Using TIGGE data to diagnose initial perturbations and their growth for tropical cyclone ensemble forecasts
Munehiko Yamaguchi, Sharanya J. Majumdar, Melinda S. Peng, Carolyn A. Reynolds and David S. Nolan
Although the accuracy of typhoon track prediction has improved significantly over the last few decades, ensemble techniques are expected to provide extra useful information on the uncertainty of track prediction, via the ensemble spread. A systematic intercomparison of global model ensembles was not possible before the establishment of the TIGGE database. In this study, we focus on the skill of ensemble typhoon prediction, as well as the characteristics and growth of ensemble perturbations in the tropical cyclone and its environment that are created in different ways among the operational centers. Among the goals of the study are to understand error growth in the ensemble perturbations and to improve the reliability of ensemble techniques for typhoon prediction.
Firstly, ensemble initial perturbations around typhoons are compared using the data from ECMWF, JMA, NCEP, NOGAPS and UKMET for the 2008 typhoon season, and in particular, Typhoon Sinlaku from the TCS-08/T-PARC field phase. We investigate how the initial perturbations modify initial structures of the typhoon and its environment such as the size, the asymmetry property and the subtropical high. In addition, horizontal and vertical energy profiles of the perturbations are compared based on the total energy, aimed to reveal the relative amplitudes of the perturbations. Secondly, a relationship between the position error and spread of tracks is compared. In addition, a relationship of spreads between any two operational centers is compared to see whether the amount of spread is model-dependent or not. Thirdly, the growth of initial ensemble perturbations is investigated in order to understand the spreading of typhoon tracks in the ensemble.
Case study: Typhoon Sinlaku
Comparison of track and synopsis
Comparison of perturbation growth
Vertical and Horizontal distribution of kinetic energy of ensemble perturbations
Vertical and Horizontal distribution of available potential energy of ensemble perturbations
Vertical and Horizontal distribution of specific humidity energy of ensemble perturbations
Symmetric and Asymmetric Wind field of non-perturbed (CTL) ensemble member
How do initial perturbations change the size and advection flow? (ECMFW and NCEP)
Perturbation Growth (ECMFW and NCEP)
Barotropic instability of a normal mode (ECMFW and NCEP)
Where in TCs do singular vectors appear?
Statistical comparison