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This study is the second part of a two-part series investigating a recent decadal modulation of interannual variability over the western Pacific Ocean around the early 2000s. Observational evidence shows that the anomalous Philippine Sea cyclonic circulation retreats eastward, with the western Pacific rainfall anomaly distribution changing from a north--south tripole pattern to an east--west dipole pattern after 2003-04. These changes are attributed to a change in ElNiño-Southern Oscillation (ENSO) properties and the associated Indo-Pacific sea surface temperature (SST) anomaly pattern. Before the early 2000s, slow-decaying ENSO events induce large SST anomalies in the northern Indian Ocean during the following summer. The northern Indian Ocean SST anomalies act together with the opposite-sign SST anomalies in the tropical central Pacific, leading to a zonally extended anomalous lower-level cyclonic (anticyclonic) circulation and an elongated rainfall anomaly band over the western Pacific. After the early 2000s, ENSO events have a shortened period and a weakened amplitude, and the eastern Pacific SST anomalies tend to undergo a phase transition fromwinter to summer.Consequently, the influence of ENSO on the Indian Ocean SST anomalies is weakened and the contribution of the northern Indian Ocean SST anomalies to the western Pacific summer rainfall variability becomes insignificant. In this case, the western North Pacific summer rainfall is mainly dominated by the well-developed tropical Pacific SST forcing following the early decay of ENSO events. The potential physical mechanism for the two types of ENSO in- fluences is validated with regional decoupled Community Earth System Model experiments. [ABSTRACT FROM AUTHOR]

This study investigates interannual aerosol variations over the Maritime Continent and the western North Pacific Ocean and aerosol-cloud-precipitation relationship during the period 2000-10 based on monthly-mean anomalies. The local aerosol-cloud-precipitation relationship displays strong regional characteristics. The aerosol variation is negatively correlated with cloud and precipitation variation over the Maritime Continent, but is positively correlated with cloud and precipitation variation over the region southeast of Japan. Over broad subtropical oceanic regions, the aerosol variation is positively correlated with cloud variation, but has a weak correlation with precipitation variation. Aerosol variations over the Maritime Continent and over the region southeast of Japan display a biennial feature with an obvious phase lag of about 8 months in the latter region during 2001-07. This biennial feature is attributed to the impacts of El Nifio events on aerosol variations in these regions through large-scale circulation and precipitation changes. Around October of El Nino-developing years, the suppressed precipitation over the Maritime Continent favors an aerosol increase by reducing the wet deposition and setting up dry conditions favorable for fire burning. During early summer of El Nitio-decaying years, suppressed heating around the Philippines as a delayed response to El Nino warming induces an anomalous lower-level cyclone over the region to the southeast of Japan through an atmospheric teleconnection, leading to an accumulation of aerosol and increase of precipitation. The aerosol-precipitation relationship shows an obvious change with time over eastern China, leading to an overall weak correlation. [ABSTRACT FROM AUTHOR]

There exists a pronounced asymmetry between the amplitudes of central Pacific (CP) and eastern Pacific (EP) El Niño sea surface temperature anomalies (SSTA). The present study examines such an asymmetry and its relationship with the North Pacific SSTA. Results indicate that the weaker CP El Niño amplitude can be attributed to the weaker anomalous zonal wind response to the east–west equatorial SSTA gradient during its growing phase compared with EP El Niño. Furthermore, the occurrence of CP El Niño is closely associated with southwesterly surface wind anomalies in the subtropical North Pacific, as well as ocean warming reminiscent of the North Pacific Gyre Oscillation (NPGO) pattern in its vicinity. Both the observations as well as the pacemaker experiments with a coupled global climate model suggest that the anomalous low-level southwesterlies, induced by the North Pacific Oscillation (NPO)-like atmospheric variability, can enhance anomalously positive SST signals and extend them southwestward to the central equatorial Pacific via the wind–evaporation–SST feedback. This will further attenuate the atmospheric response to zonal SSTA gradient, and hence weaken the amplitude of CP El Niño. Therefore, anomalous low-level southwesterlies over the subtropical North Pacific can effectively act as a conduit for tropical–subtropical air–sea interaction in that region, and can play an important role in limiting the intensity of CP El Niño. [ABSTRACT FROM AUTHOR]