Atmospheric forcing of the Oregon coastal ocean during the 2001 upwelling season

Abstract

Meteorological conditions during an intensive oceanographic observational program in May through August 2001 along the central Oregon coast are described and related to larger‐scale and longer‐term conditions. Southward wind stresses of 0.05−0.1 N m−2 occurred roughly 75% of the time, with a sustained period of dominantly southward stress from mid‐June through July. Wind variations were correlated with variations in the large‐scale Aleutian Low and North Pacific High pressure centers; correlations with the continental Thermal Low were small. Intraseasonal oscillations in alongshore wind stress (periods near 20 days) correlated with the north‐south position of the jet stream. These stress oscillations drove 20 day oscillations in upper ocean temperature, with a lag of roughly 5 days for maximum correlation and amplitudes near 4°C. The sum of sensible and latent air‐sea heat fluxes was generally into the atmosphere through June, then weakly into the ocean thereafter, with fluctuations on synoptic timescales. Semidiurnal fluctuations in surface air temperature were observed at two northern moorings, apparently forced indirectly by nonlinear internal ocean tides. The diurnal cycle of wind stress was similar for both southward and northward wind conditions, with the diurnal alongshore fluctuation southward in the evening and northward in the morning. During southward winds the marine atmospheric boundary layer (MABL) was typically defined clearly by a strong temperature inversion, and a shallow stable internal boundary layer often formed within the MABL over cool upwelled waters, with surface air temperature roughly 1°C lower inshore than offshore. During northward winds, essentially no low‐level temperature stratification was observed.