[Previous Article] [Next Article]






Forecast of Pacific-Indian Ocean SSTs Using

Linear Inverse Modeling

contributed by Cecile Penland1, Klaus Weickmann2 and Catherine Smith1

1Climate Diagnostics Center, CIRES, University of Colorado, Boulder, Colorado

2Climate Diagnostics Center, ERL/NOAA/CDC, Boulder, Colorado

Using the methods previously described in issues of the Experimental Long-Lead Forecast Bulletin, and in Penland and Magorian (1993), the pattern of IndoPacific sea-surface temperature anomalies (SSTAs), the SSTA in the Niño 3 region (6oN-6oS, 90 -150 oW), as well as the SSTA in the Niño 4 region (6oN-6oS, 150 oW-160 oE), are predicted. A prediction at lead time is made by applying a statistically-obtained Green function G() to an observed initial condition consisting of SSTAs in the IndoPacific basin. Three-month running means of the temperature anomalies are used, the seasonal cycle has been removed, and the data have been projected onto the 20 leading empirical orthogonal functions (EOFs) explaining about 70% of the variance. The Niño 3 region has an RMS temperature anomaly of about 0.7 oC; the inverse modeling prediction method has an RMS error of about 0.5oC at a lead time of nine months and approaches the RMS value at lead times of 18 months to two years. Data have been provided by NCEP, courtesy of R.W. Reynolds. The COADS 1950-79 climatological annual cycle has been removed.

The predicted IndoPacific SSTA patterns based on the SON 1996 initial condition for the following DJF, MAM, JJA and SON 1997 are shown in Fig. 1 (contour interval = 0.2oC). Figure 2a shows the predictions (light solid lines) of the Niño 3 anomaly for initial conditions DJF 1995-96, JFM, FMA, ..., SON 1996. Light dotted lines indicate the 1 standard deviation expected error for the prediction assuming a perfect model based on the JFM 1996 initial conditions. Figure 2b is the same, but for the Niño 4 region. Verifications including the truncation error (heavy solid line) are also shown.

The current forecast predicts weaker development of cold anomalies than have previous forecasts, with warm anomalies in the Niño 3 region appearing by mid-1997. It is clear from Fig. 2 that the moderate cold event predicted using summer 1996 initial conditions did not occur, and probably won't. Indeed, this year's most skillful forecast seems to be that based upon JFM initial conditions (see the March 1996 issue of the Climate Diagnostics Bulletin). This conclusion is supported by Fig. 3, which shows the pattern correlation between observed Pacific SSTA and SSTA predicted using DJF 1995-96 through JAS 1996 initial conditions. The forecast based on JFM initial conditions is clearly the most skillful in predicting the Pacific SSTA pattern.

Penland, C. and T. Magorian, 1993: Prediction of Niño 3 sea-surface temperatures using linear inverse- modeling. J. Climate, 6, 1067-1076.

Fig. 1. Linear inverse modeling forecasts of SST anomalies, relative to the standard 1950-79 COADS climatology both for the training period (1950-84) and for these forecasts. Forecast anomalies are projected onto 20 leading EOFs, based on Sep-Oct-Nov 1996 initial conditions (top panel). Contour interval is 0.2oC. Positive anomalies are represented by heavy solid lines, negative anomalies by dashed lines. SST data have been provided by NCEP. Prediction by linear inverse modeling is described in Penland and Magorian (1993).

Fig. 2. (a): Inverse modeling predictions (light solid lines) of Niño 3 SSTA for initial conditions DJF 91995-96, JFM, FMA, ..., SON 1996. Light dotted lines indicate the 1 standard deviation expected error bars for the prediction assuming a perfect model based on the JFM 1996 initial condition. Anomalies are defined as explained in Fig. 1 caption, and projected onto 20 leading EOFs. Heavy solid line indicates the verification as reconstructed from the 20 leading EOFs. (b): As in (a) except for Niño 4.

Fig. 3. The pattern correlation between observed Pacific SSTA and SSTA predicted using DJF 1995-96 through JAS 1996 initial conditions.



[Previous Article] [Next Article]