Seasonal Re-emergence of Sea Surface Temperature Anomalies in the North Atlantic: An Observational and Ocean Model Study

• Main Author: Taws, Sarah Lilian
• Format: Thesis
• Language: English
• Published: 2013
• Subjects: North Atlantic; North Atlantic oscillation; Northeast Atlantic
• Online Access: https://eprints.soton.ac.uk/359069/; https://eprints.soton.ac.uk/359069/1/Taws%252C%2520Sarah_Thesis_2013.pdf

The aim of this thesis is to provide a more comprehensive and dynamic understanding of sea surface temperature anomaly (SSTA) re-emergence in the North Atlantic, by (a) re-evaluating the utility of re-emergence for sea surface temperature (SST) variability quantitatively and/or by analysing its temporal variability, and (b) investigating the effects of horizontal advection, subduction and mesoscale phenomena on the occurrence and nature of SSTA re-emergence in the ocean. Such analyses may contribute towards an improved representation of SSTA re-emergence in seasonal forecast models, which is currently unsatisfactory. Analyses are undertaken with a new observational product and ocean model hindcasts. Through analysis of observations, it is demonstrated that SSTA re-emergence links the European winter extremes of 2009/10 and early 2010/11. Reemergence contributes towards the winter-to-winter persistence of a SSTA tripole pattern, associated with a record negative phase of the North Atlantic Oscillation (NAO). Its timing coincides with a shift to record negative NAO values. This suggests an active involvement in the extreme winter weather of early-winter 2010/11. The atmospheric and oceanic conditions of 2009-11 are analogous to previous years in the late-1960s, which suggest similar physical processes are involved in the establishment of a large and significant SSTA re-emergence. The dynamic influences of subduction and horizontal advection on SSTA re-emergence are investigated through numerical passive tracer experiments at 1º resolution. A dominant and time-dependent influence of horizontal advection upon the degree of re-emergence in the northeast Atlantic is revealed. The time-dependent role is linked to spatial variations in the subtropical-subpolar gyre boundary, caused by gyre-scale changes in the upper ocean velocity field. Subduction is more detrimental to SSTA re-emergence in the Sargasso Sea. Significant interannual variations in the amount of subduction are apparent. These variations are primarily ...