PNNL

Abstract

A parameterization scheme is proposed for the subgrid-scale transport of hydrometeors in an assumed probability density function (PDF) scheme. Joint distributions of vertical velocity and hydrometeor mixing ratios are typically unknown and only marginal (1D) PDFs of vertical velocity and hydrometeor mixing ratios are available. The parameterization is developed using high-resolution simulations of continental and tropical deep convection. The 3D cloud-resolving model used for guidance has a horizontal grid spacing of 250 m and employs the Morrison microphysics scheme, which treats prognostically mass and number mixing ratios for four hydrometeor types (rain, graupel, snow, and ice). The subgrid-scale hydrometeor transport scheme assumes input given in the form of marginal PDFs of vertical velocity and hydrometeor mixing ratios; in this study, these marginal distributions are provided by the cloud-resolving model. Conditional sampling and scaling are then applied to the marginal distributions to account for subplume correlations. The results demonstrate the potential use of the subgrid-scale hydrometeor transport scheme in an assumed PDF scheme to better represent the correlation between convective transport and subgrid-scale microphysics.