The mesoscale thermodynamic structure near cold fronts and its role for embedded convection

• Applicant: Dr. Annika Oertel
• Subject Area: Atmospheric Science
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 552794051

In boreal winter in the North Atlantic European region, high-impact weather (HIW), such as extreme surface precipitation and winds, is intricately linked to various cross-scale and interacting processes in extratropical cyclones. The prediction of local HIW, which is substantially influenced by processes on the mesoscale, still represents a challenge in current numerical weather prediction (NWP) systems. This includes the representation of deep convection embedded in the large-scale ascending circulation in the cold frontal region. Despite the relevance of embedded convection for surface precipitation intensity, momentum transport, and the evolution of the large-scale flow, the underlying processes leading to localized deep convection and the associated mesoscale variability in the near-frontal region remain widely unexplored. In particular, it remains unclear which role the strongly descending, so-called dry intrusion (DI) airstream plays, which descends behind the cold front and has been found to suppress and trigger frontal convection in different cases. To tackle these open questions, we propose a comprehensive analysis of the mesoscale variability of the thermodynamic and dynamic structure near cold fronts and during DI – cold front interactions in the lower troposphere as well as its relation to embedded deep convection in (i) observations and (ii) a hierarchy of numerical models. This key objective can be addressed through dropsonde observations at high spatial resolution which are envisaged for the North Atlantic Waveguide, Dry Intrusion, and Downstream Impact Campaign (NAWDIC) scheduled for winter 2025/2026 and proposed in the NAWDIC-HALO umbrella proposal. The here proposed NAWDIC-MESO project links directly to a primary research topic of NAWDIC-HALO which is to provide detailed observations of the mesoscale thermodynamic (stability) and dynamic (wind) structure in regions of DI – cold front interactions. The deployment of the relatively new modular multi-sensor dropsonde system for high-resolution profile measurements (KITsonde) onboard HALO will facilitate observations on the mesoscale (O(10 km)) to (i) quantify the mesoscale variability and representativity of individual dropsondes, (ii) validate NWP models on different scales, and (iii) better understand the complex interaction between DI, cold front, and embedded deep convection and their role for surface HIW.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1294: Atmospheric and Earth System Research with the "High Altitude and Long Range Research Aircraft" (HALO)
• Co-Investigators: Professorin Dr. Corinna Hoose; Dr. Bastian Kirsch; Professorin Dr. Annette Miltenberger