A Modified Approach To Initialize An Idealized Extratropical Cyclone Within A Mesoscale Model

Abstract

A technique for initializing realistic idealized extratropical cyclones for short-term (0–72 h) numerical simulations is described. The approach modifies select methods from two previous studies to provide more control over the initial cyclone structure. Additional features added to the technique include 1) deformation functions to initialize more realistic low-level fronts, tropopause structure, and enhanced jet maximum at upper levels; 2) a barotropic shear function to help develop different cyclone and frontal geometries; and 3) damping functions to create an isolated baroclinic wave in the horizontal; therefore, the initialized cyclone is not influenced by the domain boundaries for relatively short simulations. Since this procedure allows for control of the initialized cyclone structures, it may be useful for studies of frontal and cyclone interaction with topography and mesoscale predictability. The initialization system produces a variety of basic states and synoptic disturbances, ranging from weak to explosively developing cyclones. Examples are shown to provide some insight on how to adjust selected parameters. The output is compatible with the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model and the Weather Research and Forecasting model. This note describes the procedure as well as presents an example of a landfalling cyclone along the U.S. west coast with and without terrain.