Tropical Cyclone Structure Prediction Using a Regional Model

Tropical cyclone (TC) track forecasts have improved by over 50% during the past decades. Meanwhile, progress on predicting TC intensity and structure has been lagging. In particular, the prediction of TC structure remains a great challenge, not only because the TC structure is influenced by complex processes at multiple scales, but also due to insufficient observations for the TC inner-core structure. The goal of this study is to systematically examine TC structures simulated by the Coupled Ocean / Atmosphere Mesoscale Prediction System –Tropical Cyclone model (COAMPS-TC). COAMPS-TC, a regional model developed by Naval Research Laboratory, is used by FNMOC for operational TC forecasts. The study will include both idealized simulations and hindcasts of real cases. A composite inner-core structure is then constructed using simulations of over 200 cases from 15 TCs. The kinematic and thermodynamic structure of the TC inner-core is examined and validated against the composites of airborne Doppler radar analyses. The model successfully simulated azimuthally averaged inner-core structure, including the maximum tangential wind in the eyewall, the low-level inflow, the upper-level outflow, the strong updrafts in the eyewall, and the outwardly titled eyewall. However, the radar reflectivity shows significant discrepancies between the model and observations, motivating further advancements in model physics, especially the cloud microphysics. The Thompson (2008) microphysics has recently been implemented in COAMPS-TC and compared with the COAMPS microphysics scheme. It is found that TC structure is highly sensitive to the representation of clouds in the model. One distinct difference is seen in the wind radii using the two schemes. The average wind radius of the gale-force winds is significantly smaller using the Thompson scheme than using the COAMPS-TC microphysics scheme. Detailed analysis will be presented at the conference.