North Atlantic Waveguide and Downstream Impact Experiment

--- NAWDEX finished today, 18 October, after 15 very interesting IOPs with observations in a diverse set of weather systems --- see more on "News" page and on the NAWDEX Wiki ---

Recent evidence indicates that the worst weather forecast failures for Europe are associated with distinctive pre-cursor patterns (5-6 days beforehand) that propagate along the jet stream from North America. In addition, the response of regional climate in the mid-latitudes, especially in the European sector, to global warming is highly uncertain due to the large variability associated with the coupled interaction between the North Atlantic storm track and jet stream. It is hypothesized that diabatic processes (involving latent heat release due to condensation in clouds and radiative transfer) are central to both the weather and climate prediction problems in the Euro-Atlantic sector.

The overarching scientific aim of NAWDEX is 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.
The field campaign will provide a unique observational dataset, sampling the key dynamics and processes associated with the triggering, propagation and downstream impact of disturbances along the North Atlantic waveguide.

International Context

The idea for NAWDEX was seeded in 2007 and developed by the Predictability and Dynamical Processes (PDP) Working Group of the WMO programme THORPEX. After several aircraft field experiments (FASTEX, ATREC) dedicated to evaluating the potential of targeted observations it was apparent that forecast improvements associated with such an approach (reducing upstream initial condition uncertainty) were small and were not realized in all cases. It was decided that the observational focus should shift to the detailed examination of physical and dynamical processes operating within the weather systems that affect the disturbances on the waveguide, and go on to influence downstream predictability. In this way deficiencies in the representation of processes in models could be identified and, with novel theoretical and numerical approaches, could be used to improve the models used for prediction. As outlined below in more detail, this provided strong motivation to design a trans-Atlantic field experiment and modeling activity to examine different processes that trigger disturbances on the mid-latitude waveguide, propagate downstream modified by diabatic processes at waveguide level, and instigate high-impact weather at the downstream end of the storm-track. Plans for an international NAWDEX campaign, consisting of several nationally funded projects, have been developed since a PDP WG workshop in Erding, Germany, 2009. A list of funded projects and of proposals being currently reviewed can be found below.

Country Aircraft Scientific Focus/Contribution Status
HALO, DLR Falcon
  • Improved understanding of the impact of diabatic processes on midlatitude tropopause level flow structures.
  • Localization and quantification of diabatically induced errors in the numerical representation of Rossby waves and weather systems.
  • Remote sensing measurements of moisture structure in the boundary layer, mixed phase clouds in WCBs and upper-level PV with HALO and DLR Falcon.
funded by DLR, DFG and ETH Zurich
Great Britain DLR Falcon
  • Study of PV lenses (shallow negative PV anomalies) which present a significant challenge to models due to their shallow structure and the importance of diabatic processes.
  • Coordinated observations between the DLR-Falcon and UK-based stratosphere-troposphere profilers will be used to examine the evolution of PV lenses.
  • Observation of cut-off positive PV anomalies with a special focus on high impact weather.
funded by EUFAR
United States DLR Falcon
  • Better understanding of diabatic processes associated with the interactions among mesoscale and synoptic-scale disturbances in the waveguide and their impact on predictability of downstream high-impact weather.
  • Observations of humidity structures and moisture transport in the lower troposphere, with moisture and wind profile measurements within and outside of WCBs in regions of sensitivity of high priority, using the Falcon and HALO.
  • Address whether improved analyses and representations of diabatic processes within disturbances that impact the wave guide, as informed by the NAWDEX observations, will increase high-impact weather predictability and links to stratospheric prediction.
funded by NRL
France SAFIRE Falcon
  • Calibration and validation of satellite observations using the radar-lidar instrumentation on board the Falcon.
  • Preparation of EarthCare Mission.
  • Airborne observations of various cloudy regions within extratropical cyclones (deep clouds / cloud banding structures).
funded by CNES and ESA
  • Study of atmospheric rivers in the eastern Atlantic.
  • Identification and quantification of errors in atmospheric rivers model representation. Confrontation with observations made with the SAFIRE Falcon.
  • Analysis of precipitation forecasts over western Norway with the use of Ensemble Prediction systems.
funded by EUFAR
Canada on-demand radiosondes
  • Enhancing understanding of the upstream perturbations that lead to waveguide changes, including tropopause polar vortices, transitioning tropical cyclones and coastal cyclones.
funded by Environment Canada
Great Britain ground based observations
  • Dynamical structure of negative PV lenses, that have been observed upstream by HALO/DLR Falcon, using additional radiosonde ascents and the UK-based profilers for wind, static stability and humidity.
  • Observation of tropopause feature that play a leading role in high impact weather in western Europe, and their connection with low-level mesoscale structure in humidty and winds.

Due to various reasons related to facilities and funding NAWDEX has been postponed several times, but it is now firmly scheduled for 19 September to 16 October 2016. New theoretical and diagnostic research, and technical developments in forecasting systems during the last decade, make NAWDEX very timely both in terms of available airborne instrumentation and the scientific need to improve our understanding and predictive capabilities of processes along the North Atlantic waveguide.

NAWDEX is a cross-cutting topic for the scientific community focusing on both weather and climate timescales. Since the finish of THORPEX programme at the end of 2014, the leadership from the PDP WG has transferred to the new World Weather Research Programme (WWRP) WG on Predictability, Dynamics and Ensemble Forecasting (PDEF). NAWDEX also has a strong link to the High Impact Weather project (HIWeather), a new activity of the WWRP. It also deals with one of the four key questions posed by the Grand Challenge on clouds, circulation and climate sensitivity of the World Climate Research Programme (WCRP) for the next decade (Bony et al., 2015).

© 2015 by Institute for Atmospheric and Climate Science, ETH Zurich