Organizers: Rupert Klein, Sebastian Reich, Daniel Baum, Stephan Pfahl

Part A: Theoretical Meteorology

Abstract:

Significant atmospheric phenomena, such as fronts, cyclones, and heat waves, stand out amongst the daily ups and downs of the weather. They are well recognizeable owing to their specific spatial structure and their longevity relative to the ubiquitous much faster transients associated, e.g., with the convection and turbulent processes that constitute them. They are "persistent" in this sense, and it is this persistence that makes these structures identifiable in observational or simulation data and particularly accessible to theoretical analysis, efficient numerical approximation, and data-based tracking or modelling. This minisymposium collects reports from such diverse approaches towards improved scientific understanding of these often severe weather patterns.

Speakers:

11:30h: Roger Smith (LMU Munich)

The fluid dynamics of tropical cyclones

In this talk, I will review recent developments in our understanding of the fluid dynamics of tropical cyclones throughout their life cycle. These developments provide the basis for a new three-dimensional conceptual framework for interpreting observations of tropical cyclones and numerical simulations thereof, whether idealized or ones used for operational forecasting. Without going into many mathematical details, I will focus on a few fundamental physical processes that together help explain the dynamics and thermodynamics of these storms.

12:00h: Annette Rudolph (TU Berlin)

Atmospheric blocking patterns across the scales

Atmospheric blocks are long-lasting weather patterns that can cause persistent periods of extreme temperatures or heavy precipitation. Their identification and characterization are therefore important for understanding atmospheric dynamics and assessing regional impacts.

The Dynamic State Index (DSI) is directly derived from the primitive equations of atmospheric motion and captures steady and adiabatic as well as non-steady and diabatic processes. It therefore provides a physically based concept for diagnosing atmospheric blocks. Starting from the DSI derived from the three-dimensional primitive equations of motion, successive approximations lead to DSI variants for the quasi-geostrophic and barotropic Rossby models. The different DSI variants are investigated in the context of a case study of an atmospheric blocking pattern.

Two-dimensional point-vortex theory, together with the kinematic vorticity number, is considered as an approach for the automated identification of atmospheric blocks. This method allows for the localization of individual vortices within a blocked flow, which can be applied to investigate occurrence probabilities or the local-scale impacts of atmospheric blocking, e.g. on agriculture.

12:30h: Seraphine Hauser (ETH Zürich)

Complementary perspectives on the role of dry and moist dynamics for atmospheric blocking formation

Atmospheric blocking refers to quasi-stationary, large-scale atmospheric patterns characterized by a dominant anticyclonic anomaly that effectively “blocks” or redirects midlatitude weather systems. Despite progress in numerical weather prediction, blocking remains difficult for weather and climate models to represent due to the complex multi-scale processes involved in its lifecycle. While recent studies highlight the role of latent heat release in building and maintaining the upper-level anticyclonic anomaly, the relative importance of dry versus moist dynamics, and how their relative contributions vary across blocking regions, remains unclear.

In this talk, we compare potential vorticity (PV)-based frameworks for quantifying the relative contributions of dry and moist dynamics to atmospheric blocking in the North Atlantic-European region, using ERA5 reanalysis data from ECMWF. Using a March 2016 European blocking episode as a case study, we introduce Eulerian, Lagrangian, and hybrid quasi-Lagrangian approaches to demonstrate how each perspective evaluates the relative importance of dry versus moist dynamics during blocking formation. This quasi-Lagrangian framework tracks the anticyclonic anomalies linked to blocking from their genesis, well before they become stationary and form a block. We then extend these frameworks across a long-term climatology (1979–2021) to systematically assess the varying roles of dry and moist dynamics across four key blocking regions: central Europe, Scandinavia, Greenland, and the eastern North Atlantic.

Our results demonstrate that while different perspectives highlight distinct roles for dry and moist dynamics, considering them together is essential. None of these frameworks are wrong; rather, each captures complementary aspects necessary for a complete physical picture.