The Climatological Horizontal Pattern of Energy Flux in the Tropical Atlantic as Identified by a Unified Diagnosis for Rossby and Kelvin Waves

摘要

This study investigates the horizontal distribution of wave energy flux in the tropical Atlantic Ocean using shallow-water model experiments for three gravest baroclinic modes forced by climatological winds. This is the first attempt to apply a unified diagnostic scheme to the analysis of energy fluxes associated with both Rossby waves (RWs) and Kelvin waves (KWs) in the tropical Atlantic Ocean. Those analyses were difficult in previous studies owing to the difference of equatorial and quasigeostrophic dynamics. The scheme yields the transfer route (i.e., trajectories by group velocity vector) of wave energy originating from both local wind forcing and boundary reflection. The meridional flux of wave energy crossing two zonal sections (at 3 degrees N and at 2 degrees S) is examined for understanding where the equatorial and off-equatorial regions interconnect. Equatorward energy fluxes into the basin interior are found mainly on the zonal section in the Northern Hemisphere (at 3 degrees N), indicating the radiation of RWs from the Guinea coast. At the equator, seasonal transition in May from eastward wind anomaly to westward anomaly yields a significant energy input at the central basin that radiates both RWs and KWs. The energy flux of these RWs arrives at the western boundary in September, followed by reflection of KWs to yield eastward transbasin energy fluxes in October-December. The analysis also identifies an unexpected wind input in May at 4 degrees S which induces both RWs and inertial gravity waves.