1. NAWDEX North Atlantic Waveguide and Downstream impacts Experiment (Sep-Oct 2016)

2. WWRP working group on Predictability, Dynamics & Ensemble Forecasting (PDEF) Presenter: John Methven, University of Reading Co-Chairs: Richard Swinbank and Craig Bishop

3.  To advance the science of dynamical meteorology and predictability research, and application to ensemble forecasting  To improve ensemble prediction systems  To support WWRP projects with expertise ◦ Polar prediction project ◦ Subseasonal to seasonal prediction ◦ High impact weather  To promote the utilisation of ensemble datasets ◦ TIGGE (The International Grand Global Ensemble) ◦ TIGGE-LAM ◦ Other ensemble datasets from WWRP projects

4. Co-chairs ◦ Craig Bishop – NRL, USA ◦ Richard Swinbank – Met Office, UK Members ◦ Oscar Alves – CAWCR, Australia ◦ Judith Berner – NCAR, US ◦ Masayuki Kyouda – JMA, Japan ◦ Zhiyong Meng – U Peking, China ◦ John Methven – U Reading, UK ◦ Mark Rodwell – ECMWF, International ◦ Olivia Rompainnen-Martius – U Bern, Switzerland ◦ Susanne Theis – DWD, Germany ◦ Munehiko Yamaguchi – JMA/MRI, Japan ◦ Yuejian Zhu – NCEP, USA Ex officio ◦ TIGGE panel chair: Manuel Fuentes – ECMWF, International

5. 1.Stochastic representation of the effect of sub-grid- scale uncertainty in numerical models 2.Construction of ensemble initial conditions 3.Role of diabatic processes in dynamics and predictability 4.Assessment of multi-model ensembles and calibration techniques 5.Coupled modelling & data assimilation

6. Motivation for NAWDEX Worst 100 forecast busts for Europe share a common pre-cursor Rossby wave pattern 6 days beforehand (Rodwell et al, BAMS, 2013) PV forecast errors at 96 h Davies and Didone (2013) Suggestion of underestimated upper-level ridge building. Hypothesis: Linked with mis-represented moist processes

7. Ridge area forecasts Reduced forecast resolution after day 10 2.3x10 7 km 2 2006/7 2007/8 2008/9 2009/10 2010/11 2011/12 2012/13 Gray, Dunning, Methven, Masato and Chagnon (2014), GRL

8. Ridge PV gradient forecasts 2006/7 2007/8 2008/9 2009/10 2010/11 2011/12 2012/13 Reduced forecast resolution after day 10 Gray, Dunning, Methven, Masato and Chagnon (2014), GRL

9. “Diabatic PV” in section across tropopause fold  Positive diabatic PV above (on strat side) of tropopause  Negative diabatic PV beneath (on trop side) of tropopause  Tropopause elevation not significantly altered by direct diabatic PV modification Chagnon, Gray and Methven (2013), Q J R Met S

10. Diabatic PV near the tropopause 1.LW cooling max at tropopause (humidity step)  “diabatic PV dipole” but little direct PV change at tropopause  enhances tropopause PV gradient & jet strength  would be influenced by cirrus just under tropopause 2.Diabatic PV enhances PV anomaly pattern of Rossby wave  greater westward propagation and enhanced baroclinic interaction  influence on medium-range forecasts Chagnon, Gray and Methven (2013), QJRMetS

11. Phenomena central to NAWDEX Illustration of features related to PV near the tropopause (orange is stratospheric air; cyan marks upper tropospheric PV anomalies).

12. A selection of NAWDEX objectives & hypotheses Dis-entangling the different processes leading to model error growth (radiative, moist processes, model resolution). Details of moist processes within warm sector and warm conveyor belts matter to net latent heating, WCB outflow & ridge building. Vertical structure of PV and humidity anomalies in ridges matters to Rossby wave evolution (vertical resolution challenge for NWP & climate models) Influence of diabatic processes on tropopause & jet location is indirect: i) advection by enhanced divergent outflow ii) wave-mean: change in RW breaking → jet sharpening & shift Diabatic processes central to mesoscale structure & high impact weather –E.g.(1) stationary tropopause troughs and persistent heavy rainfall (2) strongest surface winds related to banding on south side of cyclones Need fine-scale observations of winds, temperature, humidity, cloud & radiation at tropopause level, connected across the North Atlantic as features evolve

13. Airborne research facilities Meteorological fields to be measured/deduced: - wind components - humidity - liquid/ice water content - nature of hydrometeors - radiative fluxes In-situ sondes DLR HALO SAFIRE Falcon DLR Falcon Drop sondesRadar-Lidar platform

14. Ground-based observations Deep wind profilers VHF (Stratosphere-troposphere radars) Shallower wind profilers UHF Microwave radiometers Doppler radar network Enhanced radiosonde obs

15. NAWDEX science plan and webpage NAWDEX web page coming online this week: http://www.nawdex.org See the NAWDEX Science Plan Participate in NAWDEX-AMIP Overarching scientific aim of NAWDEX: to increase the physical understanding and to quantify the effects of diabatic processes on disturbances to the jet stream near North America, their influence on downstream propagation across the North Atlantic, and consequences for high-impact weather in Europe.