Factors influencing the meridional width of the equatorial deep jets

Abstract

Abstract. Equatorial Deep Jets (EDJ) are vertically alternating, stacked zonal currents that flow along the equator in all three ocean basins at intermediate depth. Their structure can be described quite well by the sum of high baroclinic mode equatorial Kelvin and Rossby waves. However, the EDJs' meridional width is larger by a factor of 1.5 than inviscid theory predicts for such waves. Here, we use a set of idealised model configurations representing the Atlantic Ocean to investigate the contributions of different processes to the enhanced EDJ width. Corroborated by the analysis of shipboard velocity sections, we show that instantaneous widening of the EDJ by irreversible mixing processes contributes more to their enhanced time mean width than averaging over meandering of the jets. Most of the widening due to meandering can be attributed to the strength of intraseasonal variability in the jets' depth range, suggesting that the jets are meridionally advected by intraseasonal waves. Only a weak connection to intraseasonal variability is found for the EDJs' instantaneous widening, corroborating and connecting earlier theories that any process dissipating the EDJs' momentum would broaden them, but that intraseasonal variability maintains, not dissipates, the EDJ.