Two-dimensional unsteady incompressible flows in which the potential vorticity (PV) plays a key role are examined in this study. through the development of the evolution equation for the PV gradient. For the case where the PV is conserved. precise statements concerning topology-conservation are presented. https://www.bekindtopets.com/limited-stock-Original-U-S-Vietnam-War-Era-Operation-Igloo-White-Seismic-Sensor-Inert-Rocket-great-price/