COLA Report 15
Multiseasonal Predictions with a Coupled Tropical Ocean Global
Atmosphere System
Ben P. Kirtman, J. Shukla, Bohua Huang, Zhengxin Zhu and Edwin K
Schneider
June 1995
Abstract
The Center for Ocean-Land-Atmosphere Studies anomaly coupled prediction system, using a
sophisticated dynamical model of the tropical Pacific Ocean and the global atmosphere is described.
The resolution of the component models is moderate with the atmospheric spectral model truncated
at triangular total wavenumber 30 and 18 vertical levels. The ocean model is a Pacific basin model
with 0.5o latitude and 1.5o longitude resolution in the wave guide and 20 vertical levels. The
performance of the uncoupled component models motivates the anomaly coupling strategy and has
lead to the development of a simple empirical technique for converting the 850 mb zonal wind into
a zonal surface stress that is used in the prediction experiments described here. In developing ocean
initial conditions, an iterative procedure that assimilates the zonal wind stress based on the simulated
sea surface temperature anomaly error is applied. Based on a sample of thirty 18 month hindcasts,
the predictions have useful skill in the NINO3 region for at least 12 months. The systematic error
of the predictions is shown to be relatively small because the ocean initial conditions are in
reasonable equilibrium with the ocean model. Finally, composites of the warm and cold El Ni¤o
Southern Oscillation (ENSO) events indicate that the model simulates the basic features of ENSO,
but there are errors in the horizontal structure of the sea surface temperature anomaly that potentially
limit the predictability of the model.
Complete copies of this report are available from:
Center for Ocean-Land-Atmosphere Studies
4041 Powder Mill Road, Suite 302
Calverton, MD 20705-3106
(301) 595-7000
(301) 595-9793 Fax
last update: 25 July 1995
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