Numerical Prediction and Modification of Cyclone–Scale Precipitation

Abstract

A fine-mesh, limited-area, finite-difference model has been developed both to predict precipitation over a limited geographic region and to be utilized in experiments for precipitation modification. The model is primitive with 15 vertical levels, shows many features in common with current models of its type, but lacks resolution of the boundary layer. Lateral boundary conditions are specified when needed from a data set which also provides initial conditions and comparisons for the forecasts. Utilizing one integration as a control, a number of experiments were performed under model modifications and compared to the control. In all cases, modification did not substantially alter the flow field over a 24 h period, but precipitation forecasts were altered. Regions of marginal precipitation showed almost no precipitation in an experiment where lack of freezing nuclei was incorporated, whereas the experiment based on cloud seeding showed significant increase in total precipitation. The addition of carbon black heating to the model did not show substantial changes in precipitation. Modified initial conditions based on poor (coarse grid) resolution had a significant effect on precipitation prediction.