Wind stress forcing of the Oregon coastal ocean during the 1999 upwelling season

Abstract

[1] The wind stress forcing of the Oregon coastal ocean during June -August 1999 is estimated from a regional mesoscale atmospheric model and from satellite scatterometer observations, supplemented by moored and coastal surface data and by a land-based wind profiler. Both the mean and variable components of model alongshore wind stress increase by factors of 3 -4 from north to south along the Oregon coast. There is evidence of orographic intensification near Cape Blanco, which is supported by previous aircraft and ship observations during August 1995. The systematic southward increase of southward stress will drive enhanced ocean upwelling along the southern Oregon coast and suggests the new hypothesis that systematic variations in local wind stress may contribute to the observed offshore displacement of the coastal upwelling jet in this region. It is inferred from an analysis of the model and surface data that ocean upwelling modifies coastal surface air temperatures by 1-5°C over timescales of 12-24 hours.INDEX TERMS: 3329

Two coastal upwelling domains in the northern California Current system

“…At offshore locations, the vertical velocity at the base of the surface layer induced by Ekman pumping is proportional to the curl of the wind stress (w D ϭ curl /( f) ϭ ‫ץ(‬ y /‫ץ‬x Ϫ ‫ץ‬ x /‫ץ‬y)/( f ), where is the wind stress vector, x and y are its eastward and northward components, and is the water density). High resolution estimates of the wind stress in this region can be obtained from the SeaWinds scatterometer onboard the NASA QuikSCAT satellite launched in July 1999 (Samelson et al, 2002;Perlin et al, 2004). The QuikSCAT orbit provides twice-daily coverage at about 0300 UTC and 1400 UTC; summer observations are available for four years (2000 -2003); results are interpolated onto a 0.25°grid (Ϸ 25 km).…”

“…Gan et al (2005) have recently modeled the response of this coastal ocean to wind forcing from a regional atmospheric model. Samelson et al (2002) showed that the atmospheric model wind stress fields generally resemble QuikSCAT fields (see their Figs. 2 and 5): both show much stronger alongshore wind stress at 42N than at 45 and 47N, though details of the gradients in the lee of Cape Blanco differ.…”

Wave-Driven Inner-Shelf Motions on the Oregon Coast*

“…Station NWP03, located on the south jetty of the Newport harbor entrance (Fig. 2), is representative of nearshore winds throughout the study area during summer (Kirincich et al 2005;Samelson et al 2002). Wind stress was calculated following Large and Pond (1981), assuming neutral stability.…”

Relationships among upwelling, phytoplankton blooms, and phycotoxins in coastal Oregon shellfish

“…There was no difference between the start of upwelling calculated from yearly dates and wind climatology in Region E. This was due to the more steady southward direction of the winds in this area throughout the spring and summer. There is a change in wind, and hence upwelling, climatology around Cape Blanco (42.84°N, between the coastal Regions D and E; Samelson et al 2002, Huyer et al 2005, Venegas et al 2008. North of Cape Blanco there was no significant difference in the timing of the upwelling season, but south of Cape Blanco upwelling favorable winds started significantly earlier and finished significantly later.…”

“…upwelling favorable winds occur after late February each year. A latitudinal gradient in winds and in the onset and intensity of upwelling has been noted for the California Current System (Strub et al 1987a,b, Largier et al 1993, Strub & James 2000, Samelson et al 2002, but previous studies have not looked in detail at the Oregon coast and thus have potentially missed smaller-scale spatial patterns.…”