# The Sensitivity of Euro-Atlantic Regimes to Model Horizontal Resolution

## TL;DR

This study demonstrates that increasing horizontal resolution in climate models consistently improves the simulation of quasi-persistent regimes in the Euro-Atlantic winter atmosphere across multiple models and ensemble members, though some regime aspects remain variable.

## Contribution

It provides robust evidence that higher horizontal resolution enhances regime structure simulation in multiple climate models, addressing prior model dependency concerns.

## Key findings

- Higher resolution models better simulate persistent regimes.
- Multiple ensemble members are needed to reduce sampling variability.
- Some regime characteristics do not necessarily improve with resolution.

## Abstract

There is growing evidence that the atmospheric dynamics of the Euro-Atlantic sector during winter is driven in part by the presence of quasi-persistent regimes. However, general circulation models typically struggle to simulate these, with e.g. an overly weakly persistent blocking regime. Previous studies have showed that increased horizontal resolution can improve the regime structure of a model, but have so far only considered a single model with only one ensemble member at each resolution, leaving open the possibility that this may be either coincidental or model-dependent. We show that the improvement in regime structure due to increased resolution is robust across multiple models with multiple ensemble members. However, while the high resolution models have notably more tightly clustered data, other aspects of the regimes may not necessarily improve, and are also subject to a large amount of sampling variability that typically requires at least three ensemble members to surmount.