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 4, France
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 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, ERS1-2 winds from may 1992 until september 2000, QuikSCAT winds from october 2000) to the simulated winds as in Chen et al. (1995). The skill of the models for the NINO3 SST index over various periods and for the 1997-1998 El Niño is presented in Dewitte et al. (2002).
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 Jun-Jul-Aug 2008 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). Model 1 (Model 2 (Figure 2)) is predicting a return to neutral (slightly warm ) conditions in 2009.
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 ENSO simulation and prediction with intermediate coupled models of the Tropical Pacific: A case study for the 1997-1998 El Niño. Geoph. Res. Lett., vol. 29, no. 14, 1666, 10.1029/2001GL014452.
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 ENSO predictability an prediction, J. Climate, 11, 2804-2822
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 during DJF
2008/09, MAM 2009, JJA 2009 and SON 2009. Each forecast is an ensemble average
of 12 sets of prediction runs initialized from wind forced model outputs perturbated by random noise. Observed data through 30st
of November 2008 was used to produce the forecast. Contour interval 0.5°C.
Regions with SSTA amplitude larger than 0.5°C (lower than -0.5°C) are in yellow-orange
(blue). The longuest wind stress arrow on each map
corresponds to the value indicated on the right hand side. Only wind stress
anomalies for which wind modulus is larger than 0.1 Dyn/cm2
Fig.2: same as Fig. 1 but for the coupled model using the dynamical atmosphere.