The vertical structure of annual wave energy flux in the tropical Indian Ocean

Li, Zimeng; Aiki, Hidenori; Nagura, Motoki; Ogata, Tomomichi

doi:10.1186/s40645-021-00432-9

Cited by 4 publications

(1 citation statement)

References 57 publications

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“…8a. The AGC17 scheme was used for investigating waves in the Indian Ocean (Ogata and (16b) Aiki 2019;Li and Aiki 2020, 2022Li et al 2021), the Atlantic Ocean (Song and Aiki 2020Song et al 2023a, b), the Pacific Ocean (Toyoda et al 2021(Toyoda et al , 2023, and the atmosphere (Aiki et al 2021). In Toyoda et al (2021Toyoda et al ( , 2023 and Song and Aiki (2023), the horizontal variation of gravity wave speed c was considered in their calculation of the pseudo-streamfunction.…”

Section: Appendix B: Case Of Ekman Spiral Velocitymentioning

confidence: 99%

Wind stress curl as a driving force of annual waves in the upper ocean for interpreting energetics at all latitudes

Ye,

Aiki

2024

Prog Earth Planet Sci

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The dynamics of waves and eddies in the upper ocean plays an important role in the climate variation of tropical and subtropical regions. Previous diagnoses for annual Rossby waves in oceanic model outputs manifested zonally alternating signals (ZASs) in the time-averaged distributions of wind input as well as pressure-flux divergence terms in the budget equation of wave energy. This is the case when the annual mean of the wind input is estimated as the inner product of simulated velocity vector and wind stress vector in previous studies. The present study proposes a new mathematical expression for estimating the wind input that is analogous to one derived from the quasi-geostrophic potential vorticity equation. Namely, the wind input is estimated as the negative of the product of pseudo-streamfunction and wind stress curl, the latter of which is associated with the horizontal divergence of Ekman velocity. This can be interpreted as replacement of kinetic energy input with gravitational potential energy input. Pseudo-streamfunction in the present study is inverted from Ertel’s potential vorticity anomaly and is seamlessly available at all latitudes. This contrasts with the quasi-geostrophic streamfunction which is singular at the equator. The new expression enables reducing ZASs in the horizontal distributions of both wind input and pressure-flux divergence terms, without harming the qualitative advantage of energy flux vectors to indicate the group velocity of waves at all latitudes.

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Section: Appendix B: Case Of Ekman Spiral Velocitymentioning

confidence: 99%

Wind stress curl as a driving force of annual waves in the upper ocean for interpreting energetics at all latitudes

Ye,

Aiki

2024

Prog Earth Planet Sci

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Effective generation mechanisms of tropical instability waves as represented by high-resolution coupled atmosphere–ocean prediction experiments

Toyoda,

Urakawa,

Aiki

et al. 2023

Sci Rep

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Cusp-shaped fluctuations of the sea surface temperature (SST) front in the tropical Pacific, now known as tropical instability waves (TIWs), were discovered by remote sensing in the 1970s. Their discovery was followed by both theoretical and analytical studies, which, along with in situ observations, identified several possible generation mechanisms. Although modeling studies have shown that TIWs strongly influence the heat budget, their influence on local variations of realistically initialized predictions is not yet understood. We here evaluate a series of medium-range (up to ~ 10 days) coupled atmosphere–ocean predictions by a coupled model with different horizontal resolutions. Observational SST, surface wind stress, heat flux, and pressure data showed that representation of temporally and spatially local variations was improved by resolving fine-scale SST variations around the initialized coarse-scale SST front fluctuations of TIWs. Our study thus demonstrates the advantage of using high-resolution coupled models for medium-range predictions. In addition, analysis of TIW energetics showed two dominant sources of energy to anticyclonic eddies: barotropic instability between equatorial zonal currents and baroclinic instability due to intense density fronts. In turn, the eddy circulation strengthened both instabilities in the resolved simulations. This revealed feedback process refines our understanding of the generation mechanisms of TIWs.

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The energy flux of three-dimensional waves in the atmosphere: Exact expression for a basic model diagnosis with no equatorial gap

Aiki

Fukutomi

Kanno

et al. 2021

Journal of the Atmospheric Sciences

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A model diagnosis for the energy flux of off-equatorial Rossby waves in the atmosphere has previously been done using quasi-geostrophic equations and is singular at the equator. The energy flux of equatorial waves has been separately investigated in previous studies using a space-time spectral analysis or a ray theory. A recent analytical study has derived an exact universal expression for the energy flux which can indicate the direction of the group velocity for linear shallow water waves at all latitudes. This analytical result is extended in the present study to a height-dependent framework for three-dimensional waves in the atmosphere. This is achieved by investigating the classical analytical solution of both equatorial and off-equatorial waves in a Boussinesq fluid. For the horizontal component of the energy flux, the same expression has been obtained between equatorial waves and off-equatorial waves in the height-dependent framework, which is linked to a scalar quantity inverted from the isentropic perturbation of Ertel’s potential vorticity. The expression of the vertical component of the energy flux requires computation of another scalar quantity that may be obtained from the meridional integral of geopotential anomaly in a wavenumber-frequency space. The exact version of the universal expression is explored and illustrated for three-dimensional waves induced by an idealized Madden-Julian Oscillation forcing in a basic model experiment. The zonal and vertical fluxes manifest the energy transfer of both equatorial Kelvin waves and off-equatorial Rossby waves with a smooth transition at around 10°S and around 10°N. The meridional flux of wave energy represents connection between off-equatorial divergence regions and equatorial convergence regions.

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The vertical structure of annual wave energy flux in the tropical Indian Ocean

Cited by 4 publications

References 57 publications

Wind stress curl as a driving force of annual waves in the upper ocean for interpreting energetics at all latitudes

Wind stress curl as a driving force of annual waves in the upper ocean for interpreting energetics at all latitudes

Effective generation mechanisms of tropical instability waves as represented by high-resolution coupled atmosphere–ocean prediction experiments

The energy flux of three-dimensional waves in the atmosphere: Exact expression for a basic model diagnosis with no equatorial gap

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