Sub-grid Scale Convective Transport And Its Dependence Of Scale

In traditional convective parameterization,it is generally assumed that the sub-grid scale convective horizontal transport is negligible.However,with the development of computers and the improvement of models' horizontal resolution,the sub-grid scale convective horizontal transport may become important.In this work,the output from a cloud resolving model(CRM)simulation of convection at a tropical southern hemisphere site in Darwin was analyzed.We focused on the sub-grid scale convective transport and its scale-dependence,and explored whether the sub-grid scale convective horizontal transport was negligible when horizontal resolution increased.Closely related to the sub-grid scale convective transport,the sub-grid scale convective flux was also analyzed.The results showed that:(1)Except for the zonal flux of meridional momentum (?) by sub-grid scale convection,the sub-grid scale convective horizontal flux decreased with increasing horizontal resolution.However,the sub-grid scale convective vertical flux increased with increasing horizontal resolution.(2)For the sub-grid scale convective horizontal flux,it mainly came from convective environment.The contribution of the convection became more and more important with the increase of horizontal resolution.With regard to the sub-grid scale convective vertical flux,the contributions from the convective areas and their environment were both significant.In the middle and upper troposphere,it was mainly from convection;in the lower troposphere,it mainly came from convective environment.(3)The sub-grid scale convective transport increased with increasing horizontal resolution.When the horizontal resolution was 5 km,the horizontal zonal momentum transport by sub-grid scale convection was important,while the horizontal thermodynamic transport by sub-grid scale convection was negligible.(4)For the sub-grid scale convective horizontal transport,the contributions from the convective areas and their environment were comparable but opposite in sign,resulting in much smaller net transport when averaged over the subdomains.With regard to the sub-grid scale convective vertical transport,the contribution of the environment was significant compared with that of convection.