Indian Ocean tripole mode and its associated atmospheric and oceanic processes
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Indian Ocean tripole mode and its associated atmospheric and oceanic processes Yazhou Zhang1 · Jianping Li1,2 · Sen Zhao3,4 · Fei Zheng5 · Juan Feng6 · Yang Li7 · Yidan Xu6 Received: 12 December 2019 / Accepted: 11 June 2020 © The Author(s) 2020
Abstract Differing from the Indian Ocean dipole (IOD) that has sea surface temperature anomalies (SSTAs) of opposing signs over the tropical southeastern and western Indian Ocean, a tripole pattern, characterized by positive (negative) SSTAs over the tropical central (southeastern and western) Indian Ocean, is observed and named the Indian Ocean tripole (IOT). This study proposes the concept of the IOT and further investigates the associated atmospheric and oceanic processes. Using empirical orthogonal function (EOF) analysis, the IOT (IOD) is represented by the third (second) leading mode of the monthly SSTAs in the tropical Indian Ocean, explaining about 8.2% (10.3%) of the total variance. The IOT peaks in boreal summer, while the IOD has its mature phase in boreal fall. The spatio-temporal differences, together with the significant separation of these two EOF patterns, illustrate that the IOT is independent of the IOD. Heat budget diagnoses indicate that the anomalous temperature over the southeastern and western Indian Ocean is mainly generated by the net heat flux during April–May and by the total ocean advection in June–August. In contrast, the anomalous temperature is mainly driven by the advection of the mean temperature by the anomalous current in April and the residual term in May–June over the central Indian Ocean, which is replaced by advection of the anomalous temperature by the mean zonal current in July. Keywords Indian Ocean tripole (IOT) · Atmospheric and oceanic processes · Heat budget
1 Introduction Changes in many extreme weather and climate events have been observed since the mid-20th century. For instance, the record-breaking heat wave of 1994 that occurred in East Asia and the catastrophic rainfall of 1961 in tropical eastern Africa resulted in severe economic and societal losses. These two extreme climatic events were both closely associated with sea surface temperature (SST) anomalies (SSTAs) * Jianping Li [email protected] 1
Frontiers Science Center for Deep Ocean Multispheres and Earth System (FDOMES)/Key Laboratory of Physical Oceanography/Institute for Advanced Ocean Studies, Ocean University of China, Qingdao 266100, China
Laboratory for Ocean Dynamics and Climate, Pilot Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China
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CIC‑FEMD/ILCEC, Key Laboratory of Meteorological Disaster of Ministry of Education, and College of Atmospheric Science, Nanjing University of Information Science and Technology, Nanjing, China
over the tropical Indian Ocean rather than over the tropical Pacific Ocean (Saji et al. 1999; Guan and Yamagata 2003), leading to increasing interest in the tropical Indian Ocean during recent decades. Therefore, it is of great importance to understand tropical Indian Ocean climate va
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