Summary of current conditions in the Tropical Pacific

Other TIP pages

TIP homepage

Other TIP 5 pages

TIP 5 Table of contents

Summary

Opening of the meeting

Summary of current conditions in the Tropical Pacific

National reports

Program status reports

Science reports

Recommendations

Acknowledgments

The tropical Pacific at the time of TIP-5 was characterized by weak La Niña conditions. These conditions were the continuation of a cold phase of the ENSO cycle that developed in mid-1995 and persisted, albeit with diminishing intensity, into 1996. Specific manifestations of the La Niña in November 1996 included weak (generally less than 1°C) cold SST anomalies in the equatorial cold tongue, weak warm SST anomalies in the western equatorial Pacific warm pool, and easterly trade winds near to or slightly stronger than normal east of the date line (Figure 1). Subsurface TAO temperature data, and the NCEP ocean analysis system that assimilates these data, indicated that the equatorial thermocline was deeper than normal in the western Pacific and shallower than normal in the eastern Pacific. Consistent with these cold La Niña conditions, convection was reduced over the central equatorial Pacific and enhanced in the far western Pacific in November 1996 (Climate Prediction Center, 1996). The Southern Oscillation Index was slightly negative (-0.2), although it had been positive for nearly all of 1996 beforehand.

A westerly wind burst occurred during the latter half of November 1996 with anomalies of 3-4 m s west of the date line (Fig. 1). However, winds returned to normal by the end of the month. Whether this westerly wind burst and subsequent oceanic response are the harbingers of a switch from La Niña to El Niño conditions in 1997 is uncertain. The role of westerly wind bursts in the ENSO cycle remains a controversial topic, one which will perhaps be clarified by analyses of TOGA-COARE data sets.

According to Climate Diagnostics Bulletin (Climate Prediction Center, 1996), there was no consensus among ENSO forecasting schemes in November 1996 as to the evolution of the coupled ocean-atmosphere system over the next few seasons (although all schemes, to the extent they are initialized by Pacific ocean temperature and/or wind data, make use of TAO data in some form). The NCEP coupled ocean-atmosphere general circulation model system and the NCEP canonical correlation statistical model both predicted warming trends into the first half of 1997. Conversely, the Cane and Zebiak dynamical model forecasting scheme predicted a continuation of cold La Niña conditions into 1997. The Penland and Magorian statistical method predicted near normal conditions in the first half of 1997. It is unclear which of these model forecasts is correct, or what accounts for the spread of the forecasts.

Reference:
Climate Prediction Center, 1996: Climate Diagnostics Bulletin, November 1996. U.S. Dept. of Commerce, Washington, DC, 78 pp.

TAO Project Office
NOAA | Pacific Marine Environmental Laboratory
7600 Sand Point Way NE
Seattle, WA 98115
atlasrt@noaa.gov
Credits | Disclaimer | Privacy Policy