Two land breeze events occurred off the Oregon coast on the nights of April 19th and 20th, 1973. An array of four moored toroid buoys and one land station recorded the effect of the land breeze event on the surface mesoscale wind and temperature fields. The land breezes may have resulted from the premature summerly conditions of fair weather and southward coastal winds that were caused by an early northeastward extension of the North Pacific High. The main features of the events were as follows: 1) A cooling period of a few hours after sunset established an air temperature gradient of -0.1° C km⁻¹ in the nearshore 10 km region. 2) The advance of the land breeze-front produced a 5° C temperature drop at the land station and a 1° C temperature drop at the buoy stations. 3) Simultaneously, the front also caused a decrease in wind speed by about an order of magnitude at each of the stations. During the passage of the front the wind veered from southward at 10 m sec⁻¹ to westward at 2 to 3 m sec⁻¹. 4) At dawn the temperature gradient was rapidly reversed, but there was a 2 hour lag before the wind speed began to increase. No frontal return flow was observed, instead the wind backed to the south and increased gradually over the array. Horizontal divergence and vertical vorticity were calculated using a simplified program. The land breeze produced spans of positive vorticity (5 x 10⁻⁴ sec⁻¹) over the array, possibly due to the horizontal wind shear in the offshore direction. The land breeze also caused a zone of convergence over the nearshore 10 km. The convergence was preceeded by a brief period of intense divergence. There was no convergence zone beyond the nearshore region. Instead there appeared alternating bands of convergence and divergence with a period of around 37 minutes. The same periodicity was observed in the offshore wind velocity. These features can be explained by a model of horizontal roll vortices migrating seaward from the nearshore convergence zone. The roll wavelength is inferred to be 4.7 km, the westward migration speed is 2 m sec⁻¹, and the height of the PBL is estimated to be 1. 5 km. This leads to a PBL Reynolds number of 370 ± 80, which is lower than previous observations and suggests that the rolls are produced by buoyancy and parallel instability. A model which is compatible with all the above is presented. / Graduation date: 1975

Relationships among the surface wind, horizontal synoptic-scale pressure gradient and topography are studied in the Willamette Valley in western Oregon. Terrain features alter the standard surface wind-pressure gradient relationship such that the angle between the surface wind and the surface geostrophic wind is most frequently 60°. In winter the surface flow is predominantly southerly and surface geostrophic flow varies from southerly to westerly. Little diurnal change occurs in the average surface wind, the average surface geostrophic wind and their relationship with each other because the air in the valley is generally stably stratified throughout the day. Partially in response to the northward extension of the subtropical anticyclone summertime surface winds and surface geostrophic winds are northerly, except during afternoon episodes of marine air invasion when surface winds are westerly. The pressure gradient is 88% less intense in summer but the ratio of the magnitudes of the surface wind and surface geostrophic wind, R, is 125% greater than in winter. However, a sharp summertime morning maximum in R of -0.67 is diminished by early afternoon as differential surface heating establishes a strong afternoon pressure gradient. When the surface geostrophic wind vector is cross-valley, the surface wind is still most frequently parallel to the valley and the surface geostrophic wind speed is largest and most variable. Because of the importance of terrain and meso-scale events, little correlation between the surface winds and synoptic-scale pressure gradient is found. / Graduation date: 1975

Graduation date: 2006 / Presented on 2005-12-02 / An empirical statistical model is developed that relates the non-tidal motion of the ocean surface currents off the Oregon coast to forecasts of the coastal winds. The empirical statistical model is then used to produce predictions of the surface currents that are evaluated for their agreement with measured currents. Measurements of the ocean surface currents were made at 6 km resolution using Long-Range CODAR SeaSonde high-frequency (HF) surface current mappers and wind forecasts were provided at 12 km resolution by the North American Mesoscale (NAM) model. First, the response of the surface currents to wind-forcing measured by five coastal National Data Buoy Center (NDBC) stations was evaluated using empirical orthogonal function (EOF) analysis. A significant correlation of approximately 0.8 was found between the majority of the variability in the seasonal anomalies of the low-pass filtered surface currents and the seasonal anomalies of the low-pass filtered wind stress measurements. The U and the V components of the measured surface currents were both shown to be forced by the zonal and meridional components of the wind-stress at the NDBC stations. Next, the NAM wind forecasts were tested for agreement with the measurements of the wind at the NDBC stations. Significant correlations of around 0.8 for meridional wind stress and 0.6 for zonal wind stress were found between the seasonal anomalies of the low-pass filtered wind stress measured by the NDBC stations and the seasonal anomalies of the low-pass filtered wind stress forecast by the NAM model. Given the amount of the variance in the winds captured by the NAM model and the response of the ocean surface currents to both components of the wind, bilinear regressions were formed relating the seasonal anomalies of the low-pass filtered NAM forecasts to the seasonal anomalies of the low-pass filtered surface currents. The regressions turned NAM wind forecasts into predictions of the seasonal anomalies of the low-pass filtered surface currents. Calculations of the seasonal cycle in the surface currents, added to these predicted seasonal anomalies, produced a non-tidal estimation of the surface currents that allowed a residual difference to be calculated from recent surface current measurements. The sum of the seasonal anomalies, the seasonal cycle, and the residual formed a prediction of the non-tidal surface currents. The average error in this prediction of the surface currents off the Oregon coast remained less than 4 cm/s out through 48 hours into the future.