Modulation Of The Intraseasonal Variability Of Pacific-japan Pattern By ENSO

Pacific-Japan(PJ)teleconnection pattern is a very important mode in East Asia,which has significant impacts on the atmospheric circulation and precipitation distribution in East Asia.The El Ni?o-Southern Oscillation(ENSO)have strong impacts on PJ pattern.The ERA-Interim reanalysis data provided by the European Centre for Medium-Range Weather Forecasts(ECMWF)from 1979-2018,Sea Surface Temperature(SST)and precipitation data are used to study the impacts of ENSO on the period and spatiotemporal evolution of intraseasonal variability(ISV)of PJ pattern by applying Empirical Orthogonal Function(EOF)method,power spectrum analysis and lead lag regression method.Conclusions are as follows:(1)The wind field of intraseasonal PJ pattern during El Ni?o and La Ni?a summers both displays alternately easterly and westerly anomalies in the meridional direction over the Philippines,the vicinity of Japan and the Okhotsk Sea.However,the westerly anomaly in the mid-latitude during La Ni?a years is stronger.The centers of the mid-latitude westerly anomaly and the tropical easterly anomaly during La Ni?a years are far more westward.There are 10-25 days and 25-70 days periods for the ISV modes of PJ pattern during El Ni?o and La Ni?a years.Peaks for high frequency during El Ni?o and La Ni?a years are on 15-day and18-day,and for low frequency are on 30-day and 60-day,respectively.(2)The characteristics for the high frequency and the low frequency ISV modes of PJ pattern during El Ni?o and La Ni?a summers are different.During El Ni?o years,the intraseasonal oscillation(ISO)originating in the tropical Indian Ocean(IO)propagates eastward to the western equatorial Pacific,and then propagates northwestward to the Philippines.During La Ni?a years,the ISO originating in the tropical IO propagates northeastward to the Philippines to excite PJ pattern.The high frequency ISV modes of PJ pattern in El Ni?o and La Ni?a summers are both characterized by the westward propagating ISO over the western North Pacific(WNP),but during La Ni?a years the ISO propagates westward faster with weaker intensity.The precipitation,2-meter temperature and sea level pressure during El Ni?o and La Ni?a summers all show alternately positive and negative anomalies in the meridional direction.However,compared with El Ni?o years,La Ni?a years show stronger precipitation over the Meiyu belt,more significant temperature anomalies and weaker sea level pressure anomalies.(3)The low-frequency ISV modes during El Ni?o and La Ni?a years are highly relevant to the boreal summer intraseasonal oscillation(BSISO),and the high-frequency ISV modes are similar to the quasi-biweekly oscillation.The possible mechanism is probably attributed to the difference of background field.Due to stronger easterly vertical shear and positive moisture anomaly in the tropical Pacific during El Ni?o summers,the ISO originating in the tropical IO can propagate eastward to the equatorial western Pacific,and then propagate northwestward to the Philippines in about 15 days.On the contrary,during La Ni?a summers the ISO initiating from the IO can only propagate northeastward to the Philippines without propagating eastward to the equatorial western Pacific due to negative moisture anomaly in the tropical Pacific.