Electronic Journal of Differential Equations, Vol. 2001(2001), No. 56, pp. 1-13. Title: Dissipative quasi-geostrophic equations with $L^p$ data Author: Jiahong Wu (Oklahoma State Univ., Stillwater, OK , USA) Abstract: We seek solutions of the initial value problem for the 2D dissipative quasi-geostrophic (QG) equation with $L^p$ initial data. The 2D dissipative QG equation is a two dimensional model of the 3D incompressible Navier-Stokes equations. We prove global existence and uniqueness of regular solutions for the dissipative QG equation with sub-critical powers. For the QG equation with critical or super-critical powers, we establish explicit global $L^p$ bounds for its solutions and conclude that any possible finite time singularity must occur in the first order derivative. Submitted June 18, 2001. Published August 3, 2001. Math Subject Classifications: 35Q35, 76U05, 86A10. Key Words: 2D quasi-geostrophic equation; initial-value problem; existence; uniqueness.