Inter-comparison of Targeted Observation Guidance for Tropical Cyclones in the North Western Pacific

TitleInter-comparison of Targeted Observation Guidance for Tropical Cyclones in the North Western Pacific
Publication TypeTechnical memorandum
Date Published02/2009
Secondary TitleECMWF Technical Memoranda
AuthorsWu, C-C, Chen, J-H, Majumdar, S, Peng, MS, Reynolds, CA, Aberson, SD, Buizza, R, M. Chen, Yand.S-G, Nakazawa, T, Cho, K-H

This study compares six different guidance products for targeted observations over the Northwest Pacific for 84 cases of two-day forecasts in 2006, and highlights the unique dynamical features affecting the tropical cyclone (TC) tracks in this basin. The six products include 3 types of guidance based on total-energy singular vectors (TESVs) from different global models, the ensemble transform Kalman filter (ETKF) based on a multi-model ensemble, the deep-layer mean (DLM) wind variance, and the adjoint-derived sensitivity steering vector (ADSSV). The similarities among the six products are evaluated using two objective statistical techniques to show the diversity of the sensitivity regions in large, synoptic-scale domains, and smaller domains local to the TC. It is shown that the three TESVs are relatively similar to one another in both the large and the small domains while the comparisons of the DLM wind variance to other methods show rather low similarities. The ETKF and the ADSSV usually show high similarity because their optimal sensitivity usually lies close to the TC. The ADSSV, relative to the ETKF, reveals more similar sensitivity patterns to those associated with TESVs. Three special cases are also selected to highlight the similarities and differences between the six guidance products and to interpret the dynamical systems affecting the TC motion in the North western Pacific. Among the three storms studied, Typhoon Chanchu was associated with the subtropical high, Typhoon Shanshan was associated with the mid-latitude trough, and Typhoon Durian was associated with the subtropical jet. The adjoint methods are found to be more capable of capturing the signal of the dynamic system that may affect the TC movement or evolution than the ensemble methods.

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