2000: Relation between decadal variability of subtropical mode water and the North Atlantic Oscillation

• Main Authors: Terrence M. Joyce, Woods Hole, Clara Deser, Michael A. Spall
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Curl; North Atlantic; North Atlantic oscillation
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.528.360; http://muenchow.cms.udel.edu/html/classes/seminar2006/Joyce2000.pdf

The Bermuda station ‘‘S’ ’ time series has been used to define the variability of subtropical mode water (STMW) from 1954 to 1995. This record, which shows decadal variability at a nominal period of about 12–14 yr, has been used as a baseline for seeking correlation with large-scale atmospheric forcing and with decadal north–south excursions of the Gulf Stream position defined by the subsurface temperature at 200-m depth. A common time period of 1954–89 inclusive, defined by the data sources, shows a high degree of correlation among the STMW potential vorticity (PV), Gulf Stream position, and large-scale atmospheric forcing (buoyancy flux, SST, and sea level pressure). Two pentads with anomalously small and large STMW PV were further studied and composites were made to define a revised North Atlantic Oscillation (NAO) index associated with the decadal forcing. During years of low PV at Bermuda, the NAO index is low, the Gulf Stream is in a southerly position, and the zero wind stress curl latitude is shifted south as are the composite extratropical winter storm tracks, in comparison to the period of high PV at Bermuda. Because the NAO, Gulf Stream separation latitude, and STMW PV variations are in phase with maximum annually averaged correlation at zero year time lag, the authors hypothesize that all must be either coupled with one another or with some other phenomenon that determines the covariability. A mechanism is proposed that could link all of the above together. It relies on the