html

ppt

Abstract

Interannual variability of monthly-mean sea surface temperature is examined for the western North Atlantic continental shelf and slope between Cape Hatteras, North Carolina, and the southwestern Labrador Sea using fifteen years (1985-1999) of declouded, full-resolution, Advanced Very High Resolution Radiometer (AVHRR) data. All SST retrievals were computed using the NASA/NOAA Pathfinder SST algorithm. A spatial bathymetry-following grid was developed to focus on shelf and slope. We tracked the documented advection of cold Labrador Slope Water along the outer shelf during 1997 and 1998 as SST signal in the monthly gridded SST anomalies. The role of local forcing (net heatflux and wind) on observed IAV of SST is examined using monthly-mean winds and net heat flux for the same period using National Center for Environmental Prediction (NCEP) gridded reanalysis products. An empirical orthogonal function (EOF) analysis of monthly SST anomalies reveal that modes 1, 2 and 3 account for 22%, 14% and 8% of the variance respectively. Spatial EOF mode 1 shows a pattern of decreasing values over the shelf and slope towards both Cape Hatteras, and Hamilton Bank in the western Labrador Sea, forming a standing wave. Spatial EOF mode 2 shows a standing wave with increasingly positive values northeast of the Laurentian Channel and increasingly negative southwest of it. Spatial EOF mode 3 reveals an onshore-offshore standing wave throughout the Middle Atlantic Bight and Scotian Shelf region. Summing the first three modes and applying a 3-month triangular filter removes the effects of eddies and small scale noise from the original SST dataset, more clearly revealing IAV of SST over the study domain. Correlations between corresponding EOF temporal amplitudes of wind strength, net heat flux, SST and the North Atlantic Oscillation monthly were computed. Only low correlation and significance levels were found suggesting that other mechanisms, including horizontal and vertical advection, may play a major role controlling IAV of SST over the region. Furthermore the grid was divided into onshelf and offshelf sections using the 200m isobath as marking the shelf break. Correlation of offshore SST sections and the Gulf stream north wall anomalies at different longitudes shows generally high correlation, decreasing towards the Laurentian Channel. However, offshore SST anomalies are negatively correlated with the GSNW position at 50W, suggesting co-variation of the subpolar and subtropical gyres.