The Icelandic Low as a predictor of the Gulf Stream north wall position

Abstract

The Gulf Stream’s Northwall east of Cape Hatteras marks the abrupt change in velocity and water properties between Slope Sea to the north and Gulf Stream itself. An index of the Northwall position constructed by Taylor and Stephens (1998), called GSNW, is analyzed in terms of interannual changes in the Icelandic Low (IL) pressure anomaly and longitudinal displacement.

Sea Surface Temperature (SST) composites suggest that when IL pressure is anomalously low, there are lower temperatures in the Labrador Sea and south of the Grand Banks. Two years later, warm SST anomalies are seen over the Northern Recirculation Gyre and a northward shift in the GSNW occurs. Similar changes in SSTs occur during winters in which the IL is anomalously west resulting in a northward displacement of the GSNW 3 years later. Although time lags of 2 and 3 years between the IL and the GSNW are used in the calculations, it is shown that lags with respect to each atmospheric variable are statistically significant at 5% level over a range of years.

Utilizing the appropriate time lags between the GSNW index and the IL pressure and longitude, as well as the Southern Oscillation index, a regression-prediction scheme is developed for forecasting the GSNW with a lead-time of 1 year. This scheme, which uses only prior information, was used to forecast the GSNW from 1994 to 2015. The correlation between the observed and forecasted values for 1994-2014 was 0.60, significant at the 1% level. The predicted value for 2015 indicates a small northward shift of GSNW from its 2014 position.

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