Relationship between Sea Surface Temperature gradients and upwelling off Peru and Chile: Model/Data Analysis

Jorge Vazquez1, Boris Dewitte2, Dimitris Menemenlis3, Toshio Michael Chin3, Edward M Armstrong1 and Hector S. Torres4, (1)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (2)LEGOS/IRD, SYSCO2, TOULOUSE, France, (3)Jet Propulsion Laboratory, Pasadena, CA, United States, (4)CICESE National Center for Scientific Research and Higher Education of Mexico, Ensenada, Mexico
Abstract:
The upwelling system of Peru/Chile contains significant mesoscale to submesoscale surface variability that results from the instability of the coastal currents (due to the strong vertical and horizontal shears) and to the marked density cross-shore gradients (associated with the mean upwelling). The imprint of such mesoscale activity can be inferred from satellite SST that provides observations at high temporal and spatial resolution. We investigate to which extent Sea Surface Temperature (SST) gradients, a proxy for mesoscale and frontal activity, can be related to the dynamics of the upwelling off Peru and Chile. The study is based on satellite-derived SST data products that are made available on regular grids with 0.25° to 1 km horizontal spacing and on the analysis of high-resolution numerical ocean simulations. As a first step, a comparison between SST observations is performed, which indicates that the 1-km gridded Multi-Scale Ultra-High Resolution (MUR) SST Analysis resolves features that are not present in 0.25° analyses, along with having significantly larger horizontal gradient magnitudes near the mean upwelling front. Two numerical ocean simulations, with 2-km and 4-km horizontal grid spacing, are analyzed. The 2-km simulation is examined for the period September 13, 2011 to January 23, 2012, while a 4-km simulation is examined for the period March 6, 2011 to April 22, 2013. Comparisons made with MUR SST show comparable maximum SST gradients of 0.07 to 0.1°C/km, with upwelling scales that decrease to less than 15 km off the coast of Chile. The relationship between upwelling rate (as inferred from the vertical velocity), Eddy Kinetic Energy (EKE), and SST gradient is documented in the model for intraseasonal to seasonal timescales. Estimates of EKE help quantify the processes contributing to the SST gradient, inclusive of upwelling strength and frontal activity. The results suggest that satellite-derived SST data products could be used to monitor the intensity of coastal upwelling and its frontal activity at intraseasonal to seasonal timescales.
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