The East Australian Current (EAC) is an important western boundary current of the South Pacific subtropical Circulation with high mesoscale eddy kinetic energy (EKE). Based on satellite altimeter observations and outputs from the eddy-resolving ocean general circulation model (OGCM) for the Earth Simulator (OFES), the seasonal variability of EKE and its associated dynamic mechanism in the EAC region are studied. High EKE is mainly concentrated in the shear-region between the poleward EAC southern extension and the equatorward EAC recirculation along Australia's east coast, which is confined within the upper ocean (0-300 m). EKE in this area exhibits obvious seasonal variation, strong in austral summer with maximum (465±89 cm² s-²) in February and weak in winter with minimum (334±48 cm² s-²) in August. Energetics analysis from OFES suggests that the seasonal variability of EKE is modulated by the mixed instabilities composed of barotropic and baroclinic instabilities confined within the upper ocean, and barotropic instability (baroclinic instability) is the main energy source of EKE in austral summer (winter). The barotropic process is mainly controlled by the zonal shear of meridional velocities of the EAC southern extension and the EAC recirculation. The poleward EAC southern extension and the equatorward EAC recirculation are synchronously strengthened (weakened) due to the local positive (negative) sea level anomalies (SLA) under geostrophic equilibrium, and the barotropic instability dominated by zonal shear is enhanced (slackened), which results in a high (low) level of EKE in the EAC region.

中文翻译：

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东澳洋流区涡动能的季节变化

东澳大利亚流（EAC）是南太平洋副热带环流重要的西边界流，具有高中尺度涡动能（EKE）。基于卫星高度计观测和地球模拟器 (OFES) 的涡分辨海洋大气环流模型 (OGCM) 的输出，研究了 EKE 的季节变化及其在 EAC 区域的相关动力机制。高EKE主要集中在澳大利亚东海岸极地EAC南伸与赤道EAC环流之间的剪切区，局限于上层海洋（0~300 m）。该区EKE季节变化明显，南半球夏季强，2月最大(465±89 cm² s-²)，冬季弱，8月最小(334±48 cm² s-²)。OFES 的能量学分析表明，EKE 的季节性变化受限于上层海洋的正压和斜压不稳定性组成的混合不稳定性的调制，而正压不稳定性（斜压不稳定性）是南方夏季（冬季）EKE 的主要能量来源。正压过程主要受控于 EAC 南伸和 EAC 环流经向速度的纬向切变。由于地转平衡下局部正（负）海平面异常（SLA），极地EAC南伸和赤道EAC环流同步加强（减弱），以纬向切变为主的正压不稳定增强（减弱），导致在 EAC 地区处于高（低）水平的 EKE。