[A-CG38] 海洋と大気の波動・渦・循環の力学

[ACG38-14] Recirculation of atmospheric wave energy associated with idealized MJO events

*相木 秀則¹、福富 慶樹¹、菅野 湧貴²、尾形 友道³、豊田 隆寛⁴、中野 英之⁴ (1.名古屋大学、2.電力中央研究所、3.海洋研究開発機構、4.気象研究所)

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 midlatitude waves in a Boussinesq fluid. For the horizontal component of the energy flux, the same expression has been obtained between equatorial waves and midlatitude waves in the height-dependent framework, which is linked to a scalar quantity inverted from the isentropic perturbation of Ertel's potential vorticity (EPV). This EPV-inverted scalar quantity reduces to the geostrophic streamfunction for midlatitude Rossby waves and vanishes for gravity waves, a novel aspect for considering the universal expression of the energy flux. The expression of the vertical component of the energy flux requires computation of another scalar quantity which may be interpreted as the zonal integral of a variant of streamfunction and may be obtained by the time integration of a prognostic equation. The new energy flux diagnosis scheme, mentioned above, has been tested for three-dimensional Rossby and equatorial Kelvin waves induced by an idealized MJO-like heat forcing. The horizontal recirculation of wave energy is identified in each hemisphere with a smooth transition between equatorial and off-equatorial regions. The vertical flux of wave energy is mostly revealed by the pressure flux component of the energy flux, as it is maintained mainly by equatorial Kelvin waves.