The End of an El Nino: A View from Palau
Journal Article - Open Access
NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON United States
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The oceans response to the termination of the major 20152016 El Nino event was captured from moorings and gliders deployed near Palau as part of the Office of Naval Research Departmental Research Initiative Flow Encountering Abrupt Topography FLEAT. As the El Nino transitioned to neutral conditions in spring 2016, pulses of positive warm sea surface height anomalies SSHAs moved westward, deepening the thermocline and reaching Palau by the end of March. Observations collected nearly two months after the arrival of the warm water revealed intraseasonal oscillations ISOs with periods of similar to 30 days and vertical displacements of isotherms exceeding similar to 100 m in the deeper part of the thermocline. Arrival of these warm anomalies coincided with the disappearance of the eastward flow associated with the North Equatorial Countercurrent, and anomalously large meridional velocities 0.4 m s-1 and transports similar to 4-6 Sv over the Kyushu-Palau Ridge on the northern edge of Palau. The 120-day, high-pass-filtered, satellite-acquired SSHAs showed packets of westward moving waves with phase speeds of about 0.2 m s-1 at 8.625 degrees N, with horizontal wavelengths and periods of about 550 km and 30 days, respectively. These waves, which appear to originate in the western Pacific, fall within the characteristics of mode-1 and mode-2 Ross by waves. Similar SSHAs were found near Palau following previous El Nino events, suggesting that formation of intraseasonal oscillations is part of an oceanic response to the termination of El Nino. The transition from El Nino to neutral conditions can affect the coral ecosystem around Palau by creating anomalous circulation and strong thermal anomalies extending from the surface to bottom waters deeper than 150 m, far below the depth limit of coral growth in Palau.
- Physical and Dynamic Oceanography