U.S. Dept. of Commerce / NOAA/ OAR / PMEL / Publications
Genesis and Evolution of the 1997-98 El Niño
Michael J. McPhaden
Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, Washington
Science, 283, 950954 (1999)
Copyright ©1999 American Association for the Advancement of Science. Further electronic distribution is not
allowed.
Gallery of Figures and Tables
Figure 1. Time-series sections of surface zonal wind (left), SST (middle), and outgoing longwave radiation (OLR)
(right) from September 1996 to August 1998. Analyses are based on 5-day averages for between 2°N and 2°S for the
TAO data, and between 2.5°N and 2.5°S for OLR. Black squares on the abscissas of the wind and SST plots indicate
longitudes of data availability at the start (top) and end (bottom) of the time-series record. Positive winds are
westerly, negative winds are easterly. OLR values below about 235 W m indicate an
increased likelihood of deep cumulus cloudiness and heavy convective precipitation. OLR data are from the National
Centers for Environmental Prediction.
Figure 2. Time versus longitude sections of anomalies in surface zonal wind (left), SST (middle), and 20°C
isotherm depth (right) from September 1996 to August 1998. Analysis is based on 5-day averages between 2°N and
2°S of moored time-series data from the TAO array. Anomalies are relative to monthly climatologies that were cubic
spline-fitted to 5-day intervals. The monthly SST climatology is based on data from 195079 (Reynolds and Smith,
1995). The monthly wind climatology is based on data from 194689 (Woodruff et al., 1987). The monthly
20°C isotherm depth climatology is based on subsurface temperature data primarily from 197091 (Kessler, 1990; Kessler
and McCreary, 1993). Positive winds are westerly, and positive 20°C isotherm depths indicate a deeper
thermocline. Black squares on the abscissas indicate longitudes where data were available at the start (top) and end
(bottom) of the time series.
Figure 3. Monthly averaged sea-surface temperature (in degrees C) for December 1996 and December 1997. Monthly
average SST anomaly for December 1997 is also shown. The anomaly is relative to the SST climatology referred to in Fig. 2.
Figure 4. SST anomalies for the region from 5°N to 5°S, 90°W to 150°W from a combination of shipboard
data through 1991 and analysis of blended satellite/in situ data afterward. The shipboard data are described in (Kaplan et al.,
1998) and the blended product is described in (Reynolds and Smith, 1994). Warm anomalies (in red)
greater than about 0.5°C generally indicate El Niño events. Cold anomalies (in blue) less than about
-0.5°C generally indicate La Niña events.
Figure 5. Five-day averaged time series of surface zonal winds and SST from a mooring station on the equator at
125°W. The normal seasonal cycle is shown by magenta lines.
Figure 6. Observed heat content anomalies (from 0 to 400 m depth) averaged between 2°N and 2°S from the TAO
array. Temporal resolution is 5 days and contour interval is 0.1 × 10 J m . Heat content anomalies are
relative to the subsurface temperature climatology referred to in Fig. 2.
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