Gap winds and their effects on regional oceanography Part I: Cross Sound, Alaska

Gap-wind events flowing from Cross Sound in the eastern Gulf of Alaska (GOA) were examined using QuikSCAT wind data. The average duration of an event is 3.6 days with the longest event recorded in the QuikSCAT dataset being 12 days. Daily offshore directed winds with speeds >10 m s−1 are more common during the winter months (October–March), averaging 20.0 days per year, and less common during the summer (April – September), averaging 2.8 days per year. Interannual variability in the frequency of gap-wind events is correlated with El Niño. During gap-wind events, the spatial scales of high off-shore directed winds (>10 m s−1) reach almost 200 km off-shore and 225 km along the shelf break, suggesting that the winds directly influence both the shelf (20–65 km wide) and the off-shore waters. A model experiment suggests that a gap-wind event can result in eddy formation and changes in circulation and water properties. Increased entrainment of water from below the mixed layer due to the gap-wind event implies that mixed-layer nitrate concentrations could increase on the order of 5–10 µmole/l, potentially enhancing primary production in the region. An accompanying paper discusses part II of our study (Ladd et al., 2016) focusing on gap-wind events in the western GOA around Kodiak Island.