Usability of best track data in climate statistics in the western North Pacific

Abstract

Tropical cyclone (TC) activity for the last three decades shows strong discrepancies, deduced from different best track data (BTD) sets for the western North Pacific (WNP). This study analyses the reliability of BTD sets in deriving climate statistics for the WNP. Therefore TC lifetime, operational parameters (CI-number) and tracks are compared (for TCs identified concurrently) in BTD provided by the Joint Typhoon Warning Center (JTWC), Japan Meteorological Agency (JMA), and the China Meteorological Administration (CMA). The differences between the BTD are caused by varying algorithms used in weather services to estimate TC intensity. Available methods for minimizing these discrepancies are not sufficient. Only if intensity categories 2-5 are considered as a whole, do trends for annually accumulated TC-days show a similar behaviour. The reasons for remaining discrepancies point to extensive and not regular usage of supplementary sources in JTWC. These are added to improve the accuracy of TC intensity and center position estimates. Track- and CI- differences among BTD sets coincide with a strong increase in numbers of intense TC-days in JTWC. These differences are very strong in the period of intensive improvement of spatial-temporal satellite coverage (1987-1999). Scatterometer-based data used as a reference show that for the tropical storm phase JMA provides more reliable TC intensities than JTWC. Comparisons with aircraft observations indicate that not only homogeneity but also a harmonization and refinement of operational rules controlling intensity estimations should be implemented in all agencies providing BTD.