A decadal spiciness mode in the tropics

Abstract

Analysis of a complex climate model suggests the existence of a mode of coupled ocean‐atmosphere variability in the tropical Pacific with the following dynamics. Anomalous strong Pacific trade winds accelerate the North Equatorial current and Countercurrent. At 10° to 15°N in the central Pacific thermocline this causes anomalous advection across mean gradients of temperature and salinity on isopycnal surfaces and generates cool/fresh spiciness anomalies of the order of 0.3°K. These are advected by the mean circulation via the western boundary region to the equatorial Pacific in approximately five years. At the equatorial outcrops of the isopycnals, the cool/fresh anomalies affect the surface heat budget and are hypothesized to initiate a relaxation of the trade winds that is reinforced by positive feedbacks with the slope of the thermocline and with air‐sea fluxes of heat and freshwater. At 5° to 10°S the decrease of the trades generates by anomalous advection cool/fresh spiciness anomalies that migrate to the equator in one to two years and provide a positive feedback. At 10° to 15°N, the decrease of the trades decelerates North Equatorial current and Countercurrent and causes warm/salty anomalies on isopycnals that arrive at the equator five years later and close the cycle.