Observations of atmosphere-ocean coupling in the North Atlantic

• Main Authors: Q J R Meteorol, Soc
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2001
• Subjects: Greenland; Iceland; North Atlantic; North Atlantic oscillation
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1082.2238; http://oceans.mit.edu/JohnMarshall/wp-content/uploads/2013/08/Observations-of-atmosphere-ocean-coupling-in-the-North-Atlantic_54.pdf

SUMMARY An index of sea surface temperature (SST) variability, A T , is introduced that measures the difference in SST across the separated Gulf Stream in late winter. By analysing a long observational record of SST and sea-level pressure (SLP), it is shown that AT exhibits damped oscillations of decadal period, and covaries with the strength of a dipolar SLP anomaly reminiscent of the North Atlantic Oscillation (NAO). Analysis in the frequency domain shows a broad-band 'peak' at 10-20 years in A T , with a continuous decrease of power on longer time-scales. Similar spectral signatures are found in the northern part of the SLP dipole (the Greenland-Icelandic Low region) but not in its southern part (the subtropical High region), whose power increases on long time-scales. The observations are interpreted in the framework of a delayed-oscillator model in which the Ocean circulation introduces the delay, and modulates AT on decadal time-scales. The decrease of power seen on long time-scales (>25 years) in the AT index is captured by a model including wind-driven ocean circulation, and arises primarily as a passive response of the latter to the NAO forcing. Variability of the ocean's meridional overturning circulation could also play a role in modulating AT on decadal time-scales. If a small feedback of AT on the NAO pattern is introduced, the simple model can also reproduce the spectral stmctures seen in the SLP anomaly in the Greenland-Iceland region.