# Global Flows with Invariant Measures for the Inviscid Modified SQG Equations

## TL;DR

This paper constructs invariant measures and proves the existence of solutions with arbitrarily large lifespan for a family of modified SQG equations that interpolate between 2D Euler and SQG, extending understanding of their dynamics.

## Contribution

It introduces invariant measures for the modified SQG family and demonstrates long-time solutions for generic initial data in a rough Sobolev space.

## Key findings

- Invariant measure construction for mSQG equations.
- Existence of solutions with arbitrarily large lifespan.
- Results hold for initial data in full measure set.

## Abstract

We consider the family known as modified or generalized surface quasi-geostrophic equations (mSQG) consisting of the classical inviscid surface quasi-geostrophic (SQG) equation together with a family of regularized active scalars given by introducing a smoothing operator of nonzero but possibly arbitrarily small degree. This family naturally interpolates between the 2D Euler equation and the SQG equation. For this family of equations we construct an invariant measure on a rough $L^2$-based Sobolev space and establish the existence of solutions of arbitrarily large lifespan for initial data in a set of full measure in the rough Sobolev space.