Changes in Regional Energetics over the North Pacific5 South China Sea and the Indonesian Seas during Winter

Abstract

The energy equation was applied to specific limited to investigate the effect of barotropic and baroclinic processes upon area-averaged eddy kinetic energy during the northern winter. At 200 mb, area-averaged eddy kinetic energy was sometimes well above its 90-day winter mean over the extratropical North Pacific, tropical central North Pacific and South China Sea. Almost simultaneously, it was below its seasonal mean over the Timor Sea. Such occasions exhibited certain definite regional energetic characteristics. Upper zonal mean flows over the extratropical North Pacific were barotropically stable and received large amounts of energy from eddy motions via barotropic interactions. In the tropical central North Pacific, eddy motions at 200 and 300 mb were maintained almost equally by barotropic instability and lateral coupling. This region imported substantial amounts of energy across the northern boundary from the extratropical North Pacific. Over the South China Sea (Timor Sea), the conversion of eddy available potential to kinetic energy was more (less) pronounced than usual.