Eddy And Wind Forced Spiciness Variability In A Numerical Model Ensemble – Formation, Propagation, And Predictability Of Density Compensated Anomalies In The Pacific Thermocline

Abstract

Over the last few decades, research on the atmosphere’s response to internal ocean dynamics has matured significantly. This study uses the Japan Agency for Marine-Earth Science and Technology’s (JAMSTEC) Ocean General Circulation Model for the Earth Simulator (OFES) in a highresolution, eddy resolving configuration, and expands upon published results of a single OFES run by analyzing a five member ensemble hindcast from January 2005 to December 2014. We identify and describe spatial and temporal variability of density compensated potential temperature and salinity - called spiciness χ - in the Pacific’s upper-thermocline below the mixed layer. On the σθ 25 potential density surface, we find i) large temporal spiciness variance in regions of prominent isopycnal temperature gradients of Baja and in the western and eastern Equatorial Pacific ii) propagation of spiciness signals along mean advective pathways, while iii) large eddy induced spiciness variance in the upper-thermocline is limited to areas off Baja and the western equatorial Pacific. Quantitatively, the standard deviation of spiciness over time σt(χ) off Baja California due to winds and eddies reach 1.4 K, and 0.8 K respectively. In the eastern equatorial Pacific, σt(χ) is up to 0.6 K, and predominantly results of atmospheric forcing associated with ENSO, while eddy induced variance is smaller than 0.1 K. In the western Pacific north of New Guinea σt(χ) is 0.5 K, and 0.3 K, due to winds and eddies, respectively.