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July 24, 2023: Ocean Circulation and Climate Dynamics Colloquium
Yusuke Terada, University of Tokyo, Japan: "Interannual variation of the intraseasonal variability at 1000m depth in the eastern equatorial Pacific Ocean"
When? Monday, July 24, 2023 at 11 am
Where? Lecture Hall, Düsternbrooker Weg 20
Abstract:
It has been shown that the intraseasonal variability (ISV) in the eastern equatorial Pacific Ocean at an intermediate depth (~ 1000 m depth) has large amplitude along the equator with zonally uniform structure. However, the origin and detailed characteristics of the ISV at an intermediate depth are still open question, as well as the relationship between the ISV and the deep zonal jets on the equator. In the present study, we use the 10-day mean horizontal velocity obtained from drift data of the Argo floats and current measurements from the Tropical Atmosphere-Ocean (TAO) array in the equatorial Pacific for a period from 2010 to 2022 to evaluate the seasonal and interannual modulations of the equatorial ISV at the depth of 1000m and its relation to the ISV in the upper layer.
Based on the Argo float drift, we evaluate the meridional component of eddy kinetic energy (V-EKE) and the zonal velocity at 1000 m depth. The V-EKE, which depicts large intraseasonal variability with a period of about 30 days in the eastern tropical Pacific, shows a significant seasonality with its maximum in boreal winter. In addition, the V-EKE in winter indicates a clear interannual variation with the standard deviation of 16
and the largest amplitude appeared in 2016. The zonal velocity on the equator is also found to vary on interannual time scale, showing a significant westward flow during high V-EKE seasons. The TAO ADCP measurements above 300 m depth show the large amplitude ISV along the equator with the meridionally anti-symmetric structure, whose phase propagates upward implying downward energy transport based on linear wave theory. The upper-layer ISV signal also indicates significant interannual variation in its magnitude, which is consistent with the results from Argo-based analysis. These results suggest that the ISV and the equatorial zonal flow at a depth of 1000 m is strongly influenced by the ISV in the upper layer.
