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.

High‐Resolution Aircraft Observations of Turbulence and Waves in the Free Atmosphere and Comparison With Global Model Predictions

“…The mean wind spectra are consistent with previous results, see Appendix B. The amplitudes of the w-spectra are an order of magnitude larger than those of the NAWDEX campaign (Schäfler et al, 2018). They compare well to the DEEPWAVE (Fritts et al, 2016) campaign results, as shown in Figure B2.…”

High‐Resolution Aircraft Observations of Turbulence and Waves in the Free Atmosphere and Comparison With Global Model Predictions

“…The mean wind spectra are consistent with previous results, see Appendix B. The amplitudes of the w-spectra are an order of magnitude larger than those of the NAWDEX campaign (Schäfler et al, 2018). They compare well to the DEEPWAVE (Fritts et al, 2016) campaign results, as shown in Figure B2.…”

Dependence of predictability of precipitation in the northwestern Mediterranean coastal region on the strength of synoptic control

“…large S n ) during weakly forced weather types consistent with previous results (e.g. Keil et al, 2019;Schwartz and Sobash, 2019;Bachmann et al, 2020). Disregarding the wet bias during weak control by focussing on the 95th percentile of precipitation shows a superior pure spatial predictability of most intense precipitation in the afternoon during weak control.…”

“…Key HyMeX IOPs are classified as strongly forced weather types in agreement with literature (Hally et al, 2014;Ducrocq et al, 2014;Nuissier et al, 2016). Likewise, the prominent heavy-precipitation event that occurred during NAWDEX is clearly identified as strongly forced (Schäfler et al, 2018).…”

“…Thus, 25 % of the time (3-hourly intervals on 48 strongly forced days, i.e. for 96 time windows within SOP1) the forecasts are skilful at a scale of O(100 km), which is of the same order as found in previous studies (Clark et al, 2010;Mittermaier et al, 2011;Schwartz and Sobash, 2019;Bachmann et al, 2020), based on FSS and other neighbourhood methods. Useful precipitation forecasts are hardly encountered during weak forcing using absolute rainfall rates.…”

Convective activity in an extratropical cyclone and its warm conveyor belt – a case‐study combining observations and a convection‐permitting model simulation

“…The previous sections revealed that convection embedded in the WCB differs from (isolated) deep convection and is characterized by weak lightning activity and comparatively low updraught velocities in a region with low values of CAPE but strong large‐scale forcing for ascent. Here, we corroborate our view of the WCB cloud structure and its embedded convection using airborne radar observations from the HALO flight on 23 September 2016 (Figure a, red track; Schäfler et al ) and spaceborne radar reflectivity from the CloudSat satellite (Figure a, blue track).…”

High‐Resolution Aircraft Observations of Turbulence and Waves in the Free Atmosphere and Comparison With Global Model Predictions

“…The mean wind spectra are consistent with previous results, see Appendix B. The amplitudes of the w-spectra are an order of magnitude larger than those of the NAWDEX campaign (Schäfler et al, 2018). They compare well to the DEEPWAVE (Fritts et al, 2016) campaign results, as shown in Figure B2.…”

Dependence of predictability of precipitation in the northwestern Mediterranean coastal region on the strength of synoptic control

“…large S n ) during weakly forced weather types consistent with previous results (e.g. Keil et al, 2019;Schwartz and Sobash, 2019;Bachmann et al, 2020). Disregarding the wet bias during weak control by focussing on the 95th percentile of precipitation shows a superior pure spatial predictability of most intense precipitation in the afternoon during weak control.…”

“…Key HyMeX IOPs are classified as strongly forced weather types in agreement with literature (Hally et al, 2014;Ducrocq et al, 2014;Nuissier et al, 2016). Likewise, the prominent heavy-precipitation event that occurred during NAWDEX is clearly identified as strongly forced (Schäfler et al, 2018).…”

“…Thus, 25 % of the time (3-hourly intervals on 48 strongly forced days, i.e. for 96 time windows within SOP1) the forecasts are skilful at a scale of O(100 km), which is of the same order as found in previous studies (Clark et al, 2010;Mittermaier et al, 2011;Schwartz and Sobash, 2019;Bachmann et al, 2020), based on FSS and other neighbourhood methods. Useful precipitation forecasts are hardly encountered during weak forcing using absolute rainfall rates.…”

Convective activity in an extratropical cyclone and its warm conveyor belt – a case‐study combining observations and a convection‐permitting model simulation

“…The previous sections revealed that convection embedded in the WCB differs from (isolated) deep convection and is characterized by weak lightning activity and comparatively low updraught velocities in a region with low values of CAPE but strong large‐scale forcing for ascent. Here, we corroborate our view of the WCB cloud structure and its embedded convection using airborne radar observations from the HALO flight on 23 September 2016 (Figure a, red track; Schäfler et al ) and spaceborne radar reflectivity from the CloudSat satellite (Figure a, blue track).…”

High‐Resolution Aircraft Observations of Turbulence and Waves in the Free Atmosphere and Comparison With Global Model Predictions

“…The mean wind spectra are consistent with previous results, see Appendix B. The amplitudes of the w-spectra are an order of magnitude larger than those of the NAWDEX campaign (Schäfler et al, 2018). They compare well to the DEEPWAVE (Fritts et al, 2016) campaign results, as shown in Figure B2.…”

Dependence of predictability of precipitation in the northwestern Mediterranean coastal region on the strength of synoptic control

“…large S n ) during weakly forced weather types consistent with previous results (e.g. Keil et al, 2019;Schwartz and Sobash, 2019;Bachmann et al, 2020). Disregarding the wet bias during weak control by focussing on the 95th percentile of precipitation shows a superior pure spatial predictability of most intense precipitation in the afternoon during weak control.…”

“…Key HyMeX IOPs are classified as strongly forced weather types in agreement with literature (Hally et al, 2014;Ducrocq et al, 2014;Nuissier et al, 2016). Likewise, the prominent heavy-precipitation event that occurred during NAWDEX is clearly identified as strongly forced (Schäfler et al, 2018).…”

“…Thus, 25 % of the time (3-hourly intervals on 48 strongly forced days, i.e. for 96 time windows within SOP1) the forecasts are skilful at a scale of O(100 km), which is of the same order as found in previous studies (Clark et al, 2010;Mittermaier et al, 2011;Schwartz and Sobash, 2019;Bachmann et al, 2020), based on FSS and other neighbourhood methods. Useful precipitation forecasts are hardly encountered during weak forcing using absolute rainfall rates.…”

Convective activity in an extratropical cyclone and its warm conveyor belt – a case‐study combining observations and a convection‐permitting model simulation

“…The previous sections revealed that convection embedded in the WCB differs from (isolated) deep convection and is characterized by weak lightning activity and comparatively low updraught velocities in a region with low values of CAPE but strong large‐scale forcing for ascent. Here, we corroborate our view of the WCB cloud structure and its embedded convection using airborne radar observations from the HALO flight on 23 September 2016 (Figure a, red track; Schäfler et al ) and spaceborne radar reflectivity from the CloudSat satellite (Figure a, blue track).…”