11:45 AM - 12:00 PM
[ACG47-11] Eastward translation of heton-like vortex pairs on a β-plane
Keywords:Quasi-geostrophic eddies, β-plane, heton, vortex pair
A structure where two vortices with opposite signs exist in different layers and interact with each other is called a heton. Although there are many papers treating hetons, the behavior of heton-like eddies on a β-plane is still unclear. This study investigates the dynamics of heton-like eddies on the β-plane using a two-layer quasi-geostrophic model with equal layer thickness, mainly focusing on meridionally asymmetric heton-like vortex pairs translating eastwards. First, we consider the evolution of a purely baroclinic eddy. It is known that negative vortices on the β-plane move southwest, while positive vortices move northwest. This property causes vertically stacked vortices to separate north-south with the negative vorticity to the south and the positive vorticity to the north. The two vortices in this structure advect each other eastwards. Therefore, if the vortices are strong enough, they can overcome the westward advection due to β, and this system will translate eastward. When the strengths of the upper and lower vortices differ, the stronger vortex moves westward, aligning the vortices east-west. For example, if the negative vortex is stronger, the vortex pair moves south. However, the vortices do not move too far south and instead change direction to the east. Because the β-effect is weak, even in the situation translating eastward, the negative circulation in the south is greater than the positive circulation in the north, maintaining a meridionally asymmetric structure. When the vortex pair moves south, it also carries the surrounding fluid, which forms positive circulation. The balance between self-advection due to the vortex pair structure and the circulation of the background field is thought to allow for the forming of a heton-like vortex pair with a meridionally asymmetric structure translating eastward.