Stability and Instability on the De Gregorio Modification of the Constantin-Lax-Majda model

TL;DR

This paper investigates the stability and instability of the De Gregorio model near the excited state $- ext{sin} 2 heta$, revealing different behaviors based on initial conditions and introducing a new ODE-based analysis method.

Contribution

It provides the first detailed stability analysis near the excited state $- ext{sin} 2 heta$ and introduces a novel ODE approach for spectral analysis in this context.

Findings

Linear and nonlinear instability for broad initial data classes.

Nonlinear stability established for large classes of initial data.

Different stability patterns depending on initial conditions.

Abstract

The Constantin-Lax-Majda (CLM) model and the De Gregorio model which is a modification of the CLM model are well-known for their ability to emulate the behavior of the 3D Euler equations, particularly their potential to develop finite-time singularities. The stability properties of the De Gregorio model on the torus near the ground state $-\sin\theta$ have been well studied. However, the stability analysis near excited states $-\sin k\theta$ with $k\ge 2$ remains challenging. This paper focuses on analyzing the stability and instability of the De Gregorio model on torus around the first excited state $-\sin 2\theta$. The linear and nonlinear instability are established for a broad class of initial data, while nonlinear stability is proved for another large class of initial data in this paper. Our analysis reveals that solution behavior to the De Gregorio model near excited states demonstrates different stability patterns depending on initial conditions. One of new ingredients in our instability analysis involves deriving a second-order ordinary differential equation (ODE) governing the Fourier coefficients of solutions and examining the spectral properties of a positive definite quadratic form emerging from this ODE. The approach of this paper would be applicable to other related models and problems.