Modulation of Madden-Julian Oscillation Activity by the Tropical Pacific-Indian Ocean Associated Mode
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• Original Paper •
Modulation of Madden-Julian Oscillation Activity by the Tropical Pacific-Indian Ocean Associated Mode Lifeng LI1, Xin LI1, Xiong CHEN*1, Chongyin LI1,2, Jianqi ZHANG1, and Yulong SHAN1 1College 2State
of Meteorology and Oceanography, National University of Defense Technology, Nanjing 211101, China Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China (Received 5 January 2020; revised 18 August 2020; accepted 21 August 2020) ABSTRACT
In this study, the impacts of the tropical Pacific–Indian Ocean associated mode (PIOAM) on Madden–Julian Oscillation (MJO) activity were investigated using reanalysis data. In the positive (negative) phase of the PIOAM, the amplitudes of MJO zonal wind and outgoing longwave radiation are significantly weakened (enhanced) over the Indian Ocean, while they are enhanced (weakened) over the central and eastern Pacific. The eastward propagation of the MJO can extend to the central Pacific in the positive phase of the PIOAM, whereas it is mainly confined to west of 160°E in the negative phase. The PIOAM impacts MJO activity by modifying the atmospheric circulation and moisture budget. Anomalous ascending (descending) motion and positive (negative) moisture anomalies occur over the western Indian Ocean and central-eastern Pacific (Maritime Continent and western Pacific) during the positive phase of the PIOAM. The anomalous circulation is almost the opposite in the negative phases of the PIOAM. This anomalous circulation and moisture can modulate the activity of the MJO. The stronger moistening over the Indian Ocean induced by zonal and vertical moisture advection leads to the stronger MJO activity over the Indian Ocean in the negative phase of the PIOAM. During the positive phase of the PIOAM, the MJO propagates farther east over the central Pacific owing to the stronger moistening there, which is mainly attributable to the meridional and vertical moisture advection, especially low-frequency background state moisture advection by the MJO’s meridional and vertical velocities. Key words: tropical Pacific–Indian Ocean associated mode, MJO, moisture budget analysis, anomalous circulation Citation: Li, L. F., X. Li,, X. Chen, C. Y. Li, J. Q. Zhang, and Y. L. Shan, 2020: Modulation of Madden–Julian Oscillation activity by the tropical Pacific–Indian Ocean associated mode. Adv. Atmos. Sci., 37(12), 1375−1388, https://doi.org/ 10.1007/s00376-020-0002-1. Article Highlights:
• The PIOAM, which represents the coordinated variability of sea surface temperature anomalies over the Indian and Pacific oceans, has significant impacts on MJO activity.
• The PIOAM influences the activity of the MJO mainly by modulating the circulation and moisture. • The combined effects of circulation and moisture on different time scales play an important role in the impacts of the
PIOAM on the MJO.
1. Introduction The Madden–Julian Oscillation (MJO; Madden and Ju
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