Summertime low clouds are common in the Pacific Northwest (PNW), but spatiotemporal patterns have not been characterized. We show the first maps of low cloudiness for the western PNW and North Pacific Ocean using a 22‐year satellite‐derived record of monthly mean low cloudiness frequency for May through September and supplemented...
Coastally trapped wind reversals along the U.S. west coast, which are often accompanied by a northward surge of fog or stratus, are an important warm—season forecast problem due to their impact on coastal maritime activities and airport operations. Previous studies identified several possible dynamic mechanisms that could be responsible for...
Observations of oppositely directed, monthly mean alongshore currents and wind stress over the continental margin off the Pacific coast of North America motivate the theoretical examination of mean flow generation by topographic lee-wave drag. We formulate a barotropic model for wind-forced shelf-slope flow over variable topography. Our central objective is...
Satellite observations of wind stress and sea surface temperature (SST) are analyzed to investigate ocean–atmosphere interaction in the California Current System (CCS). As in regions of strong SST fronts elsewhere in the World Ocean, SST in the CCS region is positively correlated with surface wind stress when SST fronts are...
An analytical model of subtropical mode water is presented, based on ventilated thermocline
theory and on numerical solutions of a planetary geostrophic basin model. In ventilated
thermocline theory, the western pool is a region bounded on the east by subsurface
streamlines that outcrop at the western edge of the interior,...
An analytical model of subtropical mode water is presented, based on ventilated thermocline
theory and on numerical solutions of a planetary geostrophic basin model. In ventilated
thermocline theory, the western pool is a region bounded on the east by subsurface
streamlines that outcrop at the western edge of the interior,...
An analytical model of subtropical mode water is presented, based on ventilated thermocline theory and on numerical solutions of a planetary geostrophic basin model. In ventilated thermocline theory, the western pool is a region bounded on the east by subsurface streamlines that outcrop at the western edge of the interior,...
Satellite observations of ice motion are combined with model estimates of low‐level winds and surface wind stress to provide evidence for atmospheric control of sea‐ice motion through Nares Strait, between Ellesmere Island and Greenland, during two periods in 2004. The results suggest that ice flux through the strait, and its...
Lateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for...
Lateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for...
Two simplified ocean simulations are used to study circulation and transport within Nares Strait. The simulations are similar, except that one included a coupled sea ice model that effectively established a landfast ice cover throughout the simulation year. Comparison between the ocean-only and ocean-ice simulations reveals a systematic change in...
Lateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for...
Three mechanisms for self-induced Ekman pumping in the interiors of mesoscale ocean eddies are investigated.
The first arises from the surface stress that occurs because of differences between surface wind and
ocean velocities, resulting in Ekman upwelling and downwelling in the cores of anticyclones and cyclones,
respectively. The second mechanism...
The wind speed response to mesoscale SST variability is investigated over the Agulhas Return Current region of the Southern Ocean using the Weather Research and Forecasting (WRF) Model and the U.S. Navy Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) atmospheric model. The SST-induced wind response is assessed from eight simulations with...
The study analyzes atmospheric circulation around an idealized coastal cape during summertime upwelling-favorable wind conditions simulated by a mesoscale coupled ocean–atmosphere model. The domain resembles an eastern ocean boundary with a single cape protruding into the ocean in the center of a coastline. The model predicts the formation of an...
The dynamical response of the marine atmospheric boundary layer (MABL) to mesoscale sea surface temperature (SST) perturbations is investigated over the Agulhas Return Current during winter from a 1-month, high-resolution, three-dimensional simulation using the Weather Research and Forecasting (WRF) mesoscale model. A steady lower boundary condition for July 2002 is...
We formulate analytically and solve numerically a semigeostrophic model for wind-driven thermocline upwelling at a coastal boundary. The model has a variable-density entraining mixed layer and two homogeneous interior layers. All variables are uniform alongshore. The wind stress and surface heating are constant. The system is started from rest, with...
Linear disturbance growth is studied in a quasigeostrophic baroclinic channel model with several thousand degrees of freedom. Disturbances to an unstable, nonlinear wave-mean oscillation are analyzed, allowing the comparison of singular vectors and time-dependent normal modes (Floquet vectors). Singular vectors characterize the transient growth of linear disturbances in a specified...
The stability of a time-periodic baroclinic wave-mean oscillation in a high-dimensional two-layer quasigeostrophic spectral model is examined by computing a full set of time-dependent normal modes (Floquet vectors) for the oscillation. The model has 72 × 62 horizontal resolution and there are 8928 Floquet vectors in the complete set. The...
The local predictability of the El Nin˜o–Southern Oscillation (ENSO) is examined by the analysis of the
evolution of small disturbances to an unstable 4.3-yr ENSO cycle in the Cane–Zebiak model forced by perpetual
July conditions. The 4.3-yr cycle represents the dominant near-recurrent behavior in this weakly chaotic regime,
so analysis...
Previously unaddressed aspects of how equatorial currents affect long Rossby wave phase speeds are investigated using solutions of the shallow-water equations linearized about quasi-realistic currents. Modification of the background potential vorticity (PV) gradient by curvature in the narrow equatorial currents is shown to play a role comparable to the Doppler...
An approach developed recently to study the dynamics of vorticity defects in homogeneous
shear flow extends naturally to the case of baroclinic, quasi-geostrophic
flow. It is shown that an inviscid geostrophic flow with uniform vertical shear may
be destabilized by introducing a `potential vorticity defect', an arbitrarily small but
sufficiently...
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...
The coastal ocean may experience periods of fluctuating
along-shelf wind direction, causing shifts between
upwelling and downwelling conditions with responses that
are not symmetric. We seek to understand these asymmetries
and their implications on the Eulerian and Lagrangian flows.
We use a two-dimensional (variations across-shelf and with
depth; uniformity along-shelf)...
The Oregon Coastal Transition Zone (OCTZ) extends several hundred
kilometers offshore where shelf flows interact with the northern California Current. A
primitive-equation numerical ocean model is used to study the upwelling circulation in this
region from 1 May to 1 November 2001. This OCTZ model obtains initial and boundary
conditions...
A thermistor chain was towed 1400 km through the eastern North Pacific subtropical frontal zone in
January 1980. The observations resolve surface layer temperature features with horizontal wavelengths of
0.2-200 km and vertical scales of 10-70 m. The dominant features, which have horizontal wavelengths of
10-100 km, amplitudes of 0.2°-1.0°C,...
Data from an array of bottom pressure gauges and a string of current meters in the vicinity of 47°N,
139°W, are used to examine the deep-ocean variability forced by ocean surface wind stress curl from
August 1987 to June 1988. Bottom geostrophic currents are computed from the pressure gauge array,...
The dynamics of the growth of linear disturbances
to a chaotic basic state is analyzed in an asymptotic model of
weakly nonlinear, baroclinic wave-mean interaction. In this
model, an ordinary differential equation for the wave amplitude
is coupled to a partial differential equation for the zonal
flow correction. The leading...
Air–sea coupling during coastal upwelling was examined through idealized three-dimensional numerical simulations with a coupled atmosphere–ocean mesoscale model. Geometry, topography, and initial and
boundary conditions were chosen to be representative of summertime coastal conditions off the Oregon coast. Over the 72-h simulations, sea surface temperatures were reduced several degrees near...
Ten years of sea-surface height (SSH) fields constructed from the merged TOPEX/Poseidon (T/P) and ERS-1/2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean. The higher resolution of the merged dataset reveals that more than 50% of the variability over much of the World Ocean is accounted...