Forcing of mesoscale eddy kinetic energy variability in the southern subtropical Indian Ocean, from satellite altimeter and scatterometer data

Andrew Delman (Jet Propulsion Laboratory, United States)

CoAuthors

Tong Lee (Jet Propulsion Laboratory, United States); Bo Qiu (University of Hawai'i, United States)

Event: 2017 Ocean Surface Topography Science Team Meeting

Session: Science III: Mesoscale and sub-mesoscale oceanography

Presentation type: Type Poster

A region of elevated mesoscale eddy activity spans the southern subtropical Indian Ocean (SSIO) between Madagascar and Australia. The interannual and decadal changes in eddy activity, as represented by the variability of eddy kinetic energy (EKE), have implications for the meridional overturning circulation and heat transport. An analysis of AVISO merged satellite altimeter data decomposes the sea level anomaly (SLA) field into a spatially low-passed SLA field, and a residual SLA field that contains mesoscale activity. Near the Australian coast, where eddies are generated in the Leeuwin Current, EKE derived from the mesoscale SLA field is found to be positively correlated with the total SLA. This correlation is attributed to the remote forcing from the Pacific: a higher sea level in the western tropical Pacific (e.g., during La Niña or negative PDO conditions) propagates through the Indonesian Seas via coastal Kelvin waves to the SSIO eastern boundary. The higher eastern boundary sea level is associated with a strengthening of the Leeuwin Current, increasing the eddy activity generated from horizontal and vertical shear and radiating eddies towards the west.
In the central SSIO, mesoscale EKE correlations with tropical Pacific anomalies are not robust. Eddies in the interior SSIO are generated from barotropic and baroclinic instability between two opposing currents: the westward flowing, surface-intensified South Indian Counter Current and the eastward flowing, deeper South Equatorial Current. Analyses of surface winds from the CCMP merged scatterometer product, and of surface vorticity gradients from AVISO, indicate that changes in SSIO wind energy input and vorticity gradients may control the interannual variability of mesoscale EKE in the SSIO interior. The identification of these boundary and interior mechanisms for EKE variability may permit short-term (6-12 month) predictions of eddy activity levels in the SSIO, and assessment of model simulations of eddy activity in the region.

 

Poster show times:

RoomStart DateEnd Date
Concerto Ballroom Thu, Oct 26 2017,14:00 Thu, Oct 26 2017,18:00
Andrew Delman
Jet Propulsion Laboratory
United States
Andrew.S.Delman@jpl.nasa.gov