P-Vector Spirals and Determination of Absolute Velocities

A simple method to invert the absolute geostrophic velocity on potential-density surfaces is developed based on McDougall's (1988) conservation statements on potential-density surfaces and Chu's (1995) and McDougall's (1995) P-vector concept. This method has a capability to handle a system with diapycnal velocities and non-coincidence of potential-density and neutral surfaces. The validity of the inversion is the existence of the P-vector spirals instead of the existence of the velocity spirals (usually called the -spirals). We use a climatological T,S dataset for the Atlantic Ocean from the National Oceanographic Data Center (NODC) to show the benefit of using P-vector spirals in inverting the velocity field.