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Have steering flows in the western North Pacific and the South China Sea changed over the last 50 years?
Author(s) -
Chu PaoShin,
Kim JooHong,
Ruan Chen Ying
Publication year - 2012
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2012gl051709
Subject(s) - typhoon , subtropical ridge , tropical cyclone , climatology , subtropics , storm , geology , china , environmental science , meteorology , oceanography , geography , precipitation , archaeology , fishery , biology
Long‐term trends in steering flows over the western North Pacific (WNP) and the South China Sea (SCS) are examined during the peak typhoon season. A nonparametric and robust trend detection method is employed. Both the NCEP and ERA reanalysis data sets suggest a statistically significant decreasing trend in steering flows in the subtropical region of the western WNP (between 120°E or near Taiwan and 145°E) and the northern SCS during 1958–2001. Over this period, the decrease in the WNP is quite large with a magnitude of 1.1 m s −1 given that the background mean steering flow is only 3.26 m s −1 . This decrease corresponds approximately to one third of the mean flow. When the data are extended from 1958 to 2009 the long‐term decrease in steering flows in the aforementioned subtropical region are still significant, although more modest at a rate of 0.7 m s −1 . Time series of translational speeds averaged over the same subtropical region also exhibit a slow‐down of storms' motion over the last 52 years. This is consistent with the weakening of easterly steering flows analyzed from independent data sets. Results of this study imply a longer life span for tropical cyclones and a greater tendency for storms along prevailing typhoon tracks to recurve.