The Deep Equatorial Ocean Circulation in Wind-Forced Numerical Solutions

Abstract

propagating mostly downward, consistent with observations. We demonstrate that both types of currents arise from the rectification of DEIV, consistent with previous theories. We also find that the EDJs contribute to maintaining the EICs, suggesting that the nonlinear energy transfer is more complex than previously thought. In Solution 2, the DEC is unrealistically weak and less spatially coherent than in the first simulation probably because of its weaker DEIV. Using intermediate solutions, we find that the main reason for this weaker DEIV is the use of realistic coastlines in Solution 2. It remains to be determined, what needs to be modified or included to obtain a realistic DEC in the more realistic configuration.

The emergence of equatorial deep jets in an idealised primitive equation model: an interpretation in terms of basin modes

“…In fact Claus et al (2016) have diagnosed the forcing for the deep jets from the mooring data at 23 • W on the equator and find that the implied power input that maintains the deep jets takes place over the whole depth range occupied by the jets. Concerning the vertical phase propagation of the jets, we note that in the particular case studied by D' Orgeville et al (2007), the vertical phase propagation is not in agreement with observations, although it should be noted that their model runs are shorter than those considered by Ascani et al (2015) and Matthießen et al (2015) and possibly do not show fully developed EDJ cycles. In D 'Orgeville et al (2007), the phase propagation is such as to take energy away from the depths where the imposed destabilizing Yanai waves have relatively large amplitude to depths where the destabilizing Yanai waves have relatively low amplitude (see Fig.…”

“…Indeed, basin modes appear to be important for describing not only the EDJs in the equatorial Atlantic Ocean but also the semi-annual and annual cycles . Ascani et al (2015) also noted that in their nonlinear model the EDJs are well represented by the gravest basin mode for a high baroclinic vertical normal mode. Furthermore, Matthießen et al (2015) showed that in their idealised model experiments, most of the energy associated with the zonal velocity along the equator has both a time scale and vertical structure associated with resonant basin modes.…”

“…The lack of EDJs in Earth System Models noted above is not limited to these particular models. Even high resolution, realistic ocean models have difficulty representing EDJs (Eden and Dengler 2008;Ascani et al 2015). Nevertheless, idealised model set-ups do support EDJs (e.g.…”

“…Nevertheless, idealised model set-ups do support EDJs (e.g. D 'Orgeville et al 2007;Ménesguen et al 2009;Ascani et al 2015;Matthießen et al 2015) and hopefully analysis of these model runs can shed light on why realistic models are unsuccessful in simulating EDJs.…”

“…Eden and Dengler (2008) also investigated the generation of vertically stacked jets in a high resolution ocean model where the energy source was thought to be fluctuations of the Deep Western Boundary Current in the model. Ascani et al (2015) described a mechanism whereby Yanai waves shed from tropical instability waves interact to support the EDJs. In particular, a high vertical mode intraseasonal Yanai wave, with the same vertical scale as the EDJs, interacts with a low vertical mode intraseasonal Yanai wave to maintain the deep jets through the meridional advection term in the momentum equation.…”