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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 ContextThe 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.
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