Nonlinear structure and evolution of African easterly waves

Three dimensional isentropic potential vorticity (IPV) fields are used to describe the structure and evolution of African easterly waves (AEWs) over the Atlantic. Using gridded data from the European centre for medium range weather forecasts (ECMF), a census of localized PV maxima embedded within the waves is created. Composite horizontal and vertical structure of these localized coherent structures are examined and measures of non-linearity are computed. Along track evolution of the vertical and horizontal structures of select cases are also examined. Numerical experiments using a barotropic model linearized about observed background IPV states are performed to contrast the evolution and tracks of idealized disturbances with those of the observed AEWS.