Inter-comparison of targeted observation guidances for tropical cyclones in the western North Pacific

Targeted observation to improve the tropical cyclone (TC) predictability is among one of the most important research and forecasting issues for TCs. To optimize the aircraft surveillance observations using dropwindsondes, targeted observing strategies have been developed and examined. The primary consideration in devising such strategies is to identify the sensitive areas in which the assimilation of targeted observations is expected to have the greatest influence in improving the numerical forecast, or minimizing the forecast error.

To gain more physical insights into several existing targeted techniques, studies to compare and evaluate the techniques have been conducted by Majumdar et al. (2006), Etherton et al. (2006), and Reynolds et al. (2007). As a follow-up work, and to highlight the unique dynamics features in affecting the TC tracks, in this paper we compare six different targeted techniques based on 92 cases of two-day forecasts of the Northwest Pacific tropical cyclones in 2006. The six targeted methods are total-energy singular vectors (TESVs) form European Centre for Medium-Range Weather Forecasts (ECMWF) and Navy Operational Global Atmospheric Prediction System (NOGAPS), the TESV by Ensemble Prediction System (EPS) of Japan Meteorological Agency (JMA), the ensemble-transform Kalman-filter (ETKF) based on the multi-model ensemble members [ECMWF, National Centers for Environmental Prediction (NCEP) and Canadian Meteorological Centre (CMC)], the ensemble Deep-Layer Mean (DLM) wind variance by NCEP Global Forecast System (GFS), and the Adjoint-Derived Sensitivity Steering Vector (ADSSV) by Pennsylvania State University/National Center for Atmospheric Research fifth generation mesoscale model (MM5).

We note that different from the Atlantic Ocean, the Northwest Pacific regions have more complicated dynamical systems affecting the TC motion, such as the mid-latitude trough, the subtropical jet, the southwesterly monsoon and the binary interaction. More analyses are ongoing to identify the similarity and the difference of all these different targeted methods and to interpret their dynamic meanings. Results from this work would not only provide better insights into the physics of the targeted techniques, but also offer very useful information to assist the future targeted observations, especially for the Dropwindsonde Observations for Typhoon Surveillance near the TAiwan Region (DOTSTAR) and Typhoon Hunting 2008 (TH08) in THORPEX-PARC (T-PARC), 2008.