GFDL - Geophysical Fluid Dynamics Laboratory

Publication 8201

Harnack R., Lanzante, J., and J. Harnack, 1982: Associations among the
tropical Pacific wind and sea surface temperature fields and higher
latitude circulation.
J. Climatology, 2, 267-290.


An empirical study was conducted examining associations between seasonal
trade wind and sea surface temperature (SST) fields in the eastern half of
the tropical Pacific Ocean for the period 1949-1979. In addition, the tropical
fields were statistically related to the extratropical circulation of the
Northern Hemisphere (i.e. 700-mb heights). This study differs from most
prior studies in that the trade wind field was examined primarily in terms
of the horizontal trade wind divergence and seasonally stratified lag
relationships were computed.

Seasonally stratified autocorrelations of empirical orthogonal function
(EOF) amplitudes (out to four seasons) indicated significant persistence
of EOF1 of SST and divergence until spring-summer for any initial season;
accordingly, spring and summer (summer and autumn) EOF1 for SST
(divergence) exhibited the greatest persistence. For divergence some
tendency for a reversal of sign was seen from the autumn, winter, or spring
seasons to the following autumn, which may imply negative air-sea feedback
mechanisms operating.

Seasonally stratified cross correlations between the first EOF for SST and
divergence indicated a significant contemporaneous relationship. When
divergence leads SST, the relationship is significant at short lags
(1-3 seasons) until spring as a target season is reached. The same
is true when SST leads divergence except that a significant relationship
returns with opposite sign in the subsequent summer and autumn. Winter SST
and divergence, in particular, are well correlated with prior values of the
other parameter.

When the tropical parameters were related to the extratropical circulation
through correlation with gridded 700-mb heights, significant patterns were
found only when winter 700-mb heights were the target parameter (i.e. tropical
parameter leading winter 700-mb heights). Summer through winter
tropical SST and divergence (EOF1) display a good association with subsequent
winter extratropical circulation in the form of an expanded/contracted
circumpolar vortex. The relationship between trade wind divergence and
subsequent winter circulation is significant using the prior winter (4 season
lag), vanishes during spring, and returns with the opposite sign for summer
through winter (lags 0-2). Using either SST or divergence, the observed
relationships are stronger at lags 1 and 2 than at lag 0.

Key Words:
Tropical-midlatitude interaction; Air-sea interaction; Trade winds; Tropical
Pacific sea surface temperature.