The impact of horizontal resolution on the simulations of convective development over land

Cloud-resolving models (CRMs) can be used to provide subgrid information for use in improving the representation of the development of convection in large-scale models. However, for the CRM to be of value, it must itself give an accurate representation of the processes involved. In the work presented here we focus on the development of convection in simulations of both shallow and deep convection over land and consider sensitivity to the horizontal resolution in a CRM. In both shallow and deep cases it is found to be necessary to provide adequate resolution of the sub-cloud layer in order to obtain a satisfactory representation of the transport of moisture from the sub-cloud layer into the free troposphere. Typically this requires the horizontal grid spacings to be no coarser than around one quarter of the sub-cloud layer depth. Poorer resolution with the present model leads to significant delays in the development of convection. While a more sophisticated subgrid scheme could reduce the sensitivity to resolution, the work here has shown the resolution required to explicitly resolve the key processes. Using this improved resolution may be one technique for reducing the discrepancies between some model results and observations reported in earlier studies.