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Andreas Schäfler, 05/14/2020 12:20 PM

NAWDIC planning wiki (public area)

This wiki page serves as a platform to prepare the future North Atlantic Waveguide, Dry Intrusion, and Downstream Impact Campaign (NAWDIC). For more information please read the general information below. Additionally, registered users are able to access the internal area where more information material is shared. There you can express your interest and add details on your contribution. If you are already registered for the NAWDEX wiki, you can use the same login details.


NAWDIC is a new initiative for an international field campaign focusing on mid-latitude dynamics with the aim to provide required observations for understanding the tropopause structure and downstream high impact weather (HIW) in the eastern North Atlantic winter. NAWDIC will build directly on insights of the North Atlantic Wave guide and Downstream impact EXperiment (NAWDEX; Schäfler et al. 2018;, that observed diabatic processes and investigated their impact on the tropopause structure. While we envisage NAWDIC as an international campaign, it is initiated through its German HALO-aircraft component, scheduled to take place in the winter (within the January-March window) of 2024 or 2025. Here we outline our initial suggestions.

Scientific background

The tropopause structure is important for the extratropical large-scale circulation, as it is closely related to the strength of the jet stream, forming a wave guide for Rossby waves (e.g. Martius et al. 2010; Grams and Archambault 2016; Quinting and Vitart 2019). Two of the key findings of NAWDEX are (i) previously unobserved near-tropopause meso-scale features related to diabatic processes that enhance the jet stream wind speeds (Harvey et al. 2020; Oertel et al. 2020), and (ii) observational evidence of insufficient representation of strong humidity, temperature and wind gradients at the tropopause already in the analysis and early forecast of state-of-the-art NWP systems (Schäfler et al. 2020).

Tropopause structure has a significant influence on the formation of HIW. On the one hand, it affects the propagation and amplification of Rossby waves which can later trigger downstream HIW. A more direct – still understudied – effect is the air mass transport in so-called dry intrusions (DIs), which connect the near-tropopause air with weather phenomena at the surface downstream in a Lagrangian sense. Within DIs, air masses descend slantwise from near the tropopause towards the cold front of the cyclone downstream (Browning 1997), where they are climatologically associated with strong fronts, enhanced vertical mixing in the boundary layer and heavy frontal precipitation (Raveh-Rubin 2017; Catto and Raveh-Rubin 2019). Yet, it remains unclear under which conditions DIs trigger convection, strong and damaging winds, and how they affect the distribution of clouds and heavy precipitation. Indeed, the structure of the tropopause and the interaction of DIs with the planetary boundary layer (PBL), through their impact on surface fluxes, are potential sources of errors and uncertainty in NWP models (Magnusson and Sandu 2019).

Scientific goal

NAWDIC aims to provide high-res observations to enhance our understanding of the tropopause structure, DI-PBL interaction and their role as precursors of HIW. Aiming to further improve their representation in NWP models, model output will be evaluated by assimilation of the added observations to identify model biases and new benefits. NAWDIC will systematically sample the near-tropopause structure with a particular focus on its sharpness in the vertical and horizontal directions in regions from where DIs originate (region 1 in Fig. 1). We complement this by following and probing the descending DI airstreams from above until they reach and interact with the PBL in regions of exceptional surface heat and moisture fluxes (region 2). Finally we plan observations with high spatio-temporal resolution in downstream regions prone to HIW (region 3 in Fig. 1).

Observational aims of NAWDIC-HALO

The HALO research aircraft will perform measurements of the meso- to synoptic-scale structure near the tropopause, and of the interaction of DI air masses with the PBL over the data-sparse North Atlantic, that are related to downstream HIW over Europe. To acquire highly-resolved horizontal and vertical profiles of wind, moisture, and temperature, we envisage a novel combination of instruments: the recently developed high-density KITsonde system, and a joint operation of a Doppler wind Lidar together with the Water Vapor Lidar Experiment in Space (WALES), to allow a quantification of moisture fluxes in the PBL (Kiemle et al. 2011).

  • Browning, K. A. 1997. The dry intrusion perspective of extra-tropical cyclone development. Meteorol. Appl., 4, 317-324
  • Catto, J. L., and S. Raveh-Rubin, 2019. Climatology and dynamics of the link between dry intrusions and cold fronts during winter. Part I: global climatology. Clim. Dyn. 53, 1873-1892
  • Grams, C.M. and H.M. Archambault, 2016. The key role of diabatic outflow in amplifying the midlatitude flow: A representative case study of weather systems surrounding western North Pacific extratropical transition. Mon. Wea. Rev., 144, 3847-3869
  • Harvey, B, J. Methven, C. Sanchez, and A. Schäfler, A. Diabatic generation of negative potential vorticity and its impact on the North Atlantic jet stream. 2020. Q. J. R. Meteorol. Soc., 1-22
  • Kiemle, C., M. Wirth, A. Fix, S., Rahm, U. Corsmeier, and P. Di Girolamo, 2011. Latent heat flux measurements over complex terrain by airborne water vapour and wind lidars. Q. J. R. Meteorol. Soc., 137, 190-203
  • Magnusson, L. and I. Sandu, 2019. Experts review synergies between observational campaigns and weather forecasting, ECMWF Newsletter 161, 6-7
  • Martius O., C. Schwierz, and H. C. Davies, 2010. Tropopause-level waveguides. J. Atmos. Sci., 67, 866-879
  • Oertel, A., Boettcher, M., Joos, H., Sprenger, M., & Wernli, H. 2020. Potential vorticity structure of embedded convection in a warm conveyor belt and its relevance for large-scale dynamics. Weather and Climate Dynamics, 1, 127-153
  • Quinting, J. F., and F. Vitart, 2019. Representation of synoptic-scale Rossby wave packets and blocking in the S2S prediction project database. Geophys. Res. Let., 46, 1070-1078
  • Raveh-Rubin, S., 2017. Dry intrusions: Lagrangian climatology and dynamical impact on the planetary boundary layer. J. Climate, 30, 6661-6682
  • Schäfler, A., G. Craig, H. Wernli, et al., 2018. The North Atlantic Waveguide and Downstream Impact Experiment. Bull. Amer. Meteor. Soc., 99, 1607-1637
  • Schäfler, A., B. Harvey, J. Methven, J. D. Doyle, S. Rahm, O. Reitebuch, F. Weiler, and B. Witschas. 2020. Observation of jet stream winds during NAWDEX and characterization of systematic meteorological analysis error, Mon. Wea. Rev., accepted.