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Forcing mechanisms controlling surface and subsurface temperature anomalies along line-p, northeast Pacific Ocean Lainé, Alexandre

Abstract

The influence of different mechanisms on surface and subsurface temperature anomalies is considered along Line-P, an oceanographic line extending from Vancouver Island into the Gulf of Alaska, and sampled for almost half a century. The role of a given mechanism is determined by using Canonical Correlation Analysis (CCA) between anomalies of a parameter representing the mechanism and the main Line-P temperature anomaly variations obtained from a Principal Component Analysis (PCA) performed on cast data. For each mechanism, it is determined if its direct influence can be detected, and if it can, the domain of Line- P over which it acts. Three main sections of Line-P show different behaviors. West of 130°W (offshore domain), the main mechanisms influencing Line-P temperature anomalies are Ekman transport due to zonal wind stress anomalies and wind mixing anomalies. Between 50 and 180 km offshore, upwelling anomalies, northward propagation of temperature anomalies along the coast of North America and anomalies in the strength of the Alaska Current are important in determining Line-P temperature anomalies. Closer to the coast, upwelling anomalies and alongshore wind stress anomalies along the coast of the United States are the most influential of the parameters tested. Broad-scale anomalous situations that involve different mechanisms simultaneously are also considered. Using CCA, two broad-scale sea level pressure anomaly (SLPA) patterns associated with two Line-P temperature anomaly modes are revealed. The first SLPA pattern, consisting of an anomalously low pressure cell centered in the Gulf of Alaska, implies positive nearshore temperature anomalies along Line-P. This influence can be explained by an association with nearshore-influential mechanisms. The second SLPA pattern consists of an anomalously high pressure system centered south of Line-P, in the middle of the North Pacific Ocean (40°N, 145°W), which results in positive surface temperature anomalies in the offshore section of Line-P and negative ones nearshore. The processes involved seem to be mostly wind mixing and Alaska Current anomalies.

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