Hasselmann, Klaus MPI for Meteorology, Max Planck Society;
JD093iD09p11015.pdf (Publisher version), 593KB
Hasselmann, K. (1988). PIPs and POPs: The reduction of complex dynamical systems using principal interaction and oscillation patterns. Journal of Geophysical Research: Atmospheres, 93, 11015-11021. doi:10.1029/JD093iD09p11015.