Predictability in the extended range

Abstract

A two-level spherical quasi-geostrophic model is formulated for predictability experiments. The stationary external forcing for this model is calculated from observations. Both barotropic and baroclinic forcings are required in order to achieve a realistic model climatology. Realistic transient behavior is also present in the model. The most notable difference is that the observed transient kinetic energy has more energy in the smallest scales. Predictability experiments have an initial rms doubling time of approximately two days. This growth rate along with an initial error of about half the initial error of present operational models produces an rms error equal to the climatoloigcal rms error and a correlation of 0.5 cm on about day 12 of the forecast. At the largest scales, this limiting point is reached shortly thereafter. The error continues to growth at a decreasing rate until at about 30 days the forecast skill is extremely small and comparable to the skill of a persistence forecast. -from Author