Accurately forecasting the location, timing, and intensity of mesoscale high impact weather (HIW) events remains a challenge for state-of-the-art numerical weather prediction (NWP) models. This is to a large degree due to the multi-scale interactions of physical processes involved in the formation of HIW, ranging from upper-tropospheric Rossby waves covering several thousands of kilometers and lasting several days, to momentum transport in the planetary boundary layer (PBL) and cloud microphysics acting on scales of hundreds of meters to micrometers and minutes to seconds. A key feature that connects upper-tropospheric Rossby waves in remote regions with HIW in Europe is the dry intrusion (DI) airstream (Carlson 1980, Browning 1997). During winter months, DIs emerge most frequently from the downstream flank of upper-tropospheric ridges over eastern North America. From this region, DIs descend equatorward in the cold sector of a downstream cyclone over a horizontal distance of 1000 to 5000 km and reach the PBL about 2 days later. The DI outflow is accompanied by intense surface heat and moisture fluxes, elevated PBL heights and a destabilization of the lower troposphere leading to unusually strong wind gusts and extreme rainfall at the surface (Raveh-Rubin 2017). The DI thus constitutes a multiscale weather system that often involves HIW. 


Most of the time, the involved multiscale processes relevant to HIW in Europe occur upstream over the Atlantic Ocean and are insufficiently captured by operational observing systems. Accordingly, modern measurement systems on long-range research aircraft are the only way to obtain reliable observations with the necessary high spatial and temporal resolution in these remote regions. Therefore, the high-altitude and long-range research aircraft HALO (Fig. 1) operated by the German Aerospace Center (DLR) was chosen as the key component of NAWDIC. With its long range and advanced instrumentation, HALO allows to perform multiple consecutive flights over several days to sample the processes at two distinct stages of the DI lifecycle. 


The HALO research aircraft
Fig.1: The HALO research aircraft during the HALO-(AC)3 mission in 2022.


The core measurement period of HALO for NAWDIC is scheduled for 6 weeks from 12 January to 26 February 2026 with operation base at Shannon Airport (Ireland). A novel payload combining remote sensing observations with in-situ trace gas measurements will yield a comprehensive picture of the thermodynamic fields from the lower stratosphere to the PBL and transport and mixing processes in the DI airstream:

  • WALES (DLR): four-wavelength differential absorption lidar
  • HEDWIG (DLR): newly-developed airborne Doppler wind lidar
  • KITsonde (KIT): modular multi-sensor dropsonde system
  • specMACS (LMU Munich): imaging cloud spectrometer for the solar spectral range
  • UMAQS (JGU Mainz): quantum cascade laser spectrometer for trace gas measurements
  • FISH (FZ Jülich): fast in-situ stratospheric hygrometer
  • FAIRO (KIT): ozone detector
  • BAHAMAS (DLR): basic HALO measurement and sensor system

NAWDIC measurements will allow a targeted evaluation of the quality of operational observing and analysis systems in regions crucial for HIW. Additionally, NAWDIC will provide detailed knowledge of the physical processes acting in these regions and especially of the mechanisms responsible for errors in the prediction of HIW ultimately leading to a better representation of uncertainty in NWP systems, and better (probabilistic) forecasts.

Contact: Julian Quinting (KIT), Andreas Schäfler (DLR)

The measurements of the DI lifecycle will directly link to the ERC-StG project Extratropical-Tropical interaction: A unified view on the extratropical impact on the subtropics and tropics at weather timescales, where DIs are the central flow feature linking midlatitude large-scale dynamics with near-surface HIW at lower latitudes.

Contact: Shira Raveh-Rubin (WIS)