Midlatitude baroclinic Rossby waves
in a high-resolution OGCM simulation

Kunihiro Aoki

ABSTRACT

We investigate the effects of bottom pressure decoupling and baroclinic mean flow on mid-latitude oceanic Rossby wave dynamics, using a high-resolution OGCM. To examine these effects on the baroclinic Rossby wave, composite analysis is firstly carried out for westward propagating signals of depth anomaly of permanent thermocline (27.0 sigma-theta surface) along 32N in the simulation. The phase speed is almost 1.5 times larger than that expected from the standard theory (here, the standard theory means the assumption of flat bottom and no-mean flow ocean), and the wave has a surface intensified structure, which is in good agreement with the theoretical solution including mean flow and bottom pressure decoupling effects. The theoretical phase speed including both effects exceeds that of the wave in the simulation, where their differences are eliminated by considering the effect of finite wavelength. We also study the meridional distribution of the mid-latitude phase s peed in the simulation using frequency-wavenumber spectrum. The theory including mean flow, bottom pressure decoupling and finite wavelength effects reproduces the meridional distribution very well. The dominant factor enhancing the phase speed is the bottom pressure decoupling relating to rough bottom topography, especially in the south Pacific because of relatively strong bottom stratification. North of 30ºN, the baroclinic mean flow strongly contributes to the enhancement of the phase speed, suggesting the importance of the mode water in the Rossby wave speed.