The pattern effect in storm resolving ICON: How newly resolved processes influence the moisture distribution and large-scale circulation response to sea surface temperature perturbations

Equilibrium climate sensitivity remains highly uncertain due to cloud feedbacks, which are strongly influenced by the pattern effect—the dependence of the atmospheric response and radiative feedbacks on the spatially heterogeneous sea surface warming. The pattern effect depends on the representation of convection, boundary-layer dynamics, and the large-scale circulation. Because it links small-scale processes with global climate, it provides an ideal test of the added value of global storm resolving models for simulating climate dynamics.

We investigate the atmospheric response to an idealized 1.5 °C sea surface temperature perturbation applied to the Indo-Pacific Warm Pool using the ICON model in the XPP configuration across a range of horizontal resolutions, from CMIP-like scales to kilometer-scale simulations. A set of experiments spanning different physical parameter configurations is used to examine how variations in moisture and convective processes influence the large-scale circulation response to regional warming. While higher resolution tends to produce a stronger response, differences in moisture distribution associated with changes in the ITCZ and Walker circulation, as well as variations in convective aggregation, exert a comparably strong influence on the circulation adjustment.

These results demonstrate that the coupling between moisture, convection, gravity-wave processes, and the large-scale circulation is a key control on the simulated pattern effect, shaping the atmospheric response to spatially heterogeneous warming and influencing circulation-driven climate feedbacks under climate change.