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1996 La Nina events are clearly depicted as either stationary or as rapidly
eastward propagating waves.
Hoffmueller diagrams along the latitudes 35
◦
,45
◦
,and50
◦
north are
analyzed but are not shown here for brevity. We summarize our findings.
There are eastward moving trough from about 1986 to 1989 and moving
crests to about 1993 in these three diagrams. The pattern seems to move
slower at higher latitude. These moving patterns are shown more clearly in
the Hoffmueller diagram along the path in the North Pacific and we include
this diagram in the right panel of Fig. 2. The results we obtained here with
the AVHRR SST are in good agreement with those of SMMR SST reported
in Ref. 13. In particular, the results from the two datasets agree well in the
overlap time period of about 1985-1987. Finally, Hoffmueller diagram along
the latitude of 40
◦
south is also analyzed but not shown here. We observe
near coincidence of decreased SSTs along the 40
◦
latitude south with the
1984-1985 La Nina event in the equatorial Pacific. This is in agreement
with the ENSO teleconnection in the South Pacific Ocean reported earlier
using SMMR SSTs (see Ref. 14).
4. Conclusion
We have derived Pacific SST deviations using AVHRR data from 1985
to 1997. Hoffmueller diagrams for the SST deviations along six different
paths in the Pacific have been analyzed. Our model clearly captured both
1987 and 1997-1998 El Nino events as well as the 1984-1985, 1989 and
1996 La Nina events. An eastward propagating wave of a period of about
4-6 years is shown in the right panel of Fig. 2, following approximately the
North Pacific Current. This demonstrates the capability of AVHRR to show
actual oceanic currents and gyres via the SST retrievals. Our results also
show ENSO teleconnection for the 1984-1985 La Nina event in the South
Pacific Ocean as reported in Ref. 14. Finally, inter-comparisons between
studies using different imaging processing products are planned and can,
in general, produce a more comprehensive picture of the ocean dynamic
processes.
References
1. J. M. Wallace and Q.-R. Jiang,
Atmospheric and Oceanic Variability
,ed.
H. Cattle,
Roy. Meteor. Soc.
,
17
(1987).
2. N. E. Graham,
Climate Dyn.
6
(1994) 135.
