Improved simulation of Florida summer convection using the PLACE land model and a 1.5-order turbulence parameterization coupled to the Penn State-NCAR mesoscale model

Three major modifications to the treatment of land surface processes in the Pennsylvania State University-National Center for Atmospheric Research mes oscale model MM5, are tested in a matrix of eight model experiments. Paired together in each dimension of the matrix are versions of the code with and without one of the changes. The three changes involve 1) a sophisticated l and surface model [the Parameterization for Land-Atmosphere Convective Exch ange (PLACE)], 2) the soil moisture and temperature initial conditions deri ved from running PLACE offline, and 3) a 1.5- order turbulent kinetic energ y (TKE) turbulence boundary layer. The code without changes, defined as the control code, uses the most widely applied land surface, soil initializati on, and boundary layer options found in the current MM5 community code. As an initial test of these modifications, a case was chosen in which they sho uld have their greatest effect: conditions where heterogeneous surface forc ing dominates over dynamic processes. The case chosen is one with widesprea d summertime moist convection, during the Convection and Precipitation Elec trification Experiment (CaPE) in the middle of the Florida peninsula. Of th e eight runs, the code with all three changes (labeled TKE-PLACE) demonstra tes the best overall skill in terms of biases of the surface variables, rai nfall, and percent and root-mean-square error of cloud cover fraction for t his case. An early, isolated convective storm that formed near the east coa st, at the downwind edge of a region of anomalous wet soil, and within the dense cluster of CaPE mesoscale observation stations, is correctly simulate d only by TKE-PLACE. It does not develop in any of the other seven runs. A factor separation analysis shows that a successful simulation requires the inclusion of the more sophisticated land surface model, realistic initial s oil moisture and temperature, and the higher-order closure of the planetary boundary layer (PBL) in order to better represent the effect of joint and synergistic (nonlinear) contributions from the land surface and PBL on the moist convection.