C. Deser et Ml. Blackmon, SURFACE CLIMATE VARIATIONS OVER THE NORTH-ATLANTIC OCEAN DURING WINTER - 1900-1989, Journal of climate, 6(9), 1993, pp. 1743-1753
The low-frequency variability of the surface climate over the North At
lantic during winter is described, using 90 years of weather observati
ons from the Comprehensive Ocean-Atmosphere Data Set. Results are base
d on empirical orthogonal function analysis of four components of the
climate system: sea surface temperature (SST), air temperature, wind,
and sea level pressure. An important mode of variability of the winter
time surface climate over the North Atlantic during this century is ch
aracterized by a dipole pattern in SSTs and surface air temperatures,
with anomalies of one sip east of Newfoundland, and anomalies of the o
pposite polarity off the southeast coast of the United States. Wind fl
uctuations occur locally over the regions of large surface temperature
anomalies, with stronger-than-normal winds overlying cooler-than-norm
al SSTs. This mode exhibits variability on quasi-decadal and biennial
time scales. The decadal fluctuations are irregular in length, averagi
ng approximately 9 years before 1945 and approximately 12 years afterw
ard. There does not appear to be any difference between the wind-SST r
elationships on the different time scales. The decadal fluctuations in
SSTs east of Newfoundland are closely linked to decadal variations in
sea ice in the Labrador Sea, with periods of greater than normal sea
ice extent preceding by approximately 2 years periods of colder-than-n
ormal SSTs east of Newfoundland. Another dominant mode of variability
is associated with the global surface warming trend during the 1920s a
nd 1930s. The patterns of SST and air temperature change between 1900-
29 and 1939-68 indicate that the warming was concentrated along the Gu
lf Stream east of Cape Hatteras. Warming also occurred over the Greenl
and Sea and the eastern subtropical Atlantic. The warming trend was ac
companied by a decrease in the strength of the basin-scale atmospheric
circulation (negative phase of the North Atlantic Oscillation). In ma
rked contrast to the dipole pattern, the wind changes occurred downstr
eam of the largest SST anomalies; hence, the gradual surface warming a
long the Gulf Stream may have been a result of altered ocean currents
rather than local wind forcing.