An Empirical Tropical Instability Wave-induced Wind Stress Model in the Equatorial Pacific and its Incorporation into the Ocean Model

Abstract

Satellite observations revealed that there is a close relationship between perturbations of sea surface temperature (SST) and wind stress (τ) induced by tropical instability waves (TIWs; SST TIW and τ TIW ). Using the empirical relationship observed between TIW-induced wind stress divergence (curl) and downwind (crosswind) SST gradients, this study establishes a TIW-induced wind stress field perturbation model τ TIW = F(SST). This empirical model solves τ TIW from the TIW-induced wind stress divergence and curl, which are estimated from the downwind and crosswind SST gradients. This empirical τ TIW = F(SST) model can be incorporated into the ocean model to take into account the effect of τ TIW . By comparing two experiments with and without the τ TIW effect, this study demonstrates that τ TIW has a substantial effect on the equatorial Pacific heat budget and induces the long-term mean SST to exhibit a 0.2°C difference, which is consistent with previous studies. RÉSUMÉ [Traduit par la rédaction] Les observations émanant de satellites révèlent qu'il existe une relation étroite entre les ondes d'instabilité tropicales (TIW), et les perturbations de la température de surface de la mer (SST) et de la tension du vent (τ) que ces ondes induisent, soit SST TIW et τ TIW . Nous élaborons ici un modèle, τ TIW = F(SST), de perturbation du champ de la tension du vent que génèrent les TIW, et ce, en appliquant la relation empirique observée entre la divergence (le rotationnel) de la tension du vent et le gradient des SST en aval (perpendiculaire au vent), que produisent les TIW. Ce modèle empirique résout τ TIW à partir de la divergence et du rotationnel de la tension du vent qu'induisent les TIW, et ceux-ci sont estimés à partir des gradients de SST perpendiculaire au vent et en aval. Ce modèle empirique, τ TIW = F(SST), peut s'insérer dans le modèle océanique pour prendre en compte l'effet de τ TIW . En comparant des simulations avec et sans l'effet τ TIW , nous démontrons que τ TIW influe considérablement sur le bilan thermique du Pacifique équatorial et génère à long terme une différence de 0,2°C de la moyenne de la SST, ce qui concorde avec des études antérieures.

Assessing feedback of tropical instability wave‐induced wind stress perturbations in the equatorial Pacific

“…Then, the derived (div τ , curl τ ) TIW are used to solve the wind stress field perturbations ( τ x , τ y ) TIW as detailed in Wei et al . () and below.…”

“…Detailed model settings are given in Wei et al . (, ). This model has been demonstrated to simulate The Kuroshio Current and TIW activities adequately (Wei et al, , ).…”

“…The longitudinal resolution is 1/8 and the latitudinal resolution is 1/8 × cos(latitude), with 50 scoordinate levels in the vertical. Detailed model settings are given in Wei et al (2017Wei et al ( , 2018b. This model has been demonstrated to simulate The Kuroshio Current and TIW activities adequately (Wei et al, 2018a(Wei et al, , 2018b.…”

“…As such, this study aimed to isolate the TIW‐induced wind stress divergence and curl components and examine their respective effect on the ocean. To achieve this, we assessed the feedback of τ TIW using an empirical τ TIW model with respect to SST, that is, τ TIW = F (SST), which was established based on the empirical relationship between TIW‐induced wind stress divergence/curl and downwind/crosswind SST gradients using an inverse method (Wei et al, ). This empirical τ TIW model was incorporated into a high‐resolution ocean model to conveniently examine the respective effects of TIW‐induced wind stress curl and divergence components.…”

“…where the coefficients a 1 and a 2 denote the regression coefficients between each other derived from satellite observations. Then, the derived (div τ, curl τ) TIW are used to solve the wind stress field perturbations (τ x , τ y ) TIW as detailed in Wei et al (2018b) and below. Denoting y = (div τ, curl τ) T (unit: Nm -2 /10, 000 km) and x = (τ x , τ y ) T (unit: Nm -2 ), it is simple to calculate divergence and curl from the wind stress vector using the equation:…”