Exploring the Relationship Between SST Anomalies in the Northeast Pacific and North Atlantic and the Shape of the Polar Vortex

The winter of 2013/14 was anomalously cold for much of central North America, while sea surface temperatures (SSTs) were anomalously warm in the northeast Pacific and north Atlantic. At the same time, the stratospheric polar vortex was chronically elongated over North America. Little is known about the influence warm SSTs in both the northeast Pacific and north Atlantic have on the shape of the stratospheric polar vortex. It is hypothesized that the chronic warm eastern Pacific SST anomaly during the winter of 2013/14 led to stronger upper tropospheric anticyclonic forcing in the Pacific sector, which favored a quasi-stationary planetary wave two pattern in the stratosphere, with one lobe anchored above the cold tropospheric air mass over eastern North America.

To examine this hypothesis, we employ the daily Optimum Interpolation Sea Surface Temperature (OISST) V2 High Resolution Dataset from NOAA over 33 cold seasons (January-February 1982/83 – 2014/15) to decompose north Pacific and north Atlantic SSTs into leading modes of variability using empirical orthogonal function (EOF) / principal component (PC) analysis. After computing the EOFs for both sectors, we compute PCs in units of standard deviations and composite 10 hPa potential vorticity using ERA-Interim global atmospheric reanalysis data for overlapping days at or above +1.5 standard deviations and +1.0 standard deviations. Additionally, we composite SST anomalies on days with an elongated polar vortex as determined through a non-parametric correlation of the potential vorticity data. It is found that the elongated polar vortex exhibits a statistically significant relationship with high SST anomalies in both oceans. Results of the composites, in addition to hypothesized physical mechanisms behind the relationship, are presented and discussed.