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Summary of current conditions in the Equatorial Pacific

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Dr. McPhaden summarized current environmental conditions in the equatorial Pacific as observed from the real-time data stream of the TOGA-TAO Array. Sea surface temperature (SST) had shown progressive warming since mid-1994 near the date line where, by October, anomalies exceeded 2C and absolute temperatures were above 30C (Figure 1). Trade wind strength over and to the west of the SST anomalies was reduced by 3 - 4 m/s; and north of the equator, the trades between 150E and 180 were supplanted by westerly winds at speeds of 1 - 3 m/s. In the eastern Pacific, seasonal development of the equatorial cold tongue was evident, although temperatures were warmer than normal by over 1C east of 125W. Some of this cold tongue warming may have been mediated by the passage of downwelling equatorial Kelvin waves excited by westerly wind bursts in the western Pacific in August September and October 1994. In October, the thermocline (as measured by the 20C isotherm depth) was 20 - 30 m deeper than normal in the eastern Pacific and shallower than normal by a 10 - 20 m in the western Pacific.

According to NOAA's Climate Diagnostics Bulletin (Climate Analysis Center, 1994), the Southern Oscillation Index (SOI) was negative in October, continuing a tendency of below zero values that has extended back to 1990. The five month running mean SOI was almost as negative as the minimum values observed during the 1986 - 87 El Nino and the 1991 - 93 El Nino. In addition, although weak in October, anomalous deep convection had developed over the warm water near the date line. Thus, conditions in the equatorial Pacific indicate the possible development of mature phase El Nino conditions in the coming months. These inferences drawn from observations are supported by climate forecast schemes (both statistical and dynamical model based) that indicate the continuation of unusually warm equatorial SSTs in the eastern Pacific through mid-1995.

Reference

Climate Analysis Center, 1994: Climate Diagnostics Bulletin, October 1994. U.S. Dept. of Commerce, Washington, DC., 77 pp.

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