Double Acceleration Effects of Closely Spaced Pairs of Ocean Fronts on High‐Wind Occurrence Frequency During Boreal Winter

Abstract

AbstractPrevious studies have found that sea surface temperature (SST) fronts have significant impacts on high‐wind frequency. Strong winds over the mid‐latitude North Pacific and North Atlantic Oceans occur frequently downstream of SST fronts in boreal winter. An SST front can significantly increase the instability of the marine atmospheric boundary layer, which accelerates the wind on the warmer flank. This study uses satellite observations to examine the “double acceleration” effects of closely spaced paired fronts (with interfrontal distances of 300–1,000 km) on high‐wind occurrence frequency in the Pacific subarctic frontal zone east of Japan and over the Atlantic Ocean east of Newfoundland. During boreal winter each year, mean westerly winds frequently cross two or more closely spaced SST fronts, with probabilities of 85% over the North Pacific and 87% over the North Atlantic. Over the warmer flank of the first front, the average high‐wind occurrence frequency (wind speed) increases due to the vertical‐mixing mechanism. Downstream of the second front, average high‐wind occurrence frequency (wind speed) reaches maxima of ∼9% (11.5 m s−1) over the Pacific and ∼11.5% (12 m s−1) over the Atlantic. Stronger westerly winds lead to greater high‐wind frequency. The first front contributes to the observed high winds downstream of the second front due to little friction and suppression of upward vertical momentum transfer between paired fronts.