The North Atlantic Waveguide and Downstream Impact Experiment

Abstract

The North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) explored the impact of diabatic processes on disturbances of the jet stream and their influence on downstream high-impact weather through the deployment of four research aircraft, each with a sophisticated set of remote sensing and in situ instruments, and coordinated with a suite of ground-based measurements. A total of 49 research flights were performed, including, for the first time, coordinated flights of the four aircraft: the German High Altitude and Long Range Research Aircraft (HALO), the Deutsches Zentrum für Luft- und Raumfahrt (DLR) Dassault Falcon 20, the French Service des Avions Français Instrumentés pour la Recherche en Environnement (SAFIRE) Falcon 20, and the British Facility for Airborne Atmospheric Measurements (FAAM) BAe 146. The observation period from 17 September to 22 October 2016 with frequently occurring extratropical and tropical cyclones was ideal for investigating midlatitude weather over the North Atlantic. NAWDEX featured three sequences of upstream triggers of waveguide disturbances, as well as their dynamic interaction with the jet stream, subsequent development, and eventual downstream weather impact on Europe. Examples are presented to highlight the wealth of phenomena that were sampled, the comprehensive coverage, and the multifaceted nature of the measurements. This unique dataset forms the basis for future case studies and detailed evaluations of weather and climate predictions to improve our understanding of diabatic influences on Rossby waves and the downstream impacts of weather systems affecting Europe.

Airborne wind lidar observations over the North Atlantic in 2016 for the pre-launch validation of the satellite mission Aeolus

“…Most recently, in autumn of 2016, the A2D was employed in the frame of the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) (Schäfler et al, 2018). Based in Keflavík, Iceland, this international field campaign had the overarching goal to investigate the influence of diabatic processes, related to clouds and radiation, on the evolution of the North Atlantic jet stream.…”

“…Concerning the spectral characteristics, the bandwidth of the transmitted UV laser pulses is 50 MHz (FWHM), while the pulse-to-pulse frequency stability is approximately 3 MHz (root mean square). A comprehensive description of the laser transmitter configuration and its performance is provided in Lemmerz et al (2017) and Schröder et al (2007). In the last years, particular attention has been devoted to the cavity control mechanism which ensures high singlefrequency operation stability even under vibration conditions.…”

“…Later, at the time of the flight, the already weakened cyclone was located between Iceland and Scotland and the zonally oriented jet stream extended towards Scotland with horizontal wind speeds exceeding 80 m s −1 at altitudes of 9 to 10 km (see Fig. 5 and for a detailed description of the meteorological situation refer to Schäfler et al, 2018). To observe the high wind speeds, the Falcon aircraft flew towards the Faroe Islands and the Outer Hebrides right into the centre of the jet stream at a flight altitude of 11.5 km before returning to the air base in Keflavík.…”

Processes governing the amplification of ensemble spread in a medium‐range forecast with large forecast uncertainty

“…We analyse one case from the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX; Schäfler et al . ), namely the extratropical transition of tropical storm Karl to Ex‐Karl . This case was associated with large forecast uncertainty (Schäfler et al .…”

“…This case was associated with large forecast uncertainty (Schäfler et al . ), and the medium‐range ensemble forecast showed very different developments for the interaction between Ex‐Karl and the waveguide, with only a few ensemble members capturing this interaction correctly (Kumpf et al . ).…”