Modulation of the Intraseasonal Variability of Pacific-Japan Pattern by ENSO

Abstract

This study investigates how the El Nino–Southern Oscillation (ENSO) modulates the intraseasonal variability (ISV) of Pacific–Japan (PJ) teleconnection pattern. The PJ index during boreal summer is constructed from the empirical orthogonal function (EOF) of the 850-hPa zonal wind (U850) anomalies. Distinct periods of the PJ index are found during El Nino and La Nina summers. Although ISV of the PJ pattern is significant during 10–25 days for both types of summers, it peaks on Days 30 and 60 in El Nino and La Nina summers respectively. During El Nino summers, the 30-day ISV of PJ pattern is related to the northwestward propagating intraseasonal oscillation (ISO) over the western North Pacific (WNP), which is originated from the tropical Indian Ocean (IO). During La Nina summers, the 60-day ISV of PJ pattern is related to the northeastward propagating ISO from the tropical IO. The low-frequency ISV modes in both El Nino and La Nina summers are closely related to the boreal summer ISO (BSISO), and the high-frequency ISV modes over WNP are related to the quasi-biweekly oscillation. The underlying mechanisms for these different evolutions are also discussed.