Mock-integrability and stable solitary vortices

Localized soliton-like solutions to a (2+1)-dimensional hydro-dynamical evolution equation are studied numerically. The equation is the so-called Williams–Yamagata–Flierl equation, which governs geostrophic fluid in a certain parameter range. Although the equation does not have an integrable structure in the ordinary sense, we find there exist shape-keeping solutions with a very long life in a special background flow and an initial condition. The stability of the localization at the fusion process of two soliton-like objects is also investigated. As for the indicator of the long-term stability of localization, we propose a concept of configurational entropy, which has been introduced in analysis for non-topological solitons in field theories.