A 15-year climatology of synoptical disturbance over tropical northwestern Pacific during summer
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This work investigated the sumertime northwestward propagating waves over the tropical western North Pacific and their relationship with tropical cyclone activities. The 15-season (May-October 1974-1988) Navy tropical global band data were separated into three groups according to the degree of organization in the multiple-set canonical correlation (MCC) modes that were computed from the surface v wind. Groups A (6 seasons) and B (5 seasons) showed orderly large-scale propagating patterns at the surface and 700 hPa with an average period of 8 days and a wavelength of about 2500-3000 km. The structure is robust whether the MCC analysis was performed on each of the seasons individually or on groups of years. A strong in-phase relationship between the low-level disturbance cyclonic cells and tropical cyclone centers was found. Composite analysis of all cases in these two groups whose MCC mode 1 amplitude exceeded 1.5 m/s showed organized northwestward propagating divergence/convergence patterns at 200 hPa. Group C (4 seasons) shows the least organized structure, with a large difference between MCC modes obtained from the entire group and those from each individual season. The possibility that group C contains irregular tropical cyclone tracks was discussed.
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