Nonlinear Processes in Geophysics www.nonlin-processes-geophys.net 1023-5809 1607-7946 12 1 2005 10.5194/npg-12-129-2005 http://www.nonlin-processes-geophys.net/12/129/2005/ http://www.nonlin-processes-geophys.net/12/129/2005/npg-12-129-2005.html http://www.nonlin-processes-geophys.net/12/129/2005/npg-12-129-2005.pdf 129 138 2005-01-28 Statistical characteristics of irreversible predictability time in regional ocean models P. C. Chu L. M. Ivanov Naval Ocean Analysis and Prediction Laboratory Department of Oceanography, Naval Postgraduate School Monterey, California, USA Marine Hydrophysical Institute, Sevastopol, Ukraine Probabilistic aspects of regional ocean model predictability is analyzed using the probability density function (PDF) of the irreversible predictability time (IPT) (called τ-PDF) computed from an unconstrained ensemble of stochastic perturbations in initial conditions, winds, and open boundary conditions. Two-attractors (a chaotic attractor and a small-amplitude stable limit cycle) are found in the wind-driven circulation. Relationship between attractor's residence time and IPT determines the τ-PDF for the short (up to several weeks) and intermediate (up to two months) predictions. The τ-PDF is usually non-Gaussian but not multi-modal for red-noise perturbations in initial conditions and perturbations in the wind and open boundary conditions. Bifurcation of τ-PDF occurs as the tolerance level varies. Generally, extremely successful predictions (corresponding to the τ-PDF's tail toward large IPT domain) are not outliers and share the same statistics as a whole ensemble of predictions.