HALO

NAWDIC

North Atlantic Waveguide, Dry Intrusion, and Downstream Impact Campaign

Mission status: No information available yet.

Persons in Charge

Mission-PI

  • Christian Grams (KIT)

Scientific Co-Leadership

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Mission coordinator​

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Contact point at DLR-FX for this mission:

Address

HALO Deployment Base

Time Period

October 2025 – February 2026

 

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Project description

White Paper for the North Atlantic Waveguide, Dry Intrusion, and Downstream Impact Campaign (NAWDIC) in Winter 2023/2024
Authors: Christian M. Grams , Julian F. Quinting , Shira Raveh-Rubin , Andreas Schäfler, George Craig, Peter Knippertz, Christoph Kottmeier , and Volkmar Wirth Karlsruhe Institute of Technology;  Weizmann Institute of Science;  Deutsches Zentrum für Luft- und Raumfahrt; Ludwig-Maximilians University Munich; Johannes Gutenberg University Mainz

Context of the mission proposal

The North Atlantic Wave Guide and Downstream Impact Experiment in 2016 observed diabatic processes and investigated their impacts on the tropopause structure. This paper proposes the HALO mission NAWDIC in the research field of atmospheric dynamics, which builds directly on insights of NAWDEX. Addressing new dynamical aspects, NAWDIC will provide the required observations to advance our knowledge on the connection of the tropopause structure to downstream high impact weather (HIW), which strongly affects society and economy.

Scientific aims

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. However, numerical weather prediction (NWP) models underrepresent the sharpness of gradients in wind speed, stability, and humidity across the tropopause with increasing forecast lead time. 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, 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.

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 in a Lagrangian sense. Within DIs, air masses descend strongly from near the tropopause towards the cold front of the cyclone downstream. 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. Thus, NWP centers have identified the structure of the tropopause and the interaction of DIs with the planetary boundary layer (PBL), through their impact on surface fluxes, as a source of errors and uncertainty in their models. To improve NWP model representation of tropopause structure and PBL processes, observations of temperature and water vapor variations on the sub-grid scale are vital, but these are routinely not available. NAWDIC aims to 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. We complement this by following and probing the descending DI air streams from above until they reach and interact with the PBL downstream. The planned intensive probing of the DI-PBL interaction will enable unique observations with high spatio-temporal resolution at the sub-grid scale in regions of exceptional air-sea interaction and moisture fluxes in regions prone to HIW.

HALO observations

The HALO research aircraft demonstrated to be the ideal platform to perform measurements following dynamic features over the data-sparse North Atlantic that eventually cause downstream HIW over Europe. The focus of the NAWDIC observations is the documentation of the meso- to synoptic-scale structure near the tropopause, ideally in terms of potential vorticity (PV), as well as of the interaction of descending air masses with the PBL.

This, however, requires highly-resolved horizontal and vertical profiles of wind, moisture, and temperature. For a holistic view of the tropopause structure and the troposphere beneath, we propose a novel combination of instruments: the recently developed KITsonde system, which allows the simultaneous measurement with up to 30 dropsondes, and a joint operation of a Doppler wind Lidar together with the Water Vapor Lidar Experiment in Space (WALES). This combination of dropsonde and remote sensing instruments allows to investigate how model representation of PBL-DI interaction is linked to the forecast skill of the surface conditions. Combined observations of vertical wind and humidity profiles will allow a quantification of moisture fluxes in the PBL. As the regions and processes of interest to NAWDIC coincide with those of other HALO communities, e.g., focusing on transport processes in the upper-troposphere lower-stratosphere or ice-microphysics, we see mutual benefit through a possible extension of the payload.

Development of a campaign implementation plan

To converge towards a campaign implementation plan, we propose the organization of international workshops which will bring together atmospheric scientists, instrumentalists, as well as model developers. Through the dialogue between those groups we will (i) design an appropriate payload for achieving the scientific goals; (ii) converge into desired flight plans, including coordination with additional aircraft and ground-based measurements; (iii) reach funding agencies with coordinated proposals; and (iv) establish a new NAWDIC international research community.
The complementary targets of the campaign require an area of operation that covers the high- to midlatitudes and subtropical latitudes of the North Atlantic. Hence, we propose Shannon (Ireland) or Keflavik (Iceland) as operation base. From there, we could reach the near-tropopause features as well as areas of the DI-PBL interaction. Since DIs occur most frequently in winter, the campaign would ideally be scheduled for 5–7 weeks in winter. A new certification of the envisaged payload requires a long preparation phase, such that we propose to conduct the campaign in winter 2023/24.

National and International partners, and funding

The proposed campaign will benefit greatly from the NAWDEX network of national and international partners. On a national basis, we aim for a close collaboration with the DFG transregional collaborative research center “Waves to Weather”, which offered to support preparation workshops. Key international partners from NAWDEX have expressed their interest to support the proposed campaign with airborne and ground-based observations. For example, the HALO observations could be augmented by in-situ flux measurements and measurements of cloud-microphysical properties with the British Facility for Airborne Atmospheric Measurements (FAAM) research aircraft. Beyond the NAWDEX network, the involvement of modelers in NWP centers at an early stage of the campaign planning will help to optimally address key challenges expressed by the NWP modeling community. Currently, our partners are: Roland Potthast (Deutscher Wetterdienst), Linus Magnusson and Irina Sandu (ECMWF) as representatives of the NWP modeling community, Jim Doyle (US Naval Research Laboratory), Ron McTaggart-Cowan (Environment and Climate Change, Canada), John Methven (University of Reading, UK), Stephan Pfahl (FU Berlin), Gwendal Rivière (Laboratoire de Météorologie Dynamique, France), Harald Sodemann (University of Bergen, Norway), and Heini Wernli (ETH Zurich, Switzerland). Coordinated funding proposals will be submitted to DFG as well as national and international partner institutions. NAWDIC is in line with the WMO project High- Impact Weather, particularly with the “Processes and Predictability” theme in which A. Schäfler and S. Raveh-Rubin are engaged as task team members.

Partners

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Scientific instruments and payload configuration

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Cabin and exterior configuration of HALO for the mission

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HALO flights for this mission

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More information

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Press releases, media etc

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