Ensemble-based Diagnostics of Tropical Cyclone Outflow

The broad research goal of the Office of Naval Research Tropical Cyclone Intensity (TCI) program is to enhance our understanding of the dynamics of the upper-level outflow of tropical cyclones and its connection to the larger-scale environment. In order to address this goal and to provide forecasting support for the TCI field campaigns in 2014 and 2015, new daily ensemble products have been prepared. In addition to the conventional distributions of the positions and strengths of the tropical cyclone vortices, diagnostics related to the outflow were also produced.

The variability of the outflow structures in the ensemble predictions is hypothesized to be controlled by initial differences in the environmental flow, such as the strength, location, depth, and orientation of a nearby trough. Variations in the general lower-tropospheric structure of the tropical cyclone are also expected to influence the outflow structure. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) and Coupled Ocean/Atmosphere Mesoscale Prediction System for Tropical Cyclones (COAMPS-TC) ensembles for selected tropical cyclones, new error diagnostics will be presented to offer clues on the key features and mechanisms to which the outflow structure is sensitive. The characteristics of the errors in the ensemble predictions are assessed relative to analysis fields, as well as satellite and aircraft observations of the outflow structure.