The Predictability of Extratropical Transition and of Its Impact on the Downstream Flow

Download or read book The Predictability of Extratropical Transition and of Its Impact on the Downstream Flow written by and published by . This book was released on 2008 with total page 39 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this project we investigated the basic mechanisms that determine the predictability of tropical cyclones undergoing extratropical transition (ET) and of their impact on the downstream flow. The analysis of ensemble forecasts for five ET cases showed that uncertainty is associated with the location and amplitude of a characteristic upper-level trough-ridge-trough pattern consisting of the trough that interacts with the tropical cyclone, a ridge directly downstream and a second trough downstream of the ridge. Experiments for Typhoon Tokage (2004) with the ensemble prediction system of the European Centre for Medium Range Weather Forecasts showed that targeted perturbations led to increased spread around and shortly after ET time whereas the spread due to stochastic physics increased at a later time as the influence of the targeted perturbations decreased. Idealized modelling combined with potential vorticity inversion was used to quantify the mechanisms responsible for this variability. Furthermore, dropsonde data in the vicinity of tropical cyclones were shown to reduce the medium-range forecast error for the downstream flow.