The Observed Impacts of the Two Types of El Niño on the North Equatorial Countercurrent in the Pacific Ocean

• Published in: Geophysical research letters Vol. 45; no. 19; pp. 10,493 - 10,500
• Main Authors: Tan, Shuwen, Zhou, Hui
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.10.2018
• Subjects: Annual variations; Anomalies; Computer simulation; Ekman pumping; El Nino; El Nino events; El Nino phenomena; Flavors; Flavour; interannual variation; Interannual variations; Kelvin waves; Mathematical models; Moisture content; NECC; Ocean currents; Ocean models; oceanic waves; Oceans; Planetary waves; Rossby wave propagation; Rossby waves; Statistical analysis; Statistical methods; Tropical climate; Tropical climates; two types of El Niño; Variation; Water content; Wave propagation; Wind stress; wind stress anomalies; Pacific Ocean
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL079273

This study investigates the interannual variations in the North Equatorial Counter Current (NECC) associated with the eastern Pacific and the central Pacific types of El Niño. Using observational analysis and ocean simulations, we show that the wind stress anomalies during the two El Niño types are of comparable amplitude but have different spatial structures, which results in significant and distinct variations in the NECC. The NECC shifts southward and intensifies during the developing phase of El Niño, but the variations are confined in the central eastern Pacific for the eastern Pacific type and the western central Pacific for the central Pacific type. These differences can be attributed to modulations in equatorial Kelvin wave and tropical Rossby wave propagation as well as Ekman pumping. Plain Language Summary The North Equatorial Counter Current (NECC) is an eastward flowing surface current that transports a significant amount of water from the warm pool in the western Pacific to the east. Variations in the NECC exert profound effects on the tropical Pacific climate and need to be better understood. This study conducts statistical analyses and ocean model experiments to show that different flavors of El Niño can displace the NECC location and alter its intensity in distinct ways. The cause and the physical mechanisms behind the distinct impacts are identified and verified using specific El Niño events of each flavor. The findings reported in this study contribute to advance our understanding of El Niño diversity and its impacts on the circulation and variability of the Pacific Ocean. Key Points The eastern and central Pacific types of El Niño produce different impacts on the NECC due to the distinct wind stress patterns associated with each The NECC intensifies and shifts southward in the central eastern Pacific during EP El Niño events but in the western central Pacific during CP El Niño events Ekman pumping and oceanic wave propagations link the different wind stress patterns to the distinct NECC changes