  Convective processes are crucial in shaping exoplanetary atmospheres but are
computationally expensive to simulate directly. A novel technique of simulating
moist convection on tidally locked exoplanets is to use a global 3D model with
a stretched mesh. This allows us to locally refine the model resolution to 4.7
km and resolve fine-scale convective processes without relying on
parameterizations. We explore the impact of mesh stretching on the climate of a
slowly rotating TRAPPIST-1e-like planet, assuming it is 1:1 tidally locked. In
the stretched-mesh simulation with explicit convection, the climate is 5 K
colder and 25% drier than that in the simulations with parameterized convection
(with both stretched and quasi-uniform meshes)}. This is due to the increased
cloud reflectivity - because of an increase of low-level cloudiness - and
exacerbated by the diminished greenhouse effect due to less water vapor. At the
same time, our stretched-mesh simulations reproduce the key characteristics of
the global climate of tidally locked rocky exoplanets, without any noticeable
numerical artifacts. Our methodology opens an exciting and computationally
feasible avenue for improving our understanding of 3D mixing in exoplanetary
atmospheres. Our study also demonstrates the feasibility of a global stretched
mesh configuration for LFRic-Atmosphere, the next-generation Met Office climate
and weather model.
