A new earth system climate model of intermediate complexity has been developed and its climatology compared to observations. The UVic Earth System Climate Model consists of a three-dimensional ocean general circulation model coupled to a thermodynamic/dynamic sea-ice model, an energy-moisture balance atmospheric model with dynamical feedbacks, and a thermomechanical land-ice model. In order to keep the model computationally efficient a reduced complexity atmosphere model is used. Atmospheric heat and freshwater transports are parametrized through Fickian diffusion, and precipitation is assumed to occur when the relative humidity is greater than 85%. Moisture transport can also be accomplished through advection if desired. Precipitation over land is assumed to return instantaneously to the ocean via one of 33 observed river drainage basins. Ice and snow albedo feedbacks are included in the coupled model by locally increasing the prescribed latitudinal profile of the planetary albedo. The atmospheric model includes a parametrization of water vapour/ planetary longwave feedbacks, although the radiative forcing associated with changes in atmospheric CO 2 is prescribed as a modification of the planetary longwave radiative flux. A specified lapse rate is used to reduce the surface temperature over land where there is topography. The model uses prescribed present-day winds in its climatology, although a dynamical wind feedback is included which exploits a latitudinally-varying empirical relationship between atmospheric surface temperature and density. The ocean component of the coupled model is based on the Geophysical Fluid Dynamics Laboratory (GFDL) Modular Ocean Model 2.2, with a global resolution of 3.6°(zonal) by 1.8°(meridional) and 19 vertical levels, and includes an option for brine-rejection parametrization. The sea-ice component incorporates an elastic-viscous-plastic rheology to represent sea-ice dynamics and various options for the representation of sea-ice thermodynamics and thickness distribution. The systematic comparison of the coupled model with observations reveals good agreement, especially when moisture transport is accomplished through advection. Global warming simulations conducted using the model to explore the role of moisture advection reveal a climate sensitivity of 3.0°C for a doubling of CO 2 , in line with other more comprehensive coupled models. Moisture advection, together with the wind feedback, leads to a transient simulation in which the meridional overturning in the North Atlantic initially weakens, but is eventually re-established to its initial strength once the radiative forcing is held fixed, as found in many coupled atmosphere General Circulation Models (GCMs). This is in contrast to experiments in which moisture transport is accomplished through diffusion whereby the overturning is reestablished to a strength that is greater than its initial condition. When applied to the climate of the Last Glacial Maximum (LGM), the model obtains tropical cooling (30°N-30°S), relative to the pr...

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A diagnostic circulation model and water mass analyses are used to examine variability in the structure and circulation of the Juan de Fuca Eddy, a highly productive region at the northern end of the California Current. Results from three years of field studies demonstrate that the eddy increases in spatial extent from early to late summer as the vertically averaged contribution of California Undercurrent source water grows from ∼60% in June to ∼80% in September. Typical near‐surface eddy radii range from ∼15 km in the early summer to ∼30 km in September and increase with depth. Below 100 m, eddy radii are ∼40 km. Fresher water, associated with the estuarine outflow from the Juan de Fuca Strait, is advected around the eddy margin. During southward wind conditions, the combination of cyclonic geostrophic flow and wind‐driven currents in the surface Ekman layer cause the eddy to be “leaky” on its southern perimeter. Eddy surface circulation becomes more retentive (up to ∼32 d observed) during periods of weak winds or frequent northward reversals. The presence of the eddy facilitates large inputs of dissolved inorganic nutrients into the region through two mechanisms: doming of California Undercurrent water within the eddy and enhanced cross‐shelf advection of Juan de Fuca Strait outflow. The combination of these sources results in a persistent, broad (100 km offshore) region of elevated macronutrients. The retentive circulation patterns combined with persistent nutrient supply may favor the development of toxigenic diatom blooms of Pseudo‐nitzschia species in this region.

The spring onset of persistent upwelling‐favorable winds was later than usual in the northern California Current system in 2005, resulting in delayed provision of inorganic nutrients to the upper waters of the coastal ocean. This study uses water column measurements to illustrate the evolution of temperature, salinity, nitrate and chlorophyll a prior to and after the onset of persistent local upwelling‐favorable winds, including recovery to “typical” conditions. Warm, nutrient‐ and chlorophyll‐depleted surface conditions similar to those in an El Niño were observed from Vancouver Island to central Oregon, and extended to depths greater than 500 m. Return to typical conditions was more rapid than suggested by time‐integrated local wind stress but consistent in timing with “remote” forcing of water properties in this region by upwelling‐favorable winds off northern California. Alongshore advection also likely contributed to the observed recovery, but was much less effective than upwelling.