on the role of dynamics in surface extremes and their predictability. 250mb 250mb The activity would keep DynVar as a name, given the international community that it has built up over the last decade, but renew the leadership and focus.

8. Relevant processes for Forecasting A variety of processes contributes to predictability on all timescales Length scale extratropical stratosphere climate change solar variability planetary Rossby waves 1000km Quasi-Biennial Oscillation snow cover / sea ice El Niño -Southern Oscillation Madden-Julian Oscillation 100km monsoons extreme events synoptic waves land – atmosphere interaction km convection m Time scale days months years decades

9. Relevant processes for Forecasting A variety of processes contributes to predictability on all timescales Length scale extratropical stratosphere climate change solar variability planetary Rossby waves 1000km Quasi-Biennial Oscillation snow cover / sea ice El Niño -Southern Oscillation Madden-Julian Oscillation 100km monsoons extreme events synoptic waves land – atmosphere interaction km convection m Time scale days months years decades

10. CONNECTION BETWEEN THE TROPOSPHERE AND THE STRATOSPHERE 250mb 250mb 100mb 100mb Geopotential height averaged over Jan 17 – 21, 2017 10mb 10mb

11. Suggested research topics • Continuation of the dynamical theme of the SPARC DynVar activity with a focus on surface weather and climate extremes and their predictability. Contribution of stratospheric, tropopause, and tropospheric processes to extreme events from weather to climate timescales, focusing on the large-scale environment and the dynamics that lead to extreme events. • Examples: • anomalous precipitation or flooding events linked to storm track variability • long-lived atmospheric anomalies ranging from weekly to monthly timescales, e.g. atmospheric blocking, cold air outbreaks, or anomalously persistent NAO/AO/AAO states and their prediction • long- term changes on timescales of years to decades, e.g. a shift of the surface westerlies and storm tracks due to stratospheric changes in temperature or chemistry or tropospheric climate change • impacts of the tropical stratosphere on the surface, such as e.g. the connection between dominant weather and climate patterns such as the QBO and the MJO, as well as ENSO and the Asian monsoon.

12. Goals of the new activity • First goal: • focus on improving process understanding • Second goal: • a coordinated effort of method intercomparison for extreme events • Tools: • intercomparison of surface impacts for models with an atmosphere that is initialized or nudged in predictor locations. • A workshop to clarify and exchange these tools is envisaged.

13. Links to other initiatives • SPARC SNAP (Stratospheric Network for the Assessment of Predictability) • SPARC S-RIP (Reanalysis Intercomparison Project) • SPARC Data Assimilation • DynVarMIP • SPARC ACAM (Atmospheric Composition and the Asian Monsoon) • WCRP Grand Challenge on Weather and Climate Extremes / GEWEX initiative • WCRP Grand Challenge on Near-Term Climate Prediction

14. WCRP Focus: global energy and water cycle exchanges (includes floods) Precipitation extremes WWRP High Impact Weather Project Focus: urban floods, wildfires, heatwaves Disruptive winter weather, local extreme wind Storm tracks DynVar Large-scale and synoptic-scale dynamics associated with weather and climate extremes Heat waves Link of extremes to blocking and cyclones Role of SSTs, soil moisture and sea ice

15. Suggestions for activity lead • Preliminary suggestions for activity lead: • Daniela DomeisenAlexey Karpechko (?)& person working on e.g. storm tracks • & person working on extremes • Preliminary suggestions for Committee Members: • Olivia MartiusEdwin GerberElisa ManziniMark BaldwinAndrew Charlton-Perez • et al.