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Using the NCEP/NCAR reanalysis dataset from 1959-2004, the location and strength of the ITCZ (Inter-Tropical Con- vergence Zone), as well as their relations with typhoons in the northwestern Pacific were studied. It was found that the pentad loca- tion and strength of the ITCZ had close relations with the typhoon frequency. Higher latitude location or strengthened ITCZ were found to be favorable for the occurrence of typhoons over the Northwestern Pacific. An index was defined for ascertaining the loca- tion of the ITCZ. It was found that the index defined with the maximum value of pentad and monthly meridional shear of zonal wind speed could better describe the location of ITCZ than another index defined with the maximum value of convergence. Correlation analysis between the index of ITCZ and the maximum cloud cover in the tropics showed that there were close relations between the ITCZ determined by the index and the maximum tropical cloud belt. The strength index of an ITCZ was defined as the zonal wind speed difference at latitudes south and north of the ITCZ. It was found that there are close relations between the ITCZ intensity and typhoon occurrence in the South China Sea [10°N-20°N,100°E-120°E] and regions east of the Philippines and near the Mariana Islands [5°N-20°N, 127.5°E-150°E].
Using the NCEP / NCAR reanalysis dataset from 1959-2004, the location and strength of the ITCZ (Inter-Tropical Con- vergence Zone), as well as their relations with typhoons in the northwestern Pacific were studied. It was found that the pentad loca - tion and strength of the ITCZ had close relations with the typhoon frequency. Higher latitude location or strengthened ITCZ were found to be favorable for the occurrence of typhoons over the Northwestern Pacific. An index was defined for ascertaining the loca- tion of the ITCZ. It was found that the index defined with the maximum value of pentad and monthly meridional shear of zonal wind speed could better describe the location of ITCZ than another index defined with the maximum value of convergence. Correlation analysis between the index of ITCZ and the maximum cloud cover in the tropics showed that there were close relations between the ITCZ determined by the index and the maximum tropical cloud belt. The strength index of an ITCZ was defin It was found that there are close relationship between the ITCZ intensity and typhoon occurrence in the South China Sea [10 ° N-20 ° N, 100 ° E-120 ° E] and regions east of the Philippines and near the Mariana Islands [5 ° N-20 ° N, 127.5 ° E-150 ° E].