The large-scale environment during the Tropical Cyclone Structure 2008 and THORPEX Pacific Asian regional campaign

Abstract

This study examines the effects of large-scale circulations (e.g., ENSO, Pacific Decadal Oscillation (PDO), Indian Ocean Dipole (IOD), Antarctic Oscillation (AAO), and Monsoon Trough (MT)) on tropical cyclone (TC) activity in the Western North Pacific (WNP) during the May through October timeframe from 1979 to 2008. The specific objective is to understand how these circulations affected the THORPEX/T-PARC/TCS-08 experiments held during August to October 2008. Pivot tables and t-tests were used to analyze the effects of combinations of these circulations on TC activity. Composites of OLR and 850- and 200-hPa winds were constructed to emphasize significant differences between phases of large-scale circulations and combinations. Differences between opposing phases were also analyzed. A statistically-significant relationship exists between ENSO phase and TC activity in terms of Accumulated Cyclone Energy (ACE) values and super-typhoon (STY) numbers. The relationship is less significant, but substantial, for the PDO signal analyzed. However, IOD and AAO have even less significance. The MT signal is significant in the ACE values, but less significant in the STY numbers. The conclusions were that ENSO strongly moderates TC activity and numbers of the most intense TCs in the WNP, while PDO, IOD, and AAO merely reinforce a positive or negative phase of the ENSO circulations. The MT signal has significance on TC activity, but little effect on STY numbers.