Nonlinear Processes in Geophysics (2003) 10: 493–501 Nonlinear Processes

in Geophysics

© European Geosciences Union 2003

Conditional nonlinear optimal perturbation and its applications

M. Mu1, W. S. Duan1, and B.Wang2

1LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

2Department of Meteorology, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii

Received: 12 January 2001 – Revised: 23 July 2003 – Accepted: 13 October 2003

Abstract. Conditional nonlinear optimal perturbation

(CNOP) is proposed to study the predictability of numerical

weather and climate prediction. A simple coupled oceanatmosphere

model for ENSO is adopted as an example to

show its applicability. In the case of climatological mean

state being the basic state, it is shown that CNOP tends to

evolve into El Ni˜no or La Ni˜na event more probably than linear

singular vector (LSV) on the condition that CNOP and

LSV are of the same magnitude of norm. CNOP is also employed

to study the prediction error of El Ni˜no and La Ni˜na

events. Comparisons between CNOP and LSV demonstrate

that CNOP is more applicable in studying the predictability

of the models governing the nonlinear motions of oceans and

atmospheres.