The influence of special T-PARC observations on typhoon track and mid-latitude forecasts

A unique data set of targeted dropsonde observations was collected in the framework of the THORPEX Pacific Asian Regional Campaign (T-PARC) in autumn 2008. The campaign was supplemented by an enhancement of the operational Dropsonde Observations for Typhoon Surveillance near the Taiwan Region (DOTSTAR) program. For the first time, up to four different aircraft were available for typhoon observations and over 1500 additional soundings were collected. This study investigates the influence of additional observations during the two major typhoon events of T-PARC on the typhoon track forecast by the global models of the European Centre for Medium-range Weather Forecasts (ECMWF), the Japan Meteorology Agency (JMA), the National Center for Environmental Prediction (NCEP) and the limited area Weather Research and Forecasting (WRF) model. Additionally, the influence of T-PARC observations on ECMWF mid-latitude forecasts is investigated. All models show an improving tendency of typhoon track forecasts, but the degree of improvement varied from about 20-40% in NCEP and WRF to comparably low influence in ECMWF and JMA. This is likely related to lower track forecast errors without dropsondes in the latter two models, presumably caused by a more extensive use of satellite data and 4D-Var assimilation at ECMWF and JMA compared to 3D-Var of NCEP and WRF. The different behavior of the models emphasizes that the benefit gained strongly depends on the quality of the first-guess field and the assimilation system. However, large improvements of NCEP also indicate potential for larger improvements in the other two global models. A scanning coherent Doppler wind lidar was deployed on the DLR Falcon in addition to the dropsonde system. These wind observations are thought to be more representative of winds in a model grid by and thus more influential on the model analysis. Preliminary results also indicate improvements of the typhoon track with airborne wind lidar observations.