How does a dry model with the same wave energy as observation represent atmospheric blocking ?

Atmospheric blockings are large-scale quasi-stationary anomalies which block the mean westerlies and can trigger extreme temperature events such as heatwaves and cold spells. While the dry dynamics theory has been a key initial framework for understanding blocking mechanisms, recent studies have highlighted the significant role of moist processes in the formation and maintenance of blocking. However, it remains unclear whether moist processes introduce unique characteristics in the blocking life cycle which can not be captured by dry dynamics or they are just a source of extra energy for the atmospheric disturbances forming the blockings. We aim to gain insights into the representation of blocking mechanisms and statistics using the new dynamical core of the General Circulation Model (GCM) developed at IPSL called DYNAMICO. A long-term simulation of a dry GCMwith synoptic eddy energy and mean flow characteristics close to boreal winter climatology of ERA5 reanalysis.  The blocking statistics in the model and ERA5 are then compared using a PV-based blocking detection. Frequencies of occurrence of blocks are found to be 50% less in the model than in ERA5. This is largely due to too strong westerly background flow in the model, in the North Pacific in particular, which prevents the formation of persistent anticyclones. Despite this underestimation in frequencies of occurrence, the main characteristics of the blocks (intensity, size, duration) are similar in the model and ERA5 despite some slight structural differences. By employing Eulerian and backward Lagrangian analysis, we demonstrate how a dry model compensates for moisture deficiency to generate potential vorticity (PV) anomalies comparable in intensity to those in ERA5. This study reveals that despite distinct underlying mechanisms, the essential features of observed blocking events' life cycles can be effectively captured within a dry model framework. We also conduct a long-term moist simulation, incorporating forced sea surface temperature (SST), to observe how the moist model sensitive to warmer climate reproduces blocking characteristics    Acknowledgement: This Project of a part of the EU International Training Network (ITN). EDIPI (European Extreme weather; Drivers, predictability and impacts). EDIPI is funded under the European Commission’s H2020-MSCA-ITN programme.