The Summer Heat Balance of the Oregon Inner Shelf Over 2 Decades: Intraseasonal Variability

Abstract

This study examines the heat balance of the inner shelf along the US West Coast using 14 years of summer temperature and velocity observations in 15 m water depth. Previous work at this site found no year-to-year variability in the observed mean summer temperature change despite significant warming due to surface heat flux and variable cooling due to across-shelf heat flux. Here, the processes that affect coastal water temperatures over time scales of days and months are investigated. Synoptic temperature variability (on time scales of several days) was predominantly due to the across-shelf heat flux, as there was little synoptic variability in the surface heating and no evidence that an along-shelf heat flux would close the two-dimensional heat budget when the residual was large. The analyses suggest the across-shelf heat flux was influenced by multiple mechanisms in addition to Ekman transport by along-shelf winds. For example, there was a three-layer vertical across-shelf velocity structure 40% ± 10% of the time and during downwelling-favorable winds there was an upwelling circulation 80% of the time. The across-shelf heat flux was generally highest near the surface and bottom boundaries, where the velocity observations were most limited. The heat budget residual was positive most of the time, likely resulting from uncertainty due to the observational limitations. An improved understanding of the processes that control the across-shelf heat flux and buffer temperature variability in the coastal ocean has the potential to improve predictions of coastal temperatures under climate change scenarios.