Feedback of Tropical Instability-Wave-Induced Atmospheric Variability onto the Ocean

Abstract

The effects of atmospheric feedbacks on tropical instability waves (TIWs) in the equatorial Atlantic Ocean are examined using a regional high-resolution coupled climate model. The analysis from a 6-yr hindcast from 1999 to 2004 reveals a negative correlation between TIW-induced wind perturbations and TIW-induced ocean currents, which implies damping of the TIWs. On the other hand, the feedback effect from the modification of Ekman pumping velocity by TIWs is small compared to the contribution to TIW growth by baroclinic instability. Overall, the atmosphere reduces the growth of TIWs by adjusting its wind response to the evolving TIWs. The analysis also shows that including ocean current (mean ϩ TIWs) in the wind stress parameterization reduces the surface stress estimate by 15%-20% over the region of the South Equatorial Current. Moreover, TIW-induced perturbation ocean currents can significantly alter surface stress estimations from scatterometers, especially at TIW frequencies. Finally, the rectification effect from the atmospheric response to TIWs on latent heat flux is small compared to the mean latent heat flux.

Using Satellite Data to Represent Tropical Instability Waves (TIWs)-Induced Wind for Ocean Modeling: A Negative Feedback onto TIW Activity in the Pacific

“…Following [21], we calculate the correlation coefficients between TIW-scale perturbations of surface currents (V TIW ) and wind stress (τ TIW ), which is shown in Figure 11. It is seen that and tends to be anti-correlated well over the eastern equatorial Pacific (Figure 11(b)).…”

“…For example, Seo et al [21] identified an anti-correlation pattern between TIW-induced perturbations of surface current and wind stress, which can serve as a negative feedback having a diminishing impact on TIWs in the ocean. Also, Pezzi et al [22] showed that when TIW wind forcing is explicitly included, TIWs decrease in the ocean.…”

“…As with [21], a SST-dependent model for TIW-induced wind stress perturbations (τ TIW ) is derived using satellite observations [19,30], which is incorporated into a basin-wide ocean general circulation model (OGCM) of the tropical Pacific. As will be seen below, this empirical τ TIW modeling approach can reasonably well depict TIW-scale coupling between the ocean and atmosphere in the eastern tropical Pacific.…”

Impact of tropical instability waves‐induced SST forcing on the atmosphere in the tropical Pacific, evaluated using CAM5.1

“…For example, several previous modeling studies have suggested a negative feedback induced by TIWs (Seo et al, 2007;Imada et al, 2012;Zhang et al, 2013). In a coupled ocean-atmosphere system, the atmospheric boundary layer (ABL) almost simultaneously responds to the presence of TIWs and as a feedback it returns its signal to the oceanic surface, which interacts in an opposite way with ocean surface fields (currents and temperature) that affect the oceanic dynamical and thermo-dynamical features (Polito et al, 2001;Pezzi et al, 2004;Seo et al, 2007).…”

“…In a coupled ocean-atmosphere system, the atmospheric boundary layer (ABL) almost simultaneously responds to the presence of TIWs and as a feedback it returns its signal to the oceanic surface, which interacts in an opposite way with ocean surface fields (currents and temperature) that affect the oceanic dynamical and thermo-dynamical features (Polito et al, 2001;Pezzi et al, 2004;Seo et al, 2007). The involved ocean-atmosphere coupling leads to a negative feedback at TIW scales.…”