Interactions between Convection and the Tropical Easterly Jet in Tropical Channel Simulations

Advancements in computational power have provided the opportunity to explore global modelling at the km scale, where deep convection is mostly resolved. This step-change in ability blurs the lines between conventional modelling of the global system at coarser resolutions (>10km) that require convective parameterisation. The Met Office flagship K-SCALE project has recently developed a cyclic tropical channel at 4.4km resolution, which can be run with either RAL3.1 explicit convection science or the GAL9 parameterised convection science. This experimental setup provides the ability to identify the impact of explicitly resolving convection through the tropical belt, and potential upscale impacts this has onto the large-scale circulation. This work evaluates the representation of the tropical easterly jet during boreal summer, and considers how the treatment of convection over the Indian Ocean feedback onto the jet. The GAL9 simulations produce a substantially stronger tropical easterly jet. The reasoning behind this are explored by assessing the representation of geostrophic balance, and links to differences in diabatic heating arising from convection. Early results indicate the representation of convection has a large impact on the mean atmospheric state over this region; highlighting the importance of running large domain km-scale simulations to better understand scale-interaction of atmospheric processes.