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Modulation of Madden–Julian Oscillation activity by the tropical Pacific–Indian Ocean temperature anomaly associated mode
李力锋
国防科技大学
Impacts of the tropical Pacific–Indian Ocean temperature anomaly associated mode (PIOAM) on Madden–Julian Oscillation (MJO) activity were investigated using reanalysis data. In anomalous PIOAM years, MJO zonal wind and OLR amplitude anomalies show a dipole and tripole distribution pattern, respectively. In the positive phase of PIOAM, MJO zonal wind amplitude is weakened (enhanced) over the Indian Ocean (central Pacific) and MJO OLR amplitude is weakened (enhanced) over the eastern Indian Ocean (western Indian Ocean and central Pacific). In the negative phase of PIOAM, these features are reversed. Eastward propagation of MJO can extend to the central Pacific in the positive phase of PIOAM, while it is mainly confined to the west of 150°E in the negative phase of PIOAM. PIOAM impacts MJO activity by regulating atmospheric circulation and moisture transport. In the positive phase of PIOAM, anomalous easterly (westerly) over the Indian (Pacific) Ocean and anomalous descending (ascending) motion over the Maritime Continent (equatorial central Pacific) impedes (promotes) MJO activity over the eastern Indian Ocean (central Pacific). However, anomalous westerly over the Indian Ocean and ascending motion over the eastern Indian Ocean and western Pacific are favourable to local MJO activity in the negative phase of PIOAM. The stronger MJO activity over the eastern Indian Ocean in the negative phase of PIOAM is mainly induced by the stronger moistening to the east of the MJO convection. This moistening is associated with the zonal advection of moisture, which mainly results from the low–frequency background state (with periods longer than 90 days) moisture advection caused by MJO flows and MJO moisture advection caused by the low–frequency background state zonal wind. Both the zonal gradient of moisture and the zonal wind intensity differ significantly between the two phases of PIOAM