Density at the Surface [kg/m³] The figures show the results of a process study, in which the temporal and spatial evolution of a baroclinic perturbation wave has been investigated. The figures depict the calculated surface density distribution at two, four, six, and eight days after the initialization of the perturbation. While the perturbation wave increases because of the ageostrophic transport of vorticity, the frontal zones are intensifying and eddies are evolving. After eight days, the wave amplitude has reached its maximum and the perturbation starts to decay with eddy-detachment.