9A.2 Nonlinear structure and evolution of African easterly waves (2008

9A.2

Nonlinear structure and evolution of African easterly waves

Nathan R. Hardin, North Carolina State University, Raleigh, North Carolina 27695-8208, NC

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.