Atmospheric Blocking Characteristics in Two Storm-Resolving Gcms

Atmospheric blockings (ABs) alter the mid-latitude climate and weather, leading to extreme events and costly societal impacts. Nevertheless, the current climate models fail to capture the AB occurrence, persistence, and intensity.
Here, we evaluate the AB representation in the two next-generation (storm-resolving) Earth-system Models (NextGEMS), IFS and ICON. These high-resolution climate models (ICON at 5,10 km and IFS at 4.4, 28 km) are coupled, including an eddy-resolving ocean model, conducting a closer simulation of the climate system.
We identify AB blocking based on geopotential height anomalies and gradients at 500 hPa.
Besides the AB frequency in the Northern Hemisphere, the duration, intensity, and lifecycle are compared with 30 years of ERA5 and one CMIP6 model.

The results show some bias in AB frequency over the main AB regions in the North Atlantic and North Pacific. This spatial bias can be attributed to climate variability, given the short-period runs (around five years). In fact, this frequency deviation agrees with the mean-state bias in each model. For instance, we identify an underestimation of the AB over the UK in the IFS at 4.4 km during the winter and spring, which can be associated with a strong jet stream to the south of the UK. The eddy transient activity is also strongly affected by the mean-state bias.
Despite the high variability, improvements in the high-resolution climate models are evident when the blocking characteristics are considered.
The AB intensity and size are better solved in the IFS model with the highest resolution (4.4 km), gaining a better performance at the upper percentiles. Other blocking properties such as the zonal speed and evolution during the first days are also improved with the resolution.
We highlight the need for more extended period runs. Further evaluation will include the role of diabatic effects, and Rossby wave breaking in the atmospheric blocking dynamics.