The Center for Ocean-Land-Atmosphere Studies (COLA) has recently developed an anomaly coupled prediction system, using sophisticated dynamical ocean and atmosphere models, that produces skillful forecasts of the tropical Pacific sea surface temperature anomaly (SSTA) up to 1.5 years in advance. The details of this coupled prediction system are described by Kirtman and Schneider (1996) and a brief description of the overall skill of the 30 hindcast predictions was given in the March 1995 issue of this Bulletin. The atmospheric component is the COLA atmospheric general circulation model (AGCM; Kinter et al. 1988) that includes a state-of-the-art land surface model (Xue et al. 1991) and physical parameterizations of radiation, convection, and turbulence. The AGCM is a global spectral model that is horizontally truncated at triangular wavenumber 30 and has 18 unevenly spaced sigma levels in the vertical. The oceanic component is a Pacific basin version of the Geophysical Fluid Dynamics Laboratory (GFDL) ocean model (Pacanowski et al. 1993). In the ocean model there are 20 levels in the vertical with 16 levels in the upper 400 m. The zonal resolution is 1.5^o longitude and 0.5 ^o latitude between 20^oN and 20 ^oS. Further details of the ocean model are provided in Huang and Schneider (1995).

We have separately tested the ocean and atmosphere component models in order to evaluate their performance when forced by observed boundary conditions and improvements have been made that are also incorporated into the coupled prediction system. The effects of atmospheric model zonal wind stress errors have been ameliorated by using the zonal wind at the top of the boundary layer to redefine the zonal wind stress at the surface (Huang and Shukla 1996). We have also developed an iterative procedure for further adjusting the zonal wind stress, based on the simulated SSTA errors (Kirtman and Schneider 1996), that improves initial conditions for coupled forecasts (Kirtman et al. 1996).

The NiZo 3 SSTA root mean squared error (RMSE) and correlation as a function of forecast lead time was shown in the March 1995 issue of this Bulletin. These two verification measures are computed with respect to the observed SSTA. The correlation in the NiZo 3 region remained above 0.6 for lead times of up to 12 months and was larger than that of the persistence forecast for all lead times greater than 3 months.

Figure 1 shows the NiZo 3 time series of the predicted SSTA for three forecasts initialized on the first day of March, April and May of 1996, respectively. Each forecast is run through July 1997. All three forecasts show a consistent evolution with relatively cool SST in boreal spring of 1996 followed by a fairly rapid transition to relatively warm temperatures in boreal winter of 1996-97 that persists through 1997. The predicted SSTAs are near normal during boreal summer of 1996. The April and May 1996 forecasts plateau during boreal winter 1996-97 with some weakening during spring, but remain warm through July 1997. The March 1996 forecast has somewhat stronger anomalies during boreal winter 1996-97 and shows a more rapid decline during spring and summer of 1997. The warming trend through boreal winter 1996-97 seen in all three predictions is consistent with the six forecasts initialized in September 1996 through February 1996 shown in the December 1995 and March 1996 issues of this Bulletin.

The horizontal structure of the ensemble mean (average of all three forecasts) SSTA for boreal fall of 1996, winter 1996-97 and spring of 1997 are shown in the three panels of Fig. 2. The spatial structure and amplitude of the predicted SSTAs for fall 1996 and winter 1996-97 are remarkably similar to forecasts initialized three months earlier shown in the March 1996 issue of this Bulletin. The ensemble averaged forecast indicates positive SSTA beginning in the boreal fall of 1996 with anomalies in excess of 1EC over much of the central Pacific between 5ES-5EN during winter 1996-97. By spring 1997 the ensemble mean indicates some weakening of the positive SSTA. Given the consistency of the forecasts initialized over the previous nine months, our confidence is relatively high that there will be a warm ENSO event during the boreal winter of 1996-97.

Acknowledgments: This research is part of a larger group effort at COLA to study the predictability of the coupled system. Many members (D. DeWitt, M. Fennessy, J. Kinter, L. Marx and E. Schneider) of this group have provided invaluable advice. L. Kikas assisted in managing the data. This work was supported under NOAA grant NA26­GP0149 and NA46­GP0217 and NSF grant ATM­93­21354.

Huang, B., and J. Shukla, 1996: An examination of AGCM simulated surface stress and low level winds over the tropical Pacific ocean. Mon. Wea. Rev., 124, in press.

Huang, B., and E. K. Schneider, 1995: The response of an ocean general circulation model to surface wind stress produced by an atmospheric general circulation model. Mon. Wea. Rev., 123, 3059-3085.

Kinter, J. L. III, J. Shukla, L. Marx and E. K. Schneider, 1988: A simulation of winter and summer circulations with the NMC global spectral model. J. Atmos. Sci., 45, 2486­2522.

Kirtman, B. P., J. Shukla, B. Huang, Z. Zhu, E. K. Schneider, 1996: Multiseasonal predictions with a coupled tropical ocean global atmosphere system. Mon. Wea. Rev., 124, in press.

Kirtman, B. P. and E. K. Schneider 1996: Model based estimates of equatorial Pacific wind stress. J. Climate, 124, 1077-1091.

Pacanowski, R. C., K. Dixon, A. Rosati, 1993: The GFDL modular ocean model users guide, version 1.0. GFDL Ocean Group Tech. Rep. No. 2.

Reynolds, R.W., and T. M. Smith, 1995: A high resolution global sea surface temperature climatology. J. Climate, 8, 1571­1583.

Xue, Y., P. J. Sellers, J. L. Kinter III, and J. Shukla, 1991: A simple biosphere model for global climate studies. J. Climate, 4, 345­364.

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