SST predictions with an intermediate coupled model of the tropical Pacific.
contributed by Boris Dewitte1, Dasha Gushchina 2 and Yves duPenhoat 1
1LEGOS/CNES/IRD 14 Av. E. Belin, 31401 Toulouse Cedex
2Meteorological Department, Geographical Faculty, Moscow State University, Vorobyevy gory, Moscow, 119899, Russia
Forecasts of the tropical Pacific SST are
presented here using two intermediate coupled models. The oceanic component
consists in a three baroclinic mode ocean and the mixed layer model differs
from the Cane and Zebiak (1987) model in the parameterization of the vertical
advection terms and the basic state (cf. Dewitte, 2000). The atmospheric
component is either a statistical atmospheric model based on the singular value
decomposition (SVD) of observed sea surface temperature (SST) and wind stress
anomalies (see Périgaud et al., 2000) or a Gill(1980)'s dynamical tropical
atmosphere. Initial conditions for the prediction runs are produced in a
coupled mode by nudging the observed winds (FSU winds for the period 1961-1992,
Figure 1 shows model predicted SST and wind stress anomalies in the tropical Pacific for the next four seasons in the case of the statistical atmosphere (model 1). These are ensemble averages of 12 forecasts started from Sep-Oct-Nov 2006 conditions. For producing the initial conditions of the individual forecasts, random noise was added to the system with an approach similar to Kirtman and Schopf (1998). Models 1 and 2 (Figure 2) are predicting slightly warm conditions for 2007.
Caveat: The forecasts shown above are experimental in nature. The reader is forewarned that the methods/forecasts are new and subject to future change and improvement.
Chen, D., S. E. Zebiak, A. J. Busalacchi, and M. A. Cane, 1995: An improved procedure for El Niño forecasting: Implication for predictability. Science, 269, 1699-1702.
Dewitte B., 2000: Sensitivity of an intermediate coupled ocean-atmosphere model of the tropical Pacific to its oceanic vertical structure. J. Climate, 13, 2363-2388.
Dewitte B., D. Gushchina, Y. duPenhoat and S.
Lakeev, 2002: On the importance of subsurface variability for
Gill, A., Some simple solutions heat-induced tropical circulation. Q. J. R. Meteorol. Soc., 106, 447-462, 1980.
Kirtman, B. P. and P. S. Schopf, 1998:
Decadal variability in
Périgaud C. C. Cassou, B. Dewitte, L.-L. Fu and D. Neelin, 2000: Using data and intermediate coupled models for seasonal-to-interannual forecasts. Mon. Wea. Rev., 128, 3025-3049.
Zebiak, S. E. and M. A. Cane, 1987: A model El Niño-Southern Oscillation. Mon. Wea. Rev., 115, 2262-2278.
model forecast of tropical Pacific SST (°C) and wind stress (Dyn/cm2)
anomalies for DJF 2006/2007, MAM 2007, JJA 2007 and
Fig.2: same as Fig. 1 but for the coupled model using the dynamical atmosphere.