Abstract
ABSTRACT This paper uses China Meteorological Administration tropical cyclone (TC) best track data to analyze the characteristics of TC activity over the western North Pacific in 2011. Results derived from two other datasets, issued by the Regional Specialized Meteorological Center Tokyo and the Joint Typhoon Warning Center, were also compared. We show that the annual TC activity in 2011 was weaker than the climatology, and exhibited remarkable intraseasonal signals. The main TC genesis region migrated seasonally between the southwest (7° – 17°N, 120° – 140°E) and northeast (17°–25°N, 135°–165°E) quadrants. Moreover, three prevailing tracks were identified: westward tracks, recurving tracks between 125°–135°E, and northward tracks near 155°E. Special attention was paid to the intra-annual features of TC activity during 2011 and the potential modulators of this activity, including the tropical Indo-Pacific oceans, East Asian Monsoon (EAM), and Intraseasonal Oscillation (ISO). The seasonal migration of the main TC genesis region can be attributed to modulation by the EAM trough and ISO rather than the El Nino-Southern Oscillation. Both the EAM trough and ISO provided favorable conditions, including cyclonic vorticity in the low troposphere, limited vertical shear, and moisture convergence, in both of the main TC genesis quadrants, but unfavorable conditions outside the particular genesis quadrant. Moreover, both EAM and ISO generated a favorable circulation that steered TCs to move along the three prevailing tracks. These findings indicate that TC activity in 2011 was more significantly affected by both the EAM and ISO than by the ENSO.
Published Version
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