Journal
JOURNAL OF CLIMATE
Volume 32, Issue 2, Pages 405-421Publisher
AMER METEOROLOGICAL SOC
DOI: 10.1175/JCLI-D-17-0583.1
Keywords
Atmosphere; Atmosphere-ocean interaction; Atmospheric circulation; Climate variability; Interannual variability
Categories
Funding
- National Natural Science Foundation of China (NSFC) [41790475]
- National Key Research and Development Program of China [2016YFA0601801]
- Ministry of Science and Technology of China [2015CB953904, 2015CB453201]
- NSFC [91637312, 41575075, 91437216, 61702275, 41775008]
- National Research Foundation (NRF) of Korea through a Global Research Laboratory (GRL) grant of the Korean Ministry of Education, Science and Technology (MEST) [2011-0021927]
- Nanjing University of Information Science and Technology
- Atmosphere-Ocean Research Center at the University of Hawaii
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According to the sea surface temperature anomaly (SSTA) intensity in the Nino-3.4 region and the east-west gradient across the Pacific, three types of El Nino are identified in this work. An event with larger than average intensity is defined as a strong El Nino, all others are considered to be weak events. Almost all strong El Ninos are concurrent with a large gradient, which is featured by negative SSTAs in the western Pacific and positive SSTAs in the equatorial eastern Pacific (EP) and Indian Ocean (IO). According to the east-west gradient, the weak events can be subdivided into gradient-weak (GW) El Nino and equatorial-weak (EW) El Nino. The GW El Nino characterizes a great east-west gradient without a significant IO SSTA. In contrast, the EW event features a positive SSTA over the tropical IO and EP. The impact of GW El Nino on the North Atlantic-Eurasia continent (NA-Eurasia) displays a negative North Atlantic Oscillation (NAO)-like atmospheric anomaly, resulting in a drier and cooler-than-normal winter over Eurasia. Observational and numerical evidence indicate that the prolonged subtropical jet from the North Pacific to NA acts as a waveguide that captures the planetary Rossby waves generated by the GW El Nino. This waveguide favors the propagation of the perturbations into the downstream regions, which would affect the NA-Eurasian climate. However, the EW El Nino is accompanied by a relatively weak subtropical jet that cannot impact the NA-Eurasian climate significantly. For the strong El Nino, the absence of the NAO signal can be attributed to the counteracting of the teleconnections triggered by the Pacific and the tropical IO.
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